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CONCRETE PIL
STANDARDS
BY
HUNLEY ABBOTT
CONCRETE PILE STANDARDS
I. Standard Details for Pile Caps.
11. Standard Specifications for Concrete Piles.
III. Concrete vs. Wooden Piles. A Comparison of Costs.
IV. Method of Testing a Concrete Pile.
V. How a Pile Supports Its Load.
By
HUNLEY ABBOTTAssoc. Mem. Am. Soc.ofC. E.
Vice-Pres. and Chief Eng. of MacArthur Concrete Pile and Foundation Co.
Copyrighted and Published by
HUNLEY ABBOTT11 Pine Street, New York, N. Y.
1915
/^'9.7S?
4 O.S-^
m 23 1911
)CI.A393>38 3
•M3 /
Standard Details for Reinforced Concrete Pile Caps
Concrete piles were first driven in this country about twelve years ago and since then their
use has been widespread and increasing. Almost without exception where they have been used
the design has also included concrete or reinforced concrete caps for these piles. It is a matter
for surprise that, until now, no one has attempted to formulate and present for the considera-
tion of engineers a proposed Standard Design for reinforced concrete pile caps.
In the general field of reinforced concrete construction the movement towards standardi-
zation has been going forward steadily, not only as regards the fundamental hypotheses of the
theory of the action and amount of the forces and resistances involved, but also as regards the
lesser matters of working formulas and the details of the work in the field. The time seems
ripe, therefore, for the establishment of a standard for reinforced concrete pile caps; first, in
order that the consideration of the economic advantages of concrete piles may not be discounted
by an unnecessarily expensive capping design; second, in order to facilitate the making of con-
crete pile plans and to reduce the labor and cost of making such plans ; and third, to place the
work in the field on a known and uniform basis which should result in lower costs to the con-
tractor and owner.
The writer's work during the last six years has included the making of detailed plans for
concrete pile foundations for a large number and variety of structures, and the great amount
of time and labor that could be saved by the use of some standard detail for these concrete pile
caps was soon apparent. It was with the needs of himself and his Company in mind that he
first drew up the standards which appear in this book, but they have proven themselves so ex-
tremely useful that he ventures to present them to engineers and architects at large for their
consideration and use.
Details of Design
In drawing up these details it was first necessary to fix on a value for the safe carrying
capacity of each concrete pile. Of course, the carrying capacity of a pile will depend quite
considerably on the character of the surface soil and sub-soil penetrated, and too much stress
carmot be laid upon the desirability and importance of making a correct and thorough investi-
gation of these soil conditions by borings or test pits before the piles are driven and even before
plans are prepared. Actual experience teaches, however, that under nearly all conditions it is
possible to install piles of predetermined carrying capacity by driving them to such a depth
that the final penetration of the pile under the last blows of the hammer has decreased to a
certain recognized and agreed upon minimum penetration. In earlier years the conservatism
of engineers led them to use as low a safe load as twenty-five tons per pile, and even to-day,
under the most adverse soil conditions, this conservative value may be justified. In nearly all
cases, however, it is safe to use a load of thirty tons per pile in making concrete pile designs.
This figure is very widely accepted and used to-day; in fact, on a number of jobs which have
been executed under the writer's direction, a safe load of thirty-five and forty tons per pile
has been used with extremely satisfactory results. In making up a set of standards for general
use, however, it would seem desirable to keep on the conservative side and adopt as a basis of
design the generally accepted value of JO tons per pile as an assumed safe load. A table on
page 39 has been added for use in particular cases where, in the judgment of the engineer or
architect in charge, the soil conditions warrant the use of thirty-five tons per pile.
The proper spacing to use as a minimum distance center to center of piles is another point
which experience has settled and which general practice has fixed at 3' o". This is a desirable
minimum, not only to insure the proper formation of piles, but more particularly because in manysoils a closer spacing than this would actually decrease the ultimate carrying capacity of the pile.
This is based on the use of a pile i6" to 20" in diameter. Of course, with a smaller pile, such
as a wooden pile, the allowable minimum spacing may be less. For the purposes of these de-
tails the minimum spacing center to center of piles has been assumed as j' O"
.
The geometric arrangement of piles in a cluster to give the best result is easily determined
after a little thought; the desire being to group the piles symetrically about two or more axes
and to place them as near as possible to the center of the superimposed load in order to keep at
a minimum the bending moments in the concrete and the volume of concrete in the cap. It is
believed that the arrangements shown effect the desired result.
The proper distance from center of pile to edge of cap and the distance the pile top pro-
jects into the pile cap are two minor details that have been fairly well fixed by general usage.
One foot is used as the minimum distance from center of pile to edge of cap and three inches is
used for the projection of piles into caps. It is desirable to tie together the tops of piles in any
group and to effect a sufficient bond between piles and caps; on the other hand, as the rod rein-
forcement of the cap lies in practically all cases on top of the piles, any increase in this distance
of projection would increase the volume of concrete in the cap without increasing the effective
lever arm of the reinforcing steel.
It is assumed that the concrete for pile caps will be a 1-2-4 mixture of cement, sand and
broken stone or gravel, thoroughly and properly mixed, and that the quality of these ingredients
will conform to the requirements mentioned in the Standard Specifications for Concrete Piles.
The size of the column base which bears on the pile cap will be a determining factor in
the design of the cap, and since the load to be carried by any particular cap has already been
fixed (being the product of the number of piles in the group multiplied by thirty tons), it is
only necessary to agree upon some allowed unit bearing value of column base on concrete to find
the size of column base to be used in each case. To determine the most modern practice on this
point, the writer recently sent a letter to several prominent engineers asking "What is the maxi-
mum allowable unit pressure for steel or cast iron column bases bearing on 1-2-4 reinforced con-
crete footings?"
Mr. Emil Swensson, of Pittsburgh, advises that good concrete can be loaded up to 600
pounds, but as it is difficult to get quality in foundation concrete, he recommends 300 to 500pounds as a maximum.
Mr. Jonathan Jones, Assistant Engineer of Bridges of Philadelphia, says: "The Bridge
Division, Bureau of Surveys, allows 400 pounds per square inch. I am informed that the
Bureau of Building Inspection, which passes on all plans for buildings, allows 600 poundsper square inch."
Mr. Myron B. Reynolds, Engineer of Water Works Design of Chicago, advises that for
machine mixed concrete he uses 400 pounds per square inch and for hand mixed 350 pounds.
Mr. L. R. Bowen, Bridge Engineer of St. Louis, considers 500 pounds per square inch goodpractice, but sees no reason why the stress could not be increased to 800 or 900 pounds per square
inch when the bearing bed is properly made.
Mr. R. M. Clayton, Chief of Construction, Atlanta, Ga., states that the load used in public
works in that city is 400 pounds per square inch.
Mr. D. E. McComb, Engineer of Bridges, Washington, D. C, writes that the BuildingRegulations of the District of Columbia fixes the maximum allowable direct compression in
1-2-4 concrete at 400 pounds.
Mr. Frederic H. Fay, Division Engineer, Public Works Department, Boston, considers
400 pounds per square inch perfectly safe, and states that the Boston Building Law allows 417pounds.
Mr. Reuben J. Wood, Engineer of Buildings, San Francisco, says that engineers are al-
lowed to use 400 pounds per square inch in that city.
Mr. O. F. Lackey, Harbor Engineer, Baltimore, considers 550 to 650 pounds per squareinch safe values.
The writer understands that in New York City for reinforced concrete footings 25 tons
per square foot is allowed, and that in some special cases where the footing was large 35 tons
per square foot has been permitted.
The concrete specifications of several railroads specify:
per sq. m.New York Central 500 lbs.
N. Y., N. H. & H 500C. & 400
B. & O 300S. A. L 600
N. & W 300
Southern 300
A. R. E. & M. of W 600
Mass. R. R. Comm 400
The Progress Report of the Special Committee on Concrete and Reinforced Concrete of
the American Society of Civil Engineers, dated Feb., 1913, recommends "when compression is
applied to a surface of concrete of at least twice the loaded area, a stress of at least 32.5% of the
compressive strength may be allowed." For a concrete of 2,000 pounds compressive strength
this would give an allowed bearing value of 650 pounds.
In view of all these opinions the writer believes that ^00 pounds per square inch is a safe
and average value and has adopted it in the design of these pile caps.
The attention of engineers and architects using these standards is especially called to the
fact that if a higher unit bearing value is used in the design of their superimposed column bases
(thus making the size of the bases smaller than is called for in these Standards), that the bend-
ing moments in the cap will be greater than is anticipated by these designs. In such case the
design of the caps should be checked on the basis of these increased bending moments and the
Standards modified accordingly. However, even where engineers are inclined to allow more
than 500 pounds per square inch pressure under column bases, total economy of column base and
pile cap may result from the use of the value adopted for these Standards, because what would
be saved by using a smaller column base would probably be more than offset by the additional
strength required in the pile cap.
Where reinforced concrete columns are used instead of steel, it will sometimes be desirable
to mould a pedestal block on top of the pile cap to obtain the required bearing area, as shown
on the following page.
-Re/n^rced Concrefe Ccp/umi
Pedes^e/B/ocM
/?e/j7forcea' Concrefe
F/7e (^ep
Fig. I.
Having established a unit bearing value on the concrete, the assumed area of the column
base for each group of piles may be determined, and in all cases these bases will be assumed to
be square. With the spacing of piles in each group already chosen and the size of the column
base known, the bending moment in the cap can now be calculated. The stress conditions which
exist in the pile caps shown herein are similar to those which would exist in a cantilever slab
supported at its center (by the column base) and loaded at various points (by the upward re-
actions of the piles). From a strictly theoretical point of view, therefore, the bending mo-
ments in the caps should be calculated in accordance with some hypothesis of slab action. Such
an analysis, however, if treated with completeness, would be very complicated and laborious,
and the uncertainty involved in the assumptions made at some steps would render the correct-
ness of the results problematical. In view of this it seems justifiable to select some other solu-
tion which will be simpler to apply and yet give approximately correct results. Such a solution
may be found by considering the slab to consist of a series of cantilever beams extending in two
(or three) directions and calculate the bending moment in each separately. This theory has
been used by many engineers in designing soil-bearing footings, and it has been adopted as a
basis for determining the bending moments in these designs.
The question then arises—shall the point of maximum bending be assumed to exist at the
center of the column base as is the assumption in the usual design of steel beam grillages, or shall
it be assumed to be at the edge of the column base as is recommended by many engineers?
Opinions differ on this point and this has resulted in a wide variation of caps designed to carry
the same load— in some cases the writer has known as much as 50% variation in such caps.
Fortunately there exists some experimental data which throws additional light on this question.
Prof. Arthur N. Talbot, in University of Illinois Bulletin, No. 67, entitled, "Reinforced Con-
crete Wall Footings and Column Footings," describes and discusses actual tests made on 114
wall footings and 83 column footings. Prof. Talbot points out that, based on the theory of grill-
age beams, the maximum bending moment occurs at the center of the column, but where con-
crete columns rest on pedestal blocks (as shown in Fig. i), the resisting moment at such section
will be far greater than at the edge of the pedestal block, so that a section at the edge of the
pedestal block will be the critical section. Furthermore, even where steel or cast iron base
plates are used the frictional resistance (or bond) between the concrete and the column base
will be sufficient to offer considerable horizontal shearing resistance and so draw on the column
base for additional strength at the center section. Besides, the pressure from the column base,
instead of being uniformly distributed, will tend to concentrate on the edge of the base and this
will act to reduce differences of moments. Altogether, it may be expected that the section at the
edge of the column base will be the critical section for bending moment and resisting moment.
On page 20 of the above mentioned bulletin. Prof. Talbot says that after making a study of
all the tests it is concluded that a section through the edge of the column base is fairly repre-
sentative of the critical section, and that "this section will be used in the calculations in this
bulletin." In view of both the theory and the tests of Prof. Talbot, this conclusion seems to
be justified, and so the designs shown herein have been calculated on the assumption that the
maximum bending moment in the cap occurs at the edge of the column base.
As an example of the application of this theory, the calculations for the cap of the twelve
pile group will be given in detail. (See Fig. 2.)
Co/umn B,3se3 -2"Square
@ <g) @ ©Fig. 2.
First, the load or reaction of the pile C will be considered as passing one-half towards the
pile A and one-half towards the piles B (proper rod reinforcement being used to bring about
this transference). There will then be considered to exist in the cap two pair of cantilever
beams, one extending from the edge of the column base to pile A and the other extending from
the edge of the column base to the piles B. The force exerted at or near the pile A will be made
upof>4C + A + >4C which equals twice the total load on one pile, or 120,000 lbs. This multi-
plied by the lever arm of 2' \\" gives the maximum bending moment at the edge of the base of
4,200,000 inch pounds which is to be resisted by the cantilever girder considered to exist in
that direction. In the same way the maximum bending moment in the direction of the B piles
will be found to be 3,060,000 inch pounds, resisted by another girder considered to exist in the
opposite direction.
In determining the resisting moments of the cap (or of the cantilever beams assumed to
exist), the usual assumptions that the loads are applied at right angles to the beam, that a plain
section before bending remains a plan section after bending and that the metal and surround-
ing concrete stretch together, are made. Also, the tensile strength of the concrete is considered
negligible in calculations for the resisting moment of the beam. Sixteen thousand pounds per
square inch is taken as the safe tensile strength of the steel reinforcement and 650 pounds per
square inch as the safe compressive strength of the concrete.
The depths of the concrete caps in each case were determined by a cut-and-try method and
the amount of necessary rod reinforcement determined by the usual formula:
M = Afd' = Afjd
Where M is the resisting moment, A is the area of the reinforcement in the given direction, / is
the unit stress allowable in the reinforcing rods, d is the distance from the top of the slab (or
beam) to the center of the resisting steel area, d' is the distance from the center of the resisting
steel area to the center of gravity of the compressive stresses, and j is the ratio of d' to d. In
practically all cases the percentage of reinforcement will be found to be comparatively small,
so that the value of j will be about .90 and the tensile strength of the rod reinforcement rather
than the compressive strength of concrete will determine the strength of the cap in bending.
The punching shear of the column base on the pile cap is another consideration that will
affect the design of the thickness of the concrete. Calculating the vertical punching shear
around the periphery of the column base, it will be found that the unit shear in the concrete
does not exceed 125 pounds per square inch and in most cases is considerably less.
For the reinforcement of pile caps under isolated columns or piers some form of twisted
or deformed rod is recommended to be used in order to obtain a high value for the bond be-
tween concrete and steel which is necessary to develop the tensile strength of the rods in the
short lengths. The bond required between concrete and rods shown in these designs does not
exceed 100 pounds per square inch of rod surface except in a few of the smallest caps. In
these cases the caps might be considered as a block of unreinforced concrete, with the stresses
from the column base radiating through, the homogenious mass at an angle of 45 degrees with
the vertical, and the loads will be found to reach the top of the piles safely.
In drafting these Standard Details the allowed load per pile and the assumed size of
column base, together with the total column load, has been shown on each sheet so as to avoid
any possible misunderstanding on the part of engineer or architect using them. For the pur-
pose of estimating quantities, the volume of concrete and weight of steel is given for each cap,
as well as a bill of material for the rod reinforcement. All necessary dimensions of the caps
are given in figures to facilitate the work in the field and to obviate any necessity for scaling
dimensions.
On the larger caps the upper edges are shown beveled, which will increase slightly the cost
of forms, but this extra cost will be more than offset by the saving effected in the volume of the
concrete. The horizontal dimension of this beveling has been limited to two feet so as to avoid
any possibility of shearing or cracking of the concrete just inside the outside line of piles whichmight result if the cap were made too thin at such points.
Where soil conditions justify the use of a safe load of 35 tons per pile, the same pile spac-
ing and cap reinforcement may be used as are shown for the 30-ton pile caps, increasing only
the thickness of the cap in accordance with the table given on page 39.
On page 41 are shown some types of pile cap footings for continuous walls. Where walls
with loads exceeding 15 tons per running foot are to be carried on piles, three or more lines of
piles may be used with similar details for the pile caps.
Often it occurs that pile foundations for columns must be provided close up to an adjoining
wall or along a building line where the Standard pile grouping cannot be used. In such cases a
special grouping and cap design must be employed. A typical example of such a cap is shownon page 43. Other forms to suit the particular case in hand will readily suggest themselves
to engineers, but they are too numerous to warrant their inclusion in these Standards.
Sometimes the loads on the columns along the building line are so great as to require a
continuous pile footing extending from column base to column base. In this event the pile cap
will be considered as an inverted continuous beam, supported at the column bases and loaded
by the upward reactions of the piles. The formula for the bending moments in these contin-
LSuous beams is taken as M —~rz' where L is the total load on the piles between column centers
and S is the distance center to center of columns.
On page 45 the continuous footing is shown diagramatically. The piles are arranged
in two lines and placed on equal spaces between column centers. The number of piles required
between column centers in any particular case will determine the longitudinal spacing and also
will determine the distance between the two lines of piles since it is desirable to keep the lines
as close together as possible and still keep the piles themselves a minimum distance of three
feet apart. When the minimum distance between pile lines is found the minimum width of the
cap will be two feet greater. The depth of the concrete was determined by a cut-and-try
method, and the amount of steel reinforcement required was determined as previously ex-
plained in the case of simple footings. The same amount of steel area. As, is provided to resist
the upward bending moment at the center of the span, as is provided for the opposite bending
moment under the column bases.
The scheme of reinforcement shown is believed to be economic. One system of straight
rods with a sectional area of ^As is run continuously along the upper "flange" of the girder,
providing one-half of the required steel area at the center of the span and reinforcing the upper
part of the cap at column centers against expansion and other secondary stresses. This sys-
tem of rods will be spliced under column centers, but it will not be necessary to lap the rods the
usual distance as they are not carrying their maximum stress at that point. A second system of
rods with sectional area of J^As is also placed in the upper "flange" at center of the span, thus
making up the total required area, As. These rods are bent diagonally downward near the quar-
ter points of the beam (thus providing diagonal shear resistance) and reach the bottom "flange"
of the beam near the column centers where they serve to resist the opposite bending moment at
these points. A third system of rods with sectional area of >4As is placed in the lower "flange"
of the beam at column centers to make up the full area required at those points, and their ends
are bent up diagonally to provide additional shear reinforcement. These rods end when their
diagonal portion reaches the top of the beam. A fourth system of four ^" square rods is placed
in the lower "flange" of the beam at center of span to take care of expansion and other second-
ary stresses. The sectional areas of these systems of rods, except the last, are expressed as
fractions of As and their lengths and points of bending are given in fractions of the span center
to center of columns.
To cover some of the usual cases which may occur in building construction, a table has been
calculated and is given on page 47 for column loads between 180 tons and 480 tons per column,
and for column spacings between sixteen and twenty-five feet. Knowing the span between
columns S and the column load L, this table will give W, the width, H, the height, and As, the
area of steel reinforcement required for the pile cap. These values, together with the diagram
on page 45, will give a complete design for the pile cap.
To illustrate the use of this table, assume that along a building line concrete pile founda-
tions are to be provided for columns 18 feet on centers with loads of 270 tons per column. In
the left-hand column on the page find the span between columns, in this case, 18 feet. Follow
this line across the page until another vertical column is reached, headed 270 tons, the column
load. Here is found three figures—4' 3", the width; 4' 3", the height; and 17.7, the required
area of steel for the pile cap in question.
For the foundations of gas holders, water tanks and similar structures, a continuous footing
over a large area, supported at proper intervals by piles, is often used. A typical example of
such construction is shown on page 49. It will be noticed that around the edge of this foot-
ing or slab has been placed a girder about four feet deep. This girder serves to carry the
bottom of the concrete down below the usual frost line, prevents possible undermining of the
footing, and more particularly strengthens the edge of the slab where the loads from the super-
structure are liable to be greatest.
In conclusion it should be said that no particular novelty is claimed for these Standards,
either in pile grouping or cap design, but they are believed to conform to good and usual engi-
neering practice and they have been used already in the foundation design of a sufficient num-ber of structures to warrant that they will safely carry the loads specified.
10
Piles in allgroups exiend j'inio caps-^
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13
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L0A7O PER PILE 30 TONS
15
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17
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T4?-J Roofs 7-9"Lonff
iHHI
3-/'"Rods 7-9"Long3-^ 20-/''Rods /S'-S'Long-I—4- (Bolfom Layer)
jt —~ — ^-^ ' Assumed ColBase 3-6S^
-H^^T^HH-F^^^ Ph^ ^ Concrefe 14.8 CuYds.~r /^i <9" ^ J 5/<?(?/ IBOSLbs.
/5-PILE
13"dp g
i 4
Z8-j"''Roc/S /0'-9"Long
f/Issumeal Col3sse3-8''sq.
'Z-^XZx ^ ColumnLoad^dOlbns
rl "nNJrj_ 4^" ^^ Concrefe 12.9 Cu Yds
^/tf"-?/ /0Z3Lbs.
.L
le-p/LE:
L.O/ejD PER PILE 30 TONS
19
_ ^\.z'o'A
f"Piles in allgroups
n J / exfend 3"info caps
s"",
/Z^^f.^^X Z-9
rx^.
4-i Rods J0-9"Long4-i"''/^ods jZ'-3"Long
7- /'"Rods /O'-9"Long
Z-9"^ 2-9"^/zV t4-l'''Rods /Z-9"Long(BoifomLayer)
iP
tH^+^H^'^Vh-^1-H4 s
I
T I
I I
I
I
^ ^^^4
i
j-< /5^o"
i^ssunned Co/Base 5'-9"S(j.
CoJumn lj:>3d 3/0 7b/is
Chancrefe /7.4Cu.Yds. Sfeel /045Ll?s.
IT-P/LE
LOAID PER P/LE 30 TONS
21
fc
- - /o^o' ->^Z'0'^
^^P//es in a/Jgroupsly e>:fend 3"/n/o capsT
4-4 Rods /o'-3"LongJZ-/"°Roofs /0-3"Longl6-/"°Roo/s j3'-S"Lor?g
fBofiom LeyerJ
^^ ,1 I,—I—4,
—
i-—\—-4,—u—
I
> I
P'S'-vff
—
immm^M^TTT
T
f^-/d-o >j
I
/^Bsumed Co/.Bdse 3-loi
(H^o/umn Load S40 Tons
Concrel^e IS.OCu Yds. 5/-eeJ 1338 Lbs.
Ia --PILE
LO/7D PER PILE 30 TOMS
23
^P/les j'n a// groups
^J Gx^ena/ i"jnh caps
48-} "Rods J2-Z Long
-X V- _t-J_J \ L_J !_,J
L^ir-^-^i
I ^— a-/o— -^- 7^2 -^
/7ssun7ecf Col Base 4-0"S^.
Co/umn Load S70 ^f7s
Ccpr7crele /7.3 Cu.Yofs. She/ /118 Lbs.
/S-P/JLE
LO/^D J^eR PILE SO TONS
25
/o'-o-
'P/'/es in a//groups
_>L.
fi
1"
^4
j'-O"-^ 3-0"-^ 3-C?"-^/zV
^^3_i/ ex/end 3' //7/0 caps
4-4 Roc/s 10-9"Long/E-/''''Roo(s /o'-9"Long
/8-rRools /3'-e"Long
'^.
XT-
W^-(-
T^gtmtr-pr^g^^^^^
ii--^i{l&S±t?i:i+MEfpttW:^fflBi^
'_±;^^:^ftiStiH
;d^-
'I^-h.-HtH-'^
W-«̂-
'Wm
T
^ ^nX
1
1U-
r- /o'-o" ^I
/7ssu/r?eof Co/. Base 4-/"Scf..
Co/u/^n Losaf ^00 Tons
Concre/e /9.9 CuYds. S/ee/ l36ZLbs
SO-P/LE
^ LO^D PER P/LE 30 TONS27
k- 5'-z
. . J . . „ ^L • .I ^
/^P'f^s 11^ 3f^groups*" 3"=^ ^^-^ ?=* 5^-=?4-p, exfencij"/n/o caps
X- -A/^S*^3'-0"-A^ 3'-0"-^-3'-O"^3'-O"
S-} Rods S'9"Longa-ff^ods 7'-6"Long
E8-/''''Rods 13-3"Long
/Z\
% m mm.5; 5^
-/a'-o'^
/Assumed Co/.33se 4-2"Sc^
Co/umn Load 650 Tons
Concrete ZZ. 8 CuYds. 5heJ /5/Z Lbs.
^ LO/=ID PER PILE 30 TONS29
A
^4-
./^P//es in a//groups-^ exfend 3"/r7/o cap
4-fkaci/s 12-9"Long4-1 '')?ools 13-9 "long
lS-/'''Rools /Z-9"long
±r:z-
1
-1^'
^trnfrfi-"''li I' I*
' • ' I ' M II
I I I —
H
T
j:l'H>
r
j_-- /o-o" >i- - /4-0" -^
/7ssumeof Co/. 3sse 4-5 Sa.
Co/umnLoa^ 660 Tons
Cor7(7re/ff Z4.0 Cc/. yds. Sfee/ /4f4 Lbs.
22-PILE
LO/7D PER P/LE 30 TONS
31
m.
T7'
f^^-'y^^ /^-£>''
'" tJlDTICJlDfPi_i_, ^ ^PJIes in allgroups
f- exfeno/ 3"/nfo cap
i-'mmmm%\
4-1 Roofs 13-3''Long4-pRoafs /3'-9"lohg'//-/""Foots /5'-3"Long/4/'°Pocf3 /3'-9'long
CBoffom LayerJ
T
T
I ,
J.
k-k /^-o"~
Assumed Col. Bdse 4-4 S^.
Co/umn Load 690 Tons
Concrete 25./ Cu Yds. Sfeef /6Z7 Li>s.
S3-PILE
LOA^D PER PILE 30 7X>NS
33
X
-l-^
i^'-P/'/es In 3//groupsIf" -—j"
I I
11 11|j f^- exfend 3"/h/o caps
\
^ I
CM
+T!llii| ''linl|[
b:?e£
ZO-I Rods /3'-3"Long
ZO-/"°Rods 15-9'long
1~
IJ
I
..i_l
r< /^-^" ^k--' /^-'^^^ -^I
j^ssumeo/ Co/ Base 4-5''5cf.
Co/umn Load leo Tons
Concre/e BSJ Cu.Yds. Sfee/ 1856 lbs.
S^-'P/LE
LO^D PER P/LE 30 TONS35
£
j^^/^^q ,o'-a" A^^o'ii
-\-^vi ^v
!
w>vr_
- -} I I
l~Y e->(^enc^ 3"/nfo cap
.'a I ^"iAZ-/ R<yds /3-e Long
s5
^
i
3-0"-^ 3-0"^^ 3-oU/zV
illJLLiUiLLlliULL I
iE#r^^Tif n"Tiitt|T!-pn
mm"H«3^^l
Assumed Co/ Bdse 4- 6'"$^.
Co/umn Load 7B0 Tons
(ypncre/e Z6.1 CcfYofs. Sfee/ /964Lb5.
LO/JP P£R PILE 30 TONS
37
lYHEf^E SO/L CONDfT/ONSJUST/FY the use ofa s^e a/hyved/osaf of 3S Tons per p/'/e^ase
/he same p//e spac/ng dnd cap re/nfbn7emer?f
ds s/7oyvr? /'r? fhe preceding sfencfsrds cMngingonly fhe fh/cMress of/he cep in accorafence tvi/h
/he fo/hwng /al>/e.
NO. OFPfLESIN e/KfUP
COL. LOfJD
IN TONS SQ. GOUBfJSErM/G/fNF<^OFCFIP
/ 35 — I'-e'Z 70 /'-5' Z'-6"3 105 /-^// 2'- 6'
4 140 2'- 0" 2'~'8"
S /7S 2' -3" 5' "5"
6 2/0 2' -5' 3' -3"
7 245 2'- 7" s'-s"8 280 2' -9" 3'"^"S 3/S 2'- II' 5'--^"
lO 350 j/_ /// 3'"^"// 385 3' -3" S'-B"12 420 3'''5" 3' -9"13 455 3'-7" 5' "9"14 490 3'- a" ^'"f"15 525 3''/0^ ^'"5"16 seo y-/r g-'-s^'
17 595 4'- 1' ^'--6"
/8 630 4'- 2" ^'"9"19 6G5 4'- 4" ^' -B"20 700 4'-S' ^'-9"2/ 735 a'-e'' ^''-'9"
22 770 a'-r' a'"B"23 805 4'-e' ^'-B"24 840 4'-/o" ^f'B"25 875 a'-//" ^/~^//
m. LO/7D PER PILE" 33 7X>MS39
TYPEA}-FOR LOflDS UP TO lO TONSPER UNE/^R FXX)T Or W^LL.
-^r^
-r-^ /ib<^3 {Corjfinuoas)
\
\^P/7e spacing 3-o" f-o 6-0'
accorcf/ng fc? y\/3//load
TYPE B'-FOR LOAIDS BETWEEN lO /JND IS TONS PER LINMaRFOOTOF W/JLL
I \ 3'
;<l;":;^i"
I
•^
NOTE: This d/sfsnce variable r~"'>"~ r~ "^ -3-4 Rods (conNnuous)
increasing as iongifudinafp/ie (_x p/Je spac/ng variesspsc/ng ^G/ecreases so as fo keep according fo yva/Z/oaof
cenfre fo centre ofpiJes 3''0"
TYPE C^FOR LOA7DS OF/5 TONS PER LINERR FOOTOF W^LLK- 2-6" -A
^ rrs: ^H
^7-1^—^p^
\ \<--s'-<p-M^ -}-o- -H
^^£-J "Pods 4-9"/ong afeach pair ofp/ies
^T.l5-4 /?ods(Confinuous)
TYPES OF ViMLL FOOTINGSLOi^D PER P/LE SO TONS
\
41
J4-0"
Jl
Piles exhnd3"Info c&p
II- 1""Rods l3'9"Lon^
"cm
If -1^6'^
XS:̂ :t-eS]^fe3i.^-f
"T"0^I—
/-6 *r*/-S^ I- 6^ 1-6"^ Z-^"-'
-^^-'^^'-'^'^^i^ti?'.-^:t^§t-^ =
S
1-6'-^ /-6-.
\^i-
— /a-o"
//
zio"-.
3u//cf/r}aL/ne-i
si
-^
p/
/Assumed OolBsse. ^-e'Sa. Co/u/rjn Load Z70 Tons
nrPiC/^L EXAMPLE OFPiLE Cy9P
EXTERiOR COLUMNS /TLONS BUiLPiNeUNE
LO^£> pep PILE 30 TONS
43
45
DIMENSIONS
FIND
REINFORCEMENT
OF
CONTINUOUS
PILE
CFJPS
FOR
COLUMN
FOOTINGS
FILONG
BUILDING
LINE
if
\
1
1 1
1
1
r
5: ^ fe X ^^ ^ :>; ^ ^ 5;J5 ^ ^ « ^ :t: ^ ^ ^
-
^ ^ ^ ^ ^ ^ ^ ^ 3; ^
1
1
1 ss
1
5:
=%
^ ^4
§^ SJ
5*
K54
<5>5i
^4 ^4
5^^^s ~4 -5
"-I
^4 1Si
1 !3
5*
^4
%
^
It
1^s
K5t
^^
''J
8
% 5;1
5s
^^
^H
egC<4
5! %
5 ^^VI
y
:?^ 1
05i
^4
s•^^ i
^^
»0 Ns 1
5s
^c^
^^
^^
St
<J0
\ s
„
^ 1is
«5
-5 ^ 1
5s ^^̂ '4 1 5$ 1
5»
§
511
5j
^§
8 <n
*^^i
^
St
1
^
.?^
^^ ^ 1 ^ 551
''^
5
^
^A
5%
55
Ill
1
<0
1^ §1
5t ^^
^^ S 1
^^
§ K J(V4 \
'i 5
It 'i
t
1!1 J
in ^ ^
!9
5 ^ 5 5 S i3
47
<>
-o
t
^
I4J-M
-hTl4+r-r+-t-.+--T/ Z-4 Rods -.
IA over P//es -ST
iNTER/OR PiefNELS EXTERIOR P/^NELS
PL/JN OFTYf^a^L REINFORaSMBNT
^2 Rods^
Cenfre ofFourrcfghbr?
^2-i\ccfsover Pj/es — -"
5-0 td 6-6 eccordjng fo ioQcf
P//es exfer?d3"Info cgps
QU/^RTER RL^JSf
rrPia/JLFVuNP/^noNFOR ^/fsholderoru^rgev^stter ti^n/^£jOf90f=^RP!LE^O TO ^^O TONSD&pencd/ng upon so/7 oanol/-f-/ans.
49
Standard Specifications for Concrete Piles
Concrete piles shall be driven for the foundations, as shown on Drawing No. — . Piles
shall be Pedestal, Raymond, Simplex or other type approved by the architect.
Piles must be driven vertically and their tops brought to the elevations shown on plans,
or else must be cut ofT to such elevations.
The required length of each pile shall be determined by driving the pile (or pile forming
apparatus) until ten (lo) blows of a No. 2 Vulcan steam hammer produce not more than one
inch penetration, unless otherwise ordered by the architect.
Bids shall be based on furnishing piles of an average length of feet, with a price
per lineal foot for additional lengths, and a credit per lineal foot for lengths omitted. Pay-
ment will be made for the number of lineal feet of piling actually driven, the lengths to be
measured from the "cut-ofif," as shown on the plans, to the lower end of the pile.
Concrete for all piles shall consist of one part of Portland cement, two parts of sand and
four parts of broken stone or gravel, measured by volume, and shall be thoroughly and prop-
erly mixed. The cement shall be of some well-known brand and shall pass the Standard Tests
of the American Society for Testing Materials. Sand shall be clean, silicous material, contain-
ing not more than 5 per cent, of clay or other deleterious matter, and shall be of such size as
to pass through a 20-mesh screen and be retained on a 30-mesh screen. Broken stone or gravel
shall be of some hard stone, shall be free from earth and dust and shall have a diameter of not
more than i^ inches, nor less than 54 inch.
A loading test shall be made on one of the piles selected by the architect. After the con-
crete in the pile has been allowed to set for at least three weeks, a platform shall be balanced on
top of the pile and weight placed thereon equal to one and one-half times the safe load which
the pile is designed to carry. This weight shall remain on for 24 hours, and the settlement of the
pile shall not exceed an allowed settlement of .01 inch for each ton of load applied.
Each type of piling must conform to the specifications hereinafter given for that particular
type.
PEDESTAL PILES : Pedestal Piles, as made by the MacArthur Concrete Pile & Foun-
dation Co., shall consist of a cylindrical shaft or stem 16 inches in diameter with an enlarged
base or foot approximately 3 feet in diameter. They shall be formed by a pile apparatus con-
sisting of a cylindrical steel casing and a core (or rammer) which fits inside the casing and
extends below the bottom of the same. This apparatus shall be driven into the ground to the
required depth. The core shall then be removed and a charge of concrete dropped to the bottom
of the casing. With the core as a rammer this concrete shall be forced out against the soil at the
bottom of the casing, and this operation of charging and ramming shall be continued until a bulb
or pedestal of the required size is formed. After this the casing shall be filled with a wet mixture
of concrete and pulled slowly and evenly out of the ground, leaving in place a pile of the size
and shape mentioned above.
RAYMOND PILES: Raymond piles shall be tapered, and have a diameter at the top of
20 inches, and at the bottom of not less than 8 inches. They shall be formed by driving into the
ground to the required depth a collapsible steel mandrel (or driving form) encased in a spirally
reinforced steel shell. Then the mandrel shall be removed and the shell filled with concrete.
This steel shell shall be made of sufficient strength to maintain its shape after the mandrel
has been withdrawn. Before filling with concrete each shell shall be examined by lowering a
51
light into it, and in case the sections of the shell have slipped apart, or the shell is found to be
distorted or defective in any way it shall be removed and re-driven, or another shell driven inside
the first. In case the latter is done, the second shell shall be driven until its bottom touches the
bottom of the first shell. All such extra operations to be at the expense of the Contractor.
SIMPLEX PILES: Simplex piles shall be cylindrical, i6 inches in diameter, with a cast
iron shoe or point at the lower end. They shall be formed by driving into the ground to the
required depth a heavy steel pipe fitted at its lower end with a detachable cast iron point. Thepipe shall be filled with wet concrete and then pulled slowly and evenly out of the ground, leav-
ing the cast iron point in place surmounted by a 1 6-inch diameter concrete shaft.
All the concrete required to form the pile shall be placed in the pipe before beginning the
removal of the pipe. The cast iron point shall be strong enough to resist the shocks of driving.
PRE-MOULDED OR CAST-ABOVE-GROUND PILES: Pre-moulded piles shall
be cylindrical, i6 inches in diameter, or if square or hexagonal in cross-section shall have a sec-
tional area of at least 200 square inches. They shall be cast in water-tight forms and reinforced
with four ;54-inch round rods tied together every 12 inches with ^-inch diameter wire loops
secured to the rods in a substantial manner. For the first three feet at the top and bottom of the
pile these loops shall be spaced on 4-inch centers. If the piles exceed 30 feet in length, additional
reinforcing shall be provided in the middle half of the pile to resist the strains incident to
handling the pile. Piles shall be protected from damage while seasoning and shall not be movedwithin twenty days nor driven within forty days from date of casting. Should the pile be broken
or cracked during driving it shall be removed and another pile driven in its place, or else another
pile shall be driven alongside of it. No payment will be made for such defective piles.
52
Concrete vs. Wooden Piles
Comparison of Cost Under Various Soil Conditions
That concrete piles possess many advantages over wooden piles and have none of their
disadvantages is generally recognized to-day by engineers and architects, as is evidenced by the
decreasing use of wooden piles and the increasing use of concrete piles for important founda-
tions. The basis of this superiority rests on the following points:
1. Concrete piles are more /'ermflnf?/?^ than wooden piles for they are made of a ma-
terial which will resist the action of the elements and will maintain its full strength for
practically all time, whereas wood, being an organic substance, is liable to disintegration
and decay. Wooden piles in contact with air, either above or below ground, will speedily
rot and only by keeping them constantly saturated with water can this be prevented. Evenin this condition they are subject to destruction by worms, and, in salt water, by marine
borers. Where wooden piles are cut off below permanent ground-water level they may be
unwatered at some later date by the lowering of this ground-water level resulting from the
construction of nearby subways, sewers or other underground structures, or from the natu-
ral draining away of the ground-water which is going on in many localities, due to a num-ber of direct and indirect causes. This probability of unwatering is particularly dangerous
because the wooden piles, being under ground, are not subject to inspection from time to
time and may completely rot away and allow settlement of the structure before their con-
dition is discovered. Concrete piles are not subject to these dangers, for they are equally
strong and permanent whether wet or dry.
2. Concrete piles are more reliable than wooden piles, because they are made of a
material composed of definite proportions of known and tested ingredients, and this ma-
terial is subject to inspection in the making, while wooden piles, like Topsy, "just grew,"
and may contain wind shakes, cracks and other defects. Furthermore, the size and shape
of wooden piles is determined by the available supply of timber which is constantly de-
creasing, both in quantity and quality, whereas, concrete piles may be made of any desired
size and shape which results in the making of piles of much greater carrying capacity than
wooden piles. This permits the use of fewer concrete piles to carry a given load than
would be required with wooden piles and consequently the use of a smaller pile cap. Thewriter has known of instances where wooden piles could not be used at all for the founda-
tions of heavily loaded columns closely spaced, because the required number of wooden
piles for each column footing was more than could be properly placed in the limited area.
Using fewer concrete piles, however, the size of the footings were kept within the re-
quired limits.
Wooden piles being comparatively weak are liable to be split, broomed, buckled or
broken in driving, as has been disclosed in a number of cases where they have been ex-
posed by excavation after driving. Concrete piles can be subjected to much harder driv-
ing than wooden piles without damage to the structure of the pile, and when formed in
place by the use of a steel driving form are, of course, not liable to such damage.
3. A given foundation can usually be constructed in a shorter time with concrete piles
than with wooden piles, not only because there are fewer piles to drive, but also because,
in most cases, sheeting, excavating and pumping are required to cut off the wooden piles
below ground-water and then a large cap must be built and the earth back-filled around
53
it. On the other hand, concrete piles may be driven from the surface of the ground or from
basement level and capped at that level with a small cap in much less time. Also the ma-
terials required for concrete piles may be quickly obtained almost everywhere, while it is
becoming more and more difficult to secure prompt deliveries of suitable wooden piles.
Another disadvantage may result where wooden piles are used alongside of adjoining
structures supported on spread footings. In such case shoring and underpinning of these
structures is usually necessary, which not only increases the time required for the founda-
tion construction, but also adds very materially to the cost.
In fact, it may be said that concrete piles have every advantage over wooden piles
except in the matter of cost, and even on that point they are superior under many con-
ditions.
For the reasons already described, engineers and architects usually prefer to use concrete
piles instead of wooden piles even when the cost of the resulting foundation is somewhat greater.
Occasionally, however, the sum of money available for building a given structure is so small
that only the first cost of the construction can be considered in choosing a type of foundation.
In such a case it becomes necessary to compare closely the cost of a concrete pile foundation
with that of a wooden one. Of course, concrete piles, foot for foot, will cost more than wooden
piles, but the saving effected by the use of concrete piles comes in on the following points:
1. A concrete pile will carry about three times as much load as a wooden pile, thus
requiring fewer piles.
2. A shorter length of concrete pile than would be required with a wooden pile mayoften be installed, due to the shape and greater size of the concrete pile.
3. Having fewer concrete piles than wooden piles, the volume of the capping to
cover them will be less, which effects a saving in the cost of the capping.
4. The most important saving elTected by concrete piles over wooden piles results
from the fact that they do not have to be cut off at ground-water level, but can be brought
up to any desired grade. In this way often a considerable amount of excavating, sheeting
and pumping is eliminated, as well as the concrete pier necessary to bring the footing upfrom the top of the wooden piles to the desired grade.
In any specific case, a typical column or wall section should be selected and two foundation
designs made for this column or wall section, one on the basis of using concrete piles and one
on the basis of wooden piles. A comparison of the cost of the two footings should then be made,
assuming expected prices for piles, concrete, excavation and rod reinforcement. An exampleof such comparative designs is shown on page 55 for a column carrying a load of 240,000
pounds, and also a comparison of the costs based on certain average unit costs. In the sameway comparative designs and costs can be worked out for cases where the ground-water level is
nearer the surface of the ground and thus determine the dividing line of economy between con-
crete and wooden piles. This has been done and the results are shown at the bottom of the
page. Of course, for any particular structure these unit costs will depend upon local prices
and conditions, but for most localities the price of labor and materials will not vary sufficiently
from those assumed in the table to materially change the conclusions set forth.
54
rm
u-
i i ^ -C^ssemeni- Floor orSur^ce ofGrourygf
1
Concrefe Pi/es
Orouncf yvafer Level -
^vi
^
^^
'J-
2^S^ y\
li^ooder? Piles- M U/ m
^-/""Rods
TSP
CONCRETE PILES IVOODEN PtLES
-/^-/ "Rods
COMPARISON OF COST4 Concre/eP/7es. 230.long @,^/.00 ^/OOOO g i^oaa/en F/'Ies, £5i=f.long ®0.25 ^Se.25
25 Yds.ConcrefeJnc/ud/ngForms@ &.SO /4.9S £> ^s.Concrele /f7c/(yd/n^ Forms @S.S<P 39.00
3.5 )i^s.Exc3V3Hor? (Si (P.70 2.45 Z7Y^s.£-xcevs//on&&3^'f"^^Z.OO sa.oo
82 Li^s. f^e/nforc/r?a f^ocfs @ o.03 2.46 367 li^s. /r'einforoinciRods (g>aOJ //.<?/
Th^af ^/19.86 7b^s/ ^160.26
S6v/ng i?g f/7e use ofConcreh P//es - ^/^o. /70 or 3S.Z
%
The above f/gures s/7c>tv fhe/ econor?7if/n f/rs/ cosf resu/fs fromfhe use of Concrefe F//es /nsfead of
tvooden p/7es under fhe fo//oiV/ng cond/horis:—
For /5F. Piles — Under aif cond/f/ons.
" ZOfa. " —yVhen grour?d tvafer fevel is Sff. or more l?e/ow l>asemenif/oor orsur^ce ofground.
// 25i^.
a 30ff.
„ 35/f.
„ 6ff. ,
„ 7f^. "
« 8/f. ..
„ „ 9F. II n II // //
COMP/Jf^TiVE COSTOF CONCm:7T:i^ND WOOD^M PiLE^
55
Method of Testing a Concrete Pile
In driving concrete piles it is possible, in most cases, to predetermine the carrying capacity
of the pile from its resistance to driving under the last blows of the hammer, using a modified
Enc/ineerinq News formula or some other empirical rule. When unusual soil conditions are
encountered it is sometimes prudent to test one or more piles with a test load in order to makesure that the unusual soil conditions have not affected the general application of the rule.
The top of the pile is first thoroughly cleaned and then a concrete cap about two feet thick
and two and a quarter feet square is molded about it, the top of the pile projecting about four
to six inches into the cap. While the concrete cap is wet a steel bolt is imbedded in the center
of its top, which bolt is used as a resting point for the level rod when levels are taken to de-
termine any possible settlement of the pile. Two 12 x 12 timbers are placed on the top of the
cap parallel to each other and about three inches apart, and on top of these and at right angles
four other 12 xi2's are placed in such a manner that the weight of the platform will be equally
distributed over the four. On these 12 x 12's a platform of three-inch plank is laid, leaving a
hole in the center of the platform to enable the level rod to reach the bolt in the cap. A tin
tube is placed vertically over this hole of such a height as to leave the top of the tube above the
top of the expected load. In other words, a platform is built balanced on top of the concrete
cap like an inverted grillage. During the loading of this platform blocking may be placed
under the 12x12 timbers to avoid tipping caused by any unequal loading, but when the load is
all on, these blocks should be removed, leaving the loaded platform balanced on top of the cap
and all of the load being carried by the pile.
Should heavy material, such as pig iron or cement in sacks, be available, the platform as de-
scribed above can now be loaded. Should, however, material such as sand or broken stone be
the only available material with which to load the pile, a box should be built with 4" x 4" posts
at each corner and midway between the corners the sides should be further strengthened by
2 x 4's placed vertically. To these verticals two-inch planking is nailed to the desired height,
thus forming a square box with the platform acting as the bottom and the top open. Into this
box the sand is thrown until the desired weight is obtained. Before placing any weight on this
platform, however, a reading should be taken with the level rod resting on the top of the bolt
imbedded into the concrete cap. Further readings may be taken by lowering the rod down the
tin tube in the center of the platform during the loading to ascertain what settlement, if any,
occurs at the various stages of the loading, a final reading being taken when the load is all on.
The total load should be allowed to remain on for several hours and readings taken to ascertain
if any further settlement occurs. The experience of the writer, covering more than one hundredtests in all sorts of soils, indicates, however, that if the pile shows any tendency to settle at all
after receiving the final load that this tendency is relatively small and that the pile will come to
a complete stop in a very few hours after receiving the final load. It is believed that twenty-
four hours will be ample in all cases to settle this point.
Loading the test pile under the conditions outlined above will approximate as nearly as
possible the conditions under which the pile will receive its intended load of the structure. Careshould be taken to keep the load well balanced on the pile, as an eccentrically placed load maycause the platform to tip and fall or set up bending stresses in the pile head which would be suf-
ficient to break it.
For molded-in-place piles at least three weeks should be allowed for the setting of the con-
crete before load is placed on the pile, even under the most favorable conditions, and better re-
sults may be obtained by waiting four weeks for the pile to set.
The drawing shown on page 57 illustrates the construction of the loading platform andbox for testing the pile. The size of the platform is usually made about ten to twelve feet
square, according to the amount of load intended to be placed thereon. In order to have the load
balanced properly it is desirable to have the width of the platform above twice the height of the
box.
56
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Method ofIest/no /7 Cors/cRETE P/le
57
How a Pile Supports Its Load
Where a structure is to be built on soft or unreliable ground, spread footings cannot be de-
pended upon to carry the weight without undue and unequal settlement. Under such con-
ditions, some type of piling is usually found to be the most economical foundation. Piles pro-
vide increased carrying capacity by transmitting the load to the firmer and more reliable sub-
soil underlying the surface soil. A pile develops this carrying capacity in two ways: by the
frictional resistance of its surface with the soil penetrated, and by the direct bearing of its base
upon the sub-soil.
In "A Practical Treatise on Foundations," by Patton, the following equation is given for
the total carrying capacity of a pile:
L = bA + fS, in which
L = the safe supporting power of the pile,
b = the safe bearing power per sq. ft. of the soil at the point or base of the pile,
A = the area, in sq. ft., of the base of the pile,
f = the safe frictional resistance per sq. ft. of soil penetrated by the pile, and
S = the number of sq. ft. of surface in contact with the soil.
Patton further states that, as A and S are known from the size and shape of the pile, if weknow b and f, we can determine the supporting power of the pile under any conditions. For
most cases b, the bearing power of the soil at the foot of the pile, can be quite accurately pre-
determined, but f, the frictional resistance, is of a somewhat less determinate nature. It ranges
in general from lOO lbs. per sq. ft. in the softest soils to 600 lbs. per sq. ft. in compact sand and
gravel.
From Patton's equation the carrying capacity of different types of piles can be computedand compared.
Regarding the manner in which a pile supports its load by friction, E. P. Goodrich (Trans.
A. S. C. E. XLVIII No. 921), points out that "When a pile is supported entirely by frictional
resistance, the actual region supporting the load is some deep ground level at which the fric-
tional resistance holding the pile has been transferred through the earth in the shape of a conoid
of pressure, the base of which gives a total bearing value equal to the load and a unit bearing
value which the earth at that lower level will support. Each kind and degree of compactness
will give a different angle for the slope of the conoidal surface."
The values given by Patton for the frictional resistance between the earth and the surface
of a pile range from 100 lbs. to 600 lbs. per sq. ft., according to the nature of the soil. Elmer C.
Corthell, in his book "Allowable Pressures on Deep Foundations," gives a summary of a numberof actual cases where frictional resistance was measured:
In sinking cylinders for the Papaghni bridge the following frictional resistances wereobtained:
In upper sand 208-220 lbs. per sq. ft.
In black clay 350-560 lbs. per sq. ft.
In silt below clay 272-428 lbs. per sq. ft.
In the lower sand 258-3 16 lbs. per sq. ft.
In sinking cylinders for the Chittrivatri bridge, the frictional resistance was 232 to 377 lbs.
per square foot, through 33 feet of sand, 10 feet of clay, and 7 feet of clay and sand, clay and
38
boulders. Through 33 feet of sand, 10 feet of clay and 3 feet of sand and clay, the frictional
resistance was 293-362 lbs. per sq. ft.
At La Rochelle and Rocquefort, as reported in the minutes of the meeting of the Institute
of Civil Engineers, Vol. L, page 112, the frictional resistance was found to be 164 lbs. per sq. ft.
In silt at Laurient, 123 lbs. per sq. ft. (Colson notes on Dock Construction).
In firm sand of good quality, Dutch engineers estimate friction on piles at 614 lbs. per sq. ft.
In another section of the same report a summary of data collected shows that in two cases of
cylinder piers, the average frictional resistance was 540 lbs. per sq. ft. Gravel gave the greatest
resistance and mud the least.
Twenty-three examples of masonry piers showed an average frictional resistance in sand
and gravel of 522 lbs. per sq. ft.
Five examples of walls, quays, and other structures showed an average frictional resistance
of 270 lbs. per sq. ft.
Corthell also gives the following summary of actual bearing values:
The pressure of stable structures on fine sand range from 2.25 to 5.80 tons, average 4.5.
On coarse sand and gravel, 2.4 to 'j.'jz^ tons, average 5.1 tons.
Sand and clay, 2.5 to 8.5, average 4.9 tons.
Alluvium and silt, 1.5 to 6.2, average 2.9 tons.
Hard Clay, 2.0 to 8.0, average 5.08.
Hardpan, 3.0 to 12, average 8.7 tons.
Clay, 4.50 to 5.60, average 5.2 tons.
SAFE BEARING POWER OF SOILS
IRA O. BAKER
KIND OF MATERIAL Minimum
Safe Bearing PowerTons per sq. ft.
Maximum Average
Rock, the hardest, in thick layers, in native bed
Rock, equal to the best ashlar masonry
Rock, equal to the best brick masonry
Rock, equal to poor brick masonry
Clay in thick beds, always dry
Clay in thick beds, moderately dry
Clay, soft
Gravel and coarse sand, well cemented ........
Sand, dry, compact and well cemented
Sand, clean dry
Quicksand, alluvial soils, etc
200
25
15
5
6
4
1
8
4
2
.5
30
20
10
8
6
2
10
6
4
1
27.5
17.5
7.5
7. -
5.
1.5
9.
5.
3.
.75
59
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