Torsion shear apparatus and testing procedures - USACE

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TO R SIO N SHEAR APPARATUS

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BULLETIN NO. 38

WATERWAYS EXPERIMENT STATION

CORPS O F ENGINEERS, U. S. A R M Y

VICKSBURG, MISSISSIPPI

QBRARY

S A Y 2 7 1968

Bureau of Reclamation Colorado

BUREAU OF REC LA M A TIO N D E N V ER LIBR AR Y$ .\q;92079177

TORSION SHEAR APPARATUS

AND TESTING PROCEDURES

BULLETIN NO. 38

WATERWAYS EXPERIMENT STATION

CORPS OF ENGINEERS, U. S. ARMY

V IC K S B U R G , M IS S IS S IP P I

A R M Y -M R C V IC K S B U R G M IS S MAY 1952

P R IC E $0.75

92079177

P R E F A C E

A d e v ic e fo r p e r f o r m in g t o r s i o n s h e a r t e s t s on r i n g - s h a p e d / s o i l s p e c i m e n s 1 w as bu ilt by the W aterw ay s E x p e r i m e n t S ta t io n in 1947. T h e d e s ig n e m b o d ie s n o v e l f e a t u r e s in lo a d a p p l ic a t io n and m e a s u r e m e n t , and s p e c i a l m e th o d s w e r e d e v e lo p e d fo r p r e p a r in g and p lac in g r in g - s h a p e d t e s t s p e c i m e n s of u n d is tu rb e d s o i l . T h e a p p a r a t u s w as bu il t a t the r e q u e s t of the S p e c i a l E n g in e e r in g D iv is io n , T he P a n a m a C a n a l , and a s e r i e s of to r s io n s h e a r t e s t s hav e b e e n p e r f o r m e d on s a m p l e s of A t l a n t ic

M uck, a so f t o r g a n ic c lay .

T he in tro d u c t io n to the b u lle t in c o n ta in s a re v ie w of the g e n e r a l p r i n c i p l e s of v a r io u s ty p es of t o r s i o n s h e a r t e s t s and th e ir a d v a n t a g e s and l im ita t io n s in c o m p a r i s o n with o th er s t re n g th t e s t s on s o i l s . A d e s c r i p t io n of the to r s i o n s h e a r a p p a r a t u s b u il t by the W aterw ay s E x p e r i m e n t S ta t io n and a d e ta i le d acc o u n t of r e c o m m ended te s t in g p r o c e d u r e s , co n ta in ed in the sec o n d and th ird p a r t s of the b u l le t in p r o p e r , fo r m a l a b o r a t o r y m a n u a l which, it i s hoped , w il l h e lp to av o id d i f f i c u l t i e s in fu tu re t e s t s . T h e fo u rth and con clu d in g p a r t co n ta in s a d e ta i le d r e p o r t on the c a l ib ra t io n t e s t s , and m a y s e r v e a s a g u id e not only fo r the c a l ib r a t io n o f fu tu r e u n i t s of the t o r s i o n s h e a r a p p a r a t u s but a l s o fo r c a l i b r a t i o n of equ ip m en t fo r c o n so l id a t io n t e s t s , t r i a x i a l c o m p r e s s i o n t e s t s , and d i r e c t s h e a r t e s t s .

T he w o rk d e s c r i b e d in th is b u lle t in w as p e r f o r m e d by the S o i l s D iv i s io n ,

W aterw ay s E x p e r i m e n t S ta t io n .

Ill

C O N TEN TS

P a g eP R E F A C E .................................................................................................................................................. i

N O T A T IO N ............................................................................................................................................... v

PA RT I: IN T R O D U C T IO N .......................................................................................................... 1P r in c ip le s of T o rsio n Sh ear T e s t s ................................................................. 2E va lu ation of T e s t R e s u l t s ................................................................................. 6C o m p ariso n of Stren gth T e s t s ........................................................................... 8

PA RT II: T H E TORSION SHEAR A P P A R A T U S .............................................................. 14D esig n S p e c if ic a t io n s .............................................................................................. 14T e stin g Bench and G en era l A rra n g e m e n t.................................................... 14The Sh ear A p p aratu s P r o p e r .............................................................................. 16V e r t ic a l Loading S y ste m ................... 19T orq u e Loading S y s te m s ........................................................................................ 21

PA RT III: T E STIN G P R O C E D U R E S ....................................................................................... 2.5In troductory R em ark s ................................................................................. 25P re p a ra t io n of T e s t S p e c im e n .......................... ................................................ 25P re lim in a ry M easu rem en ts and T e s t s ........................................................... 29P la c in g of T e s t S p e c im e n ....................................... 31P re lim in a ry C o n so lid a t io n ................................................................................. 33The Sh ear T e s t ........................................................................................................... 34D ism an tlin g of A p p a r a t u s ............................................. 39E xam in atio n and F in a l W ater-content D e te r m in a t io n s ....................... 40R ecord in g and E valu ation of T e s t R e s u l t s ....................................... ... 41

PA RT IV: C A LIBR A TIO N OF A PPA R A TU S . . . ............................................................ 49Sco p e of C a lib ra tio n ................................... 49A lignm ent of A p p a r a t u s ........................................................................................ 49G overn ing D im en sion s . . ..................................................................................... 50V e r t ic a l L oad ing S y s t e m ..................................................................................... 50T orq u e Load ing - - C on tro lled S t r e s s ................................................ 57T orq u e Loading - - C on tro lled S t r a i n ................... 61D rift and T ipping of T orq u e W h e e l................................................................. 68Influence of R a is in g the U pper R in gs. ........................................................... 69T w ist M easu rem en ts and M otor Sp eeds . 71S u m m ary of R e su lts of the C a l i b r a t io n ....................................................... 72

R E F E R E N C E S ........................................................................................................................................ 75

IV

L IS T O F F IG U R E S

F i g u r e N o. T it le P a g e

1 P r in c ip le s of to r s io n sh e a r t e s t s on s o i l s ............................................ 52 D ir e c t sh e a r t e s t s ................. ...................................................................................... 93 T r i a x ia l c o m p r e s s io n t e s t ..................................................................... 114 S id e v iew of to r s io n sh e a r a p p a r a t u s ..................................................... 155 T op v ie w ................................................................................................................ 156 B o tto m v ie w ........................................................................................................... 157 C o m p o s ite se c t io n th rou gh to r s io n sh e a r a p p a r a t u s .......................... 178 D en ta ted p o ro u s p l a t e s ............................................................................................... 189 T e s t in g bench fo r to r s io n sh e a r a p p a r a t u s ................................................... 20

10 V e r t ic a l lo ad in g s y s t e m ........................................................................................... 2111 T o r s io n lo ad in g s y s t e m ............................................................................................. 2112 P r o c e d u r e fo r p r e p a r in g t e s t s p e c im e n .......................................................... 2713 M e a su r in g in it ia l h e igh t of t e s t s p e c i m e n ................................................... 2914 C u ttin g UC t e s t sp e c im e n fro m s o il c o r e ...................................................... 3015 S c r a p e r s fo r tr im m in g re m o ld e d s o i l s p e c i m e n ..................................... 3216 W ater-c o n te n t d e te r m in a t io n s a t end of t e s t ........................................... 4017 T e s t d a ta an d 'c o m p u ta tio n sh e e ts fo r t o r s io n sh e a r t e s t s .................. 4 2 -4 318 S t r e s s - t w i s t d ia g r a m fo r L a k e P ro v id e n c e C l a y ..................................... 4519 S t r e s s - t w i s t d ia g r a m s fo r A tlan tic M u ck .................................................... . 462 0 F o r m a t io n of s l ic k e n s id e s by to r s io n s h e a r t e s t s . . . . . . . . . . . 4721 V e r t ic a l load in g and le v e r r a t i o s ........................ . ........................... ... 5122 In flu en ce o f le v e r m o v e m e n t s .................................................. 5223 F o r c e s by v e r t ic a l d i a l .......................................................................................... 5424 In flu en ce of s o i l f r ic t io n and ad h e sio n . ............................................................. 5525 S e ttle m e n t of to rq u e w h e e l ....................................................... 5526 T o rq u e lo ad in g — c o n tro lle d s t r e s s ......................................................... 5727 F o r c e s by tw ist d ia l s . ................................................................. 5828 F r ic t io n in gu id e s h e a v e s ........................................................................................ 5929 T o rq u e lo ad in g - - c o n tro lle d s t r a i n ................................................................. 6130 F r ic t io n in th r u s t s h e a v e s ..................................................................................... 6231 F o r c e s by to rq u e d ia l .................................................................... 6332 In flu en ce o f d e fle c t io n o f p ro v in g f r a m e ...................................................... 6333 C a lib r a t io n o f p ro v in g f r a m e ................................................................................. 6534 P ro v in g f r a m e f a c t o r s ................................................................................................. 6635 L e v e r r a t io fo r b a la n c e b e a m ...................................................................... 6936 P a r a l l e l i s m of w ire r o p e s ................................................................................ 6937 In flu en ce o f s o i l betw een r i n g s ........................................................................... 70

V

NOTATION

T e s t d e s ig n a tio n s

T he a d je c t iv e s “ qu ick *1 and “ slow** - - a s a p p lie d to s t r e n g th t e s t s in th is b u l l e t in - - r e f e r on ly to th e r a t e of a p p lic a tio n of lo a d s o r d is p la c e m e n ts , and , in co n fo rm a n c e w ith r e c e n t u s a g e , th e t e s t s a r e p r in c ip a l ly d e s ig n a te d as “ drained** o r “ undrained,** d ep en d in g upon th e d e g re e of d ra in a g e ta k in g p la c e d u r in g a t e s t . D ouble a d je c t iv e s a r e r e q u i r e d in so m e c a s e s to avo id m is u n d e r s ta n d in g ; fo r e x a m p le , an “ undrained** t e s t m a y be e i th e r a q u ic k o r a s lo w te s t w hen th e te s t in g a r r a n g e m e n t p e r m i t s c o m p le te p re v e n tio n of d ra in a g e . D ra in a g e can n o t be fu lly p r e v en ted in so m e ty p e s of t e s t s , in w h ich c a s e “ undrained** t e s t s a c tu a lly a r e q u ic k te s t s w ith a s m a l l am o u n t of d ra in a g e tak in g p la c e d u rin g th e te s t .

S ym bo ls

T he m a n y sy m b o ls u se d in th is b u lle tin a r e ta b u la te d be low . T he m a jo r i t y of th e se sy m b o ls w e re r e q u i r e d to e x p re s s the r e s u l t s of th e c a l ib ra t io n of th e to r s io n s h e a r a p p a ra tu s , d e s c r ib e d in P a r t IV .S ym bo l D im e n s io n M ean in g

A cm ^ H o riz o n ta l a r e a of t e s t s p e c im e n^•s cm ^ E q u iv a le n t s h e a r a r e a o r % (D^ - d ^ ) / 6 D WC k g /in . P ro v in g f r a m e f a c to r , n o m in a lCe k g / in . P ro v in g f r a m e f a c to r , e f fe c tiv ed cm o r in . In s id e d ia m e te r of t e s t sp e c im e nD cm o r in . O u ts id e d ia m e te r of t e s t s p e c im e nDm cm o r in . M ean d ia m e te r of t e s t sp e c im e nD s cm o r in . D is ta n c e b e tw e e n tw is t d ia lsDw c m o r in . E ffe c tiv e d ia m e te r of to rq u e w h ee lF g g F r i c t io n in gu ide s h e a v e sF h g F o r c e e x e r te d by h o r iz o n ta l o r tw is t d ia lsF t g F o r c e e x e r te d by p ro v in g f ra m e o r to rq u e d ia lF v g F o r c e e x e r te d by v e r t i c a l o r c o n s o lid a t io n d ia lho cm o r in . H e ig h t of s o i l above s h e a r p lanehu cm o r in . H e ig h t of s o i l be low s h e a r p laneH o cm o r in . I n i t ia l to ta l h e ig h t of t e s t s p e c im e nH 1 cm o r in . T o ta l h e ig h t of t e s t s p e c im e n a f te r c o n s o l id a t io nH r cm o r in . T o ta l h e ig h t of t e s t s p e c im e n a t end of t e s t

AH cm o r in . C h ang e in h e ig h t of t e s t s p e c im e nK none C o e ff ic ie n t of e a r th p r e s s u r e a t r e s tL e in . E q u iv a le n t m e a n d is ta n c e b e tw een gu id e s h e a v e sL m cm o r in . M e a n a n n u la r le n g th of t e s t sp e c im e n o r jtDmm in . V e r t ic a l m o v e m e n t, end of c o n so lid a tio n le v e r

vi

NOTATION (Continued)

Sym bol D im en sio n M eaning

M kg cm M om ent or torque

Ph k g /c m 2 H orizon ta l n orm al s t r e s s in t e s t sp ecim en

Pv k g /c m 2 V e r t ic a l n o rm al s t r e s s in te s t sp ecim enp kg V e r t ic a l or d ire c t load, g e n e ra l

P a kg A ctu al v e r t ic a l load on te s t sp ecim en

P o kg V e r t ic a l load on te s t sp e cim en by deadweightP a kg V e r t ic a l load on te s t sp e c im en by le v e r sy ste m

APb kg C o rre c tio n fo r pivot b ea rin g fr ic t io n

A pd kg C o rre c tio n fo r v e r t ic a l d ia l fo rc eAp f kg C o rre c tio n fo r le v e r fr ic t io nA P ^ m kg C o rre c tio n for in flu ence of le v e r m ovem entA P r kg C o rre c tio n for f r ic t io n betw een so il and ring

Ap w kg C o rre c tio n fo r in fluence of se ttle m e n t of torque w heelQ kg Load on con so lid atio n hanger

R h in . D ia l read ing , h o rizo n ta l o r tw ist d ials

R t in . D ia l read in g , proving fra m e o r torque d ia l

R v in . D ia l read in g , v e r t ic a l or con so lid atio n d ial

s r k g /c m 2 Sh earin g r e s is ta n c e , end of te s t or rem olded s o il

s u k g / cm 2 Sh earin g r e s is ta n c e , in itia l fo r undisturbed so ilS kg T o rqu e load, nom inal

Sa kg Torqu e load, e ffectiv e

ASc kg C o rre c tio n fo r fr ic tio n in counterw eight sh eav es

A S6 kg C o rre c tio n for in flu en ce of d eflectio n

A Sg A s h

kg C o rre c tio n fo r f r ic t io n in guide sheaves

kg C o rre c tio n fo r fo r c e s ex erted by tw ist d ia lsA St kg C o rre c tio n for fr ic t io n in th ru st sheaves

t m in . E lap sed tim e fro m s ta r t of te s t

va in ./m in . A v erage ra te of d isp la cem en t in te s t sp ecim en

wo % In itia l w ater content of te s t sp ecim en

W1 % W ater content a fte r p re lim in a ry consolidation

wr % W ater content at end of te s tA w % Change in w ater content during te s t

6 a cm o r in. A verage lin e a r d isp la cem en t in te s t sp ecim en

Ah in . M ovem ent of tw ist d ia ls

6 t in . D eflectio n of proving fra m e

6w in . S e ttlem en t of torque w heele none A ngular d isp lacem en t or tw ist of te s t sp ecim en (ra d ia n s)

u none C o effic ie n t of fr ic t io n betw een so il and rin gs

Ta k g / cm 2 A v erag e sh earin g s t r e s s on plane of fa ilu re

fi none A ngular d isp lacem en t or tw ist of te s t sp ecim en (d e g re e s)CD l / m in R evolutions per m inute

TORSION SHEAR APPARATUS AND TESTING PROCEDURES

by

M. Juul Hvorslev* and Robert I. Kaufman**

PART I: INTRODUCTION

The failure of slopes and of most other foundation or earth structures is generally a progressive phenomenon. Failure starts at points in the earth mass where shearing stresses exceed the available shearing resistance and, since the shearing resistance of most soils decreases with increasing deformations after a certain maximum resistance is exceeded, the failure spreads through the soil until a new equilibrium is established or general failure occurs. As a consequence, the shearing resistance over part of a potential surface of sliding, and in the vicinity of an entire zone of failure, will usually be smaller than the original maximum shearing resistance of the soil.

The shearing resistance determined by laboratory tests is generally smaller than that of the soil in situ, owing to partial disturbance of the soil during sampling and preparation of test specimens, and in some cases also because of progressive failure during testing. Therefore, the above-mentioned effects of progressive failure in the field are often neglected in currently used methods of analyzing the stability of slopes and earth structures. In other cases these effects are taken into consideration by arbitrarily decreasing the allowable shearing stresses, by using the unconfined compressive strength of cohesive soils as ameasure of the average shearing resistance, or by determining such average values by field experiments or analysis of existing failures. However, continued improvement of methods for obtaining undisturbed soil samples and the development of more rigorous methods of stability analysis increase the need of reliable determination of the decrease in shearing resistance after initial failure and of its ultimate residual value.

Adequate information on the stress-deformation relationships after initial failure of stiff and brittle soils can often be obtained by means of the commonly used direct shear and unconfined or triaxial compression tests. However, in these tests, the effective cross section of the test specimen and the stress conditions in general change rapidly with increasing deformations. The tests, therefore, cannot furnish reliable data on stress-deformation relationships after failure when very large deformations are required to reach the ultimate or residual values of the shearing resistance, as in the case of soft or plastic soils and slowly performed tests. In contrast thereto, the cross section of test specimens submitted to certain types of torsion

* Consultant* * E ng inee r, Soils Division, W aterw ays E x p e r im e n t Station.

2

s h e a r t e s t s d o e s n o t c h a n g e d u r in g th e t e s t , an d th e s t r e s s e s c a n b e d e t e r m i n e d f o r a n y d e s i r e d d e f o r m a t io n o r t w i s t .

T o r s i o n s h e a r t e s t s o n s o i l s h a v e b e e n u s e d to a c o n s id e r a b l e e x t e n t in E u r o p e a n l a b o r a t o r i e s d u r in g th e l a s t tw e n ty y e a r s , a n d s e v e r a l ty p e s o f e q u ip m e n t f o r t o r s i o n s h e a r t e s t s h a v e b e e n d e v i s e d (2 , 3, 4 , 5 , 6 , 7 , 10 , 11, 12, 14, 1 5 )* . R e l a t i v e l y s im p le m e th o d s an d e q u ip m e n t fo r d e t e r m i n a t i o n of th e t o r s i o n s h e a r i n g r e s i s t a n c e o f s o i l s w e r e d e v e lo p e d in t h i s c o u n tr y a b o u t 1916 b y th e S p e c ia l C o m m i t te e to C o d ify P r e s e n t P r a c t i c e o n th e B e a r i n g V a lu e of S o i l s , A m e r ic a n S o c ie ty o f C iv i l E n g i n e e r s (1 ) , a n d a b o u t 1938 b y W . W. J o h n s o n , E n g in e e r on S p e c ia l A s s ig n m e n t , S ta te H ig h w a y C o m m is s io n of K a n s a s . H o w e v e r , in n e i t h e r c a s e d o e s th e e q u ip m e n t a p p e a r to h a v e b e e n u s e d o u ts id e th e s p e c i a l r e s e a r c h o r e n g in e e r in g d e p a r t m e n t f o r w h ic h i t w a s d e v is e d .

A t o r s i o n r i n g s h e a r d e v ic e w a s d e s ig n e d a n d b u i l t b y th e W a te r w a y s E x p e r i m e n t S ta t io n in 19 47 , a n d t e s t s p e r f o r m e d th e r e w i th o n a s e r i e s o f s a m p le s o f A t la n t ic M u c k an d o n a s in g le s a m p le o f L a k e P r o v id e n c e C la y . T h e r e s u l t s o f t h e s e t e s t s a r e p r e s e n t e d in a r e c e n t l y i s s u e d r e p o r t (1 6 ) , an d th e t o r s i o n s h e a r a p p a r a t u s , i t s c a l i b r a t i o n , a n d th e t e s t i n g p r o c e d u r e s a r e d e s c r i b e d in fo l lo w in g p a r t s o f t h i s b u l l e t i n . T h e g e n e r a l p r i n c ip l e s o f t o r s i o n s h e a r t e s t s a n d th e a d v a n ta g e s a n d l i m i t a t io n s of s u c h t e s t s in c o m p a r i s o n w i th d i r e c t s h e a r a n d c o m p r e s s i o n t e s t s a r e s u m m a r i z e d in th e fo llo w in g p a r a g r a p h s in o r d e r to f a c i l i t a t e th e u n d e r s t a n d in g o f th e m a in p a r t s o f th e b u l l e t in w i th o u t a s tu d y o f th e p u b l ic a t io n s r e f e r r e d to a b o v e .

P r i n c i p l e s o f T o r s i o n S h e a r T e s t s

A t o r s i o n s h e a r t e s t on s o i l c o n s i s t s e s s e n t i a l l y in s u b je c t in g a s h o r t , s o l id o r h o llo w c y l i n d e r of s o i l to a n o r m a l a x i a l lo a d a n d i n c r e a s i n g m o m e n ts o r t o r q u e . T h e p r i n c ip a l t e s t i n g a r r a n g e m e n t s s o f a r d e v is e d a r e sh o w n in f i g u r e 1 (p a g e 5) in a g r e a t l y s im p l i f i e d , d i a g r a m m a t i c f o r m .

C o n ta in e r w i th r o t a t i n g d i s kT h e e a r l i e r f o r m s of t o r s i o n s h e a r a p p a r a t u s c o n s i s t e d o f a c o n ta in e r in

w h ic h s o i l w a s p la c e d an d s u b j e c t e d to a v e r t i c a l n o r m a l lo a d th r o u g h a p i s to n , f i g u r e 1 -A . A d e n ta t e d d i s k , s o l id c i r c u l a r o r a n n u la r in f o r m , w a s p la c e d in a r e c e s s in th e b a s e of th e c o n ta in e r an d r o t a t e d b y m e a n s of a s h a f t e x te n d in g th r o u g h th e b a s e a n d a l e v e r a r m o r a w h e e l . T h e s h e a r i n g s t r e s s e s a n d c o r r e s p o n d in g r o t a t i o n s o f th e d i s k f o r a n a p p l ie d t o r s i o n a l m o m e n t c o u ld b e d e t e r m i n e d , b u t u n e q u a l v o lu m e c h a n g e s of s o i l o v e r th e s t a t i o n a r y a n d r o t a t i n g p a r t s o f th e b a s e t e n d e d to c a u s e a r c h a c t io n in th e s o i l . T h e r e f o r e , th e v e r t i c a l n o r m a l s t r e s s e s in th e s o i l in th e im m e d ia t e v ic in i ty of th e r o t a t i n g d i s k c o u ld n o t b e d e t e r m i n e d w i th s a t i s f a c t o r y a c c u r a c y , a n d t h i s ty p e o f t e s t i n g a r r a n g e m e n t i s n o lo n g e r u s e d .

* F i g u r e s in p a r e n t h e s e s in d ic a te r e f e r e n c e s a t th e en d of th e b u l le t in .

3

S olid c y l in d r ic a l t e s t s p e c im e nT h e p r in c ip a l d isa d v a n ta g e of the a b o v e -m e n tio n e d te s t in g a r r a n g e m e n t is

e l im in a te d w h en th e e n t i r e b a s e is ro ta te d , o r w hen the b a s e is s ta t io n a r y an d th e p is to n is r o ta t e d , f ig u re 1 -B . T h e t e s t s p e c im e n m a y be u n con fined o r l a t e r a l d e fo rm a tio n s m a y be p re v e n te d by a co n fin in g r in g o r r in g s . T he a d v a n ta g e s an d l im ita tio n s of th e d i f f e r e n t ty p e s of l a t e r a l c o n fin e m e n t a r e s im i l a r to th o se fo r a r in g - sh ap ed t e s t s p e c im e n , d is c u s s e d in th e fo llo w in g p a r a g r a p h s . T he p r in c ip a l a d v a n tag e of a fu ll c i r c u l a r o r so lid c r o s s s e c tio n in c o m p a r is o n w ith a r in g - s h a p e d t e s t sp e c im e n , is th a t b o th th e c o n s tru c t io n of the s h e a r a p p a ra tu s and th e p r e p a r a t i o n of t e s t s p e c im e n s a r e s im p lif ie d . The p r in c ip a l d is a d v a n ta g e is th a t th e s h e a r in g s t r e s s e s and s t r a in s in a so lid t e s t s p e c im e n in c r e a s e f r o m a m a x im u m a t th e c y l in d r ic a l s u r f a c e to z e r o a t th e c e n te r , and th a t p r o g r e s s iv e f a i lu re ta k e s p la c e d u r ing th e te s t . A ssu m in g th a t th e v e r t i c a l n o rm a l s t r e s s e s a r e u n ifo rm ly d i s t r ib u te d and r e m a in c o n s ta n t d u rin g th e te s t , th e tru e s t r e s s - t w i s t d ia g ra m an d th e a c tu a l sh e a r in g s t r e s s e s c an be d e te rm in e d by d i f f e re n tia t io n of th e m o m e n t - tw is t c u rv e a s s u g g e s te d by D u g u e t-L u d w ig -P ra n d t l and d e s c r ib e d by N ad a i (13). H o w e v e r , th e a s s u m p tio n s on w h ich th is m e th o d is b a s e d a r e s e ld o m c o r r e c t fo r s o i ls .

V o lu m e c h a n g e s in a so lid c y l in d r ic a l t e s t s p e c im e n su b je c te d to to r s io n a ls o in c re a s e f ro m a m a x im u m a t th e c y l in d r ic a l s u r f a c e to z e r o a t the c e n te r . T h e c o n se q u e n t u n e q u a l c h an g es in h e ig h t of th e te s t s p e c im e n a r e c o u n te ra c te d by r a d ia l d is p la c e m e n ts and p la s t ic flow of s o i l b u t c a u se a n u n e q u a l d i s t r ib u t io n of th e v e r t ic a l n o rm a l lo ad . F u r th e r m o r e , th e v a r ia t io n of th e r a t e of l in e a r d i s p la c e m e n t f ro m a m a x im u m a t th e s u r f a c e to z e r o a t th e c e n te r m a y in flu en ce th e a p p a r e n t s h e a r in g r e s i s t a n c e of th e s o i l . T h e se d if f ic u lt ie s in e v a lu a t in g the r e s u l t s of to r s io n s h e a r t e s t s a r e g r e a t ly d e c r e a s e d b u t n o t c o m p le te ly e lim in a te d w hen th e t e s t s p e c i m e n h as a r in g - s h a p e d c r o s s s e c t io n . T h e r e fo re , m o s t of the to r s io n s h e a r a p p a r a tu s in c u r r e n t u se a r e d e s ig n e d fo r r in g -s h a p e d t e s t s p e c im e n s .

U nconfined r in g - s h a p e d t e s t s p e c im e n sA s im p le c o n s tru c t io n of th e to r s io n s h e a r a p p a ra tu s and s im p le e x te r n a l

s t r e s s c o n d itio n s a r e o b ta in ed w hen th e t e s t sp e c im e n is u n co n fin ed l a t e r a l l y , f ig u re 1-C and r e f e r e n c e (2). T e s ts on u n co n fin ed s p e c im e n s c a n be p e r fo rm e d o n ly w hen the s o i l h a s a c o n s id e ra b le a m o u n t of c o h e s io n , and the s o i l w ill be s u b je c te d to u n know n c a p i l la ry f o r c e s d u rin g th e t e s t . Such a t e s t is c o m p a ra b le to an u n c o n fin e d c o m p re s s io n t e s t w ith s im i la r u n c e r ta in t ie s in in te r p r e ta t io n of the r e s u l t s o b ta in e d . F u r th e r m o r e , s p e c im e n s of so f t and p la s t ic s o i ls m a y u n d e rg o l a t e r a l d e f o r m a t io n a t and a f te r f a i lu r e , in w h ich c a s e an in v e s tig a t io n of th e s h e a r in g r e s i s t a n c e c h a r a c t e r i s t i c s of th e s o i l a f te r f a i lu r e c a n n o t be m a d e w ith s a t i s f a c to r y a c c u r a c y . T h e r e fo re , to r s io n s h e a r t e s t s on u n co n fin ed t e s t s p e c im e n s hav e b e e n u sed p r i m a r i l y fo r c o m p a r iso n w ith th e r e s u l t s of u n co n fin ed c o m p re s s io n t e s t s .

T he a b o v e -m e n tio n e d u n c e r ta in ty c o n c e rn in g c a p i l la r y and l a t e r a l f o r c e s m ig h t be e l im in a te d by p lac in g a p a r t of th e a p p a ra tu s w ith th e t e s t s p e c im e n in a

4

p r e s s u r e c h a m b e r and s u r ro u n d in g i t w ith a r u b b e r m e m b ra n e o r a liq u id w h ich w ould n o t p e n e tr a te in to th e s o i l . H o w ev e r, th e ru b b e r m e m b ra n e w ould r e s t r i c t th e p e r m is s ib le d e fo rm a tio n s to v e ry s m a l l a m o u n ts and vo id th e p r in c ip a l ad v a n ta g e of a to r s io n s h e a r t e s t . A liq u id , in o r d e r n o t to p e n e t r a te in to th e s o i l , sh o u ld h a v e a r e la t iv e ly low v is c o s i ty and a s u r f a c e te n s io n c lo s e to th a t of w a te r to av o id f o r m a tio n of m e n i s c i a t th e in te r f a c e b e tw e e n th e liq u id an d th e p o re w a te r . S uch a liq u id h a s n o t y e t b een found, and e v en if a v a i la b le w ould be a b le on ly to c o n tro l and n o t to p re v e n t an y l a t e r a l d e fo rm a tio n s of th e t e s t s p e c im e n .

C o n fin ed r in g - s h a p e d t e s t s p e c im e n s

T he c r o s s s e c tio n of a t e s t s p e c im e n co n fin ed la t e r a l ly by in n e r and o u te r r in g s r e m a in s c o n s ta n t th ro u g h o u t th e te s t , and th e t e s t s p e c im e n can b e s u b je c te d to c o n s o lid a t io n o r sw e llin g b e fo re and d u rin g th e te s t . T h e con fin in g r in g s m a y co n s i s t of a s i n g l e o r u n d iv id ed p a i r , f ig u re 1-D , in w h ich c a s e f a i lu r e u s u a lly ta k e s p la c e a s h o r t d is ta n c e be low th e u p p e r d e n ta te d p la te . T h e te e th in th is p la te w ill c a u se p a r t i a l d i s tu r b a n c e of th e s o i l c lo s e to th e zon e of f a i lu r e , and too low v a lu e s of th e m a x im u m s h e a r in g r e s i s t a n c e m a y b e o b ta in ed in t e s t s on u n d is tu rb e d and u n c o n s o lid a te d s a m p le s of s e n s i t iv e s o i l s . H o w ev er, p r e l im in a r y c o n so lid a tio n of th e t e s t s p e c im e n in th e s h e a r a p p a ra tu s m a y c a u se th e p a r t i a l ly d i s tu r b e d s o i l in th e v ic in ity of th e d e n ta te d p la te s to a c q u ir e a d d it io n a l s tr e n g th , and f a i lu r e th en w ill ta k e p la c e be low th e zo n e of e x c e s s c o n so lid a t io n and in th e u n d is tu rb e d p a r t of th e t e s t s p e c i m e n . T he f r ic t io n b e tw een s o i l and con fin in g r in g s in f lu e n c e s th e d e g re e of c o n s o l i d a tio n , and th is in flu e n c e in c r e a s e s w ith in c re a s in g h e ig h t of th e t e s t s p e c im e n ; t h e r e f o re , th e h e ig h t sh o u ld b e r e la t iv e ly s m a ll . T he a r r a n g e m e n t w ith a s in g le p a i r of con fin in g r in g s p re v e n ts any sq u e e z in g ou t of s o i l d u r in g th e te s t , and m a y b e u se d to a d v a n ta g e in t e s t s on re m o ld e d s o i ls a s w e ll a s on n o n - s e n s i t iv e u n d is tu rb e d s o i l s , p a r t i c u la r ly w h en v o lu m e c h an g es d u rin g th e s h e a r t e s t p r o p e r a r e to b e in v e s tig a te d .

The co n fin in g r in g s m a y b e d iv id e d a t m id h e ig h t in to an u p p e r and lo w e r p a i r , f ig u re 1 -E . T he u p p e r p a i r w ill th e n ro ta te w ith th e a n n u la r p is to n , and f a i lu r e of th e s o i l u s u a lly ta k e s p la c e in a p la n e s e p a ra t in g th e u p p e r and lo w e r r in g s and n o t c lo s e to th e d e n ta te d p la te s . T he u p p e r r in g s a r e r a i s e d a l i t t l e b e fo re th e s t a r t of th e s h e a r t e s t p r o p e r , in o r d e r to e lim in a te f r ic t io n b e tw e e n th e r in g s and to in s u r e th a t th e to ta l n o rm a l f o rc e is a c tin g on th e p lan e of f a i lu r e . T he a b s e n c e of l a t e r a l c o n fin e m e n t in th e c le a r a n c e b e tw e e n th e u p p e r and lo w e r r in g s c r e a te s a s m a l l zo n e of w e a k n e s s , and s lig h tly too low v a lu e s of th e m a x im u m s h e a r in g r e s i s t a n c e m a y be o b ta in e d . A t and a f te r in i t i a l f a i lu r e , so m e s o i l m a y b e sq u e e z e d ou t th ro u g h th e c le a r a n c e , and f r ic t io n b e tw e e n th is s o i l and th e co n fin in g r in g s m a y in c r e a s e th e a p p a re n t to r s io n r e s i s ta n c e a l i t t l e . A lo s s of s o i l th ro u g h th e c le a r a n c e b e tw e e n the r in g s w ill a l s o c a u s e o b s e rv a tio n s of ch an g es in h e ig h t of th e t e s t sp e c im e n to b e c o m e u n re l ia b le fo r c o m p u ta tio n of ch an g es in v o lu m e and vo id r a t io of th e s o i l . N e v e r th e le s s , th e a r r a n g e m e n t w ith d iv id ed con fin in g r in g s is u su a lly p r e f e ra b le to th a t of a s in g le p a i r of r in g s fo r t e s t s on u n d is tu rb e d s a m p le s of s o i ls s e n s i t iv e to

VERTICAL LOAD VERT ICAL LOAD

UNCO NFINED RING TEST S P EC IM ENC

CO N FIN ED RING TEST SPEC IM EN UNDIVIDED OR S IN G LE R IN G S

D

CO N FIN ED RING T E ST SPEC IM EN DIVIDED R IN G S

E

CONTAINER W ITH ROTATING D ISKA

F

F ig u r e 1. P r i n c ip l e s of t o r s io n s h e a r te s ts on s o i ls

6

d is tu r b a n c e . T he ch o ice betw een the two a r r a n g e m e n ts d e p en d s not only on the c h a r a c t e r o f the s o i l but a l s o on the type of t e s t to be p e r fo r m e d , and the a p p a r a tu s b u ilt by the W aterw ay s E x p e r im e n t S ta tio n i s so d e s ig n e d th at e ith e r s in g le o r d iv id e d co n fin in g r in g s can be u se d .

T o r s io n sh e a r t e s t s on r in g - sh a p e d t e s t s p e c im e n s con fin ed betw een in n er and o u te r r in g s o c c a s io n a lly a r e c a lle d r in g s h e a r t e s t s , but the te r m should be a v o id ed s in c e , in th is co u n try , it a l s o i s ap p lie d to d ir e c t t r a n s v e r s e sh e a r t e s t s .

L o a d a p p lic a t io n

T he u se of a r in g - sh a p e d t e s t sp e c im e n f a c i l i t a t e s a p p lic a t io n of the v e r t ic a l n o r m a l lo ad u su a l ly t r a n sm it te d to the an n u lar p is to n th rou gh a th r u s t b e a r in g and a lo a d in g ro d p a s s in g th rou gh the c e n te r of the a p p a r a tu s . S m a ll lo a d s m ay be a p p lie d d ir e c t ly by p la c in g w eigh ts on a h an ger or s c a le a ttac h e d to the lo ad in g ro d , but l a r g e n o r m a l lo a d s a r e a p p lie d by m e a n s o f a le v e r s y s t e m ; s e e f ig u r e s 6 and 10 in P a r t l l and f ig u r e 2 1 in P a r t IV .

T he to r s io n a l m o m e n t o r to rq u e i s u su a lly a p p lie d by the c o n t r o l le d - s t r e s s m eth o d . T he b a s e of the a p p a r a tu s i s h eld s ta t io n a r y w hile a known to rq u e i s t r a n s m itte d to the p is to n by m e a n s of a to rq u e w heel and i s p ro d u ce d by two v e r y f le x ib le w ire r o p e s , w hich a r e c a r r i e d o v e r gu ide s h e a v e s to a s c a le p la t fo r m , f ig u r e 1 -F and f ig u r e 26 . A w eight, S , i s p la c e d on the s c a le and p ro d u c e s the m om en t

M = 1 / 2 S D W

w h ere D w i s the e ffe c tiv e d ia m e te r of the to rq u e w h eel. T he p is to n m a y a l s o be h eld s ta t io n a r y , and the b a s e o f the a p p a r a tu s then i s p la c e d on a th r u s t b e a r in g and i s ro ta te d by m e a n s of l e v e r s , r e fe r e n c e (5 ), o r g e a r s . The W aterw ay s E x p e r im e n t S ta tio n a p p a r a tu s i s so d e s ig n e d th at a ch an ge fr o m c o n t r o l le d - s t r e s s to c o n tr o lle d - s t r a in lo ad a p p lic a t io n m a y be m a d e b e fo re o r d u r in g a t e s t . Such a ch an ge i s a c c o m p lish e d by p rev e n tin g m o v e m e n ts of the b a la n c e b e a m and ro ta tio n of the an n u lar p is to n w hile the b a se i s r o ta te d a t a c o n stan t sp e e d . T he ten sio n in the w ire r o p e s o r to rq u e lo ad i s d e te rm in e d by m e a n s of a p ro v in g f r a m e su p p o rtin g the v e r t ic a l g u id e s h e a v e s , f ig u r e s 5 and 31.

E v a lu a tio n of T e s t R e s u l t s

T he d ir e c t r e s u l t s o f a to r s io n sh e a r t e s t a r e a s e r i e s o f c o r re sp o n d in g v a lu e s o f to rq u e and tw ist . T he m e a s u r e d to rq u e s a r e c o r r e c t e d fo r the in flu en ce o f f r i c tion and o th er e x tra n e o u s f o r c e s in v a r io u s p a r t s o f the a p p a r a tu s d e te rm in e d d u rin g i t s c a l ib r a t io n . T he sh e a r in g s t r e s s e s a r e not d is tr ib u te d u n ifo rm ly o v er the p lan e o f f a i lu r e un til the c o r r e c t e d to rq u e b e c o m e s c o n sta n t o r the to r q u e - tw is t d ia g r a m h o r iz o n ta l , but th e se s t r e s s e s and the tru e s t r e s s - t w i s t c u rv e m a y be d e te rm in e d by

7

expanding the Du g u e t- L u d w ig - P r a n d t l m eth od of g r a p h ic a l d i f f e r e n t i a t io n of the t o r q u e - tw is t cu rv e to a r in g - s h a p e d c r o s s s e c t i o n * . T h is m ethod i s d e s c r i b e d in r e f e r e n c e s (6, 7) and sh a l l not be d i s c u s s e d h e r e . The e a s i e r d e te r m in a t io n of a v e r a g e s t r e s s e s and d i s p la c e m e n t s , exp la in ed in the fo llow ing p a r a g r a p h s , y i e l d s s u f f ic ie n t ly a c c u r a t e r e s u l t s when the to r q u e - tw is t d i a g r a m is r e l a t iv e ly f l a t and the p r in c ip a l p u r p o se of the t e s t i s to d e te r m in e the m a x im u m sh e a r in g r e s i s t a n c e and the d e c r e a s e and r e s i d u a l v a lu e of this r e s i s t a n c e a f t e r in i t ia l f a i lu r e . H o w e v e r , the m o r e a c c u r a t e m ethod , m en t io n ed abo ve , should be u se d when the tru e s t r e s s - t w i s t c u rv e b e fo r e f a i l u r e i s to be d e te rm in e d and a l s o when the to r q u e - tw is t d i a g r a m i s s h a r p ly c u rv e d in the v ic in ity of m a x im u m to rq u e .

T he in flu en ce of s t r e s s c o n c en tra t io n s a t , and of s o i l sq u e e z e d out through the c l e a r a n c e betw een the upper and lo w er confin ing r in g s u su a l ly is not taken into c o n s id e r a t io n . The p lan es of f a i l u r e in a t e s t s p e c i m e n su b jec te d to p u r e t o r s i o n a l s h e a r a r e not p e rp e n d ic u la r and p a r a l l e l to the a x i s of the s p e c im e n u n l e s s the an g le of in te r n a l f r i c t io n of the s o i l i s z e r o . The sh e a r in g s t r e s s e s d e te r m in e d by a p r a c t ic a l t o r s i o n a l s h e a r t e s t a r e th o se ac tin g on a h o r iz o n ta l plane and only a p p r o a c h those of a t e s t s p e c im e n su b je c te d to p u re s h e a r .

A v e r a g e s h e a r in g s t r e s s e s

T he fo llow ing e x p r e s s io n i s obta ined fo r the a v e r a g e s h e a r in g s t r e s s , Ta , c o r re s p o n d in g to the m o m e n t or to rqu e M = l / 2 S D w , when it i s a s s u m e d that the sh e a r in g s t r e s s e s a r e u n i fo rm ly d i s t r ib u te d o v e r the h o r izo n ta l p lan e of f a i l u r e ,

T _ 12 M 6 D w S

a * ( D 3 - d 3) « (D 3 - d 3)

w here D i s the e x t e r n a l d i a m e t e r and d the in t e r n a l d ia m e t e r of the t e s t s p e c i m en . T h i s equ at ion can be r e d u c e d to the fo llow ing s im p l i f ie d fo r m by se t t in g A g =

jt (D3 - d 3) / 6 D w

which i s s i m i l a r to the e x p r e s s i o n fo r the a v e r a g e s h e a r in g s t r e s s o b ta in e d by a d i r e c t s h e a r t e s t . A i s a co n stan t fo r a g iv en t o r s i o n s h e a r a p p a r a t u s and m a y be

sc a l le d the equ iv a len t s h e a r a r e a . The n o m in a l v a l u e s of M or S sh o u ld be c o r r e c te d fo r the in fluence of f r i c t io n in load t r a n s m i s s i o n and other e x t r a n e o u s f o r c e s .

A v e r a g e d i s p la c e m e n t s

S m a l l ro ta t io n s o r d i s p la c e m e n t s a r e d e te r m in e d by m e a n s of h o r iz o n t a l d ia l in d ic a t o r s a t tac h e d to a n o n -ro ta t in g b a s e p la te and ac t in g a g a in s t a d i a l s to p on the to rqu e w h ee l. L a r g e ro ta t io n s m a y be d e te r m in e d by an in d ica to r a t t a c h e d to the

* The a c tu a l sh e a r in g s t r a in s cannot be d e te rm in e d with s a t i s f a c t o r y a c c u ra c y s in c e the f r ic t io n betw een the so il and confin in g r in g s c a u se s the d e fle c t io n s to b e co m e in c re a s in g ly co n cen tra ted n ear the zone of fa i lu r e a s the t e s t p r o g r e s s e s .

8

to rq u e w h ee l and g ra d u a tio n s on th e b a s e of th e a p p a ra tu s o r by th e m o v e m e n t of th e w i r e r o p e s . T hey a ls o m a y b e d e te rm in e d a s th e p ro d u c t of e la p s e d t im e and r a te of r o ta t io n w hen c o n t r o l l e d - s t r a in lo ad a p p lic a tio n is u s e d . T he a v e ra g e d is p la c e m e n t, 6 a , b e tw e e n th e end s u r f a c e s of th e t e s t sp e c im e n is

6 = 6 , ^ 2 a h nw h e re 6 ^ is th e a v e r a g e m o v e m e n t of th e tw is t d ia ls , D g th e d i s ta n c e b e tw e e n th e tw o d ia m e tr ic a l ly o p p o sed d ia ls , and Dm th e m e a n d ia m e te r of th e t e s t s p e c im e n , d e te rm in e d by

_ 2 p3 - d3- 3 d 2 - d 2 '

T h e a v e ra g e d is p la c e m e n t c o r re sp o n d in g to n e t r o ta t io n of 0 r a d ia n s o r d e g re e s is

^ a “ ® D m = 1 8 0 ^

T h e a v e ra g e r a t e of d is p la c e m e n t , v a , c o r re sp o n d in g to co r e v o lu tio n s p e r m in u te in a c o n t r o l l e d - s t r a in t e s t is

V _ = a ) * D rv,a mc e n t im e te r o r in c h e s p e r m in u te d ep en d in g upon th e s y s te m of m e a s u r e m e n t u se d .

C o m p a r is o n of S tre n g th T e s ts

A ll ty p e s of la b o r a to ry s t r e n g th t e s t s on s o i ls a r e s u b je c t to c e r ta in l im i t a t io n s o r in h e re n t s o u r c e s of e r r o r w h ich shou ld be ta k e n in to c o n s id e ra t io n in s e le c t in g th e ty pe of t e s t to be u se d and in c o m p a rin g th e r e s u l t s o b ta in e d by v a r io u s ty p e s of t e s t s . A s u m m a ry of th e p r in c ip a l a d v a n ta g e s and l im ita t io n s of d i r e c t s h e a r , to r s io n s h e a r , and c o m p re s s io n t e s t s on s o i ls is p r e s e n te d in th e fo llow ing p a r a g r a p h s . S t r ic t ly sp e a k in g , th e s h e a r in g r e s i s t a n c e is d e te rm in e d d i r e c t ly in to r s io n s h e a r t e s t s , b u t th e te r m “ d i r e c t s h e a r t e s t s “ is u s u a lly r e s e r v e d fo r t e s t s in w h ic h f a i lu r e is p ro d u c e d by a t r a n s l a to r y d is p la c e m e n t of one p a r t of th e t e s t s p e c im e n . M any ty p e s of d i r e c t s h e a r t e s t s h av e b e e n d e v e lo p ed b u t on ly th e th r e e p r in c ip a l on es w ill be d i s c u s s e d .

D i r e c t t r a n s v e r s e s h e a r t e s t sT h e t e s t in w h ich th e s o i l is con fined b e tw een th re e s u p e r im p o s e d r in g s , f ig

u r e 2 -A , and th e c e n te r r in g is d is p la c e d la t e r a l ly d u rin g th e t e s t h a s s e v e r a ln a m e s s u c h as d i r e c t t r a n s v e r s e , d o u b le s h e a r , and r in g s h e a r t e s t . T he la t t e r t e r m is m is le a d in g s in c e r in g s a r e u se d in o th e r ty p e s of s h e a r t e s t s . O c c a s io n a lly on ly two r in g s a r e u s e d , in w h ich c a s e th e a d v a n ta g e s and l im i ta t io n s r e s e m b le th o s e of th e d i r e c t box s h e a r te s t , b u t th e e f fe c t of d is p la c e m e n ts is g r e a te r and m o r e d if f ic u lt to e v a lu a te .

A d v a n ta g e s . T he a p p a ra tu s is s im p le , and s a m p le s o b ta in e d w ith s a m p le r s

9

having l in e r s d iv id ed into s e c t io n s of a p p r o p r ia t e h e igh t m a y b e te s te d without b e in g re m o v e d f r o m the l in e r s e c t i o n s . T he s h e a r in g f o r c e s a r e t r a n s m i t t e d a s n o r m a l f o r c e s to the c y l in d r ic a l s u r f a c e of the t e s t s p e c im e n , and th is c a u s e s l e s s p r e m a tu r e d i s tu r b a n c e of the s o i l than t r a n s m i s s i o n a s tan g en t ia l f o r c e s by m e a n s of r o u g h

o r dentated end p la t e s o r p i s to n s .

A - TRANSVERSE TEST

SHEAR FORCE

NORMAL FORCE

PISTON

L i m i t a t i o n s . The to ta l height of the t e s t s p e c i m e n i s r e la t iv e ly g r e a t ; c o n seq u en tly , the t im e r e q u i r e d fo r c o n so l id a te d and d r a in e d t e s t s i s i n c r e a s e d a s i s the in flu en ce of the s id e - w a l l f r i c tion. The e f fe c t iv e c r o s s s e c t io n of the t e s t s p e c i m e n d e c r e a s e s with in c r e a s i n g d e fo r m a t io n s ; the s t r e s s conditions a r e v e r y c o m p l ic a te d , and p r o g r e s s i v e f a i l u r e in f lu en ce s the r e s u l t s to a g r e a t e r extent than in other s h e a r t e s t s .The r e l i a b i l i t y of the v a lu e s of in i t ia l s h e a r in g r e s i s t a n c e f u r n ish ed by th is t e s t i s doubtfu l when the d e fo r m a t io n s a r e l a r g e , and the t e s t i s u n su i tab le fo r i n v e s t i gat io n o f the s h e a r - r e s i s t a n c e c h a r a c t e r i s t i c s a f t e r f a i l u r e .

COLLAR

LINER SECTIONS

SHEAR PLANES

SPACE BETWEEN RINGS

COLLAR

BASE OR PISTON

NORMAL FORCE

D i r e c t box s h e a r t e s t s

The m o s t co m m o n ly u s e d d i r e c t s h e a r t e s t i s the box s h e a r t e s t , f i g u r e 2 - B , in which a r e l a t iv e ly thin s o i l s a m p l e i s c o n fined betw een two r ig id f r a m e s .The s h e a r in g f o r c e s a r e t r a n s m it te d in p a r t a s n o r m a l p r e s s u r e s betw een s o i l and f r a m e s bu t p r i m a r i l y a s tan g en t ia l fo r c e s by m e a n s o f d en ta ted p la t e s . The u p p er f r a m e i s g e n e r a l ly r a i s e d a l i t t le , b e f o r e the s t a r t of thea c tu a l s h e a r t e s t , in o r d e r to e l im in a te f r ic t io n betw een the f r a m e s a s w e l l a s the e f fe c t of s i d e - w a l l f r i c t io n on the n o r m a l s t r e s s e s on the p lan e of f a i l u r e .

F i g u r e 2. D i r e c t sh e a r t e s t s

A d v a n ta g e s . The c o n s t ru c t io n and o p e ra t io n of the s h e a r a p p a r a t u s a r e s i m p le . The d r a in a g e f a c i l i t i e s a r e good; co n se q u en t ly , p r e l i m i n a r y c o n so l id a t io n can be a c c o m p l i s h e d and d r a in e d t e s t s p e r f o r m e d in r e l a t i v e l y s h o r t p e r io d s of t i m e .

L i m i t a t i o n s . D r a in a g e i s d i f f ic u lt to p r e v e n t d u r in g the a c tu a l s h e a r t e s t , and

10

“ u n d ra in e d t e s t s ” m u s t be p e r fo r m e d a s q u ick t e s t s with a s m a l l am o u n t of d r a in a g e tak in g p la c e . T he d en tated p la te s c a u se l im ite d d is tu r b a n c e of u n d istu rb e d s a m p le s , and a zone of w e a k n e ss m a y be C re a te d in th e ir v ic in ity u n le s s c o n s id e r a b le c o n so lid a t io n h a s taken p la c e a f te r the s o i l i s p la c e d in the s h e a r bo x . A s m a l l zone o f w e a k n e s s i s a l s o c r e a te d n e a r the c le a r a n c e betw een the two f r a m e s , and s o i l m a y b e sq u e e z e d out th rou gh th is c le a r a n c e d u rin g the la t e r s t a g e s o f a te s t . The s t r e s s co n d itio n s o v er p a r t of the c r o s s se c t io n of the t e s t sp e c im e n a r e c o m p lic a te d , and p r o g r e s s iv e f a i lu r e ta k e s p la c e . T he e ffe c tiv e c r o s s s e c t io n , or s o i l in c o n ta c t w ith s o i l , d e c r e a s e s w ith in c r e a s in g d is p la c e m e n ts , but the s o i l in the r e m a in in g p a r t s o f the o r ig in a l c r o s s se c t io n i s in co n tac t w ith the m e t a l f r a m e s , and the c o r re sp o n d in g f r ic t io n a l r e s i s t a n c e in c r e a s e s the to ta l s h e a r lo a d . A p p ro x im a te c o r r e c t io n s fo r the in flu en ce of so m e of th e se s o u r c e s o f e r r o r can be m a d e , but su c h c o r r e c t io n s b e c o m e in c r e a s in g ly u n c e r ta in w ith in c r e a s in g d e fo r m a t io n s , and the t e s t p e r m it s only a l im ite d in v e s t ig a t io n of the sh e a r in g r e s i s t a n c e c h a r a c t e r i s t i c s a f te r in it ia l f a i lu r e .

S w e d ish d ir e c t s h e a r t e s t s

The R o y a l S w e d ish G e o te c h n ic a l In stitu te (9) h a s d ev e lo p ed an a p p a r a tu s , f ig u r e 2 - C , w hich i s u se d fo r c o n so lid a tio n , p e rm e a b il ity , and d ir e c t sh e a r t e s t s . The s h o r t c y l in d r ic a l s o i l s a m p le i s con fin ed l a t e r a l ly by a ru b b e r m e m b ra n e and a s e r i e s o f th in and even ly sp a c e d r in g s . T he sh e a r in g f o r c e s a r e t r a n sm it te d e n t ire ly a s ta n g e n t ia l f o r c e s by m e a n s of d en tated end p la te s .

A d v a n ta g e s . T he in flu en ce o f s id e - w a l l f r ic t io n i s e lim in a ted ; the l a t e r a l d e fo r m a t io n s d u rin g a s h e a r t e s t a r e f a i r ly u n ifo rm ly d is tr ib u te d o v e r the h eigh t and c r o s s s e c t io n of the t e s t sp e c im e n , and the h o r iz o n ta l c r o s s se c t io n r e m a in s co n stan t th rou gh o u t the te s t . T h e d ra in a g e f a c i l i t i e s a r e good , and the s o i l s a m p le is s e a le d in the a p p a r a tu s so th at the am o u n t of w ate r fo rc e d out of o r a b so r b e d by the s o i l can b e m e a s u r e d . D r a in a g e can b e p rev e n ted a t any tim e d u rin g a t e s t s im p ly by c lo s in g a v a lv e , and u n d ra in ed t e s t s can be p e r fo rm e d a t any d e s i r e d r a te o f d isp la c e m e n t o r lo a d a p p lic a t io n .

L im ita t io n s . P r o p e r p la c e m e n t of the ru b b e r m e m b ra n e and con fin in g r in g s i s n ot a lw a y s e a s y , and the m e m b ra n e m ay be p inch ed betw een the r in g s when the v e r t i c a l s e t t le m e n ts a r e l a r g e . T he r e su lta n t of the v e r t ic a l f o r c e s on the u p p er and lo w er end s u r f a c e s of the t e s t sp e c im e n m u s t fo r m a coup le in o r d e r to b a la n c e the m o m e n t p ro d u ced by the s h e a r in g o r ta n g e n tia l f o r c e s . N e ith er the v e r t i c a l n o rm a l s t r e s s e s n or the sh e a r in g s t r e s s e s a r e u n ifo rm ly d is tr ib u te d . T h is n o n -u n ifo rm ity o f s t r e s s d is tr ib u t io n in c r e a s e s w ith in c r e a s in g d e fo r m a t io n s , and the sh e a r in g r e s i s t a n c e c h a r a c t e r i s t i c s a f te r in i t ia l f a i lu r e can be in v e s t ig a te d on ly to a lim ite d ex ten t. T h e s o i l n e a r the ends i s d is tu rb e d by the d en tated end p la te s , and zo n e s of w e a k n e s s m ay be c r e a te d u n le s s p r e l im in a r y c o n so lid a tio n ta k e s p la c e . H o w ever, fo r u n d ra in e d t e s t s the d en tated end p la te s h av e r e c e n t ly b een r e p la c e d w ith sm o o th p la t e s th in ly co ated w ith g e la t in . The d ry g e la t in a b s o r b s w ate r fr o m the s o i l and

11

f o r m s a b o n d b e t w e e n s o i l a n d m e t a l , p e r m i t t i n g t r a n s m i s s i o n o f t a n g e n t i a l f o r c e s

w i t h o u t s l i p p a g e o r d i s t u r b a n c e .

T r i a x i a l c o m p r e s s i o n t e s t s

T h e b a s i c f o r m o f a t r i a x i a l c o m p r e s s i o n t e s t c o n s i s t s in e n c l o s i n g a c y l i n

d r i c a l t e s t s p e c i m e n b e t w e e n tw o end p l a t e s o r c a p s and a r u b b e r m e m b r a n e a n d s u b

j e c t i n g i t to k n o w n v e r t i c a l a n d l a t e r a l f o r c e s . T h e f o l l o w i n g c o m m e n t s a p p l y p r i

m a r i l y to th e b a s i c t e s t and d o n o t i n c l u d e s p e c i a l f e a t u r e s o r v a r i a n t s , s u c h a s th e

c e l l t e s t .

A d v a n t a g e s . T h e e x t e r n a l a x i a l a n d

l a t e r a l f o r c e s a r e d e f i n i t e l y k n o w n a n d c a n b e

v a r i e d i n d e p e n d e n t l y o f e a c h o t h e r . T h e y a r e

t r a n s m i t t e d a s n o r m a l c o m p r e s s i v e f o r c e s to

th e s u r f a c e o f t h e t e s t s p e c i m e n a n d d o n o t

c a u s e p r e m a t u r e d i s t u r b a n c e o f th e s o i l . T h e

a m o u n t o f w a t e r e x p e l l e d o r a b s o r b e d b y t h e

s o i l c a n b e m e a s u r e d , and d r a i n a g e c a n b e p r e

v e n t e d b y c l o s i n g a v a l v e s o t h a t u n d r a i n e d

t e s t s c a n b e p e r f o r m e d a t a n y d e s i r e d r a t e o f

l o a d a p p l i c a t i o n . T h e s t r e s s d i s t r i b u t i o n in

t h e c e n t r a l p a r t o f a t e s t s p e c i m e n w i t h p r o p e r

l e n g t h - d i a m e t e r r a t i o c a n b e d e t e r m i n e d w i t h

r e a s o n a b l e a c c u r a c y . O b t a in in g r e s u l t s o f

th e t e s t in t h e f o r m of r e l a t i o n s h i p s b e t w e e n

p r i n c i p a l s t r e s s e s i s d e s i r a b l e f o r s o m e f o r m s

o f s t a b i l i t y a n a l y s i s b u t d i s a d v a n t a g e o u s , in

c o m p a r i s o n w i t h a d i r e c t d e t e r m i n a t i o n of

t h e s h e a r i n g r e s i s t a n c e , w h e n s o m e s e m i -

e m p i r i c a l m e t h o d s a r e u s e d .

L i m i t a t i o n s . D r a i n a g e t h r o u g h t h e e n d s

o f t h e t e s t s p e c i m e n r e q u i r e s c o n s i d e r a b l e

t i m e w h e n th e p e r m e a b i l i t y o f th e s o i l i s l o w ,

a n d s a t i s f a c t o r y a r r a n g e m e n t s f o r d r a i n a g e

t h r o u g h t h e c y l i n d r i c a l s u r f a c e h a v e n o t y e t b e e n d e v e l o p e d . I n d e t e r m i n a t e f o r c e s a r e

c a u s e d b y th e r e s t r a i n t s e x e r t e d b y t h e r u b b e r m e m b r a n e a n d b y t h e f r i c t i o n b e t w e e n

th e s o i l a n d end p l a t e s . T h e f o r m e r i s o f i m p o r t a n c e o n ly w h e n t h e d e f o r m a t i o n s a r e

l a r g e a n d th e e x t e r n a l f o r c e s s m a l l . T h e l a t t e r f o r c e s p r o b a b l y e x e r t o n l y a m i n o r

i n f l u e n c e on t h e s t r e s s d i s t r i b u t i o n in t h e c e n t r a l p a r t o f t e s t s p e c i m e n s w i t h a l e n g t h -

d i a m e t e r r a t i o g r e a t e r th a n t w o . H o w e v e r , t h e en d r e s t r a i n t c a u s e s n o n - u n i f o r m

d e f o r m a t i o n s , p o r e - w a t e r p r e s s u r e s , a n d v o l u m e c h a n g e s in th e t e s t s p e c i m e n a s a

w h o l e ; w h e r e f o r e , th e e f f e c t i v e c r o s s s e c t i o n , th e e f f e c t i v e s t r e s s e s , a n d s i g n i f i c a n t

v o i d r a t i o s c a n n o t a l w a y s b e d e t e r m i n e d w i t h s a t i s f a c t o r y a c c u r a c y . T h e i n f l u e n c e

12

of these sou rce s of error in c r e a s e s with increasing deform ations, and the test can

be used only to a limited extent for investigation of the strength c h a r a c te r is t ic s after

initial failure.

G e n e ral com m ents. S tr e ss conditions differ during tr ia x ia l com pression tests

and d ir e c t shear tests. F u r th e r m o r e , the planes of failure in tr ia x ia l com pression

te sts u su ally in terse ct the stratification s of the soil, and their location and inclina

tion m a y be influenced by lo ca l ir r e g u la r itie s in strength; w h ereas, in direct and

torsion shear tests, failure is forced to take place along a definite plane usually p a r

a lle l to the stratifications. The actual shearing re sista n ce along a surface of failure

can be determ ined from the r e su lts of triaxial com pression tests when the surface

is distinct and plane and its inclination is m easu red before it is changed by deform a

tions after failure. However, the su rfaces of failure of undisturbed te s t specim ens

are often irregular; they m a y be c lo se to the end surfaces and influenced by the end

re strain t, and they are often indistinct when the failure is m ore or le s s plastic in

c h a ra cte r. In such c a s e s determ ination of the shearing re s is ta n c e corresponding to

the c o m p r e s s iv e strength is indirect and depends to some extent on the theory of

failure adopted and the consequent angle of internal friction used in analyzing the

te st re su lts.

Unconfined com pression tests

The unconfined co m p ression test m ay be considered as a sim plified tria xia l

com pression test in which the external lateral p r e s s u r e is ze ro and replaced with

c a p illa ry p r e ssu r e s which correspond to the ch ara cter of the soil and its s tr e s s h is

tory. The test can be perform ed only when the soil has a significant amount of true

or apparent cohesion, and drainage during the test is not possible. The soils are

usually tested at their natural water content, but for certain investigations test s p e c i

m ens a r e prepared from soil which has been subjected to additional consolidation;

for exam ple, by partial drying.

A dvan tages. The unconfined com pression test is by far the s im p le st of all

strength tests. It can be perform ed in the laboratory or in the field by m eans of

ea sily portable equipment. It is the m o st widely used of a ll strength tests on cohe

sive soils, and a large amount of data is available for co rre la tiv e purposes.

L im itation s. A s in c a s e of triaxial com pression tests, the resu lts of uncon

fined co m p ression tests m a y be influenced by end restrain t, direction of stra tif ica

tions, and lo cal irre g u la r itie s in strength of the soil. However, the g r e a te s t lim ita

tion is that the effective s t r e s s e s produced by the cap illa ry m e n isci at the surface

of the te st specim en cannot be determined by d ir e c t m eans and a rigorous evalua

tion of the test results is not po ssib le. It has been found em p irica lly that for equal

water contents at failure of n orm ally consolidated soils, the unconfined co m p ressive

strength is somewhat s m a lle r than the strength obtained by tr ia x ia l tests and also

slightly s m a lle r than twice the shearing re sista n ce obtained by d ir e c t shear tests.

13

C h an ges in c r o s s s e c t io n of the t e s t sp e c im e n d uring an u nconfined c o m p r e s s io n t e s t p rev en t co m p le te in v e s t ig a t io n of the stren g th c h a r a c te r is t ic s a fte r in it ia l fa ilu r e . T h e r e fo r e , t e s t s on u n d istu rb ed s o i l sa m p le s a r e o ften su p p lem en ted by t e s t s on rem o ld ed s o i l in o r d e r to ob ta in an in d ica tio n of the r e s id u a l sh e a r in g r e s is ta n c e . H o w ev er , adequate data a r e not y e t a v a ila b le on the r e la t io n sh ip b e tw een the unconfined c o m p r e s s iv e s tr e n g th of rem o ld ed s o i l and the r e s id u a l sh e a r in g r e s is ta n c e of u n d istu rb ed s o i l , a s d e te r m in e d by to r s io n sh e a r t e s t s or a s found a long s lic k e n s id e d s u r fa c e s of fa ilu r e in the f ie ld .

T o r s io n sh e a r t e s t s

T he d isa d v a n ta g es of so lid c y lin d r ic a l and un con fin ed t e s t s p e c im e n s h ave b een d is c u s s e d p r e v io u s ly , and the fo llo w in g co m m en ts apply on ly to to r s io n sh e a r t e s t s on a r in g -sh a p e d t e s t sp e c im e n con fin ed b etw een in n er and o u ter r in g s .

A d v a n ta g es . T he d ra in a g e co n d itio n s a r e good, and p r e lim in a r y c o n s o lid a tion of the s o i l m ay be a c c o m p lish e d and d ra in ed t e s t s p e r fo r m e d w ith in r e a so n a b le p er io d s of t im e . P r o g r e s s iv e fa ilu r e d o es occu r during the t e s t , but its in flu e n c e can be e s t im a te d w ith g r e a te r a c c u r a c y than for d ir e c t sh e a r t e s t s . T he sh e a r in g r e s is ta n c e is d e term in ed d ir e c t ly a long a d e fin ite p lane of fa i lu r e , and the c r o s s s e c tion of the t e s t sp e c im e n r e m a in s co n sta n t throughout the t e s t . Any d e s ir e d am ount of d isp la c e m e n t m ay be ob ta in ed , and the sh ea r in g r e s is t a n c e c h a r a c te r is t ic s a fter in it ia l fa ilu r e , in clu d in g the r e s id u a l sh e a r in g r e s is ta n c e and the fo rm a tio n and in flu en ce of s l ic k e n s id e d s u r fa c e s of fa i lu r e , m a y be fu lly e x p lo r e d .

L im ita tio n s . T e s t s p e c im e n s a r e m o r e d iff ic u lt to p r e p a r e than for other stren g th t e s t s . D ra in a g e cannot be fu lly p rev en ted , and “ u n d ra in ed ” t e s t s can be p erfo rm ed only a s q u ick t e s t s w ith so m e d ra in a g e tak ing p la c e . T he d en tated p la te s c a u se p a r tia l d istu rb a n ce n ea r the end su r fa c e s of sp e c im e n s of u n d istu rb ed s o i l , but the co rresp o n d in g lo c a l d e c r e a s e in sh ea r in g r e s is t a n c e i s o ften e lim in a te d w hen the s o i l is su b jec ted to p r e lim in a r y c o n so lid a tio n in the sh e a r ap p a ra tu s, and it s e l dom a ffec ts the sh ea r in g r e s is ta n c e w hen d iv id ed con fin in g r in g s a r e u se d . H o w ev er , the s m a ll c le a r a n c e produced by r a is in g the upper con fin in g r in g s m ay c r e a te a s m a ll zone of s t r e s s c o n cen tra tio n and w e a k n e ss , and s o i l m a y b e sq u e e z e d out through th is c le a r a n c e during the la s t s ta g e s of a t e s t so that the v e r t ic a l s e t t le m e n ts no lo n g er r e p r e se n t the vo lu m e ch a n g es of the t e s t sp e c im e n . It m ay b e noted that m o s t of th e se lim ita tio n s a ls o apply to b ox sh e a r t e s t s .

0<i\X>XVvr \ ÎV

,»■

Oo>

V®

$

14

P A R T H: T H E T O R SIO N SH E A R A P P A R A T U S

D e s ig n S p e c i f i c a t io n s

T h e fo llow ing g e n e r a l s p e c i f i c a t io n s go v ern e d the d e s ig n of the t o r s i o n s h e a r a p p a r a tu s b u i l t by the W aterw ays E x p e r im e n t S ta t io n . The t e s t s p e c i m e n i s r in g - sh ap e d and confined by e ith er un d iv ided or d iv id ed r in g s , a s r e q u ir e d . The a p p a r a t u s c o n fo r m s to the g e n e r a l p r in c ip le s of that d e v e lo p ed b y H V O R S L E V ( 6 ,7 ) , bu t s p e c i a l f e a t u r e s f a c i l i t a t e the handling and te s t in g of s a m p l e s of un d istu rbed s o i l . T he p r in c ip a l d im e n s io n s and d e s ig n lo a d s a r e a s fo l lo w s:

O u ts id e d ia m e t e r of t e s t s p e c im e n In s id e d ia m e t e r of t e s t s p e c im e n A p p r o x im a te height of t e s t s p e c im e n M a x im u m v e r t i c a l n o r m a l s t r e s s M a x im u m a v e r a g e s h e a r in g s t r e s s

D = 4.5 in. d = 2.5 in.H = 3 /4 in.

pv = 5 .0 k g / c m 2 Ta = 2 .0 k g / c m ^

T h e s e d im e n s io n s a r e s l ig h t ly s m a l l e r than th o se of to r s io n s h e a r a p p a r a t u s bu il t in E u r o p e . T hey w e re s e l e c t e d to p e r m i t p r e p a r a t io n of t e s t s p e c i m e n s f r o m s a m p l e s with a d i a m e t e r of 4 - 3 / 4 in. to 5 - 1 / 2 in. a s ob ta ined with c o m m o n ly u se d s o i l s a m p l e r s through b o r in g s with 6 - in . c a s in g .

The to r s io n loading s y s t e m i s so de s ig n e d that a change f r o m c o n t r o l l e d - s t r e s s to c o n t r o l l e d - s t r a i n type of lo a d in g , o r v ic e v e r s a , can be m ad e b e fo r e or d u r in g a t e s t , and a m o t o r iz e d d r iv e and g e a r s p ro v id e a w ide r a n g e in r a te of d i s p la c e m e n t . The m a x i m u m sh e a r in g s t r e s s p r e s c r i b e d above c o r r e s p o n d s to the c a p a c i t y of the m o to r and g e a r s a t the m a x im u m r a t e of d i s p la c e m e n t , but up to 50 p e r cent o v e r lo a d i s p e r m i s s i b l e fo r low r a t e s of d i s p la c e m e n t and when the c o n t r o l l e d - s t r e s s type of lo ad a p p l ic a t io n i s u se d . In s ta l la t io n of eq u ip m en t fo r au to m at ic r e c o r d in g of the t o r q u e - t w i s t d i a g r a m s w as c o n s id e r e d but h a s not y e t been e f fec ted .

T e s t in g B e n c h and G e n e r a l A r r a n g e m e n t

The t e s t in g bench with the t o r s i o n s h e a r a p p a r a t u s p ro p e r and the lo a d a p p l ic a t io n and m e a s u r i n g d e v ic e s a r e shown in f i g u r e s 4, 5, and 6. The v e r t i c a l load i s ap p lied by m e a n s of the le v e r s y s t e m under the bench , and a c o n tro l le d s t r e s s or to rqu e can be e x e r t e d through the w i r e r o p e s and guide s h e a v e s and by p la c in g w eigh ts on the c o u n te r b a la n c e d load s c a l e to the r ig h t . A c o n tro l le d s t r a in or tw is t i s a p p lied by m e a n s of the m o to r and g e a r box in the r e a r , and the c o r r e s p o n d in g to rqu e i s in d ica te d by the proving f r a m e to the r ig h t of the s h e a r a p p a r a tu s .

T he t e s t in g b e n c h p r o v id e s s p a c e fo r th re e u n its of the s h e a r a p p a r a t u s , e ach with v e r t i c a l lo a d l e v e r s but u t i l iz in g a c o m m o n to rq u e a p p lic a t io n and m e a s u r i n g s y s t e m ; s e e a l s o f i g u r e 9. The m o t o r and g e a r box can be m o v ed f r o m one unit to

15

F i g u r e 4 . S i d e v ie w of t o r s i o n s h e a r a p p a r a t u s

F i g u r e 5 . T o p v ie w F i g u r e 6. B o t t o m v iew

16

a n o th e r , b u t th e p ro v in g f r a m e a n d to r q u e lo a d in g s c a l e r e m a i n s t a t i o n a r y , a n d th e t o r q u e i s t r a n s m i t t e d by w i r e r o p e s o f d i f f e r e n t l e n g th s f o r e a c h u n it . So f a r o n ly a s in g l e t o r s i o n s h e a r a p p a r a t u s h a s b e e n b u il t ; i f m o r e a r e p r o v id e d , t e s t s p e c im e n s in tw o of th e u n i t s c a n u n d e r g o p r e l i m i n a r y c o n s o l i d a t i o n w h ile a n a c t u a l s h e a r t e s t i s b e in g p e r f o r m e d by m e a n s o f th e t h i r d u n it .

T h e S h e a r A p p a r a tu s P r o p e r

T h e c u r r e n t a p p a r a t u s

A c o m p o s i te s e c t io n th r o u g h th e c u r r e n t t o r s i o n s h e a r a p p a r a t u s i s s h o w n in f i g u r e 7 - A . S u g g e s te d r e v i s i o n s o f th i s d e s ig n , f i g u r e 7 - B , a r e d i s c u s s e d on p a g e 19 . T h e s o i l t e s t s p e c im e n (1 ) i s c o n f in e d by in n e r a n d o u te r r i n g s w h ic h a r e sh o w n d iv id e d in to a n u p p e r an d lo w e r p a i r (3 ) an d (4 ), b u t a s in g le p a i r of c o n f in in g r i n g s , (3 8 ) in f i g u r e 7 - B , a r e a l s o p r o v id e d fo r th e c u r r e n t a p p a r a t u s . T h e s o i l s a m p le is c u t a n d t r i m m e d in s u c h a m a n n e r t h a t th e r e s u l t i n g t e s t s p e c im e n i s c o n f in e d w i th in a p a i r o f th in t r a n s f e r r i n g s (5 ) . T h e s e r i n g s s u p p o r t th e t e s t s p e c im e n w h ile i t i s b e in g m o v e d to th e t o r s i o n s h e a r a p p a r a tu s a n d a r e th e n p u s h e d d o w n in to r e c e s s e s in th e lo w e r c o n f in in g r i n g s . T h e u p p e r r i n g s a r e r a i s e d a l i t t l e b y m e a n s o f th e e l e v a t o r s c r e w s (6) b e f o r e th e s t a r t o f th e a c t u a l s h e a r t e s t . T h e u p p e r in n e r r i n g i s g u id e d b y a s p e c i a l b a l l b e a r i n g (1 7 ), p e r m i t t i n g b o th r o t a t i o n a n d v e r t i c a l m o v e m e n t s . T h e lo w e r r i n g s f i t s n u g ly o v e r a r i b in th e r o t a t i n g b a s e (1 0 ) , w h ic h is s u p p o r t e d a n d g u id e d b y th e b e a r i n g s (1 5 ), (1 6), a n d (1 8 ) o n th e h o llo w f la n g e d p in io n o r s t a t i o n a r y b a s e (1 3 ). T h e b a s e (1 0 ) c a n b e r o t a t e d b y h a n d o r m o t o r th r o u g h th e s e l f - l o c k i n g w o r m g e a r (1 2 ) t h a t h o ld s th e b a s e s t a t i o n a r y w h e n th e d r i v e s h a f t i s n o t r o t a t e d .

D e n ta te d p o r o u s p la te s

V e r t i c a l a n d t o r s i o n lo a d s a r e t r a n s m i t t e d to th e t e s t s p e c im e n th r o u g h a n n u l a r d e n ta te d p la te s o f p o r o u s b r o n z e (2 ), b r a z e d to th e a n n u la r p is to n (1 9 ) an d p in - c o n n e c te d to th e r o t a t in g b a s e (1 0). D r a in a g e o u t l e t s f o r th e u p p e r p o r o u s p la te le a d to f o u r s m a l l c y l i n d r i c a l r e s e r v o i r s (7 ) in th e a n n u la r p is to n , a n d o u t l e t s (8 ) f r o m th e lo w e r p o r o u s p la te le a d to a r e s e r v o i r c r e a t e d b y a p le x ig la s c y l in d e r (9 ) f i t t e d in to a g r o o v e in th e r o t a t i n g b a s e .

T h e d e n ta te d p la te s w e r e m a c h in e d f r o m ro u n d s to c k of s t a n d a r d o i l i t e b r o n z e b e a r i n g m a t e r i a l f r o m w h ic h th e o i l w a s r e m o v e d b y s o a k in g in c a r b o n t e t r a c h l o r i d e a n d s u b s e q u e n t h e a t in g . T h e m a c h in in g te n d e d to c l o s e th e p o r e s in th e m e ta l , e v e n th o u g h p e r f o r m e d w ith d e a d s h a r p t u n g s t e n - c a r b i d e to o l b i t s , b u t th e p o r o s i t y w a s r e s t o r e d b y s o a k in g th e f i n i s h e d p l a t e s b r i e f l y in a 50 p e r c e n t s o lu t io n o f n i t r i c a c id a n d s u b s e q u e n t th o ro u g h r i n s i n g . T h e te e th a r e t r i a n g u l a r in f o r m a n d of c o n s ta n t h e ig h t , 0 .0 5 9 i n . , b u t th e to p a n g le v a r i e s f r o m 5 6 ° a t th e in n e r r i m to 9 0 ° a t th e o u t e r r i m o f th e p l a t e s , f i g u r e 8 -A , a n d th e s u r f a c e s o f th e t e e th a r e w a r p e d . T h is

LEGEND

A - ORIGINAL AND CURRENT DESIGN

9

10

12

13

14

15

16

18

19

22

RING TEST SPECIMEN

DENTATED POROUS PLATES

UPPER CONFINING RINGS

LOWER CONFINING RINGS

TRANSFER RINGS

RING ELEVATOR SCREWS

UPPER WATER OUTLET

LOWER WATER OUTLET

PLEXIGLASS CYLINDER

ROTATING BASE

BASE GEAR

WORM GEAR

PINION WITH FLANGE

FIXED BASE PLATE

BASE THRUST BEARING

BASE GUIDE BEARING

RING GUIDE BEARING

OILITE PINION BEARING

RING PISTON

TORQUE WHEEL

WIRE ROPE CLAMP

LOADING ROD

B — PRÓPOSED REVISED DESIGN

THRUST BEARING

DIAL STOP

DIAL FRAME

TWIST DIALS

VERTICAL DIAL

DIAL HOLDER

TOTAL TWIST INDICATOR

CAP

THRUST BEARING GUARD

BEARING BUSHING

LOWER OILITE BEARING

FLANGED PINION

BASE GEAR WHEEL

DETACHABLE BASE PLATE

OILITE RING GUIDE

SINGLE RINGS

SPACER RINGS

BRASS CYLINDER

DRAINAGE GROOVES

SCALE - INCHES

F i g u r e 7 . C o m p o s i t e s e c t i o n t h r o u g h t o r s i o n s h e a r a p p a r a t u s

18

d e s ig n m a k e s th e m a c h in in g m o r e d i f f i c u l t th a n t h a t o f t e e th w ith a c o n s t a n t t o p a n g le a n d v a r i a b l e h e ig h t , b u t a c o n s t a n t h e ig h t i s r e q u i r e d to p r e v e n t a r a d i a l d i s p l a c e m e n t o f s o i l a n d c o n s e q u e n t n o n - u n i f o r m d i s t r i b u t i o n o f th e v e r t i c a l lo a d w h en th e t e e t h a r e f o r c e d in to th e s o i l .

T e e th o f v e r y th in s t r i p s o f h a r d b r o n z e b e tw e e n s e g m e n t s o f p o r o u s b r o n z e , f i g u r e 8 - B , w e r e c o n s id e r e d a n d m a y b e u s e d to a d v a n ta g e in t e s t s o n r e m o ld e d s o i l s . H o w e v e r , s u c h th in b r o n z e s t r i p s w il l c a u s e a s l i g h t r a d i a l d i s p l a c e m e n t o f s o i l u n l e s s th e s t r i p s a r e t a p e r e d a lo n g r a d i a l l i n e s . M o r e o v e r , z o n e s o f e x c e s s c o n s o l i d a t io n a n d i n c r e a s e d s t r e n g t h a r e f o r m e d a r o u n d t r i a n g u l a r t e e t h d u r in g p r e l i m i n a r y c o n s o l id a t io n of th e t e s t s p e c im e n so t h a t f a i l u r e t a k e s p l a c e in u n d i s tu r b e d s o i l b e y o n d t h e s e z o n e s , b u t i t w a s f e a r e d t h a t th e o r i g i n a l d i s t u r b a n c e c a u s e d b y th e th in b r o n z e s t r i p s in f ig u r e 8 - B w o u ld n o t b e c o u n t e r a c t e d b y e x c e s s c o n s o l id a t io n .

SPACING 3 °120 TEETH

HEIGHT OF TEETH IS CONSTANT SURFACES WARPED

PLATES OF POROUS BRONZE OR BRONZE OILITE WITH OIL REMOVED

DENTATED PLATE AT INNER EDGE

A-M AC H IN ED TEETH

INSERTED TEETH

POROUS BRONZE SEGMENTS

BASE RIB

SPACING 8°45 TEETH

TEETH OF SPRING -TEMPERED BRONZE GA. 3 4 = 0.006 3"

SEGMENTS POROUS BRONZE OR BRONZE OILITE WITH OIL REMOVED - ROUGH UPPER SURFACE

B-INSERTED TEETH

F i g u r e 8. D e n ta te d p o ro u s p la te s

L o a d s a n d d e f o r m a t io n s

T h e v e r t i c a l lo a d i s t r a n s m i t t e d f r o m a l e v e r s y s t e m to th e t o r q u e w h e e l (2 0 ) a n d a n n u la r p i s to n ( l 9 ) b y m e a n s o f a lo a d in g r o d (2 2 ) a n d a s e l f - a l i g n i n g t h r u s t b e a r in g (2 3 ) . T h e to r q u e w h e e l c a n b e r o t a t e d o r h e ld s t a t i o n a r y b y m e a n s o f tw o v e r y f l e x ib l e w i r e r o p e s w h ic h a r e c o n n e c te d to th e w h e e l b y a d j u s t a b l e c l a m p s (2 1 ) . T h e d i a l c a r r i e r f r a m e (2 5 ) s u p p o r t s th e v e r t i c a l d ia l (2 7 ) f o r m e a s u r e m e n t o f v e r t i c a l m o v e m e n t s o r c h a n g e s in h e ig h t o f th e t e s t s p e c im e n a n d tw o h o r i z o n t a l d i a l s (26 ) f o r a c c u r a t e m e a s u r e m e n t o f s m a l l r o t a t i o n s o f th e t o r q u e w h e e l w ith r e s p e c t to th e f ix e d b a s e p l a t e (1 4 ) . T h e m o v e m e n t o f th e w h e e l i s t r a n s m i t t e d to th e d i a l s b y a n a d j u s t a b l e d i a l s to p (2 4 ) . A l l t h r e e d i a l s a r e h e ld in c h u c k - ty p e d ia l h o ld e r s (2 8 ) p e r m i t t in g e a s y a d j u s t m e n t s o f th e d i a l s e t t i n g a n d p r e v e n t in g b in d in g o f t h e d ia l s p in d le s . L a r g e

19

ro ta t io n s o f the to rq u e w heel w ith r e s p e c t to the ro ta t in g b a s e (10) can b e d e te rm in e d by m e a n s of the to ta l tw ist in d ic a to r (29) and g ra d u a t io n s on the p le x ig la s c y lin d e r (9 ), o r by the e la p se d tim e and r a te of ro ta tio n o r d isp la c e m e n t ; s e e p a g e 7.

P r o p o se d r e v is io n s o f d e s ig n

P r o p o se d r e v is io n s of the c u r r e n t d e s ig n of the to r s io n s h e a r a p p a r a tu s p ro p e r a r e show n in f i g u r e 7 - B . A d e ta c h a b le b a s e (36) i s p la c e d on the r e d e s ig n e d ro ta t in g b a s e and g e a r w h eel (35 ). T h is a r r a n g e m e n t p e r m it s e a s y r e m o v a l and f a c i l i t a t e s c lean in g the u p p e r p a r t of the a p p a r a tu s . T h e b a l l gu id e b e a r in g s a r e r e p la c e d w ith o i l i te b e a r in g s to s im p lify the c o n stru c t io n , and the lo w er b a l l th r u s t b e a r in g i s p r o v ided w ith a g u a rd (31 ). The p le x ig la s c y lin d e r i s r e p la c e d with a th in -w a lle d b r a s s cy lin d e r (40) w hich i s not p u sh ed into a g ro o v e but f i t s tigh tly a g a in s t a sh o u ld e r in the d e ta c h a b le b a s e .

S in g le o r u n d iv id ed con fin in g r in g s (38) a r e show n to the r ig h t in f ig u r e 7 - B , and su ch r in g s a r e a l s o p ro v id ed fo r the c u r re n t a p p a r a tu s . U se of s in g le co n fin in g r in g s n e c e s s i t a t e s su p p lem en tin g the t r a n s f e r r in g s (5) w ith a p a ir of s p a c e r r in g s (39 ). P r o p e r a lig n m e n t of the v a r io u s d r a in a g e o u tle ts w as found d if f ic u lt to ob ta in , and su c h a lig n m e n t b e c o m e s u n n e c e s s a r y when s m a l l c i r c u la r g ro o v e s (41) a r e p r o v ided in the b a s e r ib and the con fin in g r in g s . In f ig u r e 7 - B the h eigh t of the t e s t sp e c im e n i s the s a m e fo r d iv id ed and s in g le con fin in g r in g s ; h o w ev er, r e d u c t io n of the h eigh t to ab o u t l / 2 in . i s a d v a n ta g e o u s when s in g le r in g s a r e u se d so th at the in flu e n c e of f r ic t io n betw een s o i l and r in g s i s d e c r e a s e d . In the c u r re n t a p p a r a tu s the lo w er d en tated p la te i s p in -co n n ec ted to the b a s e r ib , but a s a t i s f a c t o r y f i t i s d if f ic u lt to ob ta in , and b r a z in g the p la te to the r ib w ould b e b e t te r . In c r e a s in g the n u m b e r of teeth in eac h d e n ta te d p la te to 180, w ith a c o r re sp o n d in g d e c r e a s e in h e igh t, i s co n te m p la te d in o r d e r to re d u c e the d is tu r b a n c e of s o i l c a u se d by the tee th . T h e to rq u e w h eel i s m a d e o f s t e e l b e c a u se a lu m in u m w as not a v a i la b le a t the t im e the a p p a r a tu s w as b u ilt , bu t an a lu m in u m w h eel w ill r e d u c e the d e ad w eigh t and i s p r e f e r a b le .

V e r t ic a l L o ad in g S y s te m

V e r t ic a l lo a d s on the t e s t s p e c im e n a r e p r o d u c e d by a c o u n te rb a la n c e d , d ou b le le v e r s y s t e m , f ig u r e s 6, 9, and 10, and a r e t r a n sm it te d to the to rq u e w h ee l and a n n u lar p is to n by a lo ad in g ro d . A tu rn b u ck le in th is rod p e r m its a d ju s tm e n t of the l e v e r s to h o r iz o n ta l p o sitio n . U se of d o u b le l e v e r s in s te a d o f a s in g le l e v e r r e d u c e s the s p a c e o c c u p ie d by the te s t in g ben ch . D ou b le le v e r s a l s o p e rm it lo ad in g the h an g e r fro m the fr o n t o f the ben ch , thus en ab lin g load in g to b e p e r fo r m e d and m o v e m e n ts of the v e r t i c a l o r se t t le m e n t d ia l to b e o b se r v e d s im u lta n e o u s ly by a s in g le o p e r a to r . T he h o r iz o n ta l a r e a o f a t e s t sp e c im e n co n fo rm in g to the d e s ig n s p e c i f ic a t io n s i s 7 0 .9 4 s q u a r e c e n t im e te r s and the co m b in ed r a t io of the two l e v e r s w as d e s ig n e d to b e 7 .0 9 , so th a t 10 kg on the h an g e r w ould be eq u iv a len t to 1.0 k g /c m 2 on the t e s t

SINGLE MOTOR AND GEAR BOX MOVED INTO POSITION BEFORE START OF SHEAR TEST

ELEVATION

SCALE - INCHESI I I I I I---------------1--------------- 1-------------- 1---------------1--------------- 1--------------- 1---------------1---------------15 0 5 10 15 20 25 30 35 40

F i g u r e 9 . T e s t i n g b e n c h f o r t o r s i o n s h e a r a p p a r a t u s

21

s p e c im e n . T he d im e n s io n s of the c o m p le te d a p p a r a t u s v a r ie d only s l ig h t ly f r o m th o se s p e c i f ie d ; s e e P a r t IV. The d ead w eigh t of the to rqu e w heel, a n n u la r p is to n , e tc . c o r r e s p o n d s a p p r o x im a te ly tc 0.1 k g / c m ^ on the t e s t s p e c im e n .

T o r q u e L o a d in g S y s t e m s

C o n t r o l l e d - s t r e s s lo ad a p p l ic a t io n

T he r o t a r y b a s e of the a p p a r a tu s i s held s t a t io n a r y by the s e l f - l o c k i n g w o r m g e a r , and a to rq u e i s p ro d u ce d by two v e r y f l e x ib le w ire r o p e s , l / l 6 in . in d i a m e t e r , a t tac h ed to the to rq u e w h ee l by a d ju s t a b le c l a m p s , f i g u r e s 5 and 9. T h e w ir e r o p e s p a s s o v e r h o r iz o n ta l and v e r t i c a l guide s h e a v e s to a c o u n te rb a lan c e d b e a m and s c a l e p la t fo r m on w hich w eigh ts a r e p la c e d , f i g u r e 11. A ll guide s h e a v e s c an b e r a i s e d

F i g u r e 10 . V e r t i c a l l o a d in g s y s t e m F i g u r e 11. T o r s i o n l o a d in g s y s t e m

or lo w e re d until they a r e in the s a m e p lane a s the to rqu e wheel o r s o th a t the w ire r o p e s a r e h o r iz o n ta l a t the s t a r t of the te s t . T h e v e r t i c a l gu ide s h e a v e s a r e a t tac h ed to the yo k e of the p ro v in g f r a m e , s e e p a ge 22, w hich d e f le c t s a s the to r q u e load is

22

in c r e a s e d . T h e in flu e n c e of th e c o r re sp o n d in g s l ig h t do w n w ard s lo p e of th e w ire ro p e s b e tw e e n th e h o r iz o n ta l and v e r t i c a l gu ide s h e a v e s is n e g lig ib le in c a s e of c o n t r o l l e d - s t r e s s type of lo ad in g b u t is tak en in to c o n s id e ra t io n fo r c o n t r o l l e d - s t r a in ty p e of lo a d in g . T he d ia m e te r of th e to rq u e w h ee l, 10 .26 in ., w as so d e te rm in e d th a t, f r ic t io n c o n s id e re d , th e a v e ra g e s h e a r in g cou ld b e co m p u te d by th e s im p le e x p r e s - s io n Ta = S / 25 k g /c m ^ , w h e re S is th e to rq u e lo ad in kg; s e e page 7. T h is r e la t io n s h ip w as a l t e r e d s l ig h tly by m in o r d e v ia tio n s f ro m the d e s ig n s p e c if ic a t io n s and th e e s t im a te d in flu e n c e of f r ic t io n ; s e e p ag es 50, 5 9 -6 0 .

T he a n g u la r d is p la c e m e n t o r tw is t is d e te rm in e d by m e a n s of th e tw o tw is t d i a ls , f ig u re 9. Z e ro s e t t in g of th e d ia ls is p e r fo rm e d in p a r t by m e a n s of th e d ia l h o ld e rs and in p a r t by th e a d ju s ta b le d ia l s to p . T h e d ia ls m u s t be r e s e t w hen th e m o v e m e n t a p p ro a c h e s th e i r l im it in g ra n g e , and th is m a y b e a c c o m p lish e d by m o v in g th e d ia l s to p o r ro ta t in g th e b a s e of th e a p p a ra tu s by m e a n s of th e h an d w h ee l on th e w o rm g e a r . L a r g e tw is ts c a n a ls o be d e te rm in e d o r c h e c k e d a p p ro x im a te ly by m e a n s of th e to ta l tw is t in d ic a to r and th e g ra d u a tio n s on th e p le x ig la s c y l in d e r , f ig u re 7. T h e a v e ra g e d is p la c e m e n t in th e t e s t s p e c im e n is co m p u te d by th e fo rm u la s g iv en on p ag e 8. T he tw o tw is td ia ls a r e s p a c e d 10 in . a p a r t; th a t i s , D s = 10.0 in . T he m e a n d ia m e te r of th e t e s t s p e c im e n is Dm = 3.60 in .

T o rq u e m e a s u r in g u n it

T he m a g n itu d e of th e to rq u e e x e r te d d u rin g c o n t r o l l e d - s t r a in lo ad a p p lic a tio n i s d e te rm in e d by m e a n s of a to rq u e m e a s u r in g u n it, w h ich a ls o m a y b e u se d d u rin g th e l a s t s ta g e s of c o n t r o l l e d - s t r e s s lo ad a p p lic a tio n . T he to rq u e m e a s u r in g u n it co n s i s t s of a f l a t p ro v in g f r a m e m o u n te d on an a d ju s ta b le b a s e s c re w , a yo ke w ith gu ide and th r u s t s h e a v e s , and p o lish e d th r u s tb lo c k s ; s e e f ig u re s 5, 9, and 11. T he te n s io n in th e w ire ro p e s p a ss in g o v e r th e gu id e sh e a v e s c r e a te s a p p ro x im a te ly eq u a l h o r i z o n ta l and v e r t i c a l f o rc e s on th e y o k e . T h e h o r iz o n ta l f o r c e s a r e t r a n s m i t te d to th e th r u s tb l o c k s by th e t h r u s t s h e a v e s , and only th e v e r t i c a l f o rc e s a c t on th e p ro v in g f r a m e . T he te n s io n in th e w ire r o p e s n e a r th e to rq u e w h e e l, and th e re b y th e a p p lied to rq u e , is o b ta in e d by c o r r e c t in g th e v e r t i c a l f o rc e m e a s u r e d by th e p ro v in g f r a m e fo r th e in flu e n c e of f r ic t io n in th e gu id e sh e a v e s and of th e s l ig h t d e f le c t io n of the p ro v in g f r a m e and th e v e r t i c a l gu id e s h e a v e s .

T h e p ro v in g f r a m e is m a c h in e d f ro m a s in g le p ie c e of n ic k e l c h ro m iu m s te e l and th e n h e a t - t r e a t e d and g ro u n d to f in a l sh a p e . T he f r a m e is d e s ig n e d fo r a d e f le c tio n of 0.10 in . u n d e r a lo ad of 50 kg , c o r re sp o n d in g to an a v e ra g e s h e a r in g s t r e s s in th e t e s t s p e c im e n of ab o u t 2 .0 k g / c m 2 . T he f la t sh a p e of th e f r a m e p ro d u c e s a r e - la t io n s h ip b e tw e e n fo rc e and d e f le c t io n w h ich is m o r e n e a r ly l in e a r th a n th a t o b ta in ed by a fu ll c i r c u l a r p ro v in g r in g .

C o n t r o l le d - s t r a in lo ad a p p lic a tio n

A ch an g e f ro m c o n t r o l l e d - s t r e s s load a p p lic a tio n to th a t of c o n t r o l l e d - s t r a in

23

o r r a t e of d is p la c e m e n t is m a d e by re m o v in g th e w e ig h ts f r o m th e to rq u e - lo a d s c a le and ro ta t in g th e s h e a r a p p a ra tu s by m e a n s of th e h a n d w h ee l and w o rm g e a r u n ti l th e k n ife -e d g e in th e c e n te r of th e b a la n c e b e a m b e a r s a g a in s t th e fu lc ru m show n in f ig u re 11. T h e r e a f t e r th e w ire r o p e s w ill ho ld th e to rq u e w h ee l and a n n u la r p is to n m o r e o r le s s s ta t io n a ry w h ile th e lo w e r p a r t of th e s h e a r a p p a ra tu s is ro ta te d by m e a n s of th e w o rm g e a r and m o to r iz e d d r iv e . T he to rq u e a p p lie d to th e t e s t s p e c im e n o r th e a v e r a g e s h e a r in g s t r e s s in th e s o i l is d e te rm in e d by th e d e f le c t io n of th e p ro v in g f r a m e .

The m o to r iz e d d r iv e c o n s is ts of a l / 2 0 - h p e le c t r i c m o to r , a g e a r box , and a co u p lin g . The m o to r h a s a sp e e d of 1722.5 rp m , th e w o rm g e a r h a s a r a t io of 1:80, and th e g e a r b o x p ro v id e s f iv e s p e e d s of r o ta t io n of th e s h e a r a p p a ra tu s , c o r r e s p o n d ing to a v e ra g e r a t e s of d is p la c e m e n t in the t e s t s p e c im e n ra n g in g f ro m 0.01217 in . to 12.17 in . p e r m in u te .

T he a n g u la r d is p la c e m e n t of th e b a s e of th e s h e a r a p p a ra tu s is co m p u ted a s th e p ro d u c t of th e r a t e of r o ta t io n and th e t im e e la p s e d f ro m th e s t a r t of th e te s t . T he to rq u e w h ee l and a n n u la r p is to n a r e s u b je c t to a s l ig h t r o ta t io n b e c a u s e of s t r e t c h ing of the w ire r o p e s . T h is ro ta t io n is d e te rm in e d by m e a n s of th e tw is t d ia ls and m u s t be s u b tr a c te d f ro m th e r o ta t io n of th e b a s e to o b ta in th e a c tu a l tw is t of the te s t s p e c im e n .

D e te rm in a tio n of r e s id u a l s h e a r in g r e s i s ta n c e

T he to r q u e - tw is t d ia g r a m a f te r in i t i a l f a i lu r e and th e u l t im a te r e s id u a l s h e a r ing r e s i s t a n c e of th e s o i l a r e m o s t e a s ily d e te rm in e d by u se of c o n t r o l l e d - s t r a in ty pe of lo ad a p p lic a tio n . T h e t e s t is s im p ly c o n tin u ed u n ti l no f u r th e r d e c r e a s e o r ch an g e in th e to rq u e is in d ic a te d by th e p ro v in g f r a m e . H o w ev e r, an in c r e a s e in th e r a t e of d is p la c e m e n t s h o r t ly a f te r th e in i t ia l f a i lu r e m a y be d e s i r a b le , s in c e v e ry la r g e d i s p la c e m e n ts o ften a r e r e q u i r e d to r e a c h th e u l t im a te s h e a r in g r e s i s t a n c e .

T h re e m e th o d s m a y b e u se d to d e te rm in e th e r e s id u a l s h e a r in g r e s i s t a n c e w hen a t e s t is s t a r t e d w ith c o n t r o l l e d - s t r e s s lo ad a p p lic a tio n . F i r s t , th e ty p e of lo ad a p p lic a tio n m a y be ch an g ed to th a t of c o n tro lle d s t r a i n s h o r t ly a f te r in i t i a l f a i lu r e o c c u r s . T he seco n d m e th o d c o n s is ts of re m o v in g w e ig h ts f ro m th e lo a d s c a le u n ti l the d e fo rm a tio n s c e a s e and in c re a s in g th e lo ad in su i ta b ly s m a l l in c re m e n ts u n ti l r a p id d e fo rm a tio n s r e c o m m e n c e . T h is p ro c e d u re is r e p e a te d u n ti l a d e s i r e d n u m b e r of p o in ts on th e to r q u e - tw is t d ia g ra m a r e o b ta in e d o r the r e s id u a l s h e a r in g r e s i s t an ce is r e a c h e d . T h is m e th o d is r e la t iv e ly t im e -c o n s u m in g and p r im a r i ly s u i te d fo r slo w , d ra in e d t e s t s .

The u se of a th ird and s im p le m e th o d is m a d e p o s s ib le by in s e r t in g a te n s io n s p r in g in the w ire ro p e abo ve th e c o u n te rw e ig h t fo r th e to rq u e - lo a d s c a le , f ig u re s 6 and 9, and l im itin g th e t r a v e l of th is w e ig h t by an a d ju s ta b le s to p . T h e lo ad s c a le d e sc e n d s r a p id ly a f te r in i t i a l f a i lu r e , and th e c o u n te rw e ig h t m o v e s u p w a rd u n ti l i t r e a c h e s th e s to p . T he d o w n w ard m o v e m e n t of th e lo ad s c a le c o n tin u e s , b u t an in c r e a s in g ly la r g e p a r t of th e lo ad is ta k e n up by th e te n s io n s p r in g . T h e e ffe c tiv e

24

t o r q u e i s d e c r e a s e d by a c o r r e s p o n d i n g a m o u n t , a n d t h e m o v e m e n t s c o n t i n u e u n t i l

e q u i l i b r i u m is r e a c h e d . A d i s p l a c e m e n t c o r r e s p o n d i n g to th e t r a v e l of th e c o u n t e r

w e i g h t a n d th e e x t e n s i o n of t h e s p r i n g m a y n o t b e s u f f i c i e n t to d e c r e a s e t h e s h e a r

in g r e s i s t a n c e to i t s u l t i m a t e r e s i d u a l v a lu e , b u t t h e d i s p l a c e m e n t s c a n e a s i l y b e

i n c r e a s e d b y t u r n i n g t h e h a n d w h e e l of th e w o r m g e a r a n d r o t a t i n g th e b a s e of t h e a p

p a r a t u s . T h e t o r q u e is d e t e r m i n e d b y th e d e f l e c t i o n of t h e p r o v i n g f r a m e a n d t h e n e t

d i s p l a c e m e n t s b y m e a n s of t h e t o t a l t w i s t i n d i c a t o r .

25

PA R T III: T E S T IN G P R O C E D U R E S

I n tro d u c to ry R e m a rk s

T h e a d v a n ta g e s and l im i ta t io n s of th e to r s io n s h e a r a p p a ra tu s in i t s p r e s e n t s ta te of d e v e lo p m e n t, s u m m a r iz e d in P a r t I, m u s t b e ta k e n in to c o n s id e ra t io n in th e p lan n in g and p e r fo rm a n c e of to r s io n s h e a r t e s t s . Tw o of th e s e l im i ta t io n s a r e of p a r t i c u la r im p o r ta n c e . T he f i r s t is th a t th e te e th in th e d e n ta te d p la te s c a u s e a lo c a l , in i t i a l d i s tu r b a n c e of th e s o i l and m a y c r e a te a zo n e of w e a k n e s s u n le s s th e s o i l is s u b je c te d to p r e l im in a r y c o n s o lid a t io n in th e s h e a r a p p a r a tu s . T h e r e f o r e , th e to r s io n s h e a r a p p a ra tu s is n o t s u i ta b le fo r p e r f o rm a n c e of u n c o n so lid a te d u n d ra in e d t e s t s on u n d is tu rb e d s o i l s , n o r fo r any t e s t s u n d e r n o rm a l lo a d s w h ich do n o t c a u s e c o m p le te p e n e tr a t io n of th e te e th in to th e s o i l b e f o r e th e s t a r t of th e a c tu a l s h e a r t e s t . T h is l im i ta t io n m a y b e p a r t ia l ly e l im in a te d by u s e of th e S w ed ish m e th o d of e s ta b lis h in g a bond b e tw e e n s o i l and m e ta l by m e a n s of g e la tin a s p re v io u s ly d e s c r ib e d .

T h e se c o n d l im ita t io n is th a t d r a in a g e of th e s o i l c a n n o t b e fu lly p re v e n te d d u rin g a t e s t , and th a t “ un d ra in ed * * t e s t s m u s tb e p e r fo rm e d a s q u ick t e s t s w ith so m e d r a in a g e ta k in g p la c e . T h e r e fo re , i t i s e s s e n t ia l th a t c h a n g e s in vo id r a t io o r w a te r c o n te n t d u r in g a t e s t be d e te rm in e d a s a c c u r a te ly a s p o s s ib le , and th a t th e s h e a r in g r e s i s t a n c e o b ta in e d be c o r r e c te d fo r th e in f lu e n c e of su c h c h a n g e s . A ls o , r e l i a b le c o r r e c t io n s and in g e n e ra l f in a l c o r r e la t i o n s of th e r e s u l t s of a s e r i e s of t e s t s r e q u ir e th a t th e in d iv id u a l t e s t s in a p a r t i c u la r s e r i e s be p e r f o rm e d on s o i l w ith th e s a m e p h y s ic a l p r o p e r t ie s . T h e r e f o r e , e v e ry e f fo r t sho u ld b e m a d e to o b ta in o r s e le c t s a m p le s of u n ifo rm s o i l fo r e a c h s e r i e s of t e s t s .

T h e a b o v e -m e n tio n e d l im i ta t io n s and r e q u i r e m e n ts h av e b e e n ta k e n in to co n s id e r a t io n in fo rm u la tin g th e fo llo w in g d e ta i le d d i re c t io n s fo r th e p e r f o r m a n c e of t e s t s w ith th e W a te rw a y s E x p e r im e n t S ta t io n to r s io n s h e a r a p p a ra tu s .

P r e p a r a t io n of T e s t S p ec im en

S a m p le r e m o v a l an d cu ttin g

T h e o u ts id e d ia m e te r of th e to r s io n s h e a r t e s t s p e c im e n is 4 .5 0 in ., an d th e s o i l s a m p le s u s e d in i t s p r e p a r a t io n sh o u ld h av e a d ia m e te r of n o t l e s s th a n 4 - 3 /4 in . to p e r m i t r e m o v a l of p a r t i a l ly d i s tu r b e d s o i l n e a r th e c y l in d r ic a l s u r f a c e of th e s a m p le an d a ls o to e n s u re th a t th e t e s t s p e c im e n f i ts t ig h tly in th e s h e a r a p p a ra tu s . T he s a m p le s u s e d in th e t e s t s so f a r p e r f o rm e d w e re o b ta in e d w ith a th in -w a lle d p is to n s a m p le r and w e re p r e s e r v e d in th e tub ing w h ich h ad an in s id e d ia m e te r of 5 - 1 /2 in . T h e h an d lin g of th e s e s a m p le s , a s d e s c r ib e d in th e fo llo w in g p a r a g r a p h s , m ay b e c o n s id e re d ty p ic a l fo r s a m p le s p r e s e r v e d in sa m p lin g tu b e s .

26

T h e s a m p le and tu be a r e f i r s t c u t in to 6 - in .- lo n g s e c t io n s . A h a c k saw o r ban d saw w ith f in e te e th is u s e d to c u t th ro u g h th e tu b in g , b u t th e s a m p le p ro p e r sh o u ld b e c u t w ith a w ire saw to m in im iz e d is tu r b a n c e of th e s o i l . C a r e sh o u ld b e ta k e n to p ro d u c e sm o o th c u ts p e rp e n d ic u la r to th e a x is of th e tu b in g . O ne of th e s e c tio n s is s e le c te d fo r te s t in g , an d th e o th e r s a r e r e - s e a l e d fo r f u tu re u s e . T h e top and b o tto m s e c t io n s sh o u ld n o t b e u s e d fo r im p o r ta n t t e s t s s in c e th e s o i l th e r e in u s u a lly is p a r t i a l ly d is tu rb e d . A ll th e fo llow ing c u ttin g and tr im m in g o p e ra t io n s shou ld b e p e r f o rm e d in a m o is t ro o m .

B u r r s on th e tub ing of th e s e le c te d s e c t io n a r e re m o v e d w ith a s p e c ia l s c r a p e r , and any i r r e g u l a r i t i e s of th e b o tto m of th e s a m p le a r e r e p a i r e d o r e lim in a te d by m e a n s of a b ro a d g la z ie r ’s k n ife . T h e s a m p le sh o u ld b e p u sh ed ou t in th e s a m e d i r e c t io n i t o r ig in a l ly e n te re d th e tu b in g , and i t i s im p o r ta n t th a t th e b o tto m of th e s a m p le b e p la n e and p e rp e n d ic u la r to th e a x is of th e tu b ing ; o th e rw is e , a p la s t ic flow and d i s tu r b a n c e of th e s o i l m a y ta k e p la c e d u rin g th e r e m o v a l o p e ra t io n s . T h e b o tto m of th e s a m p le is now c o v e re d w ith a s h e e t of w ax p a p e r , cu t to th e s a m e d ia m e te r a s th e s a m p le , and th en p la c e d on a p e d e s ta l hav in g a sm o o th and p lan e to p and a d ia m e te r s l ig h t ly le s s th an th a t of th e s a m p le . T h e tu be s e c tio n is th e n re m o v e d by h a n d -p u ll o r by p r e s s in g dow n on i t s u p p e r edge w ith a s te e l r in g o r s e c t io n of p ipe h av in g an in s id e d ia m e te r s l ig h t ly l a r g e r th an th a t of th e tu b in g .

P r e l im in a r y tr im m in g

T h e 6 - in . s a m p le s e c t io n is p la c e d in a m i te r bo x and a th in s l i c e c u t f ro m e a c h end to re m o v e p a r t i a l ly d i s tu r b e d s o i l . T h re e t e s t s p e c im e n s fo r to r s io n s h e a r t e s t s c a n b e c u t f ro m th e s a m p le s e c t io n , b u t on ly tw o t e s t s p e c im e n s w e re c u t f ro m e a c h s e c t io n in th e te s t s p e r f o rm e d in o r d e r to p e r m i t p r e p a r a t io n of s p e c im e n s fo r u n co n fin ed c o m p re s s io n te s t s f r o m th e c o r e s . T h e fo llow ing o p e ra t io n s a r e show n d ia g r a m m a t ic a l ly in f ig u re 12.

T h e s a m p le s e c tio n is p la c e d on a g la s s p la te c o v e re d w ith w ax p a p e r , and a 2 - 1 /2 - in . s e c t io n is cu t off by m e a n s of tw o gu id es and a w i r e s a w , f ig u re 12 — 1. T he top of th e s e c t io n is re m o v e d in a s lid in g m o tio n and p r e s e r v e d in p a ra f f in fo r fu tu re u s e . A c i r c l e w ith a d ia m e te r of 2 - 1 / 4 in . i s in s c r ib e d on e a c h end of th e s e c t io n to b e u s e d fo r te s t in g . T h is is a c c o m p lis h e d by m e a n s of a n e e d le an d an a n n u la r gu ide p la te w ith th e s a m e o u ts id e d ia m e te r a s th a t of th e s a m p le , f ig u re 1 2 -2 . Tw o o th e r a n n u la r gu id e p la te s w ith an o u ts id e d ia m e te r of 4 - 3 / 4 in . a r e now p la c e d on th e ends of th e s e c t io n and c e n te re d by m e a n s of th e in s c r ib e d in n e r c i r c l e s , f ig u re 12-3 ; w h e re u p o n , th e o u ts id e of th e s a m p le is t r im m e d and th e c o r e is c u to u t w ith a s p e c ia l w i r e s a w . A n e e d le a tta c h e d to one end of th e w ire is p u sh ed th ro u g h th e s a m p le , f ig u r e 1 2 -4 , an d lo c k e d a lo ng one s id e of th e saw in su c h a m a n n e r th a t th e >V ireis t ig h tened . A c u t is m a d e along th e in s id e edg e of th e gu id e p la te s , f ig u re 12 -5 ; th e n e e d le is th e n u n lo c k e d , and th e saw an d th e c o re a r e re m o v e d . T h e c o r e is w ra p p e d in w ax p a p e r and p la c e d in a h e r m e t ic a l ly s e a le d j a r u n ti l u s e d fo r u n co n fin ed c o m p re s s io n t e s t s ; s e e p ag e 29 .

27

CDSAMPLE SLICED HORIZONTALLY

REMOVE TOP WITH SLIDING MOTION

(2)CIRCLE SCRIBED ON TOP AND BOTTOM

OF SAMPLE WITH A NEEDLE

(3)OUTSIDE OF SAMPLE

TRIMMED TO 4 ^ IN. DIAMETER

NEEDLE OF SPECIAL WIRE SAW PUSHED INTO SAMPLE

INSIDE OF SAMPLE TRIMMED WITH SPECIAL WIRE SAW

JUST BEFORE CUTTING INTO SAM PLE IN TRANSFER RINGS

F i g u r e 12. P r o c e d u r e f o r p r e p a r i n g t e s t s p e c i m e n

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The height of the roughly trimmed annular soil section is now reduced to

I-3/4 in. by means of a carefully machined guide ring and a wire saw, figure 12-6,

since such a reduction in height facilitates the final trimming. Great care should be exercised in producing smooth and plane end surfaces, and small cavities or other

irregularities caused by extraneous matter in the soil should be repaired. A part of the discarded end of the annular section may be used for determination of the water

content of the soil; see page 30 .

Final trimming

The object of the final trimming is to produce a test specimen with the prescribed inside and outside diameters and firmly placed within the transfer rings

which have a wall thickness of l / l 6 in. The initial height of the test specimen is varied in such a manner that the distance between the teeth in the dentated plates is

not less than 3/4 in. after completion of the preliminary consolidation and at the

start of the actual shear test. An initial height of 7 / 8 in., equal to the height of the transferrings, is sufficient when the soil is stiff and the vertical normal load during consolidation and testing is small. However, initial heights up to l - l / 4 in. may be required for soft soils and high normal loads. The approximate required height can

be estimated from the results of consolidation tests or previous torsion shear tests

under relatively small normal loads.

The final trimming of test specimens consisting of hard and brittle soils

should be performed gradually while forcing the soil into the transfer rijigs. The

procedure is similar to that used for preparation of test specimens for consolidation tests, but guides for the transfer rings are required to hold them in concentric position during the trimming operation. The final trimming can be performed more

easily by use of a specimen cutter, figure 12- 7 , when the soil is more or less plastic.

The specimen cutter consists of an aluminum guide cylinder with polished

sides and bottom. Sliding on this cylinder are a pair of steel rings with sharp cutting

edges, the transfer rings, and a pair of extension rings. The cutting rings and extension rings have the same inside and outside diameters as the transfer rings. A cap with vents and a steel ball in the center is placed on top of the extension rings. The annular soil sample is transferred to a pedestal with plane and parallel end surfaces and the top surface covered with cardboard and wax paper of uniform thickness. The specimen cutter is then placed on top of the annular sample and aligned concentrically; whereupon, the assembly is moved to a testing or loading machine

with vertical and controlled travel of the yoke or piston. Pressure is applied to the steel ball in the cap, and the rings are forced slowly down through the soil until the distance from the lower end of the transfer rings to the top of the sample is equal to

the desired height of the test specimen, figure 12-8.

The assembly is now transferred back to the moist room; the soil below the

cutting rings is trimmed off, and the cap and surplus soil adhering to the rings are

29

re m o v e d . T he a s s e m b ly i s p la c e d on a p la n e s u r f a c e , b a s e dow n, and th e s a m p le i s cu t with the fin e w ire saw th rou gh the jo in t betw een the cu ttin g r in g s and t r a n s f e r r in g s ; w h ereu pon , the e x te n s io n r in g s and the a lu m in u m gu id e c y lin d e r a r e re m o v e d . T he r e su lt in g t e s t sp e c im e n su p p o rted by the t r a n s f e r r in g s i s show n in f ig u r e 1 2 -9 . T h e p r o c e d u re i s s im p lif ie d when the t e s t sp e c im e n h a s the s a m e h eigh t a s the t r a n s fe r r in g s ; the c u tte r i s then pu sh ed th rou gh the s a m p le and a cu t i s m ad e a t the top and bo ttom o f the r in g s . T he s u r f a c e s o f the t e s t sp e c im e n should be in sp e c te d fo r s c r a t c h e s and o th er im p e r fe c t io n s c a u se d by e x tr a n e o u s m a t te r in the s o i l . I f the im p e r fe c t io n s a p p e a r s e r io u s , the t e s t sp e c im e n sh ou ld be d is c a r d e d , bu t m in o r im p e r fe c t io n s m a y be r e p a ir e d , e sp e c ia l ly when th e t e s t sp e c im e n i s to be su b je c te d to p r e l im in a r y c o n so lid a tio n u n d er r e la t iv e ly h igh n o rm a l lo a d s . A p a r t o f the s o i l w ithin the cu ttin g r in g s m a y b e u se d fo r d e te rm in a t io n of w a te r co n ten ts; s e e p a g e 30,

P r e l im in a r y M e a su r e m e n ts and T e s t s

In it ia l h e igh t and w eigh t

T h e h e igh t and w eight of the t e s t sp e c im e n a f te r f in a l tr im m in g sh ou ld be d e te rm in e d c a r e f u l ly to p e rm it r e l ia b le e s t im a t e s o f the in it ia l w a te r co n ten t and of c h a n g e s in v o lu m e and w ater con tent du rin g the t e s t . The in it ia l h eigh t sh ou ld p r e f e r a b ly be d e te rm in e d by m e a n s of a c o m p a r a to r , w hich m a y be im p r o v ise d by m e a n s o f an in d ic a to r d ia l , and a r ig id su p p o r t stan d with a m ac h in ed , p lan e s u r fa c e of the b a s e p la t e a s show n in fig u re 13. T h e d ia l s te m m a y be p ro v id e d with a f la t , c i r c u la r p la te , so th a tth e h e igh t o f the t e s t sp e c im e n can be m e a s u r e d d ir e c t ly , but c o v e r in g the sp e c im e n with ce llo p h an e sh e e ts and b r a s s p la t e s of known th ic k n e ss to p r e ven t a d h e s io n o f the s o i l to o th er s u r f a c e s i s p r e f e r r e d .

U nconfined c o m p r e s s io n t e s t s

T h e s o i l c o r e ob ta in ed in the tr im m in g o p e r a t io n s , f ig u r e 1 2 -5 , m ay be u se d fo r p r e p a r a t io n of t e s t s p e c i m e n s fo r u n con fin ed c o m p r e s s io n t e s t s and c o n c u rre n t d e te rm in a tio n of the w ate r co n te n to f th e s o i l . P e r fo r m a n c e o f un confined c o m p r e s s io n t e s t s on both u n d istu rb e d and re m o ld e d s o i l i s a d v is a b le in o rd e r to ob ta in a d d itio n a l d a ta on the s tre n g th and s e n s it iv ity o f the s o i l . An u n d istu rb e d t e s t sp e c im e n , 1 in. in d ia m e te r and 2 in . lon g , m a y be o b ta in ed co n v en ien tly by m e a n s of a th in -w a ll s a m p le r with f r e e p is to n (8 ) .

F ig u r e 13. M e a su r in g in i t ia l h e igh t of t e s t sp ec im en

30

L o c a l f a i lu r e or c r a c k in g o f the s o i lm a y o c c u r u n le s s the c o r e i s su p p o rted l a t e r a l ly w h ile the p is to n s a m p le r i s be in g push ed th rou gh it , bu t the su p p o r t m u s t be s u f f i c ie n tly f le x ib le to a llo w s o i l d is p la c e d by the sa m p lin g tube p ro p e r to e s c a p e l a t

e r a l ly . Such a f le x ib le su p p o rt can be o b ta in ed by p la c in g the s o i l c o r e w ithin a se c t io n of tu b ing and f i ll in g the a n n u la r sp a c e w ith lo o s e san d , f ig u re 14.

T h e t e s t sp e c im e n should be p r e p a re d and the uncon fin ed c o m p r e s s io n t e s t p e r fo r m e d a s soon a s p o s s ib le a f te r the s o i l c o r e i s o b ta in ed , s in c e the s o i l w ill lo s e so m e w ate r even though the c o r e i s s to re d in a h e r m e t ic a l ly s e a le d j a r . T he w et w eigh t of the t e s t sp e c im e n should be d e te rm in e d im m e d ia te ly a f te r i t s p r e p a ra tio n , s in c e so m e w ate r m ay be lo s t d u r ing te s t in g , th e re b y c a u s in g e r ro n e o u s e s t im a t e s o f the in it ia l w a te r co n ten t of the to r s io n sh e a r t e s t sp e c im e n . T he u n con fined c o m p r e s s io n t e s t sp e c im e n sh ould

be w eigh ed a g a in upon c o m p le tio n of the t e s t . T e s t sp e c im e n s ob ta in ed w ith the p is to n s a m p le r h ave a c o n sta n t and known v o lu m e , and the d e g r e e of s a tu ra t io n o f the s o i l can be co m p u ted when the w et and d ry w eigh ts of sp e c im e n a r e known and the s p e c i f ic g r a v ity of the s o i l g r a in s i s d e te rm in e d or e s t im a te d . T he u n d istu rb e d t e s t sp e c im e n sh o u ld not be re m o ld e d and r e te s t e d a f te r the u n con fin ed c o m p r e s s io n t e s t s in c e l o s s of w a te r and s o i l du rin g th e se o p e r a t io n s i s d if f ic u lt to av o id . A t e s t s p e c

im e n of re m o ld e d s o i l sh o u ld be p r e p a r e d fro m the re m a in in g p a r t s o f the c o r e .

PISTON ROD

LOOSE FILL OF MEDIUM SAND,

BASE PLATE

TH IN -W A LL TUBE I.D.= I"

LEATHER PACKING

WAX PAPER

F i g u r e 14. Cutting UC t e s t s p e c im e n f r o m so i l c o r e

In it ia l w a te r-c o n te n t d e te rm in a t io n s

T h e in i t ia l v o lu m e and w et w eigh t of the a n n u la r t e s t sp e c im e n a r e known, bu t the c o rre sp o n d in g d ry w eigh t can n ot b e d e te rm in e d d ir e c t ly b e c a u s e a p a r t of the s o i l o ften i s sq u e e z e d out through the c le a r a n c e betw een the con fin in g r in g s d u rin g the t e s t . H o w ev er, the in i t ia l w a te r con ten t can be e s t im a te d by a s su m in g th at the s p e c i f ic g ra v ity o f the s o i l g r a in s and the d e g re e of s a tu r a t io n a r e the s a m e a s th o se obta in ed fo r the u n d istu rb e d , u n con fin ed c o m p r e s s io n t e s t sp e c im e n . It i s a d v is a b le a l s o to d e te rm in e the w a te r co n ten t of the s o i l d ir e c t ly abo ve and below the an n u lar t e s t sp e c im e n by u se of the s o i l s l i c e s ob ta in ed in the tr im m in g o p e r a t io n s , f ig u r e s 1 2 -6 and 1 2 -8 . D if f ic u lt ie s en cou n tered in e v a lu a tin g r e s u l t s o f t e s t s so f a r p e r fo rm e d d e m o n stra te d th at the ab o v e-m en tio n ed p re c a u tio n s in d e te rm in a tio n of the in it ia l w ate r content a r e not e x c e s s iv e when the s o i l i s v a r ia b le in c h a r a c te r .

31

P la c in g of T e s t S p e c im e n

P r e l im in a r y o p e ra t io n s

B e fo re a s s e m b lin g th e s h e a r a p p a ra tu s , th e d e n ta te d p o ro u s p la te s m u s t b e th o ro u g h ly s a tu r a te d by so ak in g th e m in d is t i l le d w a te r fo r s e v e r a l h o u r s . T he lo w e r p la te is th e n p la c e d on th e r ib in th e ro ta t in g b a s e , and th e lo w e r co n fin in g r in g s a r e add ed and so a d ju s te d th a t th e d ra in a g e h o le s in th e r in g s an d th e r ib a r e a lig n e d . T he p le x ig la s c y l in d e r is th e n p u sh ed dow n in to i t s g ro o v e , and th e r e s e r v o i r f i l le d w ith d is t i l le d w a te r u n ti l i t r e a c h e s th e b a s e of th e te e th in th e lo w e r d e n ta te d p la te .

T he a p p a ra tu s is now p a r t ia l ly a s s e m b le d w ith a lu c i te m o d e l of th e t e s t s p e c im e n in o r d e r to o b ta in c o r r e c t s e tt in g of th e v e r t i c a l d ia l . T h is m o d e l of th e t e s t sp e c im e n is a b o u t7 /8 in . h igh ; i t s a c tu a lh e ig h t is c a re fu l ly m e a s u r e d w ith a m ic r o m e te r o r c o m p a ra to r . C a r e sh o u ld be ta k e n to tig h te n th e s c r e w s b e tw een th e d ia l c a r r i e r f r a m e an d th e b a s e p la te to th e s a m e d e g re e in th e p r e l im in a r y and f in a l a s sem b ly of th e a p p a ra tu s . T h e h e ig h ts of th e lu c ite m o d e la n d th e a c tu a l t e s t s p e c im e n b e in g know n, th e d ia l is now a d ju s te d so th a t i t w ill r e a d 0 .1000 in . w hen th e te e th of th e d e n ta te d p la te s hav e b e e n fo rc e d c o m p le te ly in to th e t e s t s p e c im e n . T he h e ig h t of th e t r ia n g u la r te e th is 0 .059 in ., and each of th e d e n ta te d p la te s w ill m o v e a d i s ta n c e of l / 2 x 0 .059 in . to w a rd s th e t e s t sp e c im e n . T he d ia l is s e t a t th e a b o v e - m en tio n e d f ig u re in s te a d of z e r o b e c a u s e fu ll p e n e tr a t io n of th e te e th w ill n o t b e a t ta in ed u n d e r th e in i t i a l s m a l l n o rm a l lo a d s , and b e c a u s e s o m e s o ils m ay u n d e rg o an in i t i a l sw e llin g by c o n ta c t w ith w a te r . T he p r e l im in a r y a s s e m b ly is d is m a n tle d w hen th e d ia l s e tt in g is c o m p le te d .

P la c in g w ith d iv id e d r in g s

T h e t e s t s p e c im e n s u p p o rte d by th e t r a n s f e r r in g s is p la c e d b e tw e e n th e lo w e r con fin ing r in g s and pu sh ed dow n to th e d e n ta te d p la te . T h e do w n w ard m o v e m e n t sho u ld b e s lo w to a llo w a i r be low the t e s t s p e c im e n to e s c a p e th ro u g h th e v e ry s m a l l c le a r a n c e b e tw e e n th e r in g s . T he inner,, u p p e r co n fin in g r in g w ith i t s gu id e b e a r in g is now p laced in p o s itio n w ith th e e le v a to r s c re w s in a p lan e fo rm in g a p p ro x im a te ly 45 d e g re e s w ith th e a x is of th e te s t in g ben ch ; s e e f ig u re 9. A c y lin d e r w ith a sm o o th f i t i s now p u sh ed dow n o v e r th e lo w e r , o u te r r in g and s e r v e s a s a gu ide fo r th e u p p e r , o u te r r in g w h ich is p la c e d w ith th e e le v a to r s c re w s in a p la n e p e rp e n d ic u la r to th a t fo rm e d by th e e le v a to r s c re w s of th e in n e r r in g . T h e e le v a to r s c re w s a r e f in a l ly a lig n ed by m e a n s of a p la te in w h ich h o le s a r e d r i l le d c o r re sp o n d in g to th o se in th e to rq u e w h ee l. N e c e s s a r y a d ju s tm e n ts a r e m a d e by ro ta t in g th e in n e r r in g in p r e f e re n c e to th e o u te r r in g . P r e s s u r e i s now a p p lie d to th e p la te , and b o th u p p e r r in g s a r e fo rc e d dow n u n ti l th ey a r e in c o n ta c t w ith th e lo w e r r in g s . In th is o p e ra t io n th e t r a n s f e r r in g s a r e p u sh ed dow n in to r e c e s s e s in th e lo w e r con fin in g r in g s . T h e p la te and gu ide c y l in d e r a r e now re m o v e d . S u b seq u en t o p e ra t io n s a r e d e s c r ib e d u n d e r th e h ead in g “ C o m p le tio n of a s s e m b ly .“

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P la c in g w ith s in g le r in g s

T h e s p a c e r r in g s and gu ide b e a r in g , (39) and (37) in f ig u r e 7 - B , a r e p la c e d f i r s t , and the w ate r le v e l in the r e s e r v o i r a d ju s te d u n til i t i s s lig h tly ab o ve the tee th in the lo w er d en tated p la te . T h e t e s t sp e c im e n w ith t r a n s f e r r in g s is p la c e d in a p p ro x im a te c o n c e n tr ic p o s it io n on the d en tated p la te . F in a l a lig n m en t i s ob ta in ed by in s e r t in g f i r s t the in n er con fin in g r in g and then the o u te r r in g so th at they r id e on the t r a n s fe r r in g s ; then both con fin in g r in g s a s a u n it a r e push ed down to the b a s e . In the p r e s e n t a p p a r a tu s , the d r a in a g e h o le s in the b a s e r ib and the r in g s m u s t be a lig n e d , but su ch an a lig n m e n t i s not r e q u ire d in an a p p a r a tu s b u ilt in a c c o r d a n c e w ith the r e v is e d d e s ig n b e c a u s e of the s m a l l c i r c u la r g r o o v e s in the r ib and r in g s .

P la c in g of re m o ld e d s o i l

T e s t sp e c im e n s o f re m o ld e d c o h e s iv e s o i l s m a y b e p re p a re d and t r a n s f e r r e d to th e s h e a r a p p a r a tu s in the s a m e m an n er a s th o se of u n d istu rb e d s o i l , p ro v id ed a s u ff ic ie n t am o u n t of r e m o ld e d s o i l i s a v a i la b le . H o w ev er , in m o s t c a s e s it i s m o r e co n ven ien t to p la c e the re m o ld e d s o i l d ir e c t ly in the p a r t ia l ly a s s e m b le d sh e a r a p p a r a t u s . T h e r e q u ir e d in i t ia l h e igh t of the t e s t sp e c im e n is f i r s t e s t im a te d , and the v e r t i c a l d ia l i s s e t in a c c o r d a n c e th erew ith , u s in g p a r t ia l p r e l im in a r y a s s e m b ly w ith the lu c ite m o d e l of the t e s t sp e c im e n . It sh ou ld be noted th at only the p e n e tra t io n of the tee th in the u pper d en tated p la te shou ld be c o n s id e r e d in com pu tin g the d ia l s e t tin g . T h e a p p a r a tu s i s then a s s e m b le d with the t r a n s fe r r in g s and the in n er and ou ter co n fin in g r in g s in p la c e . When d iv id ed r in g s a r e u se d , the u p p e r , ou ter con fin in g r in g s a r e h eld in p ro p e r p o s it io n s by m e a n s of the gu id e cy lin d er d e sc r ib e d p r e v io u s ly . T h e w ate r le v e l in the b a s e r e s e r v o i r i s so a d ju ste d th at it r e a c h e s the b a s e of th e teeth in the low er d en tated p la te . T he re m o ld e d s o i l i s now p lace d in thin and o v e r la p p in g l a y e r s , c a r e b e in g tak en to avo id in c lu s io n of a i r b u b b le s in the t e s t s p e c im e n . A le v e l s u r fa c e and c o r r e c t h eigh t of the t e s t sp e c im e n a r e ob ta in ed by u se of one o f the s c r a p e r s show n in f ig u r e 15.

A -ADJUSTABLE HEIGHT

□Ö —

GUIDE EARS FOR HOLDING SCRAPER VERTICAL POSITION

F i g u r e 15. S c r a p e r s fo r t r im m in g re m o ld e d s o i l s p e c im e n

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C om p letion of a sse m b ly

T h e s u r f a c e of th e t e s t s p e c im e n i s c o v e r e d w ith d i s t i l l e d w a t e r to a d e p th o f a b o u t 1 /3 2 i n . , an d t h r e e f e e l e r g a g e s , b e n t i n t o .a 9 0 ° a n g le , a r e s p a c e d a b o u t 120 a p a r t a lo n g t h e u p p e r e d g e of t h e o u t e r c o n f in in g r i n g . T h e s e g a g e s s e r v e to g u id e th e a n n u la r p i s to n a n d to r q u e w h e e l in to c o r r e c t p o s i t io n w h e n th i s u n i t i s b e in g lo w e r e d s lo w ly u n t i l th e d e n ta te d p la te r e s t s on to p of th e s p e c im e n . T h e lo w e r in g o p e r a t i o n i s f a c i l i t a t e d b y a p a i r o f b lo c k s p la c e d on th e r o t a t i n g b a s e to s u p p o r t th e h a n d s h o ld in g th e t o r q u e w h e e l a n d p is to n . T h e e l e v a t o r s c r e w s s h o u ld n o t t o u c h th e s id e s of th e h o le s in th e t o r q u e w h e e l , a n d f in a l s l i g h t a d ju s tm e n t s m a y b e m a d e b y r o t a t i n g th e i n n e r r in g an d e l e v a to r s c r e w s ; w h e r e u p o n th e n u ts a r e a d d e d . T h e t h r e e f e e l e r g a g e s a r e r e m o v e d a f t e r a f i n a l c h e c k on th e p o s i t io n of th e a n n u la r p is to n . T h e lo a d in g r o d i s now i n s e r t e d a n d c o n n e c te d to th e l e v e r s y s t e m b y m e a n s o f th e tu r n b u c k le w h ic h i s r o t a t e d u n t i l th e l e v e r s a r e in h o r i z o n t a l p o s i t io n . T h e d i a l c a r r i e r f r a m e w i th th e p r e v io u s ly s e t v e r t i c a l d i a l i s th e n f a s t e n e d to th e b a s e p la te , an d th e w i r e r o p e s a r e a t t a c h e d to th e t o r q u e w h e e l b y th e a d ju s t a b le c l a m p s s in c e t h e i r w e ig h t i s in c lu d e d in th e d e a d w e ig h t a c t in g on th e t e s t s p e c im e n .

P r e lim in a r y C on so lid a tion

T h e o u t e r j o in t b e tw e e n d iv id e d c o n f in in g r i n g s sh o u ld b e s e a l e d w i th g r e a s e o r c e l lo p h a n e t a p e d u r in g th e p r e l i m i n a r y c o n s o l id a t io n of th e t e s t s p e c im e n . T h e lo a d l e v e r s s h o u ld b e c e n t e r e d c a r e f u l l y b e tw e e n th e f u l c r u m s u p p o r t s to a v o id f r i c t io n a n d to i n s u r e u n i f o r m d i s t r i b u t i o n of th e v e r t i c a l lo a d . A lo a d in g s c h e d u le s i m i l a r to t h a t of s t a n d a r d c o n s o l id a t io n t e s t s m a y b e u s e d ; t h a t i s , e a c h lo a d i n c r e m e n t i s a p p r o x im a t e ly e q u a l to th e e x i s t in g lo a d . T h e d e a d w e ig h t of th e t o r q u e w h e e l , a n n u la r p is to n , e t c . , c o r r e s p o n d s a p p r o x im a te ly to 0.1 k g /c m ^ , an d th e i n i t i a l lo a d in c r e m e n t on th e h a n g e r s h o u ld n o t e x c e e d 1.0 kg u n le s s th e s o i l i s v e r y s t i f f . E a c h lo a d i n c r e m e n t n e e d n o t b e c o m p le t e ly c o n s o l id a te d e x c e p t w h en a c o n s o l id a t io n d i a g r a m i s to b e o b ta in e d . H o w e v e r , c a r e s h o u ld b e ta k e n n o t to i n c r e a s e th e lo a d so r a p id ly t h a t a c o n d it io n of p l a s t i c f lo w i s c r e a t e d an d s o i l i s f o r c e d up in to th e v e r y s m a l l c l e a r a n c e b e tw e e n th e c o n f in in g r in g s an d th e a n n u la r p is to n . C o n s o l id a t io n u n d e r th e m a x im u m v e r t i c a l lo a d s h o u ld b e c o m p le te b e f o r e th e a c tu a l s h e a r t e s t i s s t a r t e d o r b e f o r e th e m a x im u m lo a d i s d e c r e a s e d to c r e a t e a s t a t e of o v e r c o n s o l i d a t io n in th e s o i l .

T h e w a t e r in th e b a s e r e s e r v o i r an d in th e f o u r h o le s in th e a n n u l a r p is to n s h o u ld b e r e p l e n i s h e d a s n e e d e d . T h e l e v e r s o f th e v e r t i c a l lo a d in g s y s t e m s h o u ld b e r e a d j u s t e d to h o r i z o n t a l p o s i t io n a t f r e q u e n t i n t e r v a l s , a n d th e d e f l e c t io n o f th e lo w e r l e v e r a n d lo a d h a n g e r s h o u ld n o t b e a l lo w e d to e x c e e d 3 /4 in . A d e f l e c t io n of th e l e v e r s d e c r e a s e s th e n o r m a l lo a d s l ig h t ly an d i n t r o d u c e s a h o r i z o n t a l f o r c e w h ic h m a y c a u s e d r i f t i n g o r t ip p in g of th e to r q u e w h e e l an d a n n u la r p is to n , t h e p o s i t i o n of w h ic h s h o u ld b e c h e c k e d by m e a n s of th e f e e l e r g a g e s a n d a s p i r i t l e v e l . D r i f t in g a n d t ip p in g o f th e a n n u la r p is to n m a y a l s o b e c a u s e d b y n o n - u n i f o r m i ty o f t h e s o i l in

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th e t e s t s p e c im e n a n d , d u r in g th e a c t u a l s h e a r t e s t , b y i m p r o p e r a d j u s t m e n t o f th e g u id e s h e a v e s o r s o i l b e in g s q u e e z e d o u t th r o u g h th e c l e a r a n c e b e tw e e n d iv id e d c o n f in in g r i n g s . A s l ig h t a m o u n t o f t ip p in g o r d r i f t i n g , a l th o u g h u n d e s i r a b l e , m a y b e t o l e r a t e d w h e n d iv id e d r i n g s a r e u s e d . M o v e m e n ts l a r g e e n o u g h to c a u s e c o n ta c t b e tw e e n th e r i n g s a n d th e p is to n a r e u s u a l l y c a u s e f o r r e j e c t i o n o f th e t e s t , e s p e c i a l ly w h e n u n d iv id e d o r s in g le r i n g s a r e u s e d .

A r e c o r d s i m i l a r to t h o s e o f s t a n d a r d c o n s o l id a t io n t e s t s s h o u ld b e k e p t o f t im e , l o a d s , a n d r e a d in g s o f th e v e r t i c a l d ia l . I t i s r e c a l l e d t h a t th e z e r o s e t t i n g f o r th e d ia l i s 0 .1 0 0 in . f o r f u l l p e n e t r a t i o n of th e t e e t h in th e d e n ta te d p l a t e s . T h e r e f o r e , a c t u a l c h a n g e s in h e ig h t o f t h e t e s t s p e c im e n a r e c o m p u te d a s th e d i f f e r e n c e b e tw e e n 0 .1 0 0 a n d th e d i a l r e a d in g . T h e r e c o r d s e r v e s m a in ly a s a g u id e f o r t h e c o n s o l i d a t io n p r o c e d u r e , a n d o n ly th e c h a n g e in h e ig h t a t c o m p le t io n o f th e c o n s o l id a t io n i s u s e d in th e f in a l e v a lu a t io n o f th e t e s t r e s u l t s f o r c o m p u ta t io n of t h e v o id r a t i o o r w a t e r c o n te n t o f th e s o i l a t th e s t a r t o f th e a c tu a l s h e a r t e s t s ; s e e p a g e 4 1 .

T h e S h e a r T e s t

I n i t i a l a d j u s t m e n t sT h is s e c t io n d e a l s w i th a d j u s t m e n t s o f th e s h e a r a p p a r a t u s w h ic h s h o u ld b e

m a d e u p o n c o m p le t io n of th e p r e l i m i n a r y c o n s o l id a t io n a n d b e f o r e th e a c t u a l s h e a r t e s t i s s t a r t e d . H o w e v e r , th e o p e r a t io n s d e s c r i b e d in th e fo l lo w in g tw o p a r a g r a p h s a p p ly o n ly to t e s t s w ith d iv id e d c o n f in in g r i n g s .

T h e c e l lo p h a n e ta p e s e a l in g th e j o in t b e tw e e n th e e x t e r i o r u p p e r a n d lo w e r r i n g s i s r e m o v e d , a n d b o th u p p e r r i n g s a r e r a i s e d a l i t t l e b y m e a n s of th e e l e v a to r s c r e w s . C a r e s h o u ld b e t a k e n to r o t a t e th e tw o s c r e w n u ts o f e a c h r in g c o n c u r r e n t ly a n d in e q u a l a m o u n t s . T h e c l e a r a n c e c r e a t e d s h o u ld b e s u f f i c i e n t to p r e v e n t i t s e l i m in a t io n b y s e t t l e m e n t o f th e u p p e r r i n g s b e f o r e th e m a x im u m s h e a r i n g r e s i s t a n c e i s r e a c h e d , a t l e a s t w h e n q u ic k t e s t s a r e p e r f o r m e d , b u t i t s h o u ld n o t b e l a r g e r th a n th e m in im u m r e q u i r e d a n d s h o u ld p r e f e r a b l y n o t e x c e e d 0 .0 5 in . V e r y l i t t l e c l e a r a n c e i s r e q u i r e d w h e n th e t e s t s p e c im e n i s s t r o n g ly o v e r c o n s o l i d a t e d , s in c e th e s o i l th e n i s s u b j e c t to s w e l l in g d u r in g th e f i r s t p a r t o f th e t e s t . T h e c l e a r a n c e r e q u i r e d f o r t e s t s o n n o r m a l l y c o n s o l id a te d t e s t s p e c im e n s d e p e n d s o n t h e c o m p r e s s i b i l i t y of th e s o i l a n d th e r a t e of d i s p l a c e m e n t , a n d v a r i e s b e tw e e n 0 .0 3 in . a n d 0 .0 5 in . f o r t e s t s on A t la n t i c M u c k .

R a is in g th e u p p e r r i n g s c a u s e s a s l i g h t i n c r e a s e in th e v e r t i c a l lo a d on th e m id p la n e o f th e t e s t s p e c im e n b e c a u s e i t a d d s th e w e ig h t o f th e r i n g s to th e d e a d w e ig h t a n d e l im in a te s th e i n f lu e n c e o f f r i c t i o n b e tw e e n th e s o i l a n d th e u p p e r r i n g s . T h e a c t u a l s h e a r t e s t s h o u ld n o t b e s t a r t e d b e f o r e c o n s o l id a t io n u n d e r th i s i n c r e a s e d lo a d i s c o m p le t e d , a s in d ic a t e d b y th e m o v e m e n ts o f th e v e r t i c a l d ia l . F o r A t la n t i c M u c k th e t im e r e q u i r e d f o r t h i s c o n s o l id a t io n w a s o n e to t h r e e h o u r s . T h e j o in t b e tw e e n th e o u te r c o n f in in g r i n g s s h o u ld b e s e a l e d a g a in w ith c e l lo p h a n e ta p e d u r in g th e a d d i t io n a l c o n s p l id a t io n , a n d th e fo l lo w in g a d ju s tm e n t s th e n m a d e .

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T h e h o r i z o n t a l g u id e s h e a v e s a r e r a i s e d o r l o w e r e d u n t i l th e w i r e r o p e s b e tw e e n t h e s e s h e a v e s a n d th e t o r q u e w h e e l a r e h o r i z o n t a l . T h e s h e a v e s a n d th e w h e e l h a v e th e s a m e t h i c k n e s s ; t h e r e f o r e , th e a d ju s tm e n t c a n b e c h e c k e d b y p la c in g o n e e n d o f a s p i r i t l e v e l on a s h e a v e a n d th e o th e r en d on th e t o r q u e w h e e l a t th e p o in t of t a n g e n c y of th e c o r r e s p o n d in g w i r e r o p e . T h e e l e v a t io n o f th e p r o v in g f r a m e an d v e r t i c a l g u id e s h e a v e s i s th e n a d ju s t e d u n t i l th e w i r e r o p e s b e tw e e n th e h o r i z o n t a l a n d v e r t i c a l g u id e s h e a v e s a r e h o r i z o n t a l .

T h e w i r e r o p e s a r e r e m o v e d f r o m th e v e r t i c a l g u id e s h e a v e s w h i le s e t t i n g th e to r q u e d ia l to r e a d 0 .0 1 0 0 in . f o r z e r o e x t e r n a l l o a d . T h e r e i s a s l i g h t d i f f e r e n c e in d i a l r e a d in g f o r i n c r e a s i n g a n d d e c r e a s i n g lo a d s . T h e z e r o s e t t i n g s h o u ld c o r r e s p o n d to i n c r e a s i n g lo a d s ; t h a t i s , a s l i g h t u p w a r d p u ll i s e x e r t e d o n th e p ro v in g f r a m e a n d th e n s lo w ly r e l e a s e d , w h e r e u p o n th e d i a l s h o u ld r e a d 0 .0 1 0 0 in . T h e w i r e r o p e s a r e now r e p l a c e d on th e v e r t i c a l g u id e s h e a v e s , a n d th e t o r q u e - lo a d s c a l e is m o v e d u p u n t i l th e k n i f e - e d g e in th e c e n t e r o f th e b a l a n c e b e a m i s in c o n ta c t w i th th e f u l c r u m ; w h e r e u p o n , th e b a s e o f th e s h e a r a p p a r a t u s i s r o t a t e d u n t i l th e d o u b le h o o k s a t th e e n d s of th e w i r e r o p e s b a r e l y to u c h th e k n i f e - e d g e s a t th e e n d s o f th e b a la n c e b e a m .

T h e g e a r s of th e m o t o r i z e d d r i v e a r e now s h i f t e d to p r o d u c e th e d e s i r e d r a t e o f d i s p l a c e m e n t f o r c o n t r o l l e d - s t r a i n lo a d a p p l i c a t io n , b u t th e g e a r s a r e l e f t in n e u t r a l p o s i t io n f o r c o n t r o l l e d - s t r e s s lo a d a p p l i c a t io n . N e x t , th e tw o t w i s t d i a l s w i th c o u n te r c lo c k w i s e r o t a t i o n a r e s e t to r e a d 0 .9 0 0 i n . , o r 0 .1 0 0 in . f o r d i a l s w i th c lo c k w is e r o t a t i o n . T h e s e d i a l s e t t i n g s a r e u s e d so th a t b o th r i g h t - h a n d a n d l e f t - h a n d r o t a t io n s of th e to r q u e w h e e l m a y b e m e a s u r e d . U p o n c o m p le t io n o f a l l t h e i n i t i a l a d j u s t m e n t s , in c lu d in g c h e c k in g th e h o r i z o n t a l p o s i t io n of th e v e r t i c a l lo a d l e v e r s , th e c e l lo p h a n e t a p e i s r e m o v e d f r o m th e o u te r r i n g s , a n d th e j o i n t b e tw e e n t h e s e r i n g s i s c o v e r e d w ith g r e a s e if th e s h e a r t e s t i s e x p e c te d to l a s t m o r e th a n a fe w m in u te s .

C o n t r o l l e d - s t r a i n t e s t s

C o n t r o l l e d - s t r a i n lo a d a p p l i c a t i o n , a c tu a l ly a c o n t r o l l e d r a t e of t w i s t o r d i s p la c e m e n t , i s p r i m a r i l y s u i t e d f o r p e r f o r m a n c e o f q u ic k , m o r e - o r - l e s s u n d r a in e d t e s t s , b u t m a y a l s o b e u s e d f o r d r a i n e d t e s t s o n r e l a t i v e l y p e r m e a b le s o i l s . H o w e v e r , th e lo w e s t r a t e of d i s p l a c e m e n t o b ta in a b le w i th th e c u r r e n t g e a r a r r a n g e m e n t d o e s n o t p e r m i t c o m p le te d r a i n a g e d u r in g t e s t s on s o i l w ith low p e r m e a b i l i t y .

R a te o f d i s p l a c e m e n t . T h e fo l lo w in g r a t e s o f a v e r a g e d i s p l a c e m e n t a r e o b t a in e d w ith th e c u r r e n t m o t o r i z e d d r i v e a n d g e a r b o x : 0 .0 1 2 1 7 , 0 .0 2 4 3 , 0 .1 2 1 7 , 1 .2 1 7 , a n d 12 .17 in . p e r m i n . In m o s t o f t h e t e s t s s o f a r p e r f o r m e d (1 6 ) a r a t e o f 0 .0 2 4 3 in . p e r m in w a s u s e d u n t i l s h o r t l y a f t e r i n i t i a l f a i l u r e . T h e c o r r e s p o n d in g lo a d in g t im e to f a i l u r e - - i . e . , d i s p l a c e m e n t a t f a i l u r e d iv id e d b y th e r a t e o f d i s p l a c e m e n t - - v a r i e d f r o m 2 .3 to 7 .2 m i n u te s , w h ic h c o n c u r s w ith th e u s u a l p r a c t i c e in p e r f o r m in g q u ic k , p a r t i a l l y d r a in e d o r u n d r a in e d d i r e c t s h e a r , t r i a x i a l c o m p r e s s i o n , a n d u n c o n f in e d c o m p r e s s i o n t e s t s . In o n e t e s t th e r a t e w a s i n c r e a s e d to 0 .1 2 1 7 in . p e r m in , a n d

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t h i s i s th e m a x im u m p e r m i s s i b l e w h e n d e t a i l s o f th e t o r q u e - t w i s t d i a g r a m b e f o r e f a i l u r e a r e to b e o b ta in e d w i th o u t a u to m a t ic r e c o r d i n g .

A f t e r i n i t i a l f a i l u r e t h e r a t e o f d i s p l a c e m e n t w a s g e n e r a l l y i n c r e a s e d to O .1 2 1 7 in . p e r m in to s h o r t e n th e d u r a t io n o f th e t e s t . T h is r a t e i s s a t i s f a c t o r y f o r r e l a t i v e l y s t i f f s o i l s , b u t i s to o lo w f o r s o f t a n d p l a s t i c s o i l s f o r w h ic h v e r y l a r g e d i s p l a c e m e n t s a r e r e q u i r e d to r e a c h th e u l t i m a t e r e s i d u a l s h e a r i n g r e s i s t a n c e ; t h a t i s , e x c e s s i v e c h a n g e s in v o id r a t i o t a k e p la c e d u r in g th e t e s t . A few t e s t s o n a s a m p l e o f L a k e P r o v i d e n c e C la y w e r e p e r f o r m e d w ith th e o b je c t o f d e t e r m in in g th e in f lu e n c e o f th e r a t e of d i s p l a c e m e n t o n th e r e s i d u a l s h e a r i n g r e s i s t a n c e , b u t th e r e s u l t s w e r e n o t c o n c lu s iv e (1 6 ) .

T h e fo l lo w in g r a t e s o f a v e r a g e d i s p l a c e m e n t a r e s u g g e s t e d f o r u s e in “ u n d r a i n e d ” t o r s i o n s h e a r t e s t s u n t i l t h e r e s u l t s of f u r t h e r i n v e s t i g a t i o n s a r e a v a i l a b le ; f o r r e l a t i v e l y s t i f f s o i l s , 0 .0 2 4 3 in . p e r m in b e f o r e f a i l u r e a n d 0 .1 2 1 7 in . p e r m in a f t e r f a i l u r e ; f o r s o f t a n d p l a s t i c s o i l s , 0 .1 2 1 7 in . p e r m in b e f o r e f a i l u r e a n d 1 .2 17 in . p e r m in a f t e r f a i l u r e .

G e n e r a l p r o c e d u r e . T h e m o t o r i z e d d r i v e a n d a s to p w a tc h a r e s t a r t e d s i m u l ta n e o u s ly , o r t h e m o t o r i s s t a r t e d a t a c o n v e n ie n t e v e n r e a d in g o f a c lo c k o r w a tc h w i th a s w e e p s e c o n d h a n d . T h e v e r t i c a l , tw is t , a n d t o r q u e d i a l s a r e a l l r e a d c o n c u r r e n t l y a t s p e c i f i e d t im e i n t e r v a l s w h ic h m a y v a r y f r o m 15 s e c o n d s a t t h e s t a r t o f th e t e s t to a fe w m in u te s a t th e e n d , d e p e n d in g u p o n th e d e t a i l s d e s i r e d a n d th e r a t e o f d i s p l a c e m e n t u s e d . M a x im u m o r m in im u m r e a d in g s o f th e t o r q u e d i a l s h o u ld b e r e c o r d e d e v e n w h e n th e y o c c u r d u r in g a r e g u l a r t im e i n t e r v a l . T h e t w i s t d i a l s m o v e r a t h e r r a p id ly a t th e s t a r t of th e t e s t , s in c e th e t o r q u e w h e e l r o t a t e s w i th t h e b a s e u n t i l th e s l a c k in th e w i r e r o p e s i s t a k e n u p . S u b s e q u e n t m o v e m e n ts o f th e t w i s t d i a l s a r e c a u s e d b y s t r e t c h i n g of th e w i r e r o p e s a n d a r e v e r y s m a l l .

T h e a m o u n t o f s o i l s q u e e z e d o u t th r o u g h th e c l e a r a n c e b e tw e e n th e c o n f in in g r i n g s b e f o r e i n i t i a l f a i l u r e o c c u r s i s u s u a l l y i m p e r c e p t i b l e , b u t a p p r e c i a b l e a m o u n ts o f s o i l m a y b e l o s t w h e n a t e s t i s c o n t in u e d f o r a c o n s id e r a b l e p e r io d of t im e a f t e r i n i t i a l f a i l u r e . T h e s t a r t of th e s q u e e z in g o u t o f s o i l b e tw e e n th e r i n g s s h o u ld b e n o te d in th e t e s t r e c o r d . S o i l s q u e e z e d o u t w i l l o b s c u r e th e c l e a r a n c e b e tw e e n th e r i n g s w h ic h th e n w o u ld b e c h e c k e d b y m e a n s o f a f e e l e r g a g e , a n d th e u p p e r r i n g s s h o u ld b e r a i s e d w h e n c o n ta c t w i th th e lo w e r r i n g s i s e s t a b l i s h e d a t a n y p o in t . I t i s u s u a l ly a d v i s a b l e to r a i s e th e u p p e r r i n g s w h e n th e t e s t i s i n t e r r u p t e d to c h a n g e th e r a t e of d i s p l a c e m e n t a f t e r i n i t i a l f a i l u r e o f t h e s o i l . T h e fo l lo w in g p r o c e d u r e s h o u ld b e fo l lo w e d f o r t h e s e o p e r a t io n s .

T h e m o t o r i s s to p p e d a n d th e g e a r s s h i f t e d in to n e u t r a l p o s i t io n ; w h e r e u p o n , th e s h e a r a p p a r a t u s i s r o t a t e d b y m e a n s o f th e h a n d w h e e l u n t i l th e w i r e r o p e s a r e s la c k an d th e t o r q u e d i a l i n d i c a t e s z e r o lo a d . T h e u p p e r r i n g s a r e f i r s t p u s h e d d o w n u n t i l th e y a r e in c o n ta c t w ith th e lo w e r r i n g s a n d a r e th e n r a i s e d e v e n ly b y tu r n in g th e n u ts o f th e e l e v a to r s c r e w s u n t i l th e i n i t i a l c l e a r a n c e i s r e - e s t a b l i s h e d . T h e e le v a t io n o f th e h o r i z o n t a l a n d v e r t i c a l g u id e s h e a v e s i s a d ju s t e d to c o r r e s p o n d to

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th e c u r r e n t p o s i t io n of th e t o r q u e w h e e l i f a p p r e c i a b l e c h a n g e s in h e ig h t of th e t e s t s p e c im e n h a v e t a k e n p la c e d u r in g th e f i r s t p a r t o f th e t e s t . T h e g e a r s a r e no w s h i f t e d to th e d e s i r e d r a t e of d i s p l a c e m e n t , a n d th e tw o t w i s t d ia l s a r e r e s e t b y r o t a t i n g th e d ia l s to p . A f t e r t h e s e a d j u s t m e n t s , th e t e s t i s c o n t in u e d u n t i l th e u p p e r r i n g s m u s t b e r a i s e d a g a i n o r u n t i l no f u r t h e r c h a n g e o c c u r s in th e in d ic a t e d s h e a r i n g r e s i s t a n c e .

C o n t r o l l e d - s t r e s s t e s t s

C o n t r o l l e d - s t r e s s lo a d a p p l i c a t io n u s u a l l y i s r e q u i r e d fo r d r a i n e d t o r s i o n s h e a r t e s t s on s o i l s of low p e r m e a b i l i t y , a n d i t m a y a l s o b e u s e d f o r q u ic k t e s t s a l th o u g h c o n t r o l l e d - s t r a i n lo a d a p p l i c a t i o n g e n e r a l l y i s s a t i s f a c t o r y a n d m o r e c o n v e n ie n t f o r s u c h t e s t s .

G e n e r a l p r o c e d u r e . A s a l r e a d y i n d i c a t e d , th e g e a r s of th e m o t o r i z e d d r i v e a r e l e f t in n e u t r a l p o s i t io n , a n d th e s h e a r a p p a r a t u s i s r o t a t e d b y h a n d u n t i l th e k n i f e - e d g e in th e c e n t e r o f th e b a l a n c e b e a m i s c l o s e to th e f u l c r u m . W e ig h ts a r e now p la c e d o n th e t o r q u e - lo a d s c a l e in a c c o r d a n c e w i th th e lo a d in g s c h e d u le s d i s c u s s e d in th e fo l lo w in g p a r a g r a p h s . T h e i n d ic a t io n s of a l l d i a l s , p r e f e r a b ly a l s o th e t o r q u e d ia l , s h o u ld b e o b s e r v e d a n d r e c o r d e d j u s t b e f o r e e a c h n e w lo a d i n c r e a s e . T h e tw i s t d i a l s m a y b e r e s e t b y r o t a t i n g th e b a s e of th e a p p a r a t u s w h e n th e a n g u l a r d i s p l a c e m e n t s a p p r o a c h th e l im i t i n g r a n g e of th e d i a l s . T h is o p e r a t io n a l s o r a i s e s th e t o r q u e lo a d s c a l e to i t s o r i g i n a l p o s i t io n . T h e t w i s t d i a l s s h o u ld n o t b e r e s e t b e f o r e th e d e f o r m a t io n s u n d e r a g iv e n t o r q u e lo a d h a v e c e a s e d ; t h a t i s , r e s e t t i n g o f t h e d i a l s c a n b e p e r f o r m e d o n ly d u r in g s lo w t e s t s , a n d l a r g e d i s p l a c e m e n t s d u r in g q u ic k t e s t s a r e d e t e r m i n e d a p p r o x im a te ly b y m e a n s o f th e t o t a l t w i s t i n d i c a t o r .

Q u ic k lo a d a p p l i c a t io n . T h e t im e i n t e r v a l b e tw e e n lo a d i n c r e a s e s s h o u ld n o t b e g r e a t e r th a n t h a t r e q u i r e d to o b s e r v e a n d r e c o r d th e d i a l r e a d i n g s , s a y 15 to 30 s e c o n d s f o r tw o o b s e r v e r s . T h e t o t a l d u r a t io n o f th e s h e a r t e s t i s r e d u c e d a n d a c c u r a c y m a in t a in e d b y s t a r t i n g w ith r a t h e r l a r g e lo a d i n c r e m e n t s - - a b o u t t e n p e r c e n t o f th e e s t im a t e d m a x im u m lo a d — a n d r e d u c in g t h e s e i n c r e m e n t s g r a d u a l ly to f iv e , tw o , a n d o n e p e r c e n t o f th e m a x im u m lo a d w h e n a p p r o a c h in g i n i t i a l f a i l u r e , a s i n d ic a t e d b y i n c r e a s i n g r a t e s o f d i s p l a c e m e n t . T h e d i s p l a c e m e n t s i n c r e a s e r a p id ly a f t e r i n i t i a l f a i l u r e ; th e t o r q u e - lo a d s c a l e d e s c e n d s , an d i t s c o u n te r w e ig h t m o v e s u p u n t i l i t a b u ts a g a i n s t th e a d j u s t a b l e s to p . T h e r e a f t e r , i n c r e a s i n g l y l a r g e p a r t s o f th e lo a d a r e t a k e n u p b y th e t e n s io n s p r in g a b o v e th e c o u n te r w e ig h t , a n d th e m o v e m e n ts c o n tin u e u n t i l th e e f f e c t iv e lo a d , a s i n d i c a t e d b y th e to r q u e d ia l , c o r r e s p o n d s to th e d e c r e a s e d s h e a r i n g r e s i s t a n c e . T h e c o r r e s p o n d i n g d i s p l a c e m e n t i s d e t e r m i n e d b y m e a n s o f t h e t o t a l tw i s t i n d i c a t o r . T h e b a s e o f th e a p p a r a t u s i s now r o t a t e d b y m e a n s of th e h a n d w h e e l , a n d th e d i s p l a c e m e n t s a r e i n c r e a s e d u n t i l th e to r q u e d i a l i n d i c a t e s th a t th e m in im u m o r r e s i d u a l s h e a r in g r e s i s t a n c e i s r e a c h e d .

S lo w lo a d a p p l i c a t io n . A s c h e d u le of lo a d i n c r e m e n t s a s i n d i c a t e d a b o v e f o r q u ic k lo a d a p p l i c a t io n s m a y b e u s e d , b u t w h e n a c o m p le te t o r q u e - t w i s t d i a g r a m f o r d r a in e d c o n d i t io n s i s d e s i r e d , th e t o r q u e lo a d s h o u ld n o t b e i n c r e a s e d b e f o r e

38

d e fo r m a t io n s under the c u r r e n t load have c e a s e d . F u l l y d r a in e d cond itions a t in i t ia l f a i l u r e a r e g e n e r a l ly s u f f i c ie n t , and the to ta l d u ra t io n of the t e s t m a y then be d e c r e a s e d by s t a r t in g with r e l a t iv e ly s m a l l t im e i n t e r v a l s betw een load a p p l ic a t io n s and g r a d u a l ly in c r e a s i n g the t im e in t e r v a l s a s the lo ad in c r e m e n t s a r e d e c r e a s e d upon a p p ro a c h in g the maximum^ sh e a r in g r e s i s t a n c e . In th is m an n e r m o s t d ra in e d t e s t s can be c o m p le te d in s i x to tw elve h o u rs , depen d in g upon the c o m p r e s s i b i l i t y and p e r m e a b i l i t y of the s o i l . T he u p p e r confining r in g s m a y h ave to be r e - r a i s e d b e fo r e in i t i a l f a i l u r e o c c u r s ; and the to rq u e load should f i r s t be r e d u c e d by 1 0 to 25 per cent, to avo id p r e m a t u r e f a i l u r e a s a r e s u l t of this o p e ra t io n . T he load should not be inc r e a s e d a g a in b e fo r e a p e r io d of t im e equal to the c u r r e n t ly u se d t im e in t e r v a l h as e l a p s e d .

D e te rm in a t io n of the r e s i d u a l s h e a r in g r e s i s t a n c e fo r a w ate r content equ al to that a t in i t ia l f a i l u r e of the s o i l i s g e n e r a l ly d e s i r e d , even fo r d r a in e d t e s t s . In th is c a s e the te s t in g p r o c e d u r e a f t e r in i t ia l f a i l u r e i s id e n t ic a l with that d e s c r i b e d fo r qu ick lo ad a p p l ic a t io n . T he in fluen ce of continued d r a in a g e and c o n so l id a t io n of the s o i l upon the r e s i d u a l s h e a r in g r e s i s t a n c e can be d e te r m in e d by r e p e a t in g the l a s t p a r t of the t e s t a f te r a r e s t p e r io d of ad eq u a te length , s a y 12 to 24 h o u r s .

T he to r q u e - tw is t d i a g r a m a f te r f a i lu r e m ay be d e te r m in e d fo r d r a in e d cond it io n s by m o v in g the a d ju s t a b le s to p c lo s e to the c o u n te rw eigh t fo r the t o r q u e - lo a d s c a l e so that the d i s p la c e m e n t s a f te r in i t ia l f a i l u r e a r e l im ite d to a s m a l l am ount. T h e c o r r e s p o n d in g to rqu e and tw is t a r e o b se r v e d and r e c o r d e d a f te r the d e f o r m a tion s c e a s e ; w hereupon , the d i s p l a c e m e n t i s i n c r e a s e d by ro ta t in g the handw heel and the to rq u e and tw ist o b s e r v e d a f t e r a new e q u i l ib r iu m i s r e a c h e d . T h e s e o p e ra t io n s a r e r e p e a te d until the u l t im a te r e s i d u a l sh e a r in g r e s i s t a n c e i s a t ta in e d .

T he w ate r content of the s o i l a t f a i lu r e i s d i f f ic u lt to d e te r m in e when d r a in a g e i s a llow ed to take p la c e both b e f o r e and a f te r in i t ia l f a i l u r e , and p e r f o r m a n c e of dup l i c a te t e s t s , s topped sh o r t ly a f t e r in i t ia l f a i lu r e o c c u r s , m a y be n e c e s s a r y .

M ix ed ty p es of lo a d a p p lic a t io n

A ch an ge f r o m c o n t r o l l e d - s t r a i n to a m o d if ie d c o n t r o l l e d - s t r e s s type of lo a d ing m a y p o s s ib ly be a d v a n ta g e o u s du r ing t e s t s when only the r e s i d u a l s h e a r in g r e s i s t a n c e i s d e s i r e d and not the sh a p e of the t o r q u e - t w is t d i a g r a m a f te r in i t ia l f a i l u r e of the s o i l . Such a change i s m a d e by stopping the m o to r sh o r t ly a f te r in i t ia l f a i l u r e o c c u r s and sh ift in g the g e a r s to n e u t r a l pos it ion . W eights in e x c e s s of the f o r c e in d ic a t e d by the to rq u e d ia l a r e p la c e d on the to r q u e - lo a d s c a l e and the t e s t i s c o m p le ted a s d e s c r i b e d on p a g e 37. Such a te s t m a y p o s s ib l y be co m p le te d without r e r a i s i n g the upper confining r i n g s , and the d u ra t io n of and ch a n g e s in w ate r content of the s o i l d u r in g the t e s t m a y be d e c r e a s e d in th is m a n n e r .

A ch an ge f r o m c o n t r o l l e d - s t r e s s to contr o i l e d - s t r a i n type of load in g m ay be u s e d fo r d e te rm in a t io n of the sh a p e of the t o r q u e - tw is t d i a g r a m a f te r f a i l u r e when it i s d e s i r e d to av o id the s t e p - b y - s t e p p r o c e d u re d e s c r i b e d on p age 37 and when the

39

p e r m e a b i l i t y of the s o i l i s n o t to o s m a l l . T h e s to p fo r th e c o u n t e r w e i g h t is so a d j u s t e d th a t th e t r a v e l of th e w e ig h t and th e d i s p l a c e m e n t s in th e t e s t s p e c i m e n a f t e r i n i t i a l f a i l u r e a r e l im i t e d to a s m a l l a m o u n t . A l l w e ig h ts a r e r e m o v e d f r o m th e lo ad s c a l e a f t e r i n i t i a l f a i l u r e , a n d th e a p p a r a t u s i s r o t a t e d u n t i l th e k n i f e - e d g e in the c e n t e r of th e b a l a n c e b e a m i s in c o n ta c t w ith th e f u l c r u m . T h e g e a r s a r e th e n sh i f te d to th e d e s i r e d r a t e of d i s p l a c e m e n t , a n d th e g u id e s h e a v e s a r e a d ju s t e d and th e d i a l s r e s e t a s n e c e s s a r y .

D i s m a n t l i n g of A p p a r a t u s

T h e s h e a r a p p a r a t u s sh o u ld b e d i s m a n t l e d and the t e s t s p e c i m e n r e m o v e d a s r a p i d l y a s p o s s i b l e a f t e r c o m p le t io n of a t e s t . T h e fo l lo w in g s e q u e n c e of o p e r a t i o n s i s r e c o m m e n d e d to m i n i m i z e c h a n g e s in w a t e r c o n te n t of th e s o i l d u r in g th e d i s m a n t l i n g . (1) T h e w e ig h ts a r e r e m o v e d f r o m th e t o r q u e - l o a d s c a l e , o r th e a p p a r a t u s i s r o t a t e d u n t i l the w i r e r o p e s a r e s l a c k ; w h e r e u p o n the r o p e c l a m p s a r e d i s c o n n e c te d f r o m th e t o r q u e w h e e l . (2) W a te r in b o th th e e x t e r i o r r e s e r v o i r a n d in the fo u r h o le s in th e a n n u la r p i s to n i s d r a w n out by m e a n s of a s y r i n g e . (3) T h e v e r t i c a l lo a d i s r e m o v e d f r o m the h a n g e r , and th e t u r n b u c k le i s u n c o u p le d f r o m th e lo ad in g r o d . (4) A f in a l r e a d in g of th e v e r t i c a l d i a l i s m a d e ; the d i a l f r a m e i s d i s c o n n e c te d ; and th e c a p , d i a l s to p , and lo a d in g r o d a r e r e m o v e d .

T h e fo l lo w in g o p e r a t io n s a p p ly to t e s t s w ith d iv id e d co n f in in g r i n g s . (5) T h e u p p e r r i n g s a r e pu l led up u n t i l th e y a r e in c o n ta c t w ith th e t o r q u e w h e e l , t h e r eby e x p o s in g th e u p p e r p a r t of th e t e s t s p e c i m e n . (6) T h e to r q u e w h e e l , a n n u l a r p i s to n , and u p p e r co n f in in g r i n g s a r e r e m o v e d a s a u n i t , an d f r e e w a te r on top of th e t e s t s p e c i m e n i s i m m e d i a t e l y b lo t te d up w i th so f t , a b s o r b e n t , t i s s u e p a p e r . (7) T h e l u c i t e c y l i n d e r a n d th e l o w e r , o u te r c o n f in in g r i n g s a r e r e m o v e d ; th e t e s t s p e c i m e n i s i m m e d i a t e l y p u s h e d ou t if i t a d h e r e s to th e r in g . (8) If th e t e s t s p e c i m e n r e m a i n s in the s h e a r a p p a r a t u s , i t i s l i f te d o u t by i n s e r t i n g two th in s p a tu l a s b e tw e e n th e s o i l and th e l o w e r d e n ta te d p la te . (9) T h e t e s t s p e c i m e n i s p la c e d , to p dow n, on a p la te c o v e r e d w i th w ax p a p e r , and f r e e w a te r on i t s lo w e r s u r f a c e is b lo t t e d up w i th a b s o r b e n t t i s s u e p a p e r . (10) T h e s p e c i m e n i s t u r n e d o v e r , top up, a n d t r a n s f e r r e d to the m o i s t r o o m fo r e x a m in a t io n and c u t t in g in to s e c t io n s fo r d e t e r m i n a t i o n of th e w a t e r c o n te n t of th e s o i l .

T h e f i r s t fo u r o p e r a t i o n s d e s c r i b e d a b o v e ap p ly a l s o to t e s t s w i th u n d iv id e d o r s in g l e co n f in in g r i n g s , and th e r e m a i n i n g d i s m a n t l i n g sh o u ld b e p e r f o r m e d a s f o l lo w s . (5) T h e o u t e r r in g i s p u l le d up to th e u n d e r s i d e of th e t o r q u e w h e e l . (6) T he r in g , a n n u l a r p i s to n , and t o r q u e w h e e l a r e r e m o v e d a s a u n i t . (7) T h e t e s t s p e c i m e n m a y a d h e r e to th e a n n u la r p i s to n , in w h ic h c a s e th e o u te r r i n g i s r e m o v e d w h i le e x e r t in g a l ig h t p r e s s u r e on th e t e s t s p e c i m e n w i th th e f i n g e r s . (8) T h e i n n e r r i n g i s r e m o v e d . (9) T h e t e s t s p e c i m e n i s s e p a r a t e d f r o m th e u p p e r o r lo w e r d e n t a t e d p la te , a s th e c a s e m a y b e , and f r e e w a t e r on i t s s u r f a c e s i s b lo t t e d up w i th a b s o r b e n t t i s s u e p a p e r . (10) T h e t e s t s p e c i m e n i s p la c e d on a p la te c o v e r e d w ith w ax p a p e r , top up, and t r a n s f e r r e d to th e m o i s t r o o m .

4 0

E xam in ation and F in a l W ater-content D eterm in atio n s

In the m o i s t r o o m the t e s t s p e c i m e n i s cut into s i x s e c t io n s a s show n in f i g u r e 16, T h e th r e e l a r g e s e c t i o n s , m a r k e d “ R , ” a r e s e p a r a t e d a long the s u r f a c e of f a i l u r e , and the po s it io n and con d ition of th is s u r f a c e a r e r e c o r d e d . R e p r e s e n t a t i v e

SECTIONS W FOR WATER CONTENT

DETERMINATIONS

DISCARD

CUT SECTIONS W INTO SLICES AS SHOWN ACCORDING TO LOCATION OF FAILURE

DISCARD

SECTIONS R FOR INSPECTION OF

SURFACE OF FAILURE TESTS ON REMOLDED SOIL FAILURE NEAR BOTTOM

F i g u r e 16. W a te r-co n ten t d e te rm in a t io n s a t end of t e s t

s e c t io n s m a y b e photograph ed to ob ta in a p e rm a n e n t v i s u a l r e c o r d of n o r m a l and a b n o r m a l co n d ition s of the s u r f a c e of f a i l u r e . D e te r m in a t io n of the unconfined c o m p r e s s i v e s t r e n g t h of r e m o ld e d s o i l f r o m a couple of the l a r g e s e c t io n s fo r c o m p a r i so n with the r e s i d u a l s h e a r in g r e s i s t a n c e i s a l s o a d v i s a b le .

T h e th re e s m a l l s e c t i o n s , m a r k e d “ W” and abo u t one inch lo n g , a r e u se d fo r w a t e r - c o n t e n t d e te r m in a t io n s . T he dentated top and bo ttom p a r t s of th e se s e c t io n s m a y h av e a b s o r b e d c o n s id e r a b l e am o u n ts of w a te r d u r in g the d i sm a n t l in g of the s h e a r a p p a r a t u s . T h e r e f o r e , a s soon a s the s e c t io n s a r e cut, the top and bottom p a r t s shou ld b e cut off to a depth of abo ut l / 3 2 in. below the g r o o v e s , and d i s c a r d e d . T h e r e m a in in g p a r t of e ach s e c t io n i s then d iv ided into th re e s l i c e s in a c c o r d a n c e with the p o s i t io n of the s u r f a c e of f a i l u r e . The s l i c e s c l o s e to or s t r a d d l in g the s u r f a c e of f a i l u r e should be thin; a th ic k n e s s of not m o r e than 0.1 in. i s te n ta t iv e ly s u g g e s te d , but v a r ia t io n s in w ate r content in the im m e d ia t e v ic in ity of the s u r f a c e of f a i l u r e m u s t b e in v e s t ig a te d b e f o r e a d e f in ite r e c o m m e n d a t io n can b e m a d e . T h e th r e e top s l i c e s a r e p la c e d in one c o n ta in e r , the c e n te r s l i c e s in a se c o n d and the b o tto m s l i c e s in a th ird c o n ta in e r ; w h ereupon , the w ate r content fo r e ac h s e r i e s of s l i c e s i s d e te r m in e d . H o w e v e r , s e p a r a t e w a te r - c o n te n t d e te r m in a t io n s fo r eac h of the th r e e s l i c e s c l o s e to or s t r a d d l in g the zone of f a i l u r e a r e s o m e t i m e s p r e f e r a b l e

41

a s a c h e c k on th e u n i f o r m i ty o r a n in d ic a t io n of th e v a r i a b i l i t y in w a t e r c o n te n t an d s o i l p r o p e r t i e s .

R e c o r d in g a n d E v a lu a t io n o f T e s t R e s u l t s

T e s t d a t a a n d c o m p u ta t io n s h e e t s

P r o p o s e d f o r m s of c o m b in e d t e s t d a t a an d c o m p u ta t io n s h e e t s f o r t o r s i o n s h e a r t e s t s a r e sh o w n in f i g u r e 1 7 -A an d B . D e t a i l s of th e p r e l i m i n a r y c o n s o l i d a t io n , w a t e r - c o n t e n t d e t e r m i n a t i o n s , a n d u n c o n f in e d c o m p r e s s i o n t e s t s a r e r e c o r d e d on s t a n d a r d f o r m s f o r t h e s e p a r t i c u l a r t e s t s . T h e d a t a s h e e t s sh o w n in f i g u r e 17 a r e p r i m a r i l y a d a p te d f o r t e s t s w i th c o n t r o l l e d - s t r a i n lo a d a p p l i c a t i o n , b u t w i th m in o r c h a n g e s o r a d d i t io n s th e y c a n a l s o b e u s e d f o r t e s t s w i th c o n t r o l l e d - s t r e s s lo a d a p p l ic a t io n . S h e e t A , f i g u r e 1 7 -A , c o n ta in s b a s i c d a t a an d a s u m m a r y o f t h e r e s u l t s of b o th th e t o r s i o n s h e a r t e s t a n d a u x i l i a r y t e s t s , s u c h a s w a t e r c o n te n t , c o n s o l id a t io n , a n d u n c o n f in e d c o m p r e s s i o n t e s t s . S h e e ts B a n d C , f i g u r e 1 7 -B , c o n ta in o b s e r v a t io n s d u r in g th e a c tu a l s h e a r t e s t s an d a p p u r te n a n t c o m p u ta t io n s . T h e s e tw o s h e e t s c a n b e jo in e d in to a s in g l e l a r g e s h e e t , o r r e a r r a n g e d w i th o n e s h e e t f o r o b s e r v a t io n s an d th e o th e r f o r c o m p u ta t io n s . H o w e v e r , c o n c u r r e n t o b s e r v a t i o n o f f o u r d ia l s d u r in g t e s t s r e q u i r e s tw o o b s e r v e r s , an d th e p r o p o s e d f o r m c o n v e n ie n t ly p r o v id e s o n e s h e e t f o r e a c h o b s e r v e r . S h e e ts B a n d C m a y b e jo in e d u p o n c o m p le t io n o f th e t e s t a n d a f t e r c u t t in g o ff th e r e p e t i t i v e d a te a n d t im e c o lu m n s on S h e e t C .

C o m p u ta t io n s

B r i e f d i r e c t i o n s f o r c o m p u ta t io n of th e a v e r a g e s h e a r i n g s t r e s s e s a n d d i s p la c e m e n t s a r e g iv e n in s o m e o f th e c o lu m n s of f i g u r e 1 7 - B . A d d i t io n a l d e t a i l s an d c o m m e n ts on th e g e n e r a l e v a lu a t io n of th e t e s t r e s u l t s a r e p r e s e n t e d in th e fo l lo w in g p a r a g r a p h s .

W a te r c o n te n t s . T h e a v e r a g e i n i t i a l w a t e r c o n te n t o f th e t e s t s p e c i m e n i s e s t im a te d b y m e a n s of i t s v o lu m e a n d w e t w e ig h t , a n d b y a s s u m in g th a t i t s d e g r e e of s a t u r a t i o n a n d th e s p e c i f i c g r a v i ty o f th e s o i l g r a i n s a r e e q u a l to th o s e o b ta in e d fo r th e u n c o n f in e d c o m p r e s s i o n t e s t s p e c im e n , p r e p a r e d f r o m th e c o r e of th e a n n u la r s p e c im e n . T h e r e s u l t i s c o m p a r e d w ith th e w a te r c o n te n t s o f th e c o r e a n d of s o i l im m e d ia t e ly a b o v e a n d b e lo w th e t e s t s p e c im e n .

T h e w a te r c o n te n t a t c o m p le t io n of th e p r e l i m i n a r y c o n s o l id a t io n a n d s t a r t o f th e a c tu a l s h e a r t e s t s c a n b e e s t im a t e d b y m e a n s o f th e c h a n g e in h e ig h t of th e t e s t s p e c im e n d u r in g c o n s o l id a t io n a n d b y a s s u m in g t h a t th e d e g r e e of s a t u r a t i o n h a s n o t b e e n c h a n g e d , o r th a t c o m p le t e s a t u r a t i o n h a s b e e n a t t a i n e d . T h e in f lu e n c e o f f r i c t io n b e tw e e n s o i l a n d c o n f in in g r i n g s c a u s e s a n o n - u n i f o r m d i s t r i b u t i o n o f n o r m a l s t r e s s e s o v e r the h e ig h t o f th e t e s t s p e c im e n ; s e e p a g e 5 4 . T h is in f lu e n c e o f s i d e - w a l l f r i c t i o n sh o u ld b e t a k e n in to c o n s id e r a t i o n w h e n u n d iv id e d o r s in g l e r i n g s a r e u s e d b u t c a n u s u a l ly b e n e g le c te d in t e s t s w i th d iv id e d r i n g s .

TORSION SHEAR TEST

Sheet ABasic Data and Snmma.ry of Test Results

Project Job No.

Boring No. Sample No. Specimen No. Test No.

Description of Soil

Type of Test

TESTING PROCEDURE

Rate of Displacement

in. /min.Preconsolidation Load kg/cm2 Before FailureNormal Load during Test kg/cm2 After Failure in. /min.Date Start of Consolidation Duration to Maximum Shear min.Date End pf Shear Test Total Duration of Shear Test min.

TEST SPECIMEN

Height Wet Weight Initial Water ContentInitial Height in. Gross Weight g Top Scraps iEnd Consolidation in. Tare and Rings g Bottom ScrapsAt Maximum Shear in. Net Wet Weight « Specimen (Estimated) *

CORE OF TEST SPECIMEN

Water Content Degree of Saturation Unconfined Compressive Strength

Undisturbed í * kg/cm2Remolded < ___ - t kg/cm2

TEST RESULTS

Shearing Resistance Average Displacement Final Water ContentInitial Maximum kg/ cm2 At Maximum Shear in. Top *Residual Strength kg/cm2 At End of Test in. Center -*Location of Failure Bottom ____ iAppearance of Failure Surfaces

REMARKS

Test Performed by: Computations by* Checked by:

F i g u r e 17-A . T e s t d a ta and co m p u ta t ion s h e e t s fo r t o r s io n sh ear t e s t s

TORSION SHEAR TEST

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F ig u r e 1 7 -B . T e s t data and com p u ta tio n s h e e ts fo r to r s io n sh ea r t e s t s

44

A c h a n g e in w ate r content be tw een the s t a r t of the a c tu a l s h e a r t e s t and the t im e when the in i t ia l m a x im u m s h e a r in g r e s i s t a n c e i s r e a c h e d can be e s t im a t e d by m e a n s of the c o r re sp o n d in g ch an ge in h e igh t of the t e s t s p e c im e n , p ro v id e d the an g u la r d i s p l a c e m e n t a t f a i l u r e i s r e l a t iv e ly s m a l l and no s o i l h as been s q u e e z e d out through the c l e a r a n c e betw een the u p p e r and lo w er confin ing r i n g s . S o m e s o i l m a y be l o s t th rou gh th is c l e a r a n c e d u r in g “ d r a in e d ” t e s t s , and a p a r t of the r e l a t iv e ly l a r g e a n g u la r d i s p la c e m e n t s and ch a n g e s in w ate r content m a y b e c o n c e n tr a te d in the zon e of f a i l u r e . In su ch a c a s e , the w ate r content a t f a i lu r e m u s t b e d e te r m in e d d i r e c t ly and by in te rru p t in g the t e s t im m e d ia t e ly a f t e r f a i l u r e or p e r f o r m in g the l a s t p a r t of the t e s t so quick ly that the ch an ge in w ate r content a f te r f a i l u r e i s n e g l ig ib le ; s e e p age 38. S e p a r a t e t e s t s a r e then r e q u ir e d to d e te r m in e the r e s i d u a l s h e a r in g

r e s i s t a n c e fo r d ra in ed co n d it io n s .

A f te r in i t ia l f a i l u r e , s o m e s o i l i s g e n e r a l ly l o s t through the c l e a r a n c e b e tw een the confin ing r in g s , and the d i s p la c e m e n t s and ch an ges in w a te r content a r e c o n c e n tra te d in the zone of f a i l u r e . T h e r e f o r e , the w a te r content a t c o m p le t io n of the t e s t cannot b e com pu ted by m e a n s of the change in heigh t of the t e s t s p e c i m e n but i s ob ta in ed d i r e c t ly a s that of the th r e e thin s o i l s l i c e s cut f r o m the zon e of f a i l u r e

a f t e r the t e s t .

N o r m a l s t r e s s e s . T he v e r t i c a l n o r m a l s t r e s s e s c o r re sp o n d in g to a g iven load on the v e r t i c a l load h an g er a r e c o m p u ted by m e a n s of the fo r m u la s g iven on p a g e 72 in P a r t IV. A s in d ica te d abo ve , the in flu en ce of s i d e - w a l l f r ic t io n m a y h av e to be taken into c o n s id e r a t io n in com pu ting the s t r e s s d i s t r ib u t io n and c o r re s p o n d in g c h a n g e s in w ate r co n tent upon co m p let io n of the p r e l im in a r y c o n so lid a t io n . H o w e v e r , the inf lu e n ce of s i d e - w a l l f r ic t io n u s u a l ly c a n b e n e g le c te d in com puting the n o r m a l s t r e s s e s ac t in g on the zon e of f a i l u r e d u r in g the a c tu a l s h e a r t e s t s , b e c a u s e th is zone i s c l o s e to the top of the te s t sp e c im e n when undivided confin ing r in g s a r e u s e d , and b e c a u s e the in f lu en ce of the f r ic t io n i s p r a c t i c a l l y e l im in a te d by r a i s in g the u p p e r r in g s in t e s t s with d iv id e d r in g s .

A v e r a g e s h e a r in g s t r e s s e s . G e n e r a l f o r m u l a s fo r com puting the a v e r a g e s h e a r in g s t r e s s e s a r e p r e s e n te d on p a ge 7, and d e ta i l e d f o r m u l a s , tak ing the in f lu e n ce of f r i c t io n and other e x t ra n e o u s f o r c e s into c o n s id e r a t io n , a r e g iven on p a g e s 72-7 3 in P a r t IV. T h e c o e f f ic ie n ts in th e se f o r m u la s v a r y s l ig h t ly with the t e s t co n d it io n s , owing to r e v e r s a l of m o v e m e n ts and f r ic t io n in s o m e p a r t s of the a p p a r a t u s when changing f r o m i n c r e a s i n g to d e c r e a s i n g s t r e s s e s or f r o m in c r e a s i n g to d e c r e a s i n g d i s p l a c e m e n t s . T he m o v e m e n t s and the in flu en ce of f r ic t io n a r e a l s o d i f f e r e n t fo r c o n t r o l l e d - s t r a i n and c o n t r o l l e d - s t r a i n load a p p l ic a t io n , and the f o r m u l a s show n on D a t a s h e e t B , f i g u r e 1 7 -B , app ly only to t e s t s with c o n t r o l l e d - s t r a in load a p p l ic a t io n .

S h e a r in g r e s i s t a n c e . T h e in i t ia l m a x im u m and the f in a l s h e a r in g s t r e s s e s ob ta in ed in a t e s t a r e r e c o r d e d on S h e e t A , f i g u r e 17-A , a s the in i t i a l and r e s i d u a l s h e a r in g r e s i s t a n c e s , r e s p e c t i v e l y . A s e c o n d a r y m a x im u m , h igh er than the in it i a l m a x i m u m , and a t e m p o r a r y m in im u m , lo w er than the f in a l s h e a r in g s t r e s s , m a y b e ob ta in ed in s o m e t e s t s b e c a u s e of in te r r u p t io n s of the t e s t and the in f lu e n c e s of

45

ch an g es in w a te r co n te n t. S uch a s e c o n d a ry m a x im u m and te m p o r a r y m in im u m s h e a r ing s t r e s s sh o u ld b e show n on S h e e t A in p a r e n th e s e s a f te r th e in i t i a l m a x im u m and th e r e s id u a l s h e a r in g r e s i s t a n c e s .

D is p la c e m e n ts . G e n e ra l f o rm u la s fo r co m p u tin g th e a v e r a g e d is p la c e m e n ts o r tw is ts a r e p re s e n te d on p ag e 8 , and f u r th e r d’e ta i l s a r e g iv en on D a ta S h e e t C , f ig u re 17 -B , and on p ag es 7 3 -7 4 in P a r t IV .

G ra p h ic a l r e p r e s e n ta t io n

T h e r e s u l t s of e a c h to r s io n s h e a r t e s t a r e g e n e ra l ly s u m m a r iz e d in a s t r e s s - tw is t o r s t r e s s - d i s p l a c e m e n td ia g r a m . E x a m p le s of su ch d ia g r a m s , o b ta in e d in t e s t s on L ak e P ro v id e n c e C lay and A tla n tic M uck, a r e show n in f ig u re s 18 and 19. A ll th e te s t s w e re p e r fo rm e d w ith d iv id e d r in g s an d c o n t r o l l e d - s t r a in lo a d a p p lic a tio n . L a k e P ro v id en ce^ C lay is a m e d iu m s t i f f c la y w ith a n a tu r a l w a te r c o n te n t of 48 to 59 p e r cen t, a liq u id l im i t of 104, an d a p la s t ic i ty in d ex of 69. A t la n tic M uck is a so f t and h igh ly o rg a n ic c la y w ith a n a tu r a l w a te r c o n te n t of 92 to 150 p e r c e n t, a liq u id l im i t of 145 to 163, and a p la s t ic i ty in d ex o f 69 to 106. T h is s o i l c o m b in e s h ig h c o m p r e s s ib il i ty w ith r e la t iv e ly h ig h p e r m e a b i l i ty an d b e c o m e s v e r y s o f t and p la s t ic upon d is tu rb a n c e .

T he sa m p le of L a k e P ro v id e n c e C lay , f ig u re 18, and s a m p le 6D of A tla n tic M uck, f ig u re 19, w e re f i r s t o v e r c o n s o lid a te d u n d e r a n o rm a l lo ad of 5 k g /c m and th en a llo w ed to s w e ll u n d e r th e re d u c e d lo ad of 2 k g /c m ^ b e f o r e th e s t a r t of th e a c tu a l s h e a r te s t . T h e h e ig h t of th e t e s t sp e c im e n s in c r e a s e d s l ig h t ly b e f o r e in i t i a l

TW IST IN DECREES

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F ig u r e 18. S t r e s s - t w i s t d ia g ra m fo r L ake P r o v id e n c e C lay

46

f a i l u r e b e c a u s e of th e s t r o n g o v e r c o n s o l i d a t i o n of th e s o i l s , b u t i t d e c r e a s e d a f t e r f a i l u r e . T h i s d e c r e a s e m a y in p a r t h a v e b e e n c a u s e d by s o i l b e in g s q u e e z e d ou t th r o u g h th e c l e a r a n c e b e tw e e n th e r i n g s , b u t a c t u a l c o n s o l id a t io n a l s o to o k p la c e a s e v id e n c e d b y a s l ig h t i n c r e a s e in r e s i d u a l s h e a r i n g r e s i s t a n c e a f t e r i n t e r r u p t i o n s of th e t e s t s . T h e d i s p l a c e m e n t r e q u i r e d to a t t a i n th e r e s i d u a l s h e a r i n g r e s i s t a n c e of A t l a n t i c M u c k i s t e n t i m e s g r e a t e r th a n th a t of L a k e P r o v i d e n c e C la y .

S a m p l e s 8B and 8D L of A t l a n t i c M u c k , f i g u r e 19, w e r e s u b j e c t e d to n o r m a l c o n s o l i d a t i o n in th e s h e a r a p p a r a t u s ; th e h e ig h t of th e t e s t s p e c im e n s d e c r e a s e d f r o m th e s t a r t of th e s h e a r t e s t , and a p p r e c i a b l e a m o u n t s of s o i l w e r e s q u e e z e d o u t th r o u g h

F i g u r e 19 . S t r e s s - t w i s t d i a g r a m s f o r A t l a n t i c M u c k

th e c l e a r a n c e b e tw e e n th e r i n g s a f t e r i n i t i a l f a i l u r e . A t e m p o r a r y m i n i m u m o c c u r r e d in t h e t e s t on s a m p l e 8B and a s e c o n d a r y m a x i m u m in th e t e s t on s a m p l e 8D L . T h e d e c r e a s e in w a t e r c o n te n t a n d c o r r e s p o n d i n g i n c r e a s e in s t r e n g t h of th e s o i l d u r in g t h e s e t e s t s w e r e so l a r g e th a t th e y s e r i o u s l y i n t e r f e r e d w ith th e f in a l i n t e r p r e t a t i o n of th e t e s t r e s u l t s . T h e r e f o r e , th e r a t e of d i s p l a c e m e n t s h o u ld b e i n c r e a s e d in f u t u r e “ u n d r a i n e d ” t e s t s on th i s s o i l ; s e e p age 36.

C o r r e c t i o n s f o r c h a n g e s in w a t e r c o n te n t

M i n o r c h a n g e s in w a t e r c o n te n t of th e t e s t s p e c i m e n t a k e p la c e d u r i n g q u ic k “ u n d r a i n e d ” t o r s i o n s h e a r t e s t s a n d in f lu e n c e th e s t r e n g t h of th e s o i l . A s a c o n s e q u e n c e , th e i n i t i a l s h e a r i n g r e s i s t a n c e d o e s n o t c o r r e s p o n d to th e w a t e r c o n te n t a t c o m p le t io n of th e p r e l i m i n a r y c o n s o l id a t io n , an d th e i n i t i a l and r e s i d u a l s h e a r i n g r e s i s t a n c e s a r e n o t d i r e c t l y c o m p a r a b l e . A p p r o x i m a t e c o r r e c t i o n s fo r th e in f lu e n c e of s m a l l c h a n g e s in w a te r c o n te n t c a n b e m a d e w h en th e r e l a t i o n s h i p b e tw e e n s t r e n g t h

47

and w ate r content h a s been e s t a b l i s h e d by a s e r i e s of s h e a r t e s t s o r unconfined c o m p r e s s i o n t e s t s on t e s t s p e c i m e n s with v a r y in g w ater c o n te n ts . H o w ev er , the in f lu e n c e of s t r o n g o v e r c o n so l id a t io n and of the fo rm a t io n of s l i c k e n s id e d s u r f a c e s of f a i l u r e on su ch a r e la t io n sh ip h a s not y e t b e e n d e f in ite ly e s t a b l i s h e d , and it i s e m p h a s i z e d that r e l i a b le c o r r e l a t i o n s and c o r r e c t i o n s can be m a d e only when a l l the t e s t s p e c i m e n s u s e d in a p a r t ic u la r s e r i e s of t e s t s a r e obta ined f r o m a s o i l s t r a t u m with u n if o r m p h y s ic a l p r o p e r t i e s .

S l i c k e n s id e d s u r f a c e s of f a i l u r e

T he s u r f a c e s of f a i l u r e p ro d u c e d in m any of the t e s t s on L a k e P r o v id e n c e C la y and A t lan t ic M uck w e r e sm o o th and g lo s s y , s i m i l a r to the s l i c k e n s i d e s o ften found in n a t u r a l d e p o s i t s of c l a y s and s h a l e s , f i g u r e 20. T h e g l o s s i n e s s of the s u r f a c e of f a i lu r e d e c r e a s e d with d e c r e a s i n g n o r m a l s t r e s s e s , and w as a b s e n t in t e s t s

LAKE PROVIDENCE CLAY ATLANTIC M U C K-SAM PLE 7 DL

VERTICAL LOAD 2 .0 KG /C M 2 VERTICAL LOAD 5.0 KG /C M 2DISPLACEMENT 2 7 .5 IN. DISPLACEMENT 9 .2 IN.

F i g u r e 20 . F o r m a t i o n of s l i c k e n s i d e s by to r s io n s h e a r t e s t s

p e r f o r m e d un der a n o r m a l s t r e s s of 0.5 k g / c m ^ . T he fo r m a t io n of s l i c k e n s id e d s u r f a c e s of f a i l u r e p ro b ab ly r e q u i r e s a m in im u m v a lu e of the n o r m a l s t r e s s in ad d it io n to a c e r t a in am o un t of d i s p la c e m e n t . H o w e v e r , the c h a n g e s in s o i l s t r u c t u r e and c o m p o s i t io n in the im m e d ia t e v ic in ity of su ch s u r f a c e s , and the in flu en ce of su c h c h a n g e s on the r e s i d u a l s h e a r in g r e s i s t a n c e a r e not yet known. T h e r e f o r e , the c o n d it ion of the s u r f a c e of f a i lu r e shou ld b e r e c o r d e d , and p h o to g rap h s of t y p ic a l e x a m p l e s m a y b e v a lu a b le in the f in a l in t e r p r e ta t io n and c o r r e l a t i o n of the t e s t r e s u l t s .

U nconfined c o m p r e s s i o n t e s t s

T h e p r e p a r a t i o n of t e s t s p e c i m e n s fo r unconfined c o m p r e s s i o n t e s t s p r o v id e s an e a s y m e a n s of d e te rm in in g the w et unit w eight and the d e g r e e of s a t u r a t io n of the s o i l . T h e r e s u l t s of the t e s t s f u r n i sh d a ta fo r e s t a b l i sh in g or ch eck ing s t r e n g t h - w a t e r content r e la t io n s h ip s and the s e n s i t iv i t y of the s o i l to d i s t u r b a n c e . A c o r r e l a t i o n of the r e s u l t s of to r s io n s h e a r t e s t s with th o se of the m o r e e a s i l y p e r f o r m e d unconfined

48

c o m p r e s s i o n t e s t s i s of p r a c t i c a l im p o r ta n c e , e s p e c i a l l y fo r d e te rm in a t io n of the r e s id u a l s t r e n g th and in v e s t ig a t io n of the in fluen ce of s l i c k e n s id e d s u r f a c e s of f a i l u r e on th is s t r e n g th .

S e r i e s of t e s t s

A d e ta i le d d i s c u s s i o n of the f ina l e v a lu a t io n and in te r p r e ta t io n of the r e s u l t s of c o m p le te s e r i e s of to r s io n s h e a r t e s t s i s o u t s id e the s c o p e of this bu lle t in , and only a few g e n e r a l c o m m e n ts w il l be m a d e . T he d a ta on S h ee t A a r e a s s e m b l e d in a s u m m a r y sh e e t c o v e r in g the whole t e s t s e r i e s . T h e s e d a ta m ay be su p p le m en ted by the co m p u ted ch an ge s in w ate r content d u r in g qu ick “ u n d ra in e d ” t e s t s and c o r r e sponding c o r r e c t io n s of the in i t ia l and r e s i d u a l s h e a r in g r e s i s t a n c e s . Two ty p es of g r a p h ic a l r e p r e s e n t a t io n of the r e s u l t s a r e u s e d . F i r s t , the l o g a r i th m s of the unc o r r e c t e d v a lu e s of the in i t ia l and r e s i d u a l s h e a r in g r e s i s t a n c e s a r e p lotted a s fu n ction s of c o r r e s p o n d in g w ate r contents of the s o i l , and the r e su l t in g d i a g r a m s a r e c o m p a r e d with eac h other and with s i m i l a r d i a g r a m s of the l o g a r i th m s of o n e -h a lf the unconfined c o m p r e s s i v e s t re n g th of u n d is tu rb ed and r e m o ld e d s o i l v e r s u s w ate r co n tent. In the s ec o n d r e p r e s e n t a t io n , v a lu e s of the in i t ia l and r e s i d u a l s h e a r in g r e s i s t a n c e s , c o r r e c t e d fo r the in fluen ce of ch a n g e s in w ate r content during the t e s t , a r e plo tted a g a i n s t the c o r r e s p o n d in g v e r t i c a l n o r m a l s t r e s s e s .

F a i r l y c o n s i s te n t d i a g r a m s of s h e a r in g r e s i s t a n c e v e r s u s n o r m a l s t r e s s w e re obta ined f r o m the r e s u l t s of the t e s t s so fa r p e r f o r m e d , but th ere w as c o n s id e r a b l e s c a t t e r i n g of the points in d i a g r a m s of s h e a r in g r e s i s t a n c e v e r s u s w ate r content. F o r the r e s i d u a l s h e a r in g r e s i s t a n c e s , the s c a t t e r in g w as so g r e a t that a d e f in ite r e la t io n sh ip could not be e s t a b l i s h e d . T h is s c a t t e r in g i s due p r im a r i ly to the non- u n i fo rm c h a r a c t e r of the s o i l in the s a m p l e s u se d , but v a r ia t io n s in the fo r m a t io n of s l i c k e n s id e d s u r f a c e s of f a i l u r e m a y be a co n tr ib u tin g c a u s e . T h is e x p e r ie n c e e m p h a s i z e s the n e c e s s i t y fo r obta in ing s a m p l e s of u n i fo rm s o i l fo r each s e r i e s of t e s t s .

49

P A R T IV : C A L IB R A T IO N O F A P P A R A T U S

S c o p e o f C a l i b r a t io n

T h e g e n e r a l o b je c t s o f th e c a l i b r a t i o n of th e t o r s i o n s h e a r a p p a r a t u s w e r e : (1) to m e a s u r e th e a c t u a l d im e n s io n s a n d l e v e r r a t i o ; (2) to c h e c k th e p r o p e r a l i g n m e n t a n d f i t of th e v a r io u s p a r t s a n d d e t e r m i n e th e i n f lu e n c e o f m o v e m e n ts o f t h e s e p a r t s ; (3 ) to d e t e r m i n e th e t a r e w e ig h ts o f p a r t s w h ic h a r e n o t c o u n te r b a la n c e d b u t c o n t r ib u t e to th e lo a d on th e t e s t s p e c im e n ; a n d (4 ) to d e t e r m i n e th e m a g n i tu d e of a u x i l i a r y f o r c e s e x e r t e d b y th e v a r i o u s d ia l i n d i c a t o r s o r c a u s e d b y f r i c t i o n in t h e s e d i a l s a n d in th e g u id e s h e a v e s .

S o m e o f th e a b o v e - m e n t io n e d a u x i l i a r y f o r c e s a r e v e r y s m a l l , a n d t h e i r c a r e fu l d e t e r m i n a t io n m a y s e e m u n w a r r a n t e d in v ie w o f th e a c c u r a c y w ith w h ic h th e m a in d im e n s io n s a n d l e v e r r a t i o s c a n b e d e t e r m i n e d . H o w e v e r , th e c o m b in e d i n f lu e n c e of s u c h f o r c e s m a y b e c o m e s ig n i f i c a n t w h e n th e n o m in a l f o r c e s a n d s t r e s s e s a r e s m a l l . F u r t h e r m o r e , s e v e r a l a u x i l i a r y f o r c e s c h a n g e s ig n w ith th e d i r e c t i o n o f th e m o v e m e n t s o f v a r i o u s p a r t s o f th e a p p a r a t u s , a n d c o r r e s p o n d in g s m a l l c o r r e c t i o n s o f te n m a k e p o s s ib le th e e l im in a t i o n o f a p p a r e n t m in o r i r r e g u l a r i t i e s in th e p r i n c ip a l r e s u l t s o f th e c a l i b r a t i o n a n d th e a c t u a l s h e a r t e s t s . T h e r e s u l t s o f th e c a l i b r a t i o n a r e p r e s e n t e d in s u m m a r i z e d a n d s im p l i f i e d f o r m on p a g e s 7 2 - 7 4 .

A l ig n m e n t o f A p p a r a tu s

T h e t e s t i n g b e n c h w a s b lo c k e d u p u n t i l th e m a in b e a m s w e r e h o r i z o n t a l . T h e f l a n g e s o f t h e s e b e a m s w e r e n o t m a c h in e d a n d t r u ly p la n e , a n d s h im s w e r e p la c e d u n d e r th e b a s e p l a t e o f th e t o r s i o n s h e a r a p p a r a t u s u n t i l t h i s p la te w a s f u l ly s u p p o r t e d a n d th e r o t a t i n g b a s e of th e a p p a r a t u s , (10) in f i g u r e 7, w a s h o r i z o n t a l . T h e lo w e r d e n ta te d p la te w a s fo u n d to b e s l i g h t l y w a r p e d , w h ic h m a y c a u s e s o m e n o n - u n i f o r m i ty in s t r e s s d i s t r i b u t i o n a n d te n d e n c y to t i l t in g of th e a n n u la r p is to n a n d t o r q u e w h e e l . T h e u p p e r d e n ta te d p la te i s b r a z e d to th e a n n u la r p is to n , a n d o r i g i n a l w a r p in g i s t h e r e b y e l im in a te d . T h e p a r a l l e l i s m o f th e lo w e r s u r f a c e o f t h i s p la te a n d th e u p p e r s u r f a c e of th e to r q u e w h e e l w a s c h e c k e d a n d fo u n d s a t i s f a c t o r y . A s l i g h t d e v ia t io n in th e p a r a l l e l i s m of th e tw o w i r e r o p e s w a s fo u n d , b u t i t s i n f lu e n c e w a s d e e m e d in s ig n i f i c a n t , e x c e p t t h a t i t m a y , i n s o m e c a s e s , c o n t r ib u t e to t i l t i n g o f th e t o r q u e w h e e l .

T h e p o s i t io n o f th e c o u n te r w e ig h t o f th e v e r t i c a l lo a d in g s y s t e m w a s a d ju s t e d u n t i l th e tw o l e v e r s w e r e p r o p e r l y b a l a n c e d in h o r i z o n t a l p o s i t io n . T h e b r a c k e t s fo r th e k n i f e - e d g e s w e r e a d ju s t e d , b y u s e of a c a r e f u l l y c e n t e r e d p lu m b b o b , u n t i l th e m a in k n i f e - e d g e w a s v e r t i c a l l y b e lo w th e c e n t e r o f th e r o t a t i n g b a s e of th e s h e a r a p p a r a t u s , a n d u n t i l th e l in k b e tw e e n th e tw o l e v e r s a n d th e w i r e r o p e to th e c o u n t e r w e ig h t l e v e r w e r e v e r t i c a l . A s l i g h t a m o u n t o f p la y fo u n d in th e s y s t e m a s a w h o le m a y b e d u e to i m p e r f e c t p a r a l l e l i s m of th e v a r io u s k n i f e - e d g e s a n d f u l c r u m s o r to a ro u n d in g of th e k n i f e - e d g e s a n d g r o o v e s in th e f u l c r u m p l a t e s . T h is p la y m a y b e th e

50

c a u s e of a s l ig h t s c a t te r in g in th e r e s u l t s of th e s u b s e q u e n t d e te rm in a t io n of th e le v e r r a t io s and of th e in flu e n c e of f r ic t io n in and d e f le c t io n s of th e le v e r s y s te m .

G o v e rn in g D im e n s io n s

T h e g o v e rn in g d im e n s io n s of th e a p p a ra tu s w e re d e te rm in e d by m e a n s of a v e r n ie r c a l i p e r , and th e c o r re sp o n d in g v a lu e s of th e m e a n d ia m e te r and le n g th of th e t e s t s p e c im e n , i t s c r o s s - s e c t io n a l a r e a , and th e e q u iv a le n t s h e a r a r e a w e re co m p u ted by th e f o r m u la s g iven on p ag es 7 and 8, and r e p e a te d b e lo w . T h e r e s u l t s a r e s u m m a r iz e d in th e fo llow ing ta b le and th e r e c o m p a re d w ith th e d e s ig n s p e c i f ic a t io n s .

D im e n -S u b je c t s io n S ym bo l D e s ig n A c tu a l

ID o u te r r in g s o r OD s a m p le cm D 11.43 11.44OD in n e r r in g s o r ID s a m p le cm d 6.35 6 .36H e ig h t of s a m p le r in g cm H 2.22 2 .16M ean d ia m e te r of s a m p le cm Dm 9.13 9 .14M ean c i r c u l a r len g th of s a m p le cm L m 28 .69 28 .72H o r iz o n ta l a r e a of s a m p le cm ^ A 7 0 .9 4 71 .02D ia m e te r of to r s io n w h ee l g ro o v e cm ° g

dw26 .08 26 .33

D ia m e te r of t r a n s m is s io n w ire ro p e cm 0.16 0.17E ffe c tiv e d ia m e te r of to r s io n w h ee l cm Dw 26 .24 26 .50E q u iv a le n t s h e a r a r e a cm ^ A s 24 .69 24 .50

_ 2 D 3 - d t = «O , m 3 D 2 - d 2

A = -2 (D 2 - d 2 ) , A s « D 3 - 6 D,

V e r t i c a l L o ad in g S y s te m

D ead w e ig h ts

T h e a r r a n g e m e n t fo r ap p ly in g v e r t i c a l o r n o rm a l lo a d s to th e s a m p le is show n d ia g r a m m a t ic a l ly in f ig u re 21; fo r d e ta i ls and e le m e n ts c o n tr ib u tin g to th e t a r e o r d ead w e ig h t s e e f ig u re 7. In th e fo llo w in g ta b le of d ead w e ig h ts o r th e in i t i a l n o rm a l lo ad on a p la n e th ro u g h th e jo in t b e tw e e n th e u p p e r and lo w er con fin in g r in g s , th e h e ig h t of th e s a m p le abo ve th is p lan e is a s s u m e d to b e 3 /8 in . and th e w e t u n it w e ig h t of th e s o i l 115 lb p e r cu f t.

T o rq u e w h ee l and a n n u la r p is to n 5.838 kgT w is t - d ia l s to p 0.214 k gT w o w ire c la m p s and p in s 0 .196 kgC ap , th r u s t b e a r in g , and lo ad in g ro d 0.256 kgT u rn b u c k le , l in k s , and do ub le hook 0.213 kg

T o ta l fo r s in g le r in g s 6.717 kg

51

O u te r - r in g and e le v a to r s c r e w s 0 .5 6 4 kgIn n e r - r in g and e le v a to r s c r e w s 0 .3 0 0 kgR in g - g u id e b e a r in g 0 .1 0 0 kgS o il to jo in t betw een r in g s 0,1 33 kg

T o ta l fo r d iv id ed r in g s 7 .8 1 4 kg

T h e d e ad w eigh ts in d icated a b o v e w ould b e ab o u t 2 .3 kg s m a l le r i f the to rq u e w h eel had b een m a d e o f a lu m in u m , a s o r ig in a l ly s p e c i f ie d .

L e v e r r a t io s

M e a su r e m e n t of the a c tu a l d is t a n c e s betw een the k n ife - e d g e s , f ig u r e 21 , g av e a co m b in ed le v e r r a t io of 7 .1 0 8 ; th at i s , a lo a d Q on the h an g e r p r o d u c e s a load 7 .1 0 8 Q on the s a m p le . T h e co m b in ed le v e r r a t io w as a l s o d e te rm in e d by d ir e c t w e igh in g , d u rin g w hich the lo ad in g ro d p a s s e d th rou gh and tr a n s m it te d the load to a b o a rd r e s t in g on two b e a m s c a l e s . F o r each lo ad Q on the h a n g e r , the s c a l e s w e re f i r s t load ed u n til a p r e l im in a r y b a la n c e w as e s t a b li sh e d w ith the l e v e r s in h o r iz o n ta l o r z e r o p o s it io n . T h e r e a f te r the lo a d s on t h e s c a le s w e re in c r e a s e d a n d d e c r e a s e d r e s p e c t iv e ly , unt i l the s t a r t o f b a r e ly p e r c e p tib le u p w ard o r dow nw ard m o v e m e n ts o f t h e l e v e r s . T h e a v e r a g e of th e se l im itin g lo a d s on the s c a l e s w a s u s e d in com pu tin g the co m b in ed le v e r r a t io , w hich w as found to v a ry b e tw een 7 .1 1 3 and 7 .1 2 0 w ith an a v e r a g e of 7 .1 1 7 . T h e m ax im u m c a p a c ity of the s c a le s w as only ab o u t 40 k g , but the le v e r r a t io d e te rm in e d by w eigh in g i s b e l ie v e d m o r e a c c u r a t e than th at ob ta in ed by m e a s u r e m e n t of the d is ta n c e s betw een the k n ife - e d g e s .

F r i c t io n in l e v e r s y s t e m

T h e l e v e r s y s te m w ith no lo ad on the h a n g e r i s in b a la n c e when the dou ble hook to the lo ad in g ro d i s re m o v e d , and a b a r e ly p e rc e p t ib le dow nw ard m o v e m e n t of the l e v e r s w ill then be p rod u ced by a lo ad of 1 g on th e h an ger p la te , e q u iv a le n t to 7 g on the s a m p le . T h e d e ad w eigh t of the le v e r s y s t e m with co u n terw eigh t p ro d u c e s p r e s s u r e s on the k n ife - e d g e s c o r re sp o n d in g a p p ro x im a te ly to th o se in a w e ig h t le s s le v e r

F i g u r e 21 . V e r t i c a l loading and l e v e r r a t i o s

52

s y s t e m w ith 2 .2 5 kg on the h a n g e r . T h e in flu en ce of the f r ic t io n in the le v e r s y s t e m m a y b e a s s u m e d p ro p o rtio n a l to the to ta l p r e s s u r e on the k n ife - e d g e s o r to (2 .25 + Q). I t s in f lu e n c e , A P j , on the t o ta l lo a d on the s a m p le m a y th en b e e x p r e s s e d a s fo llo w s:

A P f = (2 .2 5 + Q) 0 .0 0 7 / 2 .2 5 = 0 .007 + 0.0031 Q kg

w ith A p£ and Q m e a su r e d in kg and Ap£ n e g a tiv e fo r a dow nw ard m o v em en t of the l e v e r s d u r in g c o n so lid a tio n o f the s a m p le and p o s it iv e fo r upw ard m o v e m e n ts of the l e v e r s o r sw e llin g of the s a m p le .

In fluence of le v e r m ovem ent

T h e in flu en ce of a m a t e r i a l u p w ard or dow nw ard m o v em en t of the l e v e r s w as a l s o in v e s t ig a te d d u rin g d e te rm in a t io n of the le v e r r a t io by w eigh in g . T he r e s u l t s , show n in f ig u r e 2 2, r e v e a l th at the ch an ge in t r a n sm itte d lo a d , A P , i s a PPr o x im a te ly

- 1.6 - 1.4 - 1.2 - 1.0 - 0.6 - 0.6 - 0.4 - 0.2 0 0.2 0.4 0.6 0.8 1.0

F i g u r e 22. In fluence of l e v e r m o v e m e n ts

53

p r o p o r t io n a l to the m o v e m e n t of the le v e r and i n c r e a s e s s l ig h t ly w ith the load on the

h a n g e r and c o rr e s p o n d in g load t r a n s m it t e d to the s a m p le . T h e in f lu e n c e of l e v e r m o v e m e n ts f o r m a x im u m load s on the t o r s i o n s h e a r ap p a ra tu s could not b e d e t e r m ined d i r e c t l y on a cc o u n t of the l im it e d c a p a c i ty of the b e a m s c a l e s u se d in the c a l ib r a t i o n . An in d ica t io n of the c o r r e c t i o n s , A P m , fo r la r g e lo ad s w as o b ta in ed by s i m i l a r t e s t s w ith a F a i r b a n k s s c a l e and load s up to 2 33 kg on the p l a t f o r m . T h e r e s u l ts a r e a l s o shown in f ig u r e 22 and in d ic a te a d e f in i te but r e la t iv e l y s m a l l i n c r e a s e in A with i n c r e a s in g load and c o n s ta n t d e f le c t io n of the l e v e r . U s in g the t e s t swith the F a i r b a n k s s c a l e a s a guide, the c o r r e c t i o n f o r in f lu e n c e of l e v e r m o v e m e n ts

in the t o r s i o n s h e a r a p p a ra tu s m a y b e e x p r e s s e d a s fo l lo w s ,

A P = (0 .4 2 5 + 0 .0 0 2 P ) m kg m

o r e x p r e s s e d in t e r m s of the h a n g e r load Q

A P = ( 0 .4 2 5 + 0 .0 1 5 Q) m kg m t o

with the l e v e r m o v e m e n t m in in c h e s and p o s i t iv e fo r upward, n e g a t iv e fo r downw ard m o v e m e n t s . T h e l e v e r s sh o u ld b e kep t in h o r iz o n t a l p o s it io n and the c o r r e c t i o nA P w il l not b e included in the g e n e r a l s u m m a r y of c o r r e c t i o n s to the v e r t i c a l load

mbut ca n , i f need b e , be d e t e r m in e d by the a b o v e -m e n t io n e d equation .

F r i c t i o n in th e pivot b e a r in g

T h e f r i c t i o n in the pivot or r in g - g u id e b e a r in g , (17) in f ig u r e 7 , w i l l c a u s e a

s l ig h t d e c r e a s e in load a c tu a l ly t r a n s f e r r e d to th e s a m p le during c o n s o l id a t io n and a c o r r e s p o n d in g i n c r e a s e during sw e l l in g of the s o i l . T h e f r i c t i o n in the b e a r in g was d e t e r m in e d by m e a n s of sp r in g s c a l e a t ta ch e d to a s l in g betw ee n the e l e v a t o r s c r e w s of the in n e r confin ing r in g , (6) in f ig u r e 7 , and i t i s o n e - h a l f the d i f f e r e n c e b e tw een the a p p a r e n t w eights of the r in g and b e a r in g d uring upward and downw ard m o v e m e n t s . T h e r e was c o n s id e r a b le s c a t t e r i n g of r e s u l t s , but the a v e r a g e v a lu e of the

f r i c t i o n i s 15 g or

A P^ = 0 .0 1 5 kg,

p o s i t iv e fo r an upward and n e g a t iv e fo r a downward m o v e m e n t of the b e a r in g , c o r resp o n d in g to sw ellin g and c o n s o l id a t io n of the s a m p le , r e s p e c t i v e l y . I t should b e noted th a t th is f r i c t i o n does not b e c o m e a c t iv e b e f o r e the confin ing r i n g s h a v e b ee n

r a i s e d .

D ia l f o r c e s

T h e downward p r e s s u r e e x e r te d by the s t e m of the v e r t i c a l d e f o r m a t i o n d ia l ,

(27) in f ig u r e 7 , was d e te rm in e d fo r upward and downward m o v e m e n ts of th e s t e m ,

54

a n d th e r e s u l t s a r e sh o w n in f i g u r e 23. T h e d i f f e r e n c e b e tw e e n th e u p p e r a n d lo w e r v a l u e s of th e d i a l p r e s s u r e i s f a i r l y c o n s t a n t an d e q u a l to tw ic e th e v a lu e of th e i n t e r n a l f r i c t i o n in the d i a l . T h e d i a l f o r c e F v i s a l s o th e c o r r e c t i o n A P^ and can b e e x p r e s s e d a s fo l lo w s ,

A P d = 0 .450 - 0 . 5 8 R V i 0 .0 2 0 kg.

W h e re R v i s th e d i a l r e a d in g in in c h e s , th e m i n u s s ig n a p p l i e s to a d o w n w a rd m o v e m e n t o r c o n s o l id a t io n a n dth e p lu s s ig n to a n u p w a rd m o v e m e n t o r s w e l l i n g of th e s a m p le .

F r i c t i o n b e tw e e n s o i l a n d r i n g s

F r i c t i o n and a d h e s i o n b e tw e e n t h e t e s t s p e c i m e n an d the u p p e r c o n f in in g r i n g s , (3) in f i g u r e 7, w i l l d e c r e a s e th e e f f e c t iv e v e r t i c a l s t r e s s e s d u r in g c o n s o l id a t io n and in c r e a s e t h e s e s t r e s s e s d u r in g

s w e l l in g of th e s o i l , b u t th e i n c r e a s e in lo a d d u r i n g sw e l l in g i s l i m i t e d to t h a t c o r r e s p o n d in g to th e w e ig h t of th e u p p e r r i n g s . R a i s in g th e u p p e r r i n g s b e f o r e th e a c t u a l s h e a r t e s t e l i m i n a t e s th e e f f e c t of f r i c t i o n b e tw e e n s o i l and r i n g s fo r th e c e n t r a l p a r t

, of th e s a m p l e , p ro v id e d s u f f i c i e n t t i m e fo r s t r e s s a d j u s t m e n t s i s a l lo w e d b e tw e e n th e r a i s i n g of th e r i n g s a n d th e s t a r t of the s h e a r t e s t . H o w e v e r , the f r i c t i o n b e tw e e n s o i l and r i n g s w i l l a f f e c t th e in d u c e d p r e c o n s o l i d a t i o n s t r e s s in s o i l s a m p l e s s u b j e c t e d to o v e r c o n s o l i d a t i o n in th e s h e a r a p p a r a t u s , e v e n w hen th e r i n g s a r e r a i s e d b e f o r e th e s h e a r t e s t a n d u n d e r the f in a l b u t s m a l l e r v e r t i c a l lo ad .

F ig u r e 23. F o r c e s by v e r t i c a l d ia l

D u r in g th e p r i m a r y c o n s o l id a t io n , th e l a t e r a l s o i l s t r e s s , p^, m a y b e a s s u m e d to b e a l i n e a r fu n c t io n of th e v e r t i c a l s t r e s s , pv , o r p^ = K p ^ , w h e r e K i s th e c o e f f i c i e n t of e a r t h p r e s s u r e a t r e s t a n d v a r i e s b e tw e e n 0.45 a n d 0.55 f o r s a n d a n d b e tw e e n 0.67 and 0 .80 f o r c l a y s . H o w e v e r , w h e n pv is d e c r e a s e d d u r in g th e o v e r c o n s o l i d a t i o n p r o c e d u r e , r e s i d u a l l a t e r a l s t r e s s e s in the s o i l c a u s e p^ to d e c r e a s e a t a s m a l l e r r a t e th a n pv ; th a t i s , K i n c r e a s e s w ith d e c r e a s i n g pv and m a y e v e n tu a l ly b e c o m e g r e a t e r th a n u n i ty .

A n e s t i m a t e of th e in f lu e n c e of the f r i c t i o n a n d a d h e s io n b e tw e e n s o i l and r i n g s on th e v e r t i c a l n o r m a l s t r e s s d u r in g p r i m a r y c o n s o l id a t io n m a y b e m a d e a s fo l lo w s ; s e e f i g u r e 24. T h e t o t a l v e r t i c a l lo a d i s

P = | (D2 - d 2 ) pv .

55

A s s u m in g t h a t th e u n i t f r i c t i o n a n d a d h e s io n b e tw e e n s o i l and r i n g s m a y b e e x p r e s s e d

A Pr = M- Ph = V K Pv * th e to ta lf r i c t i o n to th e d e p th h b e lo w th e to p of th e t e s t s p e c i m e n i s ,

A P r = M- K p y < (D + d ) h

and th e c o r r e s p o n d i n g r a t i o of r e d u c t i o n in v e r t i c a l s t r e s s i s th e n

APM- K ■

4hP " D - d

With D = 4 .5 0 in . , d = 2 .50 in . , h = h o = 3/ 8 in . , the r a t i o

POROUSBRONZE

F ig u r e 24. In flu en ce of s o i l f r ic t io n and ad h esion

of r e d u c t i o n a t the lo w e r ed g e of th e u p p e r r i n g s i s ,

A P = 0 . 7 5 H K P . r

F o r c la y on p o l i s h e d b r o n z e , M- = 0.15 to 0 .2 5 , a n d w i th K = 0.67 to 0 .8 0 , A P ^ v a r i e s f r o m 0 .075 P to 0.15 P ; t h a t i s , t h e o r e t i c a l l y th e v e r t i c a l s t r e s s m a y b e r e d u c e d f r o m 7 .5 to 15 p e r c e n t . A c tu a l ly th e r e d u c t i o n w i l l b e s m a l l e r b e c a u s e of a c o r r e s p o n d i n g d e c r e a s e in th e l a t e r a l s t r e s s , a n d s lo w p l a s t i c d e f o r m a t i o n s of th e s o i l m a y to a c o n s i d e r a b l e e x te n t c o u n t e r a c t th e in f lu e n c e of the s id e f r i c t i o n a n d a d h e s io n . D u r in g t e s t s w i th s in g le r i n g s , th e s u r f a c e of f a i l u r e i s c l o s e to th e top of th e s a m p l e , a n d the in f lu e n c e of f r i c t i o n b e tw e e n s o i l and r i n g s i s n e g l ig ib le .

S e t t l e m e n t o f t o r q u e w h e e l

T h e t o r q u e w h e e l and h o r i z o n t a l s h e a v e s a r e c a r e f u l ly a l ig n e d b e f o r e s t a r tof th e s h e a r t e s t , so t h a t th e w i r e r o p e s a r e h o r i z o n t a l . A ny s u b s e q u e n t v e r t i c a l m o v e m e n t , 6 of the t o r q u e w h e e l w i l l c a u s e a p a r t of th e t e n s io n in e a c h of th e r o p e s - - e q u a l to o n e - h a l f of th e t o r q u e lo a d S - - to b e t r a n s m i t t e d a s a v e r t i c a l f o r c e , f i g u r e 25 . W ith a d i s t a n c e of 6 - l / 4 in . b e tw e e n th e t o r q u e w h e e l a n d th e

h o r i z o n t a l s h e a v e s , th e c o r r e c t i o n to the v e r t i c a l lo a d on the s a m p l e i s ,

A P = + S 8 J 6 .25 = + 0 .16 8 S kg w w' w °

w i th A P W a n d S e x p r e s s e d in kg a n d 8 w in in c h e s . T h e m i n u s s ig n a p p l i e s to s e t t l e m e n t a n d th e p lu s s ig n to r i s i n g of th e t o r q u e w h e e l . T h e v e r t i c a l m o v e m e n t b e f o r e f a i l u r e i s g e n e r a l l y i n s i g n i f i c a n t , b u t a n a p p r e c i a b l e s e t t l e m e n t m a y o c c u r

F ig u r e 25 . S e tt le m e n t of torque w h e e l

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a f te r f a i lu r e of th e sa m p le w h en s o i l i s b e ing sq u e e z e d ou t b e tw e e n d iv id e d r in g s . H o w ev e r, th e t e s t i s u su a lly in te r r u p te d and th e h o r iz o n ta l sh e a v e s r e a l ig n e d w ith th e to rq u e w h e e l, th e re b y e l im in a t in g ch an g es in th e v e r t i c a l lo ad and th e c o n se q u e n t n e c e s s i ty fo r c o r r e c t io n s .

S u m m a ry of v e r t i c a l fo rc e s

In th e fo llow ing ta b le , a l l w e ig h ts and f o rc e s a r e e x p re s s e d in kg and v e r t i c a l m o v e m e n ts , m and 8 w , in in c h e s . W h enev er a + s ig n is show n, th e m in u s a p p lie s to r e a l o r a p p a re n t c o n s o lid a t io n and th e p lus to sw e llin g of th e t e s t sp e c im e n .

D iv id ed R in g s S in g le R in g s(1) D ead w eig h t p o 7 .814 6.717(2) L e v e r load P q 7.117 Q(3) L e v e r f r ic t io n A p f + (0.007 + 0.003 Q)(4) L e v e r m o v em en t A P m + (0 .425 + 0.015 Q) m(5) F o r c e by v e r t i c a l d ia l A P d 0 .450 - 0.58 R v + 0 .020(6) P iv o t b e a r in g f r ic t io n A P b + 0.015 0(7) S o il and r in g f r ic t io n A p r + 0.75 ( iK P(8) T o rq u e w h ee l s e t t le m e n t * P w + 0.16 8 w S

T he f o rc e s o r c o r r e c t io n s u n d e r i t e m s (4), (7), and (8) n eed b e c o n s id e re d on ly u n d e r s p e c ia l c o n d itio n s , and th e su m s of th e re m a in in g f o rc e s c o n s ti tu te th e a c tu a l v e r t i c a l lo ad , P a , on th e s a m p le . T h e s e su m s and th e c o r r e s p o n d in g a v e ra g e u n it v e r t i c a l p r e s s u r e s , pv = P a / A = p a / 7 1 -02 k g /c m 2 , a r e :D iv ided r in g s :

P a = (7.117 i 0 .003) Q + 8.264 + 0.042 - 0 .5 8 R V kg C o n so lid a tio n , pv = 0.10017 Q + 0.1158 - 0 .008 Rv k g /c m ^S w ellin g , pv = 0.10025 Q + 0.1170 - 0 .008 Rv k g /c m ^

S in g le r in g s :P = (7.117 + 0 .0 0 3 )Q + 7.167 1 0.027 - 0 .58 R v kg a » ^C o n so lid a tio n , pv = 0.10017 Q + 0.1005 - 0 .008 R v k g /c mS w ellin g , pv = 0 .10025 Q + 0.1013 - 0 .008 R y k g /c m 2

A ssu m in g a d ia l se tt in g R v = 0 .100 in ., and u n le s s th e to ta l v e r t i c a l f o rc e is v e ry s m a l l o r g r e a t e x a c tn e s s is r e q u i r e d , th e fo llow ing s im p lif ie d e x p re s s io n s m ay b e u s e d in r o u t in e t e s t s :

D iv ided r in g s P a = 7.117 Q + 8 .206 kgpv = 0.1002 Q + 0 .116 k g /c m 2

P a = 7 .117 Q + 7 .109 kgpv = 0.1002 Q + 0 .100 k g /c m 2S in g le r in g s

57

T o rq u e L o ad in g - - C o n tro l le d S t r e s s

A d ia g ra m m a t ic s k e tc h of th e to rq u e - lo a d in g s y s te m fo r c o n tro l le d s t r e s s i s show n in f ig u re 26, and a s im i l a r sk e tc h fo r c o n tro lle d r a t e of s t r a i n in f ig u re 29. In ea c h c a s e a l l n o n e s s e n t ia l d e ta i l s a r e e l im in a te d , b u t, a s p re v io u s ly m e n tio n e d , th e

F ig u r e 26 . T orq u e load ing - - co n tr o lled s t r e s s

tw o s y s te m s a r e in te rc o n n e c te d and i t is p o s s ib le ev en d u rin g a t e s t to ch an g e f ro m one ty p e of lo ad in g s y s te m to th e o th e r . W ith th e e f fe c tiv e d ia m e te r of th e to rq u e w h e e l = 26 .50 cm and th e to rq u e lo ad S kg , th e m o m e n t o r to rq u e a c tin g on th e s a m p le is

M = 1 /2 S D W = 13.25 S k g c m

and th e c o r re sp o n d in g a v e r a g e s h e a r in g s t r e s s is

T a = 1 2 M / jc (D 3 - d 3) = S /A g = S /2 4 .5 0 k g /c m 2 .

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C o r r e c t io n s fo r v a r io u s a u x i l ia r y fo r c e s o r m o m e n ts , d i s c u s s e d in the fo llow in g p a r a g r a p h s , w ill be e x p r e s s e d a s the e q u iv a len t c o r r e c t io n s to the to rq u e load S . It sh o u ld b e noted that so m e of th e se fo r c e s and m o m e n ts a r e p r e s e n t in both the c o n t r o l le d - s t r e s s and the c o n tr o l le d - s t r a in s y s t e m s , but they m a y , in so m e c a s e s , a c t in o p p o s ite d ire c t io n s fo r the two lo ad in g s y s t e m s .

F o r c e s e x e r te d by the tw is t d ia l s

T h e tw ist d ia ls in the s h e a r a p p a r a tu s , (26) in f ig u r e 7 , a r e p la c e d in h o r iz o n ta l p o s it io n and the f o r c e s e x e r te d by the d ia l s m u s t b e d e te rm in e d w ith the d ia ls in th e s a m e p o sitio n . T h is w as a c c o m p lish e d by the a r r a n g e m e n t and with the r e s u lt s show n in f ig u r e 27 . T h e a v e r a g e fo r c e e x e r te d by e ith er one of the two d ia ls can b e e x p r e s s e d by

F h = 210 - 204 x R h + 11 g

w h ere th e 11 g r e p r e s e n t s the f r ic t io n in the d ia l , n e g a tiv e fo r in c r e a s in g tw ist and

R ̂5 DIAL READING IN INCHES

F i g u r e 27. F o r c e s by tw is t d i a l s

p o s it iv e fo r d e c r e a s in g tw ist . T h e d is ta n c e betw een the d ia l s te m s i s 10 .0 in . = 2 5 .4 cm , and the c o r re c t io n to the to rq u e load c o r re sp o n d in g to the tw is t - d ia l fo r c e s i s ASh = 2 F h (2 5 .4 /2 6 .5 0 ) , o r w ith A e x p r e s s e d in k g ,

A Sh = 0 .402 - 0.391 x + 0.021 kg

w h ere i s the a v e r a g e d ia l r e a d in g in in c h e s .

F r i c t io n in g u id e sh e a v e s

T h e in flu e n ce of f r ic t io n in the h o r iz o n ta l and v e r t ic a l gu id e sh e a v e s and bending of the w ire ro p e s o n e - q u a r te r tu rn aro u n d eac h sh e a v e w as d e te rm in e d by

59

the te s t in g a r r a n g e m e n t show n in f ig u r e 28 , d u rin g w hich a h o r iz o n ta l sh e a v e te m p o r a r i ly i s p la c e d o r c lam p e d in v e r t ic a l p o s it io n . T h e t e s t s w ere re p e a te d fo r e ac h

ozazUJCO

200 Qz<zoho

150 £H

100

50

00 2.5 5 7.5 10 12.5 15 17.5

P = CABLE LOAD = -|- IN Kg

F i g u r e 28. F r i c t io n in gu ide s h e a v e s

p a ir of s h e a v e s a f te r a g e n e r a l c lea n in g and re p a c k in g of the b e a r in g s w ith g r e a s e , and s lig h tly s m a l le r f o r c e s w e re then ob ta in ed . T h e fo r c e fo r e a c h p a ir o f s h e a v e s , r e q u ire d to p ro d u ce a s l ig h t m o v em e n t in e ith e r d ir e c t io n , can b e e x p r e s s e d by

F = 13 + 8 .8 x P g g *

w h ere P i s the load on the h a n g e r s or te n sio n in the c a b le in k g . D u r in g a t e s t P = S / 2 , w h ere S i s the to rq u e lo ad in kg , and the to ta l r e q u ir e d c o r r e c t io n to th is load i s then ,

A S - + 2 F = + (0 .026 + 0 .0 0 8 8 x S) kgo o

w hich c o r r e c t io n i s n e g a tiv e fo r in c r e a s in g tw ist an d p o s it iv e fo r d e c r e a s in g tw ist .

F r ic t io n in co u n terw eigh t sh e a v e s

T h e te n sio n in the w ire ro p e to the c o u n te rw e ig h t and the c o r re sp o n d in g p r e s s u r e on the sh e a v e b e a r in g s a r e co n stan t. T h e r e fo r e , the fo r c e re q u ir e d to p ro d u ce

60

a m o v e m e n t in e i t h e r d i r e c t i o n i s c o n s t a n t a n d w a s fo u n d to b e 45 g . T h e c o r r e sp o n d in g c o r r e c t i o n to th e t o r q u e lo a d i s

A = + 0 .0 4 5 kgw h ic h i s n e g a t iv e f o r i n c r e a s i n g t w i s t a n d p o s i t iv e f o r d e c r e a s i n g t w i s t .

S u m m a r y f o r c o n t r o l l e d - s t r e s s s y s t e m

In t h e fo l lo w in g s u m m a r y , S r e p r e s e n t s th e n o m in a l to r q u e lo a d in k g a n d R ^ th e a v e r a g e r e a d in g of t h e h o r i z o n t a l o r t w i s t d i a l s in i n c h e s . W h e n e v e r a + s ig n i s s h o w n , th e u p p e r s ig n a p p l i e s to i n c r e a s i n g tw i s t a n d th e lo w e r s ig n to d e c r e a s i n g t w i s t .

N o m in a l t o r q u e lo a dF o r c e b y tw is t d ia l s AS^F r i c t i o n in g u id e s h e a v e s ASgF r i c t i o n in c o u n te r w e ig h t s h e a v e s ASC

T h e e f f e c t i v e o r a c tu a l t o r q u e lo a d i s th e n ,

Sa = (1 + 0 .0 0 8 8 ) S - 0 .391 x R h + 0 .4 0 2 + 0 .0 92 kg

a n d th e a v e r a g e s h e a r in g s t r e s s i s T& = Sa / A g = S &/ 2 4 .5 0 k g / c m ^ , o r w h e n r e s o lv e d in to s e p a r a t e e x p r e s s io n s f o r i n c r e a s i n g a n d d e c r e a s i n g tw is t ,I n c r e a s i n g t w i s t :

S = 0 .9 9 1 2 x S - 0 .391 x R h + 0 .3 1 0 kg aTa = 0 .0 4 0 4 6 x S - 0 .0 1 6 x + 0 .0 1 3 k g /c m ^

D e c r e a s in g tw i s t : S a = 1 .0 0 8 8 x S - 0 .391 x R ^ + 0 .4 9 4 kg= 0 .0 4 1 1 8 x S - 0 .0 1 6 x R h + 0 .0 2 0 k g / c m 2

A f t e r i n i t i a l f a i l u r e th e e f f e c t i v e to r q u e lo a d , S , i s o f te n d e t e r m i n e d b y m e a n s of t h e d e f l e c t io n , 8^., o f th e p ro v in g f r a m e a n d th e fo l lo w in g r e s u l t s of i t s c a l i b r a t i o n , s e e p a g e 67 .

I n c r e a s i n g s t r e s s S = 4 9 5 .9 x 5̂ . - 0 k gD e c r e a s in g s t r e s s S = 4 9 5 .9 x 8^ - 0 .0 75 kg

T h e s e v a lu e s o f S s h o u ld b e i n s e r t e d in th e g e n e r a l f o r m u l a s g iv e n a b o v e . I t s h o u ld b e n o te d t h a t th e f o r m u la s f o r c o n t r o l l e d - s t r a i n lo a d a p p l i c a t io n d o n o t a p p ly , e v e n w h e n th e b a s e o f th e s h e a r a p p a r a t u s i s r o t a t e d b y h a n d , b e c a u s e th e r o t a t i o n of th e b a s e i s s to p p e d b e f o r e th e i n d i c a t i o n of th e t o r q u e d i a l i s o b s e r v e d .

S= 0 .4 0 2 - 0 .391 x R h + 0 .021 = ; (0 .0 2 6 4 0 .0 0 8 8 x S)= + 0 .0 4 5

61

T o rq u e L o a d in g — C o n tro lle d S t r a in

A d ia g r a m m a t ic sk e tc h of the to r s io n lo a d in g s y s t e m fo r c o n tro lle d r a t e of s t r a in i s show n in f ig u r e 29 . T h e b a la n c e b e a m i s d raw n up a g a in s t the fu lc r u m and i s s ta t io n a ry d u rin g the te s t , s o th at the f r ic t io n in the co u n terw eigh t s h e a v e s d o e s

F i g u r e 29 . T o r q u e loading - - c o n tro l le d s t r a in

not a f fe c t the r e s u l t s of the t e s t . T h e b a s e of the sh e a r a p p a r a tu s i s r o ta te d coun te rc lo c k w ise , w h e re a s the to rq u e w h ee l i s h eld m o r e or l e s s s ta t io n a r y by the w ire ro p e s and b a la n c e b e a m ; h o w e v e r, w ith in c r e a s in g te n sio n in and s tr e tc h in g of the r o p e s , the to rq u e w heel w ill .m o v e s lig h tly in the s a m e d ir e c t io n a s the b a s e and a g a in s t th is d ire c t io n w ith d e c r e a s in g ten sio n in the w ire r o p e s . T h e r e fo r e , th e c o r rec tio n fo r fr ic t io n in the gu ide w h ee ls and ben din g of the w ire r o p e s , A S ^ , i s p o s i tive du rin g an in c r e a s e in to rq u e and sh e a r in g s t r e s s , and it i s n e g a tiv e d u r in g p e r io d s of d e c r e a s in g sh e a r in g s t r e s s . T he fo r c e s e x e r te d by the tw ist d ia l s a c t in the sa m e m an n e r , and the c o r re sp o n d in g c o r re c t io n to the to rq u e lo ad , AS^» i s the s a m e a s fo r the c o n t r o l le d - s t r e s s s y s t e m , b u t the in c r e m e n t co n trib u ted by f r ic t io n in the d ia l s , 0.021 k g , i s p o s it iv e fo r in c r e a s in g sh e a r in g s t r e s s e s and n e g a tiv e fo r d e c r e a s in g s t r e s s e s . A d d ition a l f o r c e s to b e c o n s id e r e d in the c o n tr o l le d - s t r a in s y s tem a r e the fr ic t io n in the th ru s t s h e a v e s , the f o r c e e x e r te d by the p ro v in g f r a m e or to rqu e d ia l , and the in flu en ce of a d e fle c tio n of the p ro v in g f r a m e an d c o r r e sponding dow nw ard m ov em en t of the v e r t i c a l gu ide s h e a v e s . Som e o f th e se f o r c e s

62

w ill be c o n s id e re d s e p a r a te ly and o th e r s tak en into c o n s id e r a t io n in the c a l ib r a t io n of the p ro v in g f r a m e .

F r i c t io n in th r u s t sh e a v e s

T h e f r ic t io n in the th r u s t sh e a v e s w as d e te rm in e d by p lac in g the two sh e a v e s on h o r iz o n ta l, p o lish ed p ie c e s of s t e e l , load in g the yok e a s show n in f ig u re 30, and

m ov in g the a s s e m b ly fo rw a rd and b a c k w ard by m e a n s of a p u sh -p u ll g ag e . The a v e r a g e f o r c e , P̂ _, r e q u ir e d to p ro d u ce m o v em e n t in e ith e r d ir e c t io n w as found to be P .̂ = 1 .46 x P g = 0 .0015 x P k g , w h ere P i s the to ta l n o rm a l load in kg . In n o r m a l te s t in g p o s it io n , the s h e a v e s a r e p r e s s e d a g a in s t the b lo c k s by a c e r ta in unknown fo r c e and fu ll co n tac t i s a s su r e d a t a l l t im e s . T h is fo r c e i s a l s o a c t iv e and taken in to c o n s id e r a t io n d u rin g the c a l i b r a t io n o f the p rov in g f r a m e . D u rin g t e s t s the te n sio n in the c a b le s w ill c a u s e an a d d itio n a l h o r iz o n ta l lo a d , equ al to the

to rq u e load S , on the s h e a v e s , and the in flu en ce of the f r ic t io n in the th ru s t s h e a v e s , AS on the a c t iv e to rq u e lo ad i s ,

AS, Z 0 .0015 X S kg

w hich i s p o s it iv e fo r in c r e a s in g d e fle c t io n of the p ro v in g f r a m e and sh e a r in g s t r e s s e s in the s a m p le and n e g a tiv e fo r d e c r e a s in g s t r e s s e s .

F o r c e s e x e r te d by the to rq u e d ia l

T h e fo r c e e x e r te d by the p ro v in g fr a m e or to rq u e d ia l , f ig u r e s 11 and 12, a l though tak en in to c o n s id e ra t io n in the c a l ib r a t io n of the p ro v in g f r a m e , w as d e t e r m in e d s e p a r a te ly in an e f fo r t to e x p la in the d if fe r e n c e in c a l ib r a t io n r e s u l t s fo r in c r e a s in g and d e c r e a s in g s t r e s s e s . T h e r e s u l t s of the d e te rm in a t io n of fo r c e e x e r te d b y th e to rq u e d ia l a r e show n in f ig u r e 31, and th is fo r c e can b e e x p r e s s e d by

F t = 92 - 615 x R t + 25 g

63

w h e r e R^. i s th e d i a l r e a d in g in in c h e s , d i a l a n d i s n e g a t iv e f o r i n c r e a s i n g s t r e s s a n d p o s i t iv e f o r d e c r e a s i n g s t r e s s o r d o w n w a r d m o v e m e n ts of th e d ia l s t e m .

T h e + 25 g r e p r e s e n t s t h e f r i c t i o n in th e

I n f lu e n c e o f d e f l e c t io n o f p r o v in g f r a m e

T h e w i r e r o p e s f r o m th e h o r i z o n t a l to th e v e r t i c a l g u id e s h e a v e s a r e h o r i z o n t a l a t th e s t a r t o f a t e s t , b u t th e y a c q u i r e a s l i g h t d o w n w a rd s lo p e to w a r d s th e v e r t i c a l g u id e s h e a v e s w h e n t h es h e a r i n g s t r e s s e s i n c r e a s e a n d th e p r o v in g f r a m e d e f l e c t s , f i g u r e 3 2 . T h is d e f l e c t io n h a s o n ly a n in s ig n i f i c a n t i n f lu e n c e o n th e t e n s io n , S / 2 , in e a c h o f t h e w i r e r o p e s , b u t i t r e d u c e s th e e f f e c t iv e d o w n w a rd f o r c e o n th e y o k e an d p ro v in g f r a m e b y

R = D IA L READING IN INCH ES

F ig u re 31. F o rc e s by to rq u e d ia l

A C - S _ ! l û b8 2 2 L

w h e r e L i s th e d i s t a n c e b e tw e e n th e f r o n t s h e a v e s , b e tw e e n th e r e a r s h e a v e s ,a n d 8 ̂ a n d § £ a r e th e c o r r e s p o n d in g d e f l e c t io n s o f th e s h e a v e s . S in c e L,^ = 2 0 .3 8

in . i s a b o u t tw ic e a s g r e a t a s = 10 . 12 i n . , th e r e d u c t io n o r u p w a r d f o r c e w i l l b e s m a l l e r f o r th e r e a r th a n f o r th e f r o n t e n d o f t h e y o k e ,a n d th i s w i l l c a u s e a s l i g h t t ip p in g o f th e p ro v in g f r a m e . H o w e v e r , t h i s t ip p in g w i l l n o t a f f e c t th e t e n s io n in th e w i r e r o p e s

F ig u re 32. In fluence of d e flec tio n of p rov ing fra m e s in c e th e y a r e c o n n e c te dt o t h e b a l a n c e b e a m .

T h e d i f f e r e n c e b e tw e e n 6 ̂ a n d 8 2 i s s o s m a l l th a t t h e s e d e f l e c t io n s m a y b e r e p la c e d b y th e a v e r a g e d e f l e c t io n , 8 .̂, o f th e p r o v in g f r a m e , a n d th e c o r r e c t i o n A S g m a y th e n b e e x p r e s s e d a s fo l lo w s ,

A S - 8 . L 1 " L 2L 1 L 2

64

wh e r e L,^ = 2 L, ^ / - L^) = 13. 52 in. i s an e q u iv a len t m e a n d i s t a n c e betw een theh o r iz o n ta l and v e r t i c a l s h e a v e s . A s shown on p a g e 67, the c o r r e c t io n ASg w il l be taken into c o n s id e r a t io n in the f in a l d e te r m in a t io n of the prov ing f r a m e f a c t o r .

G e n e r a l c a l i b r a t i o n of p rov in g f r a m e

The p ro v in g f r a m e w as c a l i b r a t e d by d i r e c t load in g ; that i s , the b a la n c e b e a m and t o r q u e - lo a d s c a l e without the co u n te rw e igh t w e r e su sp en d e d f r o m the v e r t i c a l gu ide s h e a v e s by looping the w ire r o p e s aroun d the s h e a v e s and a ttach in g the to rq u e- w heel c l a m p s to the double h oo k s . T h e g e n e r a l a r r a n g e m e n t and the p r in c ip a l r e s u l t s of the c a l i b r a t i o n a r e shown in f i g u r e 3 3 -A . T h e s e r e s u l t s w e r e obta ined fo r a z e r o se t t in g of the d ia l a t 0 .0100 in .; that i s , with only the w eight of the yoke and the gu ide and t h r u s t s h e a v e s ac t in g on the prov in g f r a m e ; s e e p age 35. The d ia l w as tap p ed lightly b e f o r e each re ad in g , which p ro b ab ly i s equ iva len t to a s l ig h t v ib ra t io n of the d r iv e m e c h a n i s m du r ing c o n t r o l l e d - s t r a i n t e s t s . In g e n e ra l , the r e la t io n sh ip betw een lo a d s and d e f le c t io n s i s v e r y c l o s e to the d e s ig n sp e c i f i c a t io n of one d ia l d iv i s io n o r 0 .0001 in. be in g e q u iv a len t to 5 0 g, but the d ia g r a m show s a v e r y s l ig h t c u r v a t u r e and a v e r y s m a l l am ount of h y s t e r e s i s . The h y s t e r e s i s o r d i f fe r e n c e b e tween d e f le c t io n s fo r in c r e a s i n g and d e c r e a s i n g lo a d s i s shown to a 1 0 0 - t im e s enl a r g e d s c a l e a s the so l id l ine in f i g u r e 3 3 - B . T h i s d i f f e r e n c e v a r i e s but i t s a v e r a g e i s about 1.5 d i a l r e a d i n g s , c o r r e s p o n d in g to a d i f f e r e n c e in a c tu a l load of 75 g for equ al d ia l r e a d i n g s . A bout 50 g of the d i f f e r e n c e i s c a u s e d by f r ic t io n in the torqu e d ia l , f i g u r e 31, and the r e m a in d e r by z e r o f r ic t io n in the th ru s t s h e a v e s , page 62, and by a c tu a l h y s t e r e s i s .

O m is s i o n of tapping the d ia l d u r in g c a l i b r a t i o n c a u s e d the in d icated d e f l e c t ion s du r in g i n c r e a s i n g lo a d s to b e abo ut 0.6 d ia l d iv i s io n s s m a l l e r and th o se during d e e r e a s in g lo a d s to be 0.5 to 2 .0 d iv i s io n s l a r g e r than when the d ia l w as tapped . The r e su l t in g d i f fe r e n c e s betw een d ia l r e a d i n g s fo r i n c r e a s i n g and d e c r e a s in g lo a d s without tapping a r e shown a s the dotted l in e in f i g u r e 3 3 - B , and they a r e c l o s e to 3 d ia l d iv i s io n s . In a n o th er c a l ib r a t io n t e s t the d ia l w a s tapped but a z e r o se t t in g of 0 .0500 in. w as u se d . T he d i f fe r e n c e betw een the r e s u l t s of th is t e s t and the t e s t with a z e r o se t t in g of 0 .0100 in. v a r ie d with the load and r e a c h e d a m a x im u m of 3 d ia l d iv i s io n s . T h is d i f f e r e n c e i s p r im a r i ly c a u s e d by i n a c c u r a c i e s in the co n stru c t io n of the d ia l . On a cco u n t of t h e s e s o u r c e s of e r r o r , i t i s im p o r ta n t that the d ia l and the z e r o s e t ting u se d d u r in g the c a l ib r a t io n of the prov in g f r a m e a l s o be u sed d u ring the ac tu a l s h e a r t e s t s .

P r o v in g f r a m e f a c t o r s

T he r e s u l t s of the c a l ib r a t io n of the prov in g f r a m e m a y be e x p r e s s e d m o r e a c c u r a t e l y by m e a n s of the prov ing f r a m e f a c t o r , C, defined by

P = C x 6

DE

FL

EC

TIO

N

IN

INC

HE

S

65

0.13

0.12

0.11

0.10

0.09

0.08

0.07

0.06

0.05

0 .0 4

0 .0 3

0.02

0.010 5 10 15 20 2 5 30 3 5 4 0 4 5 50 5 5 60

P = LOAD IN KG

A - MAIN RESULTS

P = LOAD IN KG

B -D E V IA T IO N S FOR DECREASING LOAD

F i g u r e 3 3 . C a l i b r a t i o n o f p r o v i n g f r a m e

DIA

L D

IVIS

ION

S —

(l

DIV

. 0

.00

01

"]

66

w h e r e P i s th e lo a d in kg a n d 8 ̂ th e d e f l e c t io n in i n c h e s . V a lu e s o f C o b ta in e d f o r i n c r e a s i n g lo a d s , w i th a n d w i th o u t ta p p in g o f th e d ia l , a n d w i th tw o z e r o s e t t i n g s a r e s h o w n in f i g u r e 3 4 -A . T h e i n a c c u r a c i e s in c o n s t r u c t i o n of th e d i a l c a u s e th e

6t = FR A M E DEFLECT IO N IN IN CH ES

A - V A L U E S BY D IRECT CALIBRATION

0 0.01 0.02 Q03 0.04 0.05 0.06 0.07 0.08 0.09 0.10 0.11 0.126t = FR A M E DEFLECT IO N IN INCHES

B - VA LU ES A D JUSTED FOR IN FLU EN C E OF D EFLECTION

F i g u r e 34. P r o v i n g f r a m e f a c t o r s

s c a t t e r i n g o f th e v a lu e s o f C , a n d th e s l i g h t c o n v e x c u r v a t u r e o f th e m a in d ia g r a m in f i g u r e 3 3 -A i s r e f l e c t e d in a g e n e r a l d e c r e a s e o f C w ith i n c r e a s i n g lo a d an d d e f l e c t io n .

A s p r e v io u s ly m e n t io n e d , th e d e f l e c t io n of th e p r o v in g f r a m e a n d c o n s e q u e n t s l i g h t s lo p e of th e w i r e r o p e s d u r in g a c t u a l t e s t s c a u s e th e v e r t i c a l f o r c e on

67

th e p ro v in g f r a m e to b e re d u c e d by th e a m o u n t AS = S---- , and th is f o rc e m u s t be^ e

ad d ed to th e lo ad in d ic a te d by th e p ro v in g f r a m e to o b ta in th e a c tu a l to rq u e lo ad , th a t is0 tS = P + A S_ = C 8. + S — .6 t L e

T h is c o r r e c t io n m a y b e in c lu d e d in e v a lu a tio n of th e r e s u l t s of th e c a l ib r a t io n by in tro d u c in g an e f fe c tiv e p ro v in g f r a m e f a c to r , C e , d e te rm in e d by th e e q u a tio n s

8 tS = C e 8 t and C = C ( 1 + — ).b p

V alu es of C e fo r in c re a s in g s t r e s s , d ia l ta p p e d , and a z e r o s e t t in g of 0 .0100 in . a r e show n in f ig u re 3 4 -B . C e a p p e a rs f a i r ly in d e p e n d e n t of th e lo ad o r d e f le c t io n and h as an a v e r a g e v a lu e C e = 49 5 .9 k g / in . , w h ich v a lu e m a y b e u se d in ro u t in e t e s t s . In a c c u r a c ie s in th e c o n s tru c t io n of th e to rq u e d ia l c a u se so m e s c a t t e r in g in th e a c tu a l v a lu e s of C e . T he m a x im u m p o s it iv e d e v ia t io n f ro m th e a v e r a g e v a lu e is 2.1 k g /in . o r 0.42 p e r c e n t , and th e m a x im u m n e g a tiv e d e v ia tio n is 1.8 k g / in . o r 0 .36 p e r c en t.

S u m m a ry - - c o n t r o l l e d - s t r a in s y s te m

T h e fo llow ing s u m m a ry is b a s e d on th e u s e of an a v e r a g e e ffe c tiv e p ro v ing f r a m e f a c to r C e = 4 9 5 .9 k g / in . , w h ich a p p lie s to th e c o n d itio n s of in c re a s in g s t r e s s e s , tap p in g of th e d ia l , and a z e r o s e t t in g of 0 .0100 in . T h is f a c to r a ls o in c lu d e s th e in f lu e n c e of th e d e f le c t io n of th e p ro v in g f r a m e , f o rc e s e x e r te d by th e to rq u e d ia l , and th e b a s ic f r ic t io n in th e th r u s t sh e a v e s b u t n o t th e a d d it io n a l f r ic t io n c a u se d by e f fe c tiv e lo a d s . T he d ia l r e a d in g s d u rin g d e c r e a s in g s t r e s s e s a r e on an a v e r a g e 1.5 d ia l d iv is io n s l a r g e r th an fo r in c re a s in g s t r e s s e s b e c a u s e of a r e v e r s a l of f r ic t io n in th e to rq u e d ia l and th r u s t s h e a v e s . T h e r e fo re , a c o r r e s p o n d in g fo rc e of 0.075 kg m u s t b e s u b tr a c te d f ro m to rq u e lo ad in d ic a te d by th e d ia l d u r in g d e e r e a s ing s t r e s s e s . W henever i s ig n s a p p e a r in th e s u m m a ry , th e u p p e r s ig n a p p lie s to in c re a s in g s t r e s s e s and th e lo w e r s ig n to d e c r e a s in g s t r e s s e s . T h e p ro v in g f r a m e d e f le c t io n s , 8 .̂, and th e a v e r a g e re a d in g of th e tw o tw is t d ia ls , a r e e x p re s s e din in c h e s , and a l l f o rc e s a r e g iven in kg .

In d ic a te d to rq u e lo ad C o r r e c t io n fo r d e c r e a s in g s t r e s s e s F o r c e by tw is t d ia ls F r i c t io n in gu ide s h e a v e s F r i c t io n in th r u s t s h e a v e s

S = 495 .9 x 8 1 -0 .0 7 5

Sh = 0.402 - 0.391 X R h ± 0.021 Sg = t (0 .026 + 0 .0088 x S)St = t 0.0015 x S

T he e ffe c tiv e o r a c tu a l to rq u e load is th en ,S = (1 t 0 .0103) S - 0.391 Bv + 0.365 t 0 .085 kg , o r aSa = (1 t 0.0103) 49 5 .9 6t - 0.391 Rh + 0 .365 t 0.085 kg,

and w hen r e s o lv e d in to s e p a r a te e x p re s s io n s fo r in c re a s in g and d e e r e a s in g s t r e s s e s and fo r th e a v e ra g e s h e a r in g s t r e s s Ta = Sa / 24 .50 k g /c m ^ ,

68

I n c r e a s i n g s t r e s s e s :

D e c r e a s in g s t r e s s e s :

S = 5 0 1 .0 x 6, — 0 .391 x R , + 0 .4 5 0 kg a t n/ 2= 2 0 .4 5 x 8 t - 0 .0 1 6 x R ^ + 0 .0 1 8 k g / c m

S a = 4 9 0 .8 x 8 - 0 .391 x R h + 0 .2 8 0 kgT = 2 0 .0 3 x 6 . - 0 .0 1 6 x R , + 0 .011 k g / c m 2a t h °

D r i f t a n d T ip p in g of T o r q u e W h e e l

A s l i g h t t ip p in g a n d / o r d r i f t o f th e to r q u e w h e e l a n d a n n u la r p i s t o n w e r e o b s e r v e d in s o m e c a s e s w h e n th e t e s t s w e r e c o n t in u e d f o r p ro lo n g e d p e r i o d s a f t e r i n i t i a l f a i l u r e o f th e s o i l . T h e t ip p in g m a y b e c a u s e d b y u n e q u a l c o n s o l id a t io n o f th e s o i l in v a r i o u s p a r t s of th e t e s t s p e c im e n , b u t i s p r i m a r i l y o w in g to u n e q u a l a m o u n ts of s o i l b e in g s q u e e z e d o u t b e tw e e n th e u p p e r a n d lo w e r r i n g s a t v a r i o u s p o in ts a lo n g th e p e r i p h e r y . A d r i f t i n d i c a t e s t h a t th e f o r c e s a c t in g on th e t o r q u e w h e e l a n d a n n u la r p is to n d o n o t c o n s t i t u t e a p u r e m o m e n t b u t h a v e a s m a l l r e s u l t a n t f o r c e . T h is c o n d it io n m a y b e d u e to o n e of th e fo l lo w in g c a u s e s :

a . T h e c o n s i s t e n c y of th e s o i l a n d th e s h e a r i n g r e s i s t a n c e a r e n o t u n i f o r m o v e r th e e n t i r e c r o s s s e c t io n of th e t e s t s p e c im e n . T h is i s p r o b a b ly th e m a in c a u s e of b o th d r i f t a n d t ip p in g .

b . E x c e s s iv e d e f l e c t io n of th e v e r t i c a l lo a d l e v e r s w i l l p r o d u c e a s m a l l h o r i z o n ta l f o r c e a t r i g h t a n g le s to th e a x i s of th e t e s t i n g b e n c h , p a g e 33-. H o w e v e r , th e l e v e r s w e r e a d ju s t e d a t f r e q u e n t i n t e r v a l s , a n d th e d e f l e c t io n s p e r m i t t e d w e r e v e r y s m a l l .

c . U n e q u a l f r i c t i o n in th e f r o n t a n d r e a r g u id e s h e a v e s w i l l c a u s e a c o r r e s p o n d in g d i f f e r e n c e in t e n s io n in th e w i r e r o p e s . H o w e v e r , th e c a l i b r a t io n t e s t s i n d i c a t e t h a t s u c h a d i f f e r e n c e i n f r i c t i o n i s n e g l i g ib l e , f i g u r e 2 8 .

d . A d i f f e r e n c e in t e n s io n in th e tw o w i r e r o p e s w i l l a l s o b e p r o d u c e d w h e n th e c e n t r a l k n i f e - e d g e in th e b a la n c e b e a m s i s n o t e q u id i s t a n t f r o m th e k n i f e - e d g e s a t th e e n d s of th e b e a m . I t w a s fo u n d b y a w e ig h in g t e s t , f i g u r e 35 , th a t th e r a t i o b e tw e e n th e tw o d i s t a n c e s o r l e v e r a r m s i s 1 .0 0 2 2 ; t h a t i s , th e te n s io n in th e tw o w i r e r o p e s d i f f e r s b y th e a m o u n t

0 .0 0 2 2 x S /2 = 0 .0 0 1 1 x Sw h ic h i s th e r e s u l t a n t f o r c e a c t in g a t r i g h t a n g le to th e a x i s o f th e t e s t i n g b e n c h .

e . A s m a l l r e s u l t a n t h o r i z o n t a l f o r c e , a c t in g p a r a l l e l to th e a x i s of t h e t e s t in g b e n c h , w i ll b e p ro d u c e d w h e n th e w i r e r o p e s f r o m th e h o r i z o n t a l g u id e

69

sh e a v e s to th e to rq u e w h e e l a r e n o t p a r a l l e l . C a r e fu l m e a s u r e m e n ts in d i c a te d a d e v ia t io n of 0.01 in . in 6 .19 in ., f ig u re 36, c o r re sp o n d in g to a f o r c e

S 0.01 2 x 6.19 = 0 .0008 x S

a c tin g f ro m le f t to r ig h t .T h e f o rc e s e s t im a te d in i te m s D and E a c t a t r ig h t a n g le s to e a c h o th e r

and th e ir r e s u l t a n t issVo.00112 + 0 .0 0 0 8 2 = 0.00137 x S.

T h e m a x im u m v a lu e of S is 5 0 k g , and th e c o r re sp o n d in g m a x im u m v a lu e of th e a b o v e - m e n tio n e d r e s u l t a n t f o rc e if 0 .069 kg . I t is u n lik e ly th a t th is s m a l l f o rc e a lo n e c a n

B ALAN CE BEAM INVERTED

F ig u r e 35. L e v e r ra tio for b a la n ce b eam F ig u re 36. P a r a l le l i s m of w ir e r o p e s

p ro d u c e a d r i f t of th e to rq u e w h e e l and a n n u la r p is to n , and v a r ia t io n s in th e c o n s i s t ency and s h e a r in g r e s is ta n c e of th e s o i l a r e p ro b a b ly th e m a in c a u s e s , of su c h a d r i f t .

In flu e n c e of R a is in g th e U p p e r R in g s

T he u p p e r co n fin in g r in g s a r e r a i s e d a b o u t l / 3 2 in . upon c o m p le tio n of th e p r e l im in a r y c o n so lid a t io n in o r d e r to t r a n s f e r th e e n t i r e v e r t i c a l lo ad to th e t e s t sp e c im e n and to e lim in a te f r ic t io n b e tw e e n th e u p p e r and lo w er r in g s d u rin g th e a c tu a l s h e a r t e s t . R a is in g of th e r in g s c a u s e s s t r e s s c h a n g e s in th e t e s t s p e c im e n , and th e a c tu a l s h e a r t e s t sh o u ld n o t b e s ta r te d b e fo re c o r re sp o n d in g s t r e s s a d ju s tm e n ts h av e b e e n c o m p le te d . E v en th e n a zo n e r e m a in s in w h ich th e con fin in g l a t e r a l fo r c e s

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a r e r e p l a c e d w ith c a p i l l a r y f o r c e s , a n d t h e r e i s a l s o a s m a l l z o n e o f c o n c e n t r a t io n of s h e a r in g s t r e s s e s n e a r th e e d g e s o f th e r i n g s d u r in g th e s h e a r t e s t . T h e r e s u l t i s p ro b a b ly a s l i g h t d e c r e a s e in th e a p p a r e n t s h e a r i n g r e s i s t a n c e o f th e t e s t s p e c im e n . T h is d e c r e a s e d e p e n d s to a c o n s id e r a b l e e x te n t o n th e p r o p e r t i e s o f th e s o i l a n d i s d i f f ic u l t to e s t i m a t e . J u d g in g f r o m c o m p a r i s o n s o f v a r i o u s ty p e s of s t r e n g t h t e s t s , th e d e c r e a s e i s v e r y s m a l l a n d p r o b a b ly w i l l n o t e x c e e d a few p e r c e n t e v e n in e x t r e m e c a s e s .

A s q u e e z i n g - o u t o f s o i l th r o u g h th e c l e a r a n c e b e tw e e n th e u p p e r a n d lo w e r r i n g s w a s s e ld o m o b s e r v e d b e f o r e i n i t i a l f a i l u r e o f th e s o i l , b u t t h e r e a f t e r a p p r e

c i a b l e a m o u n ts o f s o i l m a y b e s q u e e z e d o u t u n l e s s th e c l e a r a n c e b e tw e e n th e r i n g s i s v e r y s m a l l . F r i c t i o n b e tw e e n t h e s q u e e z e d - o u t s o i l a n d th e r i n g s w i l l i n c r e a s e th e t o r q u e r e s i s t a n c e an d th e a p p a r e n t s h e a r i n g r e s i s t a n c e of th e s o i l . A n e s t i m a te o f th e m a x im u m p o s s i b l e i n c r e a s e in a p p a r e n t s h e a r i n g r e s i s t a n c e m a y b e m a d e b y a s s u m in g th a t th e f r i c t i o n i s c o n f in e d to th e l / 3 2 - i n . - w id e h o r i z o n ta l en d s u r f a c e s o f th e r i n g , f i g u r e 37, a n d t h a t th e f r i c t i o n i s e q u a l to th e s h e a r i n g r e s i s t a n c e of th e s o i l . T h is i s e q u iv a l e n t to a n i n c r e a s e in th e e f f e c

t iv e o u t s id e d i a m e t e r o f th e t e s t s p e c i m e n f r o m 1 1 .4 4 c m to 1 1 .60 c m , a n d a d e c r e a s e o f th e e f f e c t iv e i n s i d e d i a m e t e r f r o m 6 .3 6 c m to 6 .2 0 c m . T h e r a t i o b e tw e e n t o r q u e s o r a p p a r e n t s h e a r i n g r e s i s t a n c e s w ith an d w ith o u t s o i l b e in g s q u e e z e d o u t b e tw e e n th e r i n g s i s th e n

F ig u r e 37 . In flu en ce of s o i l b e tw een r in g s

11 . 603 - 6 .203

1 1 .4 4 6 .3 6 '= 1 .0 6 7

o r a n i n c r e a s e of 6 .7 p e r c e n t . T h e a c tu a l i n c r e a s e p r o b a b ly i s m u c h s m a l l e r s in c e th e c o e f f i c i e n t o f f r i c t i o n f o r s o i l o n p o l i s h e d b r o n z e i s s m a l l e r th a n f o r s o i l o n s o i l , a n d s in c e th e v e r t i c a l c o n ta c t p r e s s u r e b e tw e e n th e s q u e e z e d - o u t s o i l a n d th e r i n g s i s s m a l l e r th a n th e v e r t i c a l s t r e s s in th e t e s t s p e c im e n p r o p e r .

In s u m m a r y , th e m a x im u m s h e a r in g r e s i s t a n c e o b ta in e d b y t o r s i o n s h e a r t e s t s m a y b e s l i g h t l y lo w e r th a n th e a c t u a l s h e a r i n g r e s i s t a n c e of th e s o i l , a n d w h e n s o i l i s b e in g s q u e e z e d o u t b e tw e e n th e u p p e r a n d lo w e r r i n g s a f t e r i n i t i a l f a i l u r e , th e m in im u m s h e a r i n g r e s i s t a n c e th e n o b ta in e d m a y b e s l i g h t l y l a r g e r th a n th e a c tu a l r e s i d u a l s h e a r i n g r e s i s t a n c e .

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T w is t M e a s u re m e n ts and M o to r S p eed s

T he a c tu a l tw is t of th e t e s t s p e c im e n is th e d if f e re n c e b e tw e e n th e ro ta t io n s of th e b a s e and th e to rq u e w h ee l. T he r o ta t io n of th e la t t e r is d e te rm in e d by m e a n s of th e tw is t d ia ls and th a t of th e b a s e by th e e la p s e d t im e , th e g e a r r a t i o , and th e m o to r sp e e d . G e n e ra l fo rm u la s fo r co m p u ta tio n of th e tw is t o r a v e r a g e d is p la c e m e n ts in th e t e s t s p e c im e n a r e g iven on page 8.

M o to r s p e e d s

T h e n o m in a l m o to r sp e e d is 1720 rp m , b u t c a r e fu l o b s e rv a tio n of th e ro ta t io n of th e b a s e fo r th e v a r io u s g e a r r a t i o s r e v e a le d th a t th e a c tu a l m o to r s p e e d is 1722.5 rp m . T h is sp e e d re m a in e d c o n s ta n t fo r a l l g e a r r a t i o s u n ti l th e to rq u e lo a d o r s h e a r ing s t r e s s a p p ro a c h e d th e d e s ig n v a lu e of xa = 2 .0 k g /c m ^ . F o r th e h ig h e s t g ea r r a t io o r m a x im u m r a te of ro ta t io n of th e b a s e , th e m o to r sp eed d e c r e a s e s r a th e r a b ru p tly w hen th e s h e a r in g s t r e s s e s a p p ro a c h th e d e s ig n l im i t , a s show n by th e fo llow ing r e s u l t s of th e c a l ib ra t io n .

S h e a r S t r e s s k g / c m 2

1.001.961.982 . 0 0

B a s e S peed r p m

1.0766 1.07 62 1.0753 0.978

M o to r S p eed r p m

1722.5 1721 .91720.5 1564 .8

The c a p a c ity of th e m o to r a p p e a r s to b e r e a c h e d w h en th e h ig h e s t g e a r r a t io is u sed and th e to rq u e c o r r e s p o n d s to an a v e ra g e s h e a r in g r e s i s t a n c e of 1.95 k g /c m . F o r a l l lo w e r g e a r r a t io s , th e m o to r sp e e d m ay b e a s s u m e d c o n s ta n t and e q u a l to 1722.5 rp m , even w h en th e a v e ra g e s h e a r in g s t r e s s is c o n s id e ra b ly in e x c e s s of 2 .0 k g /c m . T he r a t e s of a v e r a g e d is p la c e m e n t c o r re sp o n d in g to th e v a r io u s g e a r , r a t io s and the a b o v e -m e n tio n e d m o to r sp e e d a r e g iven in th e s u m m a ry a t the end of th is p a r t .

T r a n s m is s io n and t im e lag

T h e p lay in th e g e a r s and in th e co u p ling to th e w o rm g e a r v a r i e s w ith the g e a r s e t t in g , and th e m a x im u m v a lu e s w e re fo u n d to p ro d u c e m o v e m e n ts of th e tw is t d ia ls 6 k = 0 .004 to 0.008 in ., w h ich c o r r e s p o n d s to th e a v e ra g e d is p la c e m e n ts 8 = 0.0015 to 0 .003 in . T he in f lu e n c e of th is p lay d u r in g a c tu a l te s t s v a r i e s b e tw eenz e r o and th e in d ic a te d m a x im u m v a lu e s , d ep en d in g on th e d i re c t io n of r o ta t io n d u rin g th e f in a l a d ju s tm e n ts of th e a p p a ra tu s b e fo re th e z e r o s e tt in g of th e tw is t d ia ls . The e r r o r in c o m p u ted d is p la c e m e n ts c a u se d by p lay in th e t r a n s m is s io n m a y b e o ffse t o r in c r e a s e d by a tim e d i f f e re n c e in s t a r t of th e m o to r and s t a r t of th e s to p w atch .

T h e in f lu e n c e of th e a b o v e -m e n tio n e d s o u r c e s of e r r o r is so s m a l l th a t i t can b e n e g le c te d in ro u tin e t e s t s , b u t i t p re v e n ts v e ry a c c u ra te d e te rm in a tio n of

72

d i s p l a c e m e n t s a t th e s t a r t o f a t e s t . A l a r g e - s c a l e p lo t o f th e f i r s t p a r t o f th e s t r e s s - d i s p l a c e m e n t d i a g r a m w i l l sh o w a s l i g h t o f f s e t o r i n i t i a l d i s p l a c e m e n t , an d a n a p p r o x im a te c o r r e c t i o n f o r th e in f lu e n c e o f t im e la g a n d p la y in th e t r a n s m i s s i o n c a n b e d e t e r m i n e d b y m e a s u r in g t h i s o f f s e t on th e d i a g r a m .

S u m m a r y o f R e s u l t s o f th e C a l i b r a t i o n

T h is s u m m a r y p r e s e n t s in c o n d e n s e d f o r m , a n d f o r u s e d u r in g r o u t i n e t e s t s , f o r m u l a s f o r d e t e r m i n a t i o n o f th e v e r t i c a l n o r m a l s t r e s s , th e a v e r a g e s h e a r in g s t r e s s e s , a n d th e c o r r e s p o n d i n g t w i s t s o f o r a v e r a g e d i s p l a c e m e n t s in th e t e s t s p e c - im e n . I t i s e m p h a s iz e d t h a t t h e s e f o r m u l a s e m b o d y c e r t a i n s i m p l i f i c a t i o n s an d do n o t c o n s id e r th e in f lu e n c e o f s o m e i n h e r e n t s o u r c e s o f e r r o r in t o r s i o n s h e a r t e s t s o r o f s o m e f a c t o r s w h ic h a r e a c t i v e o n ly u n d e r s p e c i a l c o n d i t io n s a n d w h e n th e a p p a r a t u s i s n o t p r o p e r ly a d ju s t e d b e f o r e an d d u r in g th e t e s t s .

V e r t i c a l n o r m a l s t r e s s e s

N o ta tio n : Q = w e ig h t on h a n g e r in kg ; R = r e a d in g o f v e r t i c a l d i a l in in c h e s ; pv = v e r t i c a l n o r m a l s t r e s s in k g / c m .

D iv id e d r in g s C o n s o l id a t io n S w e ll in gG e n e r a l (R y = 0 .1 0 in . )

S in g le r i n g s C o n s o l id a t io n S w e ll in gG e n e r a l (R y = 0 .1 0 in .)

d = 0 .1 0 0 1 7 x Q + 0 .1 1 5 8 - 0 .0 0 8 x RL V y

p v = 0 .1 0 0 2 5 X Q + 0 .1 1 7 0 - 0 .0 0 8 x R y p y = 0 .1 0 0 2 x Q + 0 .1 1 6

pTr = 0 .1 0 0 1 7 x Q + 0 .1 0 0 5 - 0 .0 0 8 x Rr v vp = 0 .1 0 0 2 5 x Q + 0 .1 0 1 3 - 0 .0 0 8 x R v* y V

p = 0 .1 0 0 2 x Q + 0 .1 0 0r v

T h e s e f o r m u l a s d o n o t in c lu d e th e in f lu e n c e s of f r i c t i o n b e tw e e n s o i l a n d c o n f in in g r i n g s , o f a d e v ia t io n o f th e l e v e r s f r o m h o r i z o n t a l p o s i t io n , n o r o f a s e t t l e m e n t of th e t o r q u e w h e e l d u r in g th e t e s t .

A verage shearing stresses

N o ta tio n : S = w e ig h ts o n t o r q u e - lo a d s c a l e in kg ; R ^ = a v e r a g e r e a d in g of th e tw o t w i s t d i a l s in i n c h e s ; 6 ̂ = d e f l e c t io n o f p r o v in g f r a m e in i n c h e s w ith ta p p in g of t h e t o r q u e d i a l a n d a z e r o s e t t i n g of 0 .0 1 0 0 in . ; T a = a v e r a g e s h e a r i n g s t r e s s in k g / c m ^ .

C o n t r o l l e d - s t r e s s s y s t e mI n c r e a s i n g tw i s t = 0 .0 4 0 4 6 x S - 0 .0 1 6 x R ^ + 0 .0 1 3D e c r e a s in g t w i s t T a = 0 .0 4 1 1 8 x S - 0 .0 1 6 x R ^ + 0 .0 2 0

73

T h e to r q u e m a y b e d e t e r m i n e d b y th e d e f l e c t io n s of th e p r o v in g f r a m e and th e fo l lo w in g e x p r e s s i o n s ,

I n c r e a s i n g s t r e s s S = 495 .9 x 5^ ■ 0 kgD e c r e a s i n g s t r e s s S = 495 .9 x 8̂ . - 0 .075 kg.

T h e r e s u l t i n g v a l u e s of S sh o u ld be i n s e r t e d in th e f o r m u l a s fo r th e a v e r a g e s h e a r ing s t r e s s e s g iv e n ab o v e . D i r e c t e v a lu a t io n by i n s e r t i n g 8^ in th e f o r m u l a s f o r th e c o n t r o l l e d - s t r a i n s y s t e m i s i n c o r r e c t , e v e n w hen th e b a s e of th e s h e a r a p p a r a t u s i s r o t a t e d b y h a n d , b e c a u s e th e r o t a t i o n i s s to p p e d b e f o r e th e i n d i c a t io n of th e t o r q u e d i a l i s o b s e r v e d .

C o n t r o l l e d - s t r a i n s y s t e mI n c r e a s i n g s t r e s s Ta = 20 .4 5 x - 0 .016 x + 0 .018D e c r e a s i n g s t r e s s = 2 0 .03 x 8 ̂ - 0 .016 x + 0.011

A n a v e r a g e e f f e c t iv e p ro v in g f r a m e f a c t o r of 495 .9 kg p e r in . i s u s e d , b u t d e v ia t i o n s up to 1 0 .4 p e r c e n t m a y o c c u r b e c a u s e of i n a c c u r a c i e s in th e c o n s t r u c t i o n of th e t o r q u e d i a l . T h e f o r m u l a s do no t in c lu d e th e in f lu e n c e of a s t r e s s c o n c e n t r a t i o n a t t h e e d g e s of th e d iv id e d r i n g s n o r th e i n f lu e n c e of so i l b e in g s q u e e z e d ou t b e tw e e n th e r i n g s .

T w i s t s a n d d i s p l a c e m e n t s

N o ta t io n : 8 ^ = a v e r a g e m o v e m e n t of t w i s t d i a l s in i n c h e s ; 8a = a v e r a g e l i n e a r d i s p l a c e m e n t in t e s t s p e c im e n , in c h e s ; v a = a v e r a g e r a t e o f d i s p l a c e m e n t c a u s e d by r o t a t i o n of th e b a s e , i n . / m i n ; t = e la p s e d t im e in m i n u t e s . 5 a an d v a r e f e r to d i s p l a c e m e n t s a lo n g th e c i r c l e w i th th e m e a n d i a m e t e r , Dm = 3 .600 in. V a lu e s of v a fo r a c o n s t a n t m o t o r s p e e d of 1722.5 r p m a n d v a r i o u s g e a r s e t t i n g s a r e g iv e n in th e t a b l e b e low . T h e w o r m g e a r h a s a r a t i o of 1:80.

G e a r No. M o to r 1 2 3 4

S u c c e s s i v e g e a r r a t i o s 1:20 1:10 1:10 1:5 1:2B a s e r p m 1.0766 0 .10766 0.010766 0 .0 0 2 1 5 3 0 .001 0 7 6 6A v e r a g e r a t e ) c m / m i n

of )30.92 3.092 0.3092 0 .06 1 8 4 0.03092

d i s p l a c e m e n t ) i n . / m i n 12.17 1.217 0 .1217 0 .0 2 4 3 4 0.01217

I t sh o u ld b e n o te d th a t the m o t o r s p e e d d e c r e a s e s when th e h i g h e s t b a s e s p e e d i su s e d and th e a v e r a g e s h e a r i n g s t r e s s in th e s o i l e x c e e d s 1.95 k g / c m ^ . S o m e v i b r a -t io n o c c u r s a t m a x i m u m r a t e of d i s p l a c e m e n t , 12.17 i n . / m i n , an d i s p r o b a b l y c a u s e d by r e s o n a n c e .

T h e fo l lo w in g g e n e r a l r e l a t i o n s e x i s t b e tw e e n l i n e a r a n d a n g u l a r d i s p l a c e m e n t ,

«0 = 8

a D . 1.80 r a d i a n s 180 _jt a

100 J— - d e g r e e s .

u n i t s of

74

U nder c o n t r o l l e d - s t r e s s type of load in g , the b a s e i s s t a t io n a r y and the to rq u e wheelr o t a t e s c l o c k w is e . The l in e a r d i s p la c e m e n t i s d e te r m in e d by the a v e r a g e m o v e m e n tof the tw is t d i a l s , 8 , and h

8 = 0 .360 x 6 . in c h e s ,a h

With c o n t r o l l e d - s t r a in type of lo ad in g the b a s e r o t a t e s c o u n te r c lo c k w ise , and the to rq u e w h ee l i s su b je c t to s m a l l m o v e m e n t s in the s a m e d ir e c t io n . T h e d i f fe r e n c e betw een th e se m o v e m e n ts i s the a c t u a l tw ist or d i s p la c e m e n t of the t e s t s p e c im e n .

8 = v . t - 0 .360 8, in c h e s ,a a h

F o r both ty p es of loading the a c t u a l a n g u la r d i s p la c e m e n t , ff) in d e g r e e s , m a y b e d e te r m in e d d i r e c t ly but only a p p r o x im a t e ly by m e a n s of the to ta l tw is t in d ic a t o r , and the a v e r a g e l in e a r d i s p la c e m e n t i s then 6 a = f6 ir / l OO in ch e s .

lr

f

75

R E F E R E N C E S

A m e r ic a n S o c ie ty o f C iv i l E n g i n e e r s , “ P r o g r e s s R e p o r t o f th e S p e c ia l C o m m i t te e to C o d ify P r e s e n t P r a c t i c e on th e B e a r in g V a lu e of S o i l s . “ P r o c e e d in g s , A m . S o c . C iv . E n g ., P a p e r s a n d D i s c u s s io n s ( A u g u s t 1 9 17 ), p 1 1 7 4 .C o o l in g , L . F ., a n d S m i th , D . B . , “ T h e S h e a r in g R e s i s t a n c e o f S o i l s . “ P r o c . F i r s t In t . C o n f. on S o i l M e c h a n ic s a n d F o u n d a t io n E n g in e e r in g , v o l. 1 (1 9 3 6 ) , p 37 .F r a n z i u s , S t r e c k a n d H in d e r k s , “ T h e E x p e r im e n t I n s t i t u t e f o r H y d r a u l i c s a n d F o u n d a t io n s a t th e T e c h n ic a l U n iv e r s i ty a t H a n o v e r , “ in A m . S o c . M e c h . E n g . , e d . , H y d r a u l i c L a b o r a t o r y P r a c t i c e (N ew Y o r k , 1 9 29 ), pp 5 9 9 - 6 0 1 .G r ü n e r , H . E #, a n d H a e f e l i , R ., “ B e i t r a g z u r U n te r s u c h u n g d e s p h y s ik a l i s c h e n a n d s t a t i s c h e n V e r h a l t e n s k o h ä r e n t e r B ö d e n .“ S c h w e iz e r i s c h e B a u z e i tu n g , v o l. 103 (1 9 3 4 ) , pp 1 7 1 -1 7 4 .H a e f e l i , R., “ M e c h a n is c h e E ig e n s c h a f t e n v o n L o c k e r g e s t e i n e n . “ S c h e i z e r i s c h e B a u z e i tu n g , v o l. 111 (1 9 3 8 ) , pp 2 9 9 -3 0 3 a n d 3 2 1 -3 2 5 .H v o r s l e v , M . J . , “ U e b e r d ie F e s t i g k e i t s e i g e n s c h a f t e n g e s t ö r t e r b in d ig e r B ö d e n .“ I n g e n iö r v id e n s k a b e l ig e S k r i f t e r , S e r i e s A , N o . 4 5 . C o p e n h a g e n , D a n m a r k s N a tu r v id e n s k a b e l ig e S a m fu n d (1 9 3 7 ) .H v o r s l e v , M . J . , “ T o r s i o n S h e a r T e s t s a n d T h e i r P l a c e in th e D e t e r m in a t i o n of th e S h e a r in g R e s i s t a n c e o f S o i l s . “ P r o c e e d in g s , A m . S o c . T e s t i n g M a t e r i a l s , v o l. 39 (1 9 3 9 ) , pp 9 9 9 -1 0 2 2 .H v o r s l e v , M . J , , “ P o c k e t - S i z e P i s t o n S a m p l e r s a n d C o m p r e s s i o n T e s t A p p a r a t u s . “ P r o c . S e c o n d In t . C o n f, on S o i l M e c h a n ic s a n d F o u n d a t io n E n g in e e r i n g , v o l. 7 ( R o t t e r d a m , 1 9 4 8 ), pp 7 6 -7 9.K je l lm a n , W ., “ T e s t i n g th e S h e a r S t r e n g th o f C la y in S w e d e n .“ G e o te c h n iq u e ( J u n e 1 9 5 1 ), pp 2 2 5 - 2 3 5 .K o l lb r u n n e r , C u r t F . , F u n d a t io n u n d K o n s o l id a t io n , V o l. 1, pp 2 3 9 - 2 4 3 . Z u r i c h , S c h w e iz e r D r u c k u n d V e r l a g h a u s , 1 945 .L a n g e r , C h a r l e s , “ P r o p r i é t é s M é c a n iq u e s e t P h y s i q u e s d e s T e r r a i n C o h é r e n t s . ” C o m p te R e n d u d e s R e c h e r c h e s E f f e c tu é e s d u r a n t l* A n n e e ! 9 3 8 , pp 1 9 -2 7 , P a r i s , L a b o r a t o i r e s d u B a t i m e n t e t d e s T r a v a u x P u b l i c s .M a y e r , A r m a n d , S o ls e t F o n d a t io n s . P a r i s , C o l l e c t io n A r m a n d C o l in , 1 9 39 . N a d a i , A ., P l a s t i c i t y . N ew Y o rk , M c G r a w - H i l l B o o k C o . , 1 9 3 1 .

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14. S t r e c k , O ., “ F o r t s c h r i t t e au f d e m G e b ie t d e r B a u g r u n d f o r s c h u n g .” Z e n ta lb la t t

d e r B a u v e rw a ltu n g , No. 9 (1928 ) .

15. T ie d e m a n n , B . , “ U e b e r d ie S c h u b fe s t ig k e i t b in d ig e r B ö d e n .“ D ie B a u t e c h n ik ,

v o l. 15 (1 9 3 7 ) , pp 4 0 0 -4 0 3 and 4 3 3 -4 3 5 .

< i . W a te rw a y s E x p e r i m e n t S ta tio n , T o r s i o n S h e a r T e s t on A tlan t ic M u ck , T h e P a n a m a C a n a l . Conclu ding R e p o r t . T e c h n ic a l M e m o r a n d u m No. 3 -3 2 8 , V ic k s b u r g ,

M i s s . , A u g u s t 1951.

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