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ENGR. MD SHAHIDUZZAMAN (KIRON)
Soil Test cÖ‡qvRbxqZv wK?
cÖ_gZ: GKwU Structure Gi Foundation depth Ges Foundation
wK Type n‡e Zv Rvbvi Rb¨ cÖ‡qvRb| 2qZ D³ Foundation Gi Load bearing capacity ‡Kgb n‡e Zv Rvbvi Rb¨ | 3qZ D³ Foundation Earthquake Gi Rb¨ KZUzKz vulnerable.
4_©ত cvnvox GjvKv ev †hLv‡b Foundation Gi wb‡Pi soil
slide Kivi m¤¢ebv _v‡K †mLv‡b wK ai‡bi protection wb‡Z n‡e A‡`Š wK retaining wall wKsev sheet pile, bulk heads
wKsev brace cut Gi cÖ‡qvRbxqZv Av‡Q wKbv Zv LwZ‡q
†`Lvi Rb¨| 5gZ GKwU Structure Gi m¤ú~b© load RwbZ Kvi‡b wK cwigv‡b Settlement n‡Z cv‡i Zv Rvbvi Rb¨ Ges Estimate
Kivi Rb¨ | 6ôZ Ground water level ‡Kv_vq Av‡Q Zv Rvbvi Rb¨|
7gZ Foundation Gi bx‡Pi soil wK cohesive ev Non cohesive
Zv Rvbvi Rb¨ | 8gZ soil G Liquefaction Gi m¤¢vebv Av‡Q wKbv Zv LwZ‡q †`Lvi Rb¨| Field Test:
Field Test G hvIqvi c~‡e© GKRb BwÄwbqvi‡K Rvb‡Z n‡e †h, Structure wU KZ Storiyed nIqvi m¤¢vebv Av‡Q| †Kbbv Field Test
ENGR. MD SHAHIDUZZAMAN (KIRON)
Gi †evwis Depth KZUzKz n‡e Zv Gi Dci wbf©i K‡i|
Depth wbY©q Kivi Rb¨ Multi storiyed Gi †¶‡Î D = C S0.7 [ sowers & sowers , 1970 Page -418
Dr. K.R. Arora, Formula-17.1]
‡hLv‡b D= Depth of Exploration
C= Constant , 3 for light steel & Narrow concrete building
6 for Heavy steel & Wide concrete building
S= No. of storey
Field test G hvIqvi c~‡e© GKRb BwÄwbqvi‡K Aek¨B Rvb‡Z n‡e †h, cÖ¯—vweZ f~wg‡Z wK cwigvb †evwis Ki‡Z n‡e| mvavibZ †QvU fe‡bi Rb¨ GKUv †evwis B h‡_ó | Avi hw` f~wgi cwigvb 0.4 hectares Gi KvQvKvwQ nq ZLb 5wU †evi †nvj B h‡_ó | hvi g‡a¨ GKUv Centre G Ges Ab¨¸wj Pvi KY©v‡i | Multi storied building Gi Rb¨ Bore hole building Gi me KYv©‡i Ges important location G Ki‡Z n‡e, Spacing n‡e 10 - 30m depend Ki‡e subsurface condition Ges loading Gi
Dc‡i| Highway Gi Rb¨ proposed centre line A_ev along the proposal
ditch line eivei drill Ki‡Z n‡e| G †¶‡Î †evi †nvj 150-300m
cici Ki‡Z n‡e. Concrete dam Gi †¶‡Î bore hole Gi Spacing 40 - 80 m vary
K‡i|
ENGR. MD SHAHIDUZZAMAN (KIRON)
[Page-419, Dr. K.R Arora]
mvaviZ Soil Gi Characteristics Rvb‡Z soil exploration Kivi Rb¨ cvP ai‡bi Method use Kiv nq|
(i)Auger boring (ii) Wash boring (iii) Rotary boring (iv)
Percussion boring (v) core boring
evsjv‡`‡k Avgiv mvaviYZ Wash Boring Method G Soil
test Kivi Rb¨ Field SPT Ges Soil sample collect Kwi| Zvi Rb¨ Avgiv Standard Penetration Test Use Kwi| Standard Penetration Test Kiv nq mvavibZ cohesionless
soil Gi Rb¨| GUv me‡P‡q †ekx useful cohesionless soil
Gi †¶‡Î Relative Density Ges Angle of Shearing
Resistance ‡ei Kivi Rb¨ | GUv Aek¨ cohesive soil Gi Rb¨ unconfined compressive strength wbY©q Kivi Rb¨ e¨eüZ nq | GB Test Gi †¶‡Î mvaviYZ GKUv Split Spoon Sampler
_v‡K hv w`‡q Soil Sample Collect Kiv nq Ges G‡Z 63.5†KwR GKUv Hammer _v‡K hv w`‡q H sampler
‡K Drilling rod mnKv‡i drive Kiv nq| G ‡¶‡Î D³ Hammer 760mm Dci †_‡K c‡o Ges wgwb‡U 30 blows
‡`q| mvavibZ SPT Collect Kiv nq cÖwZ 1.5 wgUvi Aš—i Aš—i 6 © © 6© © 6©© © Gi Rb¨ | Gi g‡a¨ cÖ_g 6© © †evwis Gi Rb¨ KZUzKz blow jv‡M, 2q
ENGR. MD SHAHIDUZZAMAN (KIRON)
Ges 3q 6© © Gi Rb¨ KZ blow jv‡M Zv count Kiv nq| Z‡e SPT wnmve Kivi mgq cÖ_g 6© © Gi Rb¨ cÖ‡qvRbxq blow wnmv‡e Avbv nq bv| Zvi ci 6© © , 6© © Gi Rb¨ hv jv‡M Zv †hvM K‡i total SPT wbY©q Kiv nq| hw` 6© © Gi Rb¨ 50 blows Gi Dc‡i jv‡M ZLb Avi drive Kiv nq bv& Ges Test discontinuous wnmv‡e Mb¨ Kiv nq| [ Dr. K.R. Arora, Page-427]
Split Spoon Sampler n‡”Q hv w`‡q Soil Sample collect Kiv nq| mvavibZ GwU 675mm j¤^v nq Ges Gi Af¨š—ixb Dia 38mm Ges ewn©fv‡M 50mm nq| GB Sampler
‡K Drilling rod mv‡_ attach K‡i ivLv nq| Avgiv mvavibZ wdì n‡Z `y ai‡bi Soil Sample collect
Kwi | (i) Disturbed Sample : Soil Gi index property Rvbvi
Rb¨ †hgb Grain size , Plasticity Characteristics,
Specific gravity wbb©q Kivi Rb¨ e¨envi Kiv nq| (ii) Undisturbed Sample : mvavibZ Unconfined
Compressive strength , Settlement Characteristics
Compressibility, Permeability BZ¨vw` wbY©q Kivi Rb¨ e¨envi Kiv nq| wdì n‡Z Avgiv †h SPT collect
Kwi Zvi Øviv Avgiv eyS‡Z cvwi †h Soil
Condition ‡Kgb n‡e|
wb‡æ SPT Value Gi Dci wbf©i K‡i Soil condition wK iKg n‡Z cv‡i Zv Table Gi gva¨‡g †`Iqv nj|
ENGR. MD SHAHIDUZZAMAN (KIRON)
For Clay : [ Table 17.3, P-567, B.M. Das]
SPT ( N) Consistency Unconfined compressive
Strength
KN/m2 lb/ft2
0-------- --------------------- 0 0
Very Soft
2-------- -------------------- 25 500
Soft
4---------- --------------------- 50 1000
Medium soft
8--------- -------------------- 100 2000
Stiff
16-------- ------------------- 200 4000
Very stiff
32-------- ----------------- 400 8000
Hard
>32 >400 >8000
ENGR. MD SHAHIDUZZAMAN (KIRON)
For Clay [ Table 17.2, P-429, Dr. K.R. Arora ]
SPT N
Consistency б qu (KN/m2)
0-2 Very Soft 0 <25
2-4 Soft 0 25-50
4-8 Medium Soft 14 50-100
8-15 Stiff 17 100-200
15-30 Very stiff 22 200-400
30-50 Hard 22 >400
>50 Very hard 22 -----
ENGR. MD SHAHIDUZZAMAN (KIRON)
For Sand [P-429, Table 17.1 Dr. K.R. Arora]
SPT N Consistency Angle of internal
friction (Ф)
0-4 Very loose 6 250 -320
4-10 Loose 10 270 -350
10-30 Medium Loose 17 300 -400
30-50 Dense 19 350 -450
>50 Very dense 19 >450
Correlation between relative density & co-efficient of earth
pressure to know the stress history of the soil deposit-
(M. Tomlinson)
Relative Density K0
Loose 0.5
Medium dense 0.45
Dense 0.35
SPT K
0-10 0.5
30-50 1.0
Foundation Analysis Ges Design Kivi Rb¨ soil Gi physical Ges
Engineering properties Rvbv cÖ‡qvRb|
ENGR. MD SHAHIDUZZAMAN (KIRON)
1. Strength Parameter:
Angle of internal friction Ф
Cohesion, c (Mpa)
Stress-strain relationship
Unconfined Compression strength (Mpa)
(2) Compressibility Index for amount and rate of Settlement
- Natural void ratio, eo
- Compression Index , Cc
(3) Gravimetric Data:
- Natural moisture content (%)
- Specific gravity, G
- Unit weight, γ (gm/cc)
- Liquid Limit (%)
- Plastic limit (%)
mvaviYZ laboratory ‡Z Avgiv wb‡æi Test ¸‡jv Perform
Kwi|
(1) Natural Moisture Content.
(2) Grain Size Analysis
(3) Atterberg Limits.
(4) Direct Shear Test.
(5) Unconfined Compression Test.
(6) Consolidation Test.
(7) Specific Gravity Test.
ENGR. MD SHAHIDUZZAMAN (KIRON)
(1) Moisture content:
Apparatus Name: Metal container with lid (air-tight, non-
corrodible) Temp-1050-1100 C controlled. Desiccators,
Tong (one pair)
GwU mvavibZ mass of water Gi mv‡_ mass of solid Gi GKwU AbycvZ| G‡K % Abymv‡i cÖKvk Kiv nq |
W = Ms
M w
W= 13
32
WW
WW
*100
W1 = wt of two container with lid
W2 = ― ― ― ― + wet soil
w3 = ― ― ― ― + dry soil
High water content liquid satate.
1. No shearing resistance.
2. Can flow like liquids.
3. No resistance to shear deformation.
4. Shear strength=0 (zero)
Low water content Stiffer state
Develop resistance to Shearing resistance.
ENGR. MD SHAHIDUZZAMAN (KIRON)
Typical value of moisture content:
Type of soil Value (%)
Soft organic clay
Soft Clay
Stiff Clay
Loose Uniform Sand
Dense “ “
Loose Angular Grained Silty Sand
Dense “ “ “ “
90-120
30-50
21
30
20
25
15
Grain size Analysis:
Grain size Analysis Kiv nq gyjZ Soil grain Gi size Rvbvi Rb¨ Ges Full Soil profile percent Abymv‡i wK cwigv‡b †Kvb particle Dcw¯‟Z Zv Rvbvi Rb¨ |
Apparatus name:
Table 1.1, P-5 ,R.B. Peck & Hanson:-
Practical size limits of soil constituents
ASTM classification (in mm):-
Gravel >4.75 mm.
Coarse sand 4.75 -2.00 mm
Medium sand 2.00 - 0.425
Fine sand 0.425-0.075 mm
Fines (combined silt & clay) <0.075 mm
ENGR. MD SHAHIDUZZAMAN (KIRON)
P-90, Dr. K.R. Arora, MIT system (in mm)
Gravel >2 mm
Sand 0.060 - 2.0 mm
Silt 0.002 -0.06 mm
Clay <0.002 mm (2μ)
N.B: 0.075 mm Gi †P‡q smaller size grain determine Kiv nq Hydrometer analysis Gi gva¨‡g|
ENGR. MD SHAHIDUZZAMAN (KIRON)
Specific Gravity : Specific Gravity n‡”Q ratio of mass of a
given volume of solids to the mass of equal volume of water.
ENGR. MD SHAHIDUZZAMAN (KIRON)
Apparatus Name: mvavibZ Void ratio ‡ei Kivi Rb¨ GwU use Kiv nq|
G=
)( 43 WWW
WG
d
dk [Eq-3.6, P-23, Alam Singh]
‡hLv‡b Gk= SP. Gravity of water at T0C
Wd= wt of dry soil = w2-w1
W3= wt. of Pyc + soil + water
W4= wt. of Pyc + water
Typical value for G:
[ P-20, Table 2.1, K.R. Arora & P-24, Alam Singh
Table 3.2]
Soil Type Specific Gravity
Gravel 2.65- 2.68
Clean sand 2.67- 2.70
Clay 2.68- 2.80
Silty Grained sands 2.67- 2.70
Inorganic clay 2.70- 2.80
Soil High in mica, iron 2.75- 2.85
Silt 2.66- 2.70
Organic soil Variable may low 0.2
Dry Density :
ENGR. MD SHAHIDUZZAMAN (KIRON)
Mass of solids per unit volume
- - Soil wK iKg dense Ges Compacted Zv eySvi Rb¨ e¨envi Kiv nq| -- Dry Density Gi Value h‡Zv †ekx n‡e ZZ †ekx soil
Compacted n‡e| Apparatus :
Dry Density of a soil [Dr. K. R. Arora, P-24]
(ρd) Soil =WG
G w
1
Here, e = WG: W= s
w
M
M
G = Se
G
e = WG
S S= 1.00
e = WG
(ρd ) Soil = e
G w
1
2.35 [K.R. Arora P-24)
[Table 2.5, P-37, K.R. Arora ]
Type Loosest state Densest State
Gravel 1.6 2.0
Coarse sand
/medium
1.5 1.9
Uniform/fine sand 1.4 1.9
ENGR. MD SHAHIDUZZAMAN (KIRON)
Coarse silt 1.3 1.8
Fine silt 1.3 1.9
Lean clay 1.3 1.9
Fat clay 1.0 2.0
Atterberg Limits :
Soil Gi Physical properties Gi Water content Gi Dci wbf©i K‡i| GKUv Soil Sample wK fluid n‡e bvwK soil n‡e bvwK Plastic materials n‡e Zv depend K‡i Zv KZUzKz water absorb Ki‡e Zvi Dci| [Dr. K.R. Arora, P-69,70]
Liquid Limit :
‡mB cwigvb water content hv‡Z K‡i GKUv soil sample
liquid state
‡_‡K plastic state G i“cvš—wiZ nq| [LL, Wl]
Plastic Limit :
‡mB cwigvb water content hv‡Z K‡i GKUv soil sample
plastic state ‡_‡K Semi Solid state G i“cvš—wiZ nq| (PL,WP] ZLb G‡K mould crack K‡i|
Shrinkage Limit :
‡mB cwigvb water content hv‡Z K‡i GKUv soil sample Gi Shrinking nIqv eÜ nq Ges GKUv constant volume AR©b K‡i|
ENGR. MD SHAHIDUZZAMAN (KIRON)
Plasticity Index:
liquid limit Ges plastic limit Gi gv‡S soil plastic B _v‡K G‡K Plasticity index e‡j| PI = LL-PL= Wl-Wp
----- Shear strength at plastic limit is 100 times that at liquid
limit.
--- mvavibZ Plasticity index fine grained soil classify Kivi †¶‡Î cÖ‡qvRb nq|
Liquidity index Il = 100
p
p
I
WW
Consistency Index Ic = 100
p
l
I
WW
Soil Gi PI Dci wfwË K‡i soil †K classify Kiv hvq |
Table 3.4, P-67, B.M Das] By Bur mister 1949
PI Description
0 Non Plastic
1-5 Slightly plastic
5-10 Low plasticity
10-20 Medium plasticity
20-40 High plasticity
>40 Very high plasticity
ENGR. MD SHAHIDUZZAMAN (KIRON)
SL PL LL
[Fig 4.1, P-70, K.R. Arora
[Page- 23, Peck & Hanson Fig 1.11]
Diagram of the soil moisture scale showing atterberg limits
corresponding physical state & approximate consistency of
remolded soils
Soil moisture scale Physical state consistency
WL liquid limit liquid very soft
Plastic range -------- Soft
Wp Plastic limit Semi Solid Stiff
--------------- Very stiff
Ws Shrinkage limit
Air dry solid extremely stiff
Hygroscopic moisture Hard
Oven dry
--------------- Very Hard
Volm
Water content
Solid Semi Solid
Plastic Liquid
ENGR. MD SHAHIDUZZAMAN (KIRON)
-- If water content close to liquid limit soil is normally
consolidated.
-- If water content is close to plastic limit soil is some to
heavily over consolidated.
-- If water content is intermediate soil is some what over
consolidated.
-- If water content is greater than liquid limit soil is on verge
of being a viscous liquid.
[K.R.Arora, P-81]
Sensitivity:- A cohesive soil is its natural state of occurrence
has a certain structure when the structure is disturbed, the
soil becomes remolded & its engineering properties change
considerably. Sensitivity of a soil indicates its weakening
due to remolding. It is defined as the ratio of the undisturbed
strength to the remolded strength at the same water content.
St = ru
uu
q
q
)(
)(
(qu)u = Unconfined Compressive strength of undisturbed clay
(qu)r = unconfined Compressive strength of remolded clay
Sensitivity Soil Type
< 1.00 Insensitive
ENGR. MD SHAHIDUZZAMAN (KIRON)
1.0-2.0 Little sensitive
2.0-4.0 Moderately sensitive
4.0-8.0 Sensitive
8.0-16.0 Extra Sensitive
<16.0 Quick
Uniformity Co- efficient :
The uniformity of a soil is expressed qualitatively by a term
known as uniformity Co- efficient (Cu).
Cu= 10
60
D
D
D 60 = particle size such tent 60% of the soil is finer than
this size.
D10 = Particle such that 10% of the soil is finer than this
size.
---The larger the Cu the more is the range of particles.
For soils Cu ≤ 2 are uniform soil
For sandy Cu ≥ 6 ― Well Graded
For Gravels Cu ≥ 4 ― More well graded
Tests Perform by Disturbed Sample :
1. Water Content
ENGR. MD SHAHIDUZZAMAN (KIRON)
2. Specific Gravity
3. Dry Density
4. Liquid limit / plastic limit / Plasticity index
5. Direct shear test
6. Grain size Analysis
Test Perform by undisturbed sample
1. Unconfined Compression Test
2. Consolidation Test
mvaviYZ wZb ai‡bi Stage G shear Test Kiv nq| [Drainage system Gi Dci Depend K‡i|
(i) Unconsolidated- undrained condition – Quick test
(ii) Consolidated undrained condition – slow test
(iii) Consolidated – drained condition – slow test
Direct Share Test mvavibZ cohesion less soil Gi Dci Kiv nq| G‡K CD test I e‡j| GB Test mvavibZ Shear Strength Parameter Gi †¶‡Î fvj result ‡`q| Direct Shear Test mvavibZ `y‡Uv ¸i“Z¡cyY© shear strength
parameter Gi gvb wbY©q K‡i|
1. Interparticle attraction or cohesion , C
ENGR. MD SHAHIDUZZAMAN (KIRON)
2. Resistance to interparticle slip or angle of internal
friction Ф
Apparatus Name
Shear Strength Gi Dci wfwË K‡i Soil ‡K wZb fv‡M fvM Kiv nq|
(i) Cohesion Less soil : sand, Gravel Where
C=0
(ii) Purely cohesive soil : Saturated clays &
silts under undrained condition Ф =0
(iii) Cohesive fractioned soil : Clayey
sand, silty sand, sandy clay etc. where
soil having both c & Ф values – also
called cohesive soil
Standard value of Angle of internal friction
(Sands & Silts)
[Table 4.1, P-87, Peck & Hanson)
Type Loose Dense
Sand, round grains , uniform 27.50 340
Sand, angular grains, well
graded
330 450
Sandy gravel 350 500
Silty Sand 270-330 300-350
Inorganic Silt 270-300 300-340
Standard Value of cohesion (for clay)
(Table 13.3, P-346, Dr. K.R. Arora)
ENGR. MD SHAHIDUZZAMAN (KIRON)
SPT Type Cohesion (Mpa)
0-2 Very Soft <0-012
2-4 Soft 0.012-0.025
4-8 Medium soft 0.025- 0.05
8-15 Stiff 0. 05-0.1
15-30 Very Stiff 0.1-0.2
30-50 Hard >0.2
>50 Very Hard -----
Cohesion less Soil Ges Cohesive soil Gi Dci Direct shear
test Gi result GKUv summery table Ges stress- strain curve
Gi gva¨‡g cÖKvk Kiv hvq| A stress – strain curve normally consists of shear stress,
various shear displacements for both the undisturbed & the
remolded tests under a specified normal load. The normal
load usually varies from 2/3
1 cmkg .
Another curve normal stress VS shearing stress will give
Angle of internal friction & cohesion for cohesive soil.
ENGR. MD SHAHIDUZZAMAN (KIRON)
[Fig: 13.8, P_316, Dr. K.R. Arora]
Fig: Stress- strain curve
Unconfined compressive strength test :
GwU Ggb GKwU Special form of triaxial test ‡hLv‡b soil
confining pressure ‡K Zero aiv nq Ges GB test ïaygvÎ undisturbed clayey soil ‡¶‡Î cÖ‡hvR¨ †hLv‡b confinement
Gi cÖ‡qvRb nq bv| GB test ‡_‡K Avgiv
Stress- strain relationship cvB unconfined compressive strength qu cvB hv soil Gi
bearing capacity wbY©‡q cÖ‡hvRb nq| Avevi GLv‡b unsupported specimen & failure measure
Kiv nq| (undisturbed soil sample )
7.5 cm height & 3.5 cm dia sample box
load applied axially
ENGR. MD SHAHIDUZZAMAN (KIRON)
Cohesion intercept:
S= Cu = 2
1 = 2
uq [13.25, P-331, K.R. Arora]
Standard value of unconfined compressive strength
---------------------For Clay ------------------------------
[Page-20, Table 1.3, R.B peck & Hanson]
N Condition Unconfined Compressive Strength
TSF KN/m2
0-2 Very soft <0.25 < 25
2-4 Soft 0.25-0.5 25-50
4-8 Medium soft 0.5-1.00 50-100
8-15 Stiff 1.00-2.00 100-200
15-30 Very stiff 2.00-4.00 200-400
30-50 Hard 4.00-above >400
>50 Very Hard -----------
In the above table the shear strength of cohesive soil is equal
to 1/2 of unconfined compressive strength & the angle of
internal shearing resistance is equal to zero.
It should be remembered that the co-relation for cohesive soil
is always much reliable.
Liquefaction :
ENGR. MD SHAHIDUZZAMAN (KIRON)
Avgiv Rvwb †h, Soil Gi Shear Strength
S= σtan Ф [ 13.53, P-343, K.R. Arora]
hLb sand ground water table Ges ground Gi wb‡P _v‡K ZLb
= zzz wsat
tanzS
Avevi hLb sand deposit earth quake Gi Kvi‡b A_ev Ab¨ †Kvb load RwbZ Kvi‡b Kw¤úZ nq ZLb Gi g‡a¨ extra pore
water pressure develop K‡i|
ZLb )tan)( uzS
hu w
tan)( hzS w
hw` pore water pressure Gi cwigvb †e‡o hvq Z‡e shear
strength K‡g hvq| GKmgq Ggb Ae¯‟vq †cŠ‡Q hLb e¯„Z soil G †Kvb shear strength _v‡K bv|
ZLb 0 hz w
w
w
w
cre
Gizh
1
1
)1(/
e
Gicr
1
1
0tan0 S
ENGR. MD SHAHIDUZZAMAN (KIRON)
‡h Ae¯‟vi Kvi‡b sand Zvi shear strength lose K‡i due to
oscillatory motion Zv‡K liquefaction of sand ejv nq|
ENGR. MD SHAHIDUZZAMAN (KIRON)
The structure resting on such soils sink. In the case of partial
liquefaction the structure may undergo excessive settlement &
the complete failure may not occur.
The soils most susceptible to liquefaction are the saturated , fine
& medium sands of uniform particle size- when such deposits
have a void ratio greater than the critical void ratio & are
subjected to a sudden shearing stresses, these decrease in volm
&
the pore pressure u increases, the soil momentarily liquefies &
behave as a dense fluid
Extreme care shall be taken when construction structures on such
soils. If the deposits are compacted to a void ratio smaller than
critical void ratio , the chances of liquefaction are reduced.
[P-343,344, K.R. arora/P-89 T William lambe ]
ENGR. MD SHAHIDUZZAMAN (KIRON)
ENGR. MD SHAHIDUZZAMAN (KIRON)
ENGR. MD SHAHIDUZZAMAN (KIRON)
ENGR. MD SHAHIDUZZAMAN (KIRON)
ENGR. MD SHAHIDUZZAMAN (KIRON)
Cohesion less soil Gi †¶‡Î Shear Characteristics :
The shear strength of cohesion less soils such as sands &
non- plastic silts is mainly due to friction betn particles. In
dense sand interlocking between particles, also contributes
significantly to the strength.
`y ai‡bi shear failure ‡`Lv †`q|
((i) Plastic failure – loose sand Gi †¶‡Î (ii) Brittle failure – dense sand ‘ ‘ ‘ ‘
[P-344, Dr. K.R.Arora]
Consolidations of Soil:
mvavibZ soil G compression N‡U wZbwU Kvi‡b (i) Compression of solid particles & water in the
voids.
(ii) Compression & expulsion of air in the voids.
(iii) Expulsion of water in the voids.
The compression of a saturated soil under a steady
static pressure is known as consolidation. GUv nq mvavibZ expulsion of water from the void Gi Kvi‡b | Settlement n‡”Q gradual sinking of a
structure due to compression of the soil below. A study of consolidation characteristics is
extremely useful for forecasting the magnitude &
time of the settlement of the structure. [P-256, K.R. Arora]
ENGR. MD SHAHIDUZZAMAN (KIRON)
The property of soil due to which a decrease in volm
occurs under compressive force in known as the
compressibility of soils. This compression of a
saturated soil under steady static pressure is known
as consolidation. mvavibZ consolidation test Kiv nh consolidometer
or an odometer gva¨‡g| Consolidation test ïaygvÎ undisturbed soil sample G Kiv nq|
Compressibility index parameter n‡”Q-
1. Natural void ratio C0
2. Compression index Cc
Cc =
0
010
)(log
e
Cc= e1
e
Cc Settlement wbY©q Kivi Rb¨ e¨eüZ nq| Cc = 0.009 (Wl-10) for undisturbed soil
Cc = 0.007 (Wl-10) for remolded soil
Cc Varies between 0.3 for highly plastic clay & 0.075 for
low plastic clay
Cc=0.54 (e0-0.35)
Cc= 0.0054 (2.6w0-35)
[P-266, Dr. K.R. Arora]
ENGR. MD SHAHIDUZZAMAN (KIRON)
Standard Values of consolidation test
Natural void ratios e0 80% -- 98.8%
Compression index, Cc (Mpa) 0.15--- 0.20
Consolidation settlement for normally consolidated soils.
S= )log(1 0
0
0
Ho
e
cc
Sf = )(log1 0
010
0
Ho
e
cc (eq-12.58, P-283, Dr. K.R. Arora)
‡mLv‡b Ho= Initial height, ΔH = Change is height
For Pre-consolidated soils : The final settlements are small
in the case of pre- consolidated soils as the recompression
index Cr is considerably smaller than the compression index
0
0log(
eCr
Sf = )log(1 0
0
0
Ho
e
cr
The above eqn is applicable when ( 0 ) is smaller than the
Pre-consolidation pressure c . If the pre-consolidation
pressure c is greater than 0 but less than ( 0 ) the
Settlement is computed in two parts
(i) settlement for pressure 0 to c
(ii) ― ― ― ― c to ( 0 )
ENGR. MD SHAHIDUZZAMAN (KIRON)
For (i) the recompression index is applicable & (ii) the
compression index is applicable
Sf = )log(1
log(1 0
0
000
e
HoCHo
e
C ccr
1st part is relatively small & is some times neglected.
[ P-282, 283, K.R. Arora]
Settlement of Foundation:
(a) Settlements under loads :
(i) Immediate or elastic settlement (si):
Immediate or elastic settlement takes place during or
immediately after the construction of the structure. It is also
known as the distortion settlement as it is due to distorting
within the foundation soil. Although the settlement is not
truly elastic, it is computed using elastic theory especially
for cohesive soils.
(ii) Consolidation settlement (Sc) :
This component of the settlement occurs due to gradual
expulsion of water from the voids of the soil. this
component is determined using Terzaghi’s theory of
consolidation.
(iii) Secondary Consolidation settlement (Ss) :
This component of the settlement is due to secondary
consolidation. This settlement occurs after completion of
ENGR. MD SHAHIDUZZAMAN (KIRON)
the primary consolidation. It can be determined from the co-
efficient of secondary consolidation. The secondary
consolidation is not significant for inorganic clays & silty
soils.
Total Settlement S= Si+Sc+Ss
(b) Settlement due to other causes :
(i) Underground condition
(ii) Structural collapse of soil
(iii) Thermal changes
(iv) Frost heave
(v) Vibration & shocks
(vi) Mining subsidence
(vii) Load slides
(viii) Creep
(ix) Changes in the vicinity
[P-613, Dr. K.R. Arora]
[mvaviYZ Settlement- 25mm- 40 mm ch©š— very K‡i individual footing ]
Permissible Total and differential settlements for shallow
foundation in soils
(From soil testing for Engineers by S. Mittal & J.P. Shukla)
ENGR. MD SHAHIDUZZAMAN (KIRON)
SL
N
Types of
Structure Isolated foundations Raft foundations
Sand & hard clay Plastic clay Sand & hard clay Plastic clay Maxm
Settlement
(mm)
Differential
Settlement
(mm) Maxm
Settlement
(mm)
Differential
Settlement
(mm) Maxm
Settlement
(mm)
Differential
Settlement
(mm) Maxm
Settlement
(mm)
Differential
Settlement
(mm) 1 For Steel
Structure 50 0.0033L 50 .0333L 75 .0033L 100 .0033L
2 For Reinforced
concrete structure
50 .0015L 75 .0015L 75 .0021L 100 .002L
3 For multi storied
building
a) RC or steel framed building
with panel walls
b) for load
bearing walls
60
.002L
75
.002L
75
.0025L
125
.0033L
1. L/H=2 60 .0002L 60 .0002L
2.L/H=7 60 .0004L 60 .0004L
4 For water towers
& silos
50 .0015L 75 .0015L 100 .0025L 125 .0025L
L= Length of deflected part of wall/raft or c/c distance between
columns .
H= Height of wall from foundation footing.
FOUNDATION DESIGN
Bearing Capacity
Values from Soil Test
]
Values from laboratory Soil Test Values from Field Soil Test
ENGR. MD SHAHIDUZZAMAN (KIRON)
Note: So, ensure the laboratory test result from authentic company.
Enquiry please.
PILE DESIGN
Skin Friction End Bearing Capacity
Angle of internal friction
&
Cohesion (Mpa)
Dry Density
Unconfined Compression
Strength
SPT Value
Direct Shear Test Standard
Penetration Test
Unconfined
Compression Test Density Test
K and δ value
SPT from STANDARD PENETRATION TEST
ENGR. MD SHAHIDUZZAMAN (KIRON)
δ = Friction between sand & pile.
K =Earth pressure coefficient
Bearing Capacity :
A foundation is required for distributing the loads of the
super structure on a large area. The foundation should be
designed such that
(i) The soil below does not fail in shear &
(ii) The settlement is within the safe limits.
The pressure which the soil can safely with stand is known
as the allowable bearing pressure.
ENGR. MD SHAHIDUZZAMAN (KIRON)
ENGR. MD SHAHIDUZZAMAN (KIRON)
Foundations may be broadly two categories-
(i) Shallow foundation : Transmits the loads to the
strata at a shallow depth.
(ii) Deep foundation : Transmits the loads at
considerable depth below the ground surface.
Ultimate bearing capacity (qu) : The ultimate bearing
capacity is the gross pressure at the base of the foundation at
which the soil fails in shear.
Net ultimate bearing capacity (qnu) : it is the net increase in
pressure at the base of foundation that causes shear failure of
the soil.
qnu = qu- Df
γ = unit wt. of soil, Df = Depth of foundation.
ENGR. MD SHAHIDUZZAMAN (KIRON)
Net Safe Bearing Capacity (qns): It is the net soil pressure
which can be safely applied to the soil considering only shear
failure
qns = F
qnu F= F.S = 3.0
Gross safe bearing capacity (qs): It is the max m gross
pressure which the soil can carry safely without shear failure
qs = Dff
qnu
Net safe settlement pressure (qnp) : It is the net pressure
which the soil can carry without exceeding the allowable
settlement. The maxm allowable settlement generally varies
betn 25 mm -- 40 mm for individual footings.
Net Allowable Bearing Pressure ( qna) : The net allowable
bearing pressure is the net bearing pressure which can be
used for the design of foundations.
qna=qns if qnp > qns
qna= qnp if qns > qnp
Evaluation of Bearing Capacity :
By standard penetration Test : ( N. Tang) :
ENGR. MD SHAHIDUZZAMAN (KIRON)
For Strip footing :
Bearing capacity
qnu = 0.5 n2 B Wγ + 0.83 (100+N2) Df Wq [ F.S=3.0]
= 0.167 N2 BWγ + 0.227 (100+N2) DfWq
For Circular or Square footing:
Bearing capacity
qnu = 0.33N2BWγ + 1.0 (100+N2)DfWq
= 0.11 N2 BWγ + 0.33 (100+N2)DfWq
Where N. = SPT Value, B = Width of footing
Df = Depth of footing if Df> B use Df = B
Wq & Wγ the water table correction factor
[P-610,611, Dr. K.R. Arora)]
Wq= 1-0.5 a/Df ≤1
Wγ = 0.5 + 0.5 b/B ≤1
a= If position of the footing is under the water table.
b= If position of the footing is above the footing.
[P-600, 601. Dr. K. R. Arora]
By using direct shear test:
[ Terzaghi bearing capacity formula]
For cohesive soil:
Strip footing, circular or square footing
0 , Bearing capacity = CNcq + fD [ F.S=3]
ENGR. MD SHAHIDUZZAMAN (KIRON)
Ncq depend on Df/B ratio of the footing & on the adhesion
off the sides of the footing [By Meyerhof’s]
[ P- 603, Dr. K.R. Arora]
For Non- Cohesive soil: C=0
qu = 0.5 rqBN
‡hLv‡b Ncq Gi Maximum value = 8.30 Ges Adhesion =0
Avevi , Ncq Gi maxm value = 8.8 ZLb adhesion = cohesion
of the soil.
From unconfined compression Test :
For cohesive soils:
Qult = CNc= 2
cu NQ
qall = DfNcq
DNQ u
fcu
322
qall = fcu D
Nq
6 [ F.S=3.00]
qu= unconfined compressive strength in Tsf
Nc= Bearing capacity factor
= 6.8 for square footing
= 5.7 for continuous footing
For non-cohesive soil:
Qult = CNc Sc+ γDfNq + 0.5 γBNγSγ [ J.E Bowles]
ENGR. MD SHAHIDUZZAMAN (KIRON)
C= cohesion , γ= unit wt of soil
Df = Depth of footing , B= width of footing
Nc, Nq &Nγ = Bearing capacity factor
Sc & Sγ= Shape factors
Qallowable = SF
qult
. [ F.S = 3.0]
[J.E Bowles P-213- 277]
By Terzaghi Bearing capacity theory :
qu= c´Nc+γDfNq+05γBNγ 23.25 (a)
[Dr. K.R. Arora P-594]
For square footing :
qu = 1.2.c´Nc + γDfNq+0.4γBNγ— 23.37
For circular footing
qu =1.2 c´Nc+γDfNq + 0.3γBNγ— 23.38
[P-601, Dr. K.R. Arora]
Effect of water table on Bearing capacity :
Case 1 : Water table located above the base of footing :
if Dw = 0 [i.e. a = Df]
qu = c´Nc +γ´DfNq+ 0.5 γ´BNγ - 23.33 (a)
If a =0 , Df = Dw
qu= c´Nc+γDf Nq+ 0.5γ´BNγ - 23.33 (b)
γ´= γsat – γw = v
wsub [P-601, K.R Arora]
Case 2: Water table located at a depth b below base
When: b=o i . e w/T at the base
ENGR. MD SHAHIDUZZAMAN (KIRON)
qu= c´Nc+γDfNq+ 0.5 Bγ´ Nγ - 23.35 (b)
When b = B i.e. W/T at depth B below base
qu = c´Nc +γDfNq+ 0.5 BγNγ – [23 . 25]
[Page - 601, 602, Dr. K.R. Arora]
Shape Factors By Hansen’s
[Table 23.3, P-604, K.R. Arora]
Shape of footing Sc Sq Sγ
Continuous footing
(strip)
1.0 1.0 1.0
Rectangular footing 1+0.2B/L 1+0.2B/L 1-0.4B/L
Square footing 1.3 1.2 0.8
Circular footing 1.3 1.2 0.6
mvaviYZ wZb ai‡bi shear failure N‡U _v‡K hv Vesic .
(1973) mv‡j classify K‡ib|
(i) General shear failure: A strip footing resting on
the surface of a dense sand or a stiff clay. A shear
failure occur and failure surfaces extend to the
ground surface.
A heave on the sides always observed in general
shear failure.
ENGR. MD SHAHIDUZZAMAN (KIRON)
(a) General shear failure
(ii) Local shear failure : A strip footing resting on a
medium dense sand or on a clay of medium
consistency. Failure surfaces gradually extend
outwards from the foundations.
A heave is observed only when there is substantial
vertical settlement.
ENGR. MD SHAHIDUZZAMAN (KIRON)
Local shear Failure
(iii) Punching shear failure : A strip footing resting on
a loose sand or a soft clay. The failure surfaces do
not extend up to the ground surface.
--- No heave is observed. There is only vertical movement of
footing.
© Punching shear failure
[P-595-597, Dr. K.R. Arora]
A failure will be general or local shear conditions will be
known from these values below ---
(i) For a cohesion less soil
If Ф´ > 360 – General shear failure
Ф <290 – Local ― ― ―
29<Ф´<360- interpolation
(ii) If relative density
ENGR. MD SHAHIDUZZAMAN (KIRON)
Df>70% - General shear failure
Df <35% - Local shear failure
(iii) If SPT >30 – General shear failure
If SPT <5- Local shear failure
(iv) If void ratio e <0.55-General shear failure
e>0.75—local shear failure
[Table 23.1, P-595 Dr. K.R. Arora]
Terzaghi’s bearing capacity factors
Ф´ General shear failure Local shear failure N´q(vesic)
Nc Nq Nγ Nc Nq Nγ
0 5.7 1.0 0.0 5.7 1.0 0.0 1.0
5 7.3 1.6 0.5 6.7 1.4 0.2 1.2
10 9.6 2.7 1.2 8.0 1.9 0.5 1.6
15 12.9 4.4 2.5 9.7 2.7 0.9 2.2
20 17.7 7.4 5.0 11.8 3.9 1.7 3.3
25 25.1 12.7 9.7 14.8 5.6 3.2 5.3
30 37.2 22.5 19.7 19.0 8.3 5.7 9.5
35 57.8 41.4 42.4 25.2 12.6 10.1 18.7
40 95.7 81.3 100.4 34.9 20.5 18.8 42.5
45 172.3 173.3 297.5 51.2 35.1 37.7 115.0
50 347.5 415.1 1153.2 81.3 65.6 87.1 329.10
ENGR. MD SHAHIDUZZAMAN (KIRON)
Bearing capacity of the shallow foundation
[ Values in TSf , F.S=3.0]
SPT Range Allowable bearing capacity (Tsf )
Continuous footing
B=4’
Isolated colm
footing (B=8’)
0-2 0.00-0.225 0.00-0.30
2-4 0.225-0.45 0.30-0.60
4-8 0.45-0.90 0.60-1.20
8-15 0.90-1.80 1.20-2.40
15-30 1.80-3.60 2.40-4.80
>30 >3.60 >4.80
Note : a. width = 4’ for strip footing
Width=8’ for isolated footing
b. The above values are the net allowable leaving capacity
c. The cohesive soil has been considered in a saturated
condition.
ENGR. MD SHAHIDUZZAMAN (KIRON)
[Table 23.9, P – 618, Dr. K.R. Arora]
Maxm Differential settlement (IS: 1904-1978)
Sand & Hard clay Plastic clay
Max
settlement
Diff-
settlement
Angular
distortion
Max
settlement
Diff-
settlement
Angular
distortion
Isolated
foundation
(i) Steel
structure
50mm
0.0033L
1/300
50mm
0.0033L
1/300
ii) RCC
str
50mm 0.015L 1/666 75mm 0.0015L 1/666
iii) Raft 75mm 0.0033L 1/300 100mm 0.0033L 1/300
v) RCC 75mm 0.002L 1/500 100mm 0.002L 1/500
Ultimate Skin Friction (fs) & End bearing (fb)
For cohesive soil
fs= F*Cd F= 1.0 = Unity
fs= Cd = 2
uq
qu= 2*fs
qu = unconfined compressive strength of soil.
F= Bearing capacity factor [0.6- 45]
ENGR. MD SHAHIDUZZAMAN (KIRON)
For Non – cohesive soils:
For light displacement piles , fs =2.0 N KN/m2
(Timber, precast,pre-stress concrete, steel tube, Rotary etc.
For low displacement piles , fs= 1.0N kN/m2
[Precast concrete, pre-stressed , steel H- section, steel tube)
Where N is the avg. of corrected value of Nf
Along the length of the pile.
In very fine & silty sands below the WT
Ncor= 15+0.5 (Nf-15) –- [5.28, M.J Tomlinson-P-265]
When the material is gravel or sandy gravel by Burland &
Burlidge
Ncor= 1.25N-- [5.29, P-265, M.J. Tomlinsion]
For bored piles in sand 9
fb = 14N(Db/3) KN/m2
= 0.053N
Where Db= Actual penetration into the granular soil.
For bored piles in sand, the unit frictional resistance fb is
given by----
fb= 0.67 N KN/m2 [ Dr. K.R. Arora]
ENGR. MD SHAHIDUZZAMAN (KIRON)
ENGR. MD SHAHIDUZZAMAN (KIRON)
(Table 2.7 Page 39 M.J Tomlinsion)
Nominal working loads & dimensions for ordinary soils
Internal dia
(mm)
Area of
concrete
Working load
(KN) for
ordinary soils
Working load
for rock
254 50670 150 200
305 72960 300 350-450
356 99300 400 500-650
406 129700 500 600-850
457 164100 650 800-1000
508 202700 800 1000-1300
559 245200 1000 1250
610 291800 1200 1500
ENGR. MD SHAHIDUZZAMAN (KIRON)
Ordinary soil – sand , gravel or very stiff clay roce – row,
very dense sand or gravel or very hard mari or hard
shale
Individual pile capacity:
Pu= αC * (Perimeter ) *L + Point bearing.
Point bearing = 9*c* Area of pile [P-1011, J.E Bowles]
& From Fig 16-14 using API curve (soil to soil )
[P-899] [J.E Bowles ]
Example
Given, C= Su= qu/2 = 30 kpa
D= 400 mm, L=20m.
From fig 16-14, α = 0.6.
Pu = 0.6 *30 *π*0.4*20+9*30*π*4
4.0 2
Pu=452.16+33.91
pu=486.072 KN/Pile
For group capacity.
Qult=9*c*Ab+ Block shear.
Block shear =α*Su*perimeter*length,
Block Area =L*B=14,21m2
L=4.1+2*(0.2+025)=4.9
B=2*1+2*(0.2+0.25)=2.9
Perimeter =2(4.9+2.9)=15.6m
ENGR. MD SHAHIDUZZAMAN (KIRON)
Here Qult=9*30*14.21+0.6*30*15.6*20
=3807+5616=942 KN
But Qult=15*486.0 KN/Pile=7290 KN
Whichever is smaller value will be taken for safe.
Table No: 9-1
Range of Modulus of Subgrade Reaction k
(Page-565, J.E. Bowles)
SOIL
k, kN/m3
Loose sand 4800-16000
Medium Dense Sand 9600-80000
Dense Sand 64000-128000
Clayey Medium dense sand 32000-80000
Silty medium dense sand 24000-48000
Clayey Soil
qa 200 kpa
200<qa 800 kpa
qa > 800 kpa
12000-24000
24000-48000
> 48000
ENGR. MD SHAHIDUZZAMAN (KIRON)
ENGR. MD SHAHIDUZZAMAN (KIRON)