Download pdf - Soil Handbook by engr. kiron

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


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|


[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¨ eëüZ 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


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¨ eënvi Kiv nq| (ii) Undisturbed Sample : mvavibZ Unconfined

Compressive strength , Settlement Characteristics

Compressibility, Permeability BZ¨vw` wbY©q Kivi Rb¨ eënvi 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 †Ìqv nj|


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


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 -----


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|


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.


(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.


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


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|


Specific Gravity : Specific Gravity n‡”Q ratio of mass of a

given volume of solids to the mass of equal volume of water.


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 :


Mass of solids per unit volume

- - Soil wK iKg dense Ges Compacted Zv eySvi Rb¨ eënvi 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


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|


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


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


-- 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


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


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


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)


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.


[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


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 :


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


‡h Ae¯‟vi Kvi‡b sand Zvi shear strength lose K‡i due to

oscillatory motion Zv‡K liquefaction of sand ejv nq|


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 ]






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]


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¨ eëüZ 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]


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 )


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


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


[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)


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


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


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.



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.


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) :


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]


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]


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= cŃc+γDfNq+05γBNγ 23.25 (a)

[Dr. K.R. Arora P-594]

For square footing :

qu = 1.2.cŃc + γDfNq+0.4γBNγ— 23.37

For circular footing

qu =1.2 cŃc+γDfNq + 0.3γBNγ— 23.38


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 = cŃc +γ´DfNq+ 0.5 γ´BNγ - 23.33 (a)

If a =0 , Df = Dw

qu= cŃc+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


qu= cŃc+γDfNq+ 0.5 Bγ´ Nγ - 23.35 (b)

When b = B i.e. W/T at depth B below base

qu = cŃc +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.


(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.


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


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


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.


[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]


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]



(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


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


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

