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8/1/2019 Soil Parameters & Applied Foundation
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E2-E3: CIVIL
CHAPTER-3
SOIL PARAMETERS & APPLIED
FOUNDATION DESIGN
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Soil Parameters & Applied Foundation Design
1.0 Introduction
Geotechnical Engineering is a relatively modern branch of civilengineering. As a discipline, it is academically as exciting as
practically challenging Geotechnical engineering is actually the new
name of a subject known earlier as Soil Mechanics and Foundation
Engineering. Of this, foundation engineering, at least as an art, is as
ancient as civil engineering whereas the roots of Soil Mechanics, which
forms its scientific base, can be traced on ly from 1773 with Coulombs
law for shear strength of soil given in that year. Subsequent
contributions were few upto the year 1925, which was the birth of
modern Soil Mechanics with the publication of Terzaghis celebrated
book Erdbaumechanik . Professor Karl von Terzaghi, who is rightly,
regarded as the father of modern Soil Mechanics.
Before designing a foundation for a structure it is essential to know the
behavior of soils under loads. For study of behavior of soils in depth
knowledge of soil mechanics is required. It is essential to associate thestructural engineer in drawing up the soil investigation programme and
interpretation of the report. He must visit the site to facilitate proper
scrutiny of the soil investigation report by comparing the results and
the recommendation with the information available from similar sitesand constructed projects.
2.0 Field Identification Of Soils
Soil grains consist of inert rock minerals (cobble, gravel, sand, silt),
often combined with significant amounts of clay (say, more than 5
percent). While inert silt grains may be angular or rounded (thus
contributing to greater or less angle of internal friction, ), particles
of clay are small platelets with negative charges on both faces which
attract the positively charged ends of water molecules. This bond isresponsible for the cohesion ends of water molecules. This bond is
responsible for the cohesion C of clay. Silt or sand with appreciable
amounts of clay (say, more than 15 percent) behaves like clayey soil
since the permeability of clay is of the order of 10 -7 centimeters/second
compared to 10cms/ second for sand. This capacity of the clay to hold
the water molecules for long even when pressure is applied on the soil,
greatly influences its behavior i.e. shears strength, compressibility and
permeability.
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2.1 Simple and Quick Methods of Field Identification of Soils:
(i) Fine sand is differentiated from silt by placing a spoonful of soil in a glass jar
or test tube, mixing with water and shaking it to a suspension. Sand settles
first, followed by silt which may take about five minutes. This test may also be
used for clay which takes more than 10 minutes to start settling. Thepercentages of clay, silt and sand are assessed by observing the depths of the
sediments.
(ii) Silt is differentiated from clay as follows: -
(a) Clay lumps are more difficult to crush with fingers thansilt. When moistened, the soil lump surface texture is felt
with the finger. If it is smooth, it is clay; if rough, it is
silt .
(b) A ball of the soil is formed and shaken horizontally on thepalm of the hand. If the material becomes shin y from water
coming to the surface, it is silt.
(c) If soil containing appreciable percent clay is cut with aknife, the cut surface appears lustrous. In case of silt, the
surface appears dull.
(iii) Field: indication for the consistency of cohesive soils are as
follows:-
Stiff : Cannot be moulded with in the figure
Medium: Can be moulded by the fingers on strong pressure.Readily indented with thumb nail.
Soft : Easily moulded with the fingers.
(iv) Color of the soil indicates its origin and the condition under
which it was deposited.
Sand and gravel deposits may contain lenses of silt, clay or even
organic deposits. If so, the presumptive bearing capacity is
reduced.
Based on the field identification of the soil, the presumptive
bearing capacity of the soil can be guessed by referring to table
2 of IS 1904 1986. The objectives of preliminary soil
investigation are to drawn up an appropriate program for detailed
soil investigation and to examine the sketch plans and
preliminary drawings prepared by the Architect from the point of
suitability of the proposed structure.
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TABLE 1 : SAFE BEARING CAPACITY
S.
No. TYPE OF ROCKS/ SOILS
SAFE
BEARINGCAPACITY
REMARKS
(1) (2) (3) (4)
a) Rocks kN/m2
1 . Rocks (hard) without lamination defects,for example, granite , t rap and diori te
3 240 -
2 . Laminated rocks, for example, stone andlimestone in sound condit ion
1 620 -
3 . Residual deposits of shattered and brokenbed rock and hard shale , cementedmaterial
880 -
4 . Soft rock 440 -b) Non-cohesive soils
5. Gravel, sand and gravel , compact andoffering high resistance to penetrationwhen excavated by tools
440 (See Note 2)
6 . Coarse sand, compact and dry 440 Dry means that theground water level is a ta depth not less than thewidth of foundationbelow the base of thefoundation
7. Medium sand, compact and dry 245 -8 . Fine sand, si te(dry lumps easily pulverized
by the fingers)150 -
9 . Loose gravel or sand gravel mixtures,loose coarse to medium sand, dry
245 (See Note 2)
10. Fine sand, loose and dry 100 -c) Cohesive soils
11. So ft sha le, or st iff cla y in dee p bed , dr y 440 This group is susceptible tolong term consolidation
settlement
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12. Medium clay, readily indented with athumb nail
245 -
13. Moist c lay and sand-clay mixture whichcan be indented with strong thumbpressure
150 -
14. Soft c lay indented with moderate thumbpressure
100-
15. Very soft c lay which can be penetratedseveral centimeters with the thumb
50-
NOTE : Values are very much rough for the following reasons:a) Effect of characteristics of foundations (that is, effect of depth,
width, shape, roughness, etc) has not been considered.b) Effect of range of soil properties (that is, angle of frictional
resistance, cohesion, water table, density, etc) has not beenconsidered.
c) Effect of eccentricity and indication of loads has not beenconsidered.
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3.0 Soil Mechanics Basic Concepts
3.1 Soil Mass Represented By 3-Phase System: -Soil solids, water and air are constituents of soil mass are representeddiagrammatically as three phase system shown below.
Vs =Volume of soil solids. Ws =Weight of soil solids.Va =Volume of air. Wa =Weight of air considered as
negligible.Vw =Volume of water. Ww =Weight of water.V=Total volume of soil mass =Vs+ Va + Vw
W=Total Weight of soil mass = W s+ Ww
1) Water content. : The water content w, also called the moisture content, isdefined as ratio of weight of water & weight of soil solids.
w = Weight of water x 100Weight of soil solids
The water content is generally expressed as a percentage.
2) Unit Weights : The weight of soil per unit volume is defined asunit weight or specific weight . In SI units is expressed as N/m 3
or kN/m3 . In soil Engineering five different five unit weights areused in various computations.
i) Bulk Unit Weight (). The bulk unit weight is the total mass W of the soil per unit of its total
volume.
Thus, = WV
ii) Dry Unit Weight (d). : The dry unit weight is the weight ofsoil solids per units total volume of the soil mass.
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d = Ws
V
The dry unit weight is used to express the denseness of the soil.
iii) Unit Weight of Soil Solids (s) : The unit weight of soil solidsis the mass of soil solids (w s) per units of volume of solids (Vs):
s = W s
Vs
iv) Saturated Unit Weight ( sa t) : When the soil mass is saturated,
its bulk unit weight () is called saturated unit weight. The
saturated unit weight is the ratio of the total soil mass of
saturated sample to its total volume.
sa t = W s (saturated)
V
v) Submerged Unit Weight (): When the soil exits below water it
is in submerged condition. The submerged unit weight () of
soil is defined as the submerged weight per unit total volume.
= W su b = sa t - w
V
3. Specific gravity G : is defined as the ratio of the unit weight of
soil solids to that of water:
G = s / w
4. Voids ratio . (e) Voids ratio e of a given soil sample is the
ratio of the volume of voids to the volume of soil solids in the
given soil mass.
Thus, e = V v/V s = n / 1-n
5. Porosity . (n) The porosity n of a given soil sample is the ratioof the volume of voids to the total volume of the given soil mass.
Vv e
n = =V e +1
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The voids ratio e is generally expressed as a fraction, while the
porosity n is expressed as a percentage and is, therefore also referred
to as percentage voids.
6 Degree of Saturation . The degree of saturation Sr is defined asthe ratio of the volume of water present in a given soil mass to
the total volume of voids in it.
Sr = Vw
Vv
6. Various Inter-Relationsi) e. S r = w.Gii) e = w.G (for Sr = 1 or fully saturated soil degree of
saturation 100% )G . w
i i i) d = 1 + e
iv) ( G + e.S r ) w = 1 + e
v) For S r = 0 ,G . w
= d = 1 + e
vi) For S r = 1 , = sa t = ( G + e)w
1 + e
vi) d = 1 + w
vii) = (G -1)w
1 + e
7. Density Index : The term density index ID or relative density ordegree of density is used to express the relative compactness of a
natural soil deposit. The density index is defined as the ratio of
the difference between the voids ratio of the soil in its loosest
state and its natural voids ratio (e) to the difference between the
voids ratios in the loosest and densest states:
emax - e
ID emaxemin
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where emax = voids ratio in the loosest stateemin = voids ratio in the densest statee = natural voids ratio of the deposit.
This term is used for cohesion less spoil only. When the natural state of the cohesion
less soil is in its loosest form e = emax and hence ID = 0. When the natural deposit is in
its densest state e = emin and hence ID = 1.
4.0 Plasticity Characteristics of SoilsPlasticity of soil is its ability to undergo deformation without cracking
or fracturing. Plasticity is an important index property of fine grained
soils, especially clayey soils.
Fine grained soil may be mixed with water to form a plastic paste which can be
moulded into any form by pressure. The addition of water reduces the cohesion
making the soil still easier to mould. Further addition of water reduces the cohesion
until the material no longer retains its shape under its own weight, but flows as a
liquid. Enough water may be added until the soil grains are dispersed in a suspension.
If water is evaporated from such a soil suspension, the soil passes through various
stages or states of consistency. In 1911,the Swedish agriculturist Atterberg divided
the entire range from liquid to solid state into four stages : (i) the liquid state, (ii) the
plastic state, (iii) the semisolid state and (iv) the solid state. He set arbitrary limits,
known as consistency limits or Atterberg limits. As shown in the fig. below.
a) Liquid limit (wl). Liquid limit is the water content corresponding to thearbitrary limit between liquid and plastic state of consistency of a soil. It is
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defined as the minimum water content at which the soil is still in the liquid
state, but has a small strength against flowing.
b) Plastic limit (wp). Plastic limit is the water content corresponding to anarbitrary limit between the plastic and the semi solid states of consistency of a
soil. It is defined as the minimum water content at which a soil will just beginto crumble when rolled into a thread approximately 3 mm in a diameter.
c) Shrinkage limit (ws). Shrinkage limit is defined as the maximum watercontent at which a reduction in water content will not cause decrease in the
volume of soil mass. It is lowest water content at which a soil can still be
completely saturated.
d) Plasticity index (Ip). The range of consistency with in which a soil exhibitsplastic properties is called plastic range and is indicated by plasticity index.
The plasticity index is defined as the numerical difference between the liquid
limit and the plastic limit of soil:
Ip = wl - wp
5. Unified Soil Classification And Indian Standard Classification.USC system and as adopted by the ISI (IS : 14981970: Classification and
Identification of soils for general engineering purpose) is given below.
Soils are broadly divided into three divisions.
Coarse grained soil. In these soils, 50% or more of the total material by
weight is larger than 75 micron IS sieve size.
Fine grained soils. In these soils, 50% or more of the total material by
weight is smaller than 75 micron IS sieve size.
Highly organic soils and other miscellaneous soil materials. These soil
contain large percentage of fibrous organic matter, such as peat, and
the particles of decomposed vegetation. In addition, certain soilscontaining shells, cinders and other non soil materials in sufficient
quantities are also grouped in this division.
1. Coarse grained soils. Coarse grained soils are further divided intotwo subdivisions:
(a) Gravels (G). In these soils more than 50% the coarse fraction (+ 75micron) is larger than 4.75 mm sieve size. This sub division includes
gravels and gravelly soil, and is designated by symbol G.
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(b) Sands (S). In these soils more 50% the coarse fraction is smaller than4.75 mm IS sieve size. This sub division includes sands and sandy
soils.
Each of the above sub-divisions are further sub divided into fourgroups depending upon grading and inclusion of other materials.
W : Well graded
C : Clay binder
P : Poorly graded
M : Containing fine materials not covered in
other groups.
These symbols used in combination to designate the type of coarse grained soils. For
example, GC means clayey gravels.
2. Fine grained soils. Fine grained soils are further divided into three subdivisions.
(a) Inorganic silts and very fine sands :M(b) Inorganic clays :C(c) Organic silts and clays and organic matter : OThe fine grained soils are further divided into the following groups on the
basis of the following arbitrarily selected values of liquid limit which is a
good index of compressibility:(i) Silts and clays of low compressibility, having a liquid less than 35, and
represented by symbol L.
(ii) Silts and clays of high medium compressibility, having a liquid limitgreater than 35 and less than 50, and represented by symbol I .
(iii) Silts and clays of high compressibility, having liquid limit greater than50, and represented by a symbol H.
Combination of these symbols indicates the type of fine grained soil. For
example, ML means inorganic silt with low to medium compressibility.
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TABLE 2.0 BASIC SOIL COMPONENTS (IS CLASSIFICATION)
SoilSoilComponents Symbol
Particle size range and description
CoarseGrained
Boulder
Cobble
Gravel
Sand
None
None
G
S
Round to angular, bulky hard, rock particle,Average diameter more than 30 cm
Round to angular, bulky hard, rock particle,Average diameter smaller than 30 cm butretained on 80 mm sieve.
Rounded to angular, bulky, hard, rockparticle, passing 80mm sieve but retained on
4.75 mm sieveCoarse : 80 mm to 20 mm sieveFine : 20 mm to 4.75 mm sieve
Rounded to angular bulky, hard, rockyParticle, passing 4.75 mm sieve retained on75 micron sieve.Coarse : 4.75 mm to 2.0 mm sieveMedium : 2.0 mm to 4.25 micron sieve.Fine : 425 micron to 75 micron sieve.
Fine grainedComponents
Silt
Clay
M
C
Particle smaller than 75 micron sieveidentified by behavior , that it is slightlyplastic or non plastic regardless of moistureand exhibits little or no strength when airdried.
Particles smaller than 75 micron sieveidentified by behavior , that is, it can bemade to exhibit plastic properties within acertain range of moisture and exhibitsconsiderable strength when air dried.
Organic matter OOrganic matter in various sizes and stages ofdecomposition.
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Table 3.0 Classification of Coarse-grained Soils (ISC System)
Divi si on Su bd ivi si on Grou p sy mbol Ty pi ca l
Na mes
La bo ra to ry Cr it er ia Remark
(1) Coarse-grained soils(More thanhalf ofmaterial is
larger than75-micro
Gravel (G)(more thanhalf of coarsefraction islarger than
4.75 mm ISsieve)
Cleangravels(Fines lessthan 5%)
(1) GW
(2) GP
Well gradedgravels
Poorlygradedgravels
Cu greater than 4Cc between than 1 and 3
Not meeting all gradationrequirements for GW
When fines arebetween 5% to12% borderline casesrequiring dual
symbols suchas GP-GM,SW-SC, etc.
Gravelswithappreciableamount offines (Finesmore than12%)
(3) GM Silty gravels
Clayeygravels
Atterberglimitsbelow A-line or Ip less than4
Atterberglimitsbelow A-line or Ip
less than7
AtterbergLimits plottingabove A-linewith Ip between 4 and7 are border-line casesrequiring useof dual symbolGM-GC
(4) GC
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Table (Continued)
Di vi si on Su bd ivi si on Gr ou p sym bo l Ty pi ca l
Nam es
La bo rat or y Cri ter ia Re ma rk
Sand (S) (morethan half of
coarse fractionis Smaller than4.75 mm ISsieve)
Clean Sand(Fines less
than 5%)
(5) GW
(6) SP
Well - gradedgravels
Poorly -gradedgravels
Cu greater than 6Cc between than 1 and 3
Not meeting all gradationrequirements for SW
Sands withappreciableamount offines
(Fines morethan 12%)
(7) SM
(8) SC
Silty Sands
Clayeygravels
Atterberglimitsbelow A-line or Ip less than4Atterberglimitsbelow A-
line or Ip less than7
Atterbergs
Limits plottingabove A-linewith Ip between 4 and7 are border-line casesrequiring use
of doublesymbol SM-SC
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(Continued)
Di vi sio
n
Subdivision Group
Symbols
Typical names Laboratory Criteria (see Fig 5.6) Remarks
(2) Fine
grainedsoils(morethan50 %pass 75ISSieve)
Low-compressibili
ty (L)(Liquid Limitless than35%)
Intermediatecompressibility
(I )(Liquid limit
greater than35 but lessthan 50%
(1) GW
(2) CL
(3) OL
(4) MI
(5) CI
(6) OI
Inorganic siltswith none to lowplasticity
Inorganic clays oflow plasticity
Organic silts oflow plasticity
Inorganic silts ofmedium plasticity
Inorganic clays of
medium plasticity
Organic silts ofmedium plasticity
Atterberg limitsplot below A-line or Ip less
than 7Atterberg limitsplot below A-line or Ip lessthan 7
Atterberg limitsplot below A-line
Atterberg limitsplot below A-line
Atterberg limits
plot above A-line
Atterberg limitsplot below A-line
Atterberg limitsplotting above A-line with Ip
between 4 to 7(hatched zone) ML-CL
(1) Organic and inorganicsoils plotted in the samezone in plasticity chart
are distinguished by odourand colour or liquid limittest after oven-drying. Areduction in liquid limitafter oven-drying to avalue less than three-fourth of the liquid limitbefore oven-drying ispositive identification oforganic soils.
(2) Black cotton soils ofIndia lie along a bandpartly above the A-lineand partly below the A
line
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(Continued)
Di vi si o
n
Subdivision Group
Symbols
Typical names Laboratory Criteria (see Fig
5.6)
Re ma rks
Highcompressibility (H)(Liquidlimitgreater than50%)
(7) MH Inorganic silts of highcompressibility
Atterberg limits plot belowA-line
Seeplasticitychart (Fig.56 )
(8) CH Inorganic clays of highplasticity
Atterberg limits plot belowA-line
(9) OH Organic clays ofmedium to highplasticity
Atterberg limits plot belowA-line
(3 )Highlyorganicsoil
PT Peat and other highlyorganic soils
Readily identified bycolour, odour, spongy feeland fibrous texture
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6.0 Bearing Capacity
Definitions1. Footing: - A footing is a portion of the foundation of a structure that transmits
loads directly to the soil.
2. Foundation: - A foundation is that part of the structure which is in directcontact with and transmits loads to the ground.
3. Foundation soil: - It is the upper part of the earth mass carrying the load ofthe structure.
4. Bearing capacity: - The supporting power of a soil or rock is referred to as itsbearing capacity. The term bearing capacity is defined after attaching certain
qualifying prefixes, as defined below.
5. Gross pressure intensity (q):- The gross pressure intensity q is the totalpressure at the base of the footing due to the weight of the superstructure, self
weight of the footing and the weight of the earth fill, if any.
6. Net pressure intensity (qn) :- It is defined as the excess pressure, or thedifference in intensities of the gross pressure after the construction of the
structure and the original overburden pressure.
Thus, if D is the depth of footing
qn = qDwhere is the average unit weight of soil above the foundation base.
7. Ultimate bearing capacity (qu):-The ultimate bearing capacity is defined asthe minimum gross pressure intensity at the base of the foundation at which
the soil fails in shear.
8. Net ultimate bearing capacity (qnu):- It is the net increase in pressure at thebase of foundation that causes shear failure of soil.
qnu = quD
9. Net safe bearing capacity (qns) :-The net safe bearing capacity is the netultimate bearing capacity divided by a factory of safety F.
qns = qnf
F
10. Gross Safe bearing capacity (qs) :-The maximum pressure which the soil cancarrying safely without risk of shear failure is called the safe bearing capacity.
It is equal to the net safe bearing capacity plus original overburden pressure.
qs = qns+ D.
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11. Allowable bearing capacity or pressure. (qna) :- It is the net loadingintensity at which neither the soil fails in shear not there is excessive
settlement detrimental to the structure.
Failures in Soil
1. General Shear Failure: - An analysis of the condition of completebearing capacity failure, usually termed general shear failure, can be
made by assuming that the soil behaves like an ideally plastic material. In
such a failure, the soil properties are assumed to be such that a slight
downward movement of footing develops fully plastic zones and the soil
bulges out.
2. Local Shear Failure:-In the case of fairly soft or loose and compressiblesoil, large deformation may occur below the footing before the failure
zones are fully developed. Such a failure is called a local shear failure.
I.S. Code Method for Computing Bearing Capacity:
GeneralIS Code (IS: 6403 1981) recognizes, depending upon the deformations
associated with the load and the extent of development of failure, three types
of failure of soil support beneath the foundations, they are (a) General Shear
Failure; (b) Local Shear Failure; and (c) Punching Shear Failure, occurs onsoils of high compressibility. In such a failure, there is vertical shear around
the footing, perimeter and compression of soil immediately under the footing,
with soil on the sides of the footing remaining practically uninvolved.
2. Bearing capacity equation for strip footing for c- soils
The ultimate net bearing capacity of strip footing is given by the following
equations:
i) For the case of General shear failure:qnu = cNc+ D (Nq1) + 0.5 B N ---------------(1)
ii) For the case of local shear failure:qnu = 2/3 cNc
+ D (Nq1) + 0.5 B N------------(2)
For obtaining Nc, Nq , N bearing capacity facotorscorresponding to local shear
failure, calculate(m) = tan-1(0.67 ) and read Nc, Nq , N for general shear
failure as given in table 4.0 below.
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Table 4.0 Bearing Capacity Factors (Is : 64031981)
Degree Nc Nq Nr0 5.14 1.0 0.05 6.49 1.57 0.45
10 8.35 2.47 1.2215 10.98 3.94 2.6520 14.83 6.40 5.39
25 20.72 10.66 10.8830 30.14 18.40 22.4035 46.12 33.30 48.03
40 75.31 64.20 109.4145 138.88 134.88 271.76
50 266.89 319.07 762.89
3.Shape factor, depth factor and inclination factorThe above bearing capacity equations, applicable for strip footing, shall be modified
to take into account, the shape of the footing, inclination of loading, depth of
embedment and effect of water table. The modified bearing capacity formulate are
given below :
i) For general shear failureqnu = cNc Sc dc ic+ D (Nq-1) Sq dq iq+1/2 B N S d i w
-------(1)
ii) For local shear failure
qnu = 2/3 cNc
Sc dc ic+ D(Nq-1) Sq dq iq+1/2 B N
S d i w
---(2)
The depth factors are given as under ;
dc =1+ 0.2 (D/B ) N1/2 where N = tan
2 (45+ /2)dq = d =1 for 100
Shape Shape factors
Sc Sq S 1.Continous strip 1.0 1.0 1.0
2. Rectangle (1+ 0.2 B/L) (1+0.2 B/L) (1-0.4 B/L)3. Square 1.3 1.2 0.84. Circle 1.3 1.2 0.6
The depth factors are to be applied only when the back filling is done withproper compaction.
The inclination factors are given as under
ic = iq =(1- /90)2 and i = (1- / )
2
Where = inclination of the load to the vertical, in degrees.
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4. Effect of water tableThe effect of water table is taken into account in the form of a
correction factor w.The value of w may be chosen as indicated below.
a) w=1.0 If the water table is likely to permanently remain at or below ata depth of (D+B) beneath the ground level surrounding the footing
below.
b) W=0.5 If the water table is located at a depth D or likely to rise to thebase of footing or above,
If the water table is likely to permanently get located at depth Dw below the
G.L. such that D
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value is determined for each one of the location and the minimum of the average
value is used in the design.
The net ultimate bearing capacity of shallow strip footing oncohesion less soil deposit is then determined from Fig. given in the ISCode.
6. Bearing Capacity of Cohesive Soils ( = 0)The net ultimate bearing capacity immediately after construction on
fairly saturated homogenous cohesive soils can be calculated from the
expression.
qnu = c Nc Sc dc i c
Where Nc = 5.14 (for =0)
The value of c is obtained from unconfined compressive strength test.
Alternatively, cohesion c may be determined from the static cone pointresistance.
7.0 Planning for Soil Investigation
Soil investigation must conform to the provisions in I.S. 1892 1979.
The scope of investigation is indicated in para 2.1 and 2.2 of this code.
Engineering properties of soil depend on the soil structure, i.e. nature
of soil grains and their arrangement, volume of air and water (degree
of saturation and porosity). Since these vary from one location to
another, the program of soil investigation needs to be evolved for each
project. It should provide for adequate data and make appropriate
recommendation supported by proper calculations in respect of the
following:
1. The type of foundation.2. Allowable bearing capacity for the foundation.3. Total and differential settlements.4. Highest groundwater level ever reached.5. Anticipated construction problems and suggested solution
(sheep piling, dewatering, boulders/rock excavation,differential, settlements, damage to adjacent property,
environment etc.)
A copy of the surveyed site plan and layout plan of buildings
indicating the type and sizes of the buildings are required. It is
essential that the location of bore holes together with the reduced
levels are marked on the site plan.
To determine the nature and extent of detailed soil investigation, a
preliminary investigation is necessar y as stipulated in para 3.1.1 of
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I.S. 1892 - 1979. Knowing the type of superstructure, the first step is
to inspect the site and its neighborhood and collect the information
about the soil profile, type of foundation generally adopted and to
guess the presumptive allowable bearing pressure for the soil. This is
done through reconnaissance and simple visual/manual tests. If soilinvestigation details are not available for nearby sites, a test pit or a
bore hold may be dug to examine the soil at foundation level.
Knowledge of regional soil deposits corresponding to the locality,
prevalent practices of subsoil investigation and foundation design
greatly facilitate drawing up an appropriate program of soil
investigation. Major regional soil deposits of India are - Alluvial soils,
Black cotton soils, Laterities, Desert soils and Sub marine soils
(Reference may be made to Indian contributions to Geotechnical
Engineering published by Indian Geotechnical society for sources of
information of the Regional deposits).
1. Detailed soil investigati on
Deg rees o f a pp l ica b i l i ty o f v a r io us f i e ld a nd la bo ra to ry
tes t s a re ind ica ted in Ta b les 1 a nd 2 . The s i tua t io ns in
which ea ch tes t i s a pp l ica b le a nd the l imi ta t io ns o f such
tes t s a re d i scussed in the fo l lo wing pa ra g ra phs .
In arriving at the allowable bearing pressure onfoundations, both the ultimate bearing capacity (based on shear
strength and the permissible settlement are taken into account.
Normally settlement governs the design but for narrow strip
foundations on soft at shallow depths, bearing capacity based on
shear failure may govern.
1.1 Characteris tics of soil in foundation
a) Cohesion less soils and soils with cohesion and angle ofinternal friction ( c - soils )
Sand and silt are cohesion less soils. Silt wit h even 5 to 8 percent ofclay has significant cohesion. Shear strength, s of soil is developeddue to resistance to rolling, sliding and deformation of soilparticles/skelet al structure. Cohesion, c is due to inter particleattraction due to p resence of clay and the angle of internal friction is essentially due to resistance to inter particle slip of coarser grainslike silt and sand.
Shear strengths is given by s = c + tan
Where is normal stress on the shear plane.
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Since water has no shear strength, the entire shear strength is due to
inter-granular pressure which is affected by the excess pore water
pressure developed in cla yey soils. The parameters c and
corresponding to maximum shear strength are determined by
considering effective pressures which are equal to total pressureminus pore water pressure. These are determined by consolidated
drained test for cohesion less soils (and for c - soils if insitu drainage
occurs as the load is applied). During testing, the excess pore water
pressure is dissipated completely through a slow process of
consolidation and an equally slow process of shear. The time required
for gradual increment of load upto shear failure is determined as per
appendix A of I.S. 2720 (part 13) 1986. soil in situ exists, generally,
in a consolidated state ( 3 ). As construction proceeds, additional
loads come on to the soil. If the permeability of the soil is low, which
can occur if the fine grained soil contains more than 15 percent clay
and is classified as clay with intermediate or high compressibility, the
excess pore water pressures developed in the clayey soil can not
dissipate as fast as the rate of application of load. Hence for clayey
soils with appreciabl e clay content ( say more than 15 percent), the soil
parameters C and are determined from consolidated un -drained test
in which the soil is consolidated slowly but sheared quickly. If the
clay content is high ( say more than 30 percent) or very low ( say less
than 15 percent), the tests are performed by Box shear as per I.S. 2720
(Part 13) 1986. The results are representative of field conditionsunder plane shear only (which is 15 to 20 percent higher than for
tri-axial shear). For semi pervious cohesive soils, the consolidated
un-drained Test is performed by Tri- axial Test (as per I.S. 2720 ( part
II ) since the inevitable (though small) drainage of the soil during
shearing in Box Shear Test introduces an element of error. Shear
strength of stiff intact clays such as boulder clays, clayey silts are
better determined by drained tests since the soils are generally over
consolidated.
Saturation reduces the shear strength and long term time dependant
consolidation of clay takes place during testing, only if the soil is
saturated. It is thus necessary to determine shear strength of the soil in
saturated condition if the soil in situ is likely to be saturated due to
rising of the ground water table. Hence it is essential to ascertain the
highest ground water level ever reached. Due to the capacity of clay to
absorb water by capillary action and the very large variation in shear
strength of unsaturated clayey soils with moisture content, results of
Box Shear Test cannot reliably represent in situ shear strength of
unsaturated clay. Even while considering the results of consolidatedun-drained Tri-axial Test or in situ test on unsaturated soils, the
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effect of variation of insitu shear strength due to possible change in
moisture content due to rain or rise in water table needs to be
considered.
Satisfactory undisturbed samples of cohesion less soils are difficult toobtain from bore holes. Soil obtained from the split spoon sampler
from standard penetration test may possess large shear strains due to
disturbance. Hence shear tests in the laboratory on cohesion less soils
do not represent the true site condition. The most common field test
is the standard penetration test (Ref. I.S. 2131 1981). This test, if
carefully executed, in soil undisturbed by boring operations, enables to
estimate satisfactor ily the bearing capacity as per I.S. 6403 - 1981
and allowable bearing pressure on settlement considerati on as per I.S.
8009 (Part 1) 1976. By using the same equipment and with the same
driller, N values in the same soil can be reproduced with a
coefficient of variation of about 10 percent. Use of defective
equipments such as a damaged anvil, worn out driving shoe,
old/oily/poorl y lubricated rope sheaves etc. can result in significantl y
erroneous N values. Pushing a boulder while driving the sampler,
rapid withdrawal of sugar or bit plug causing a quick condition at the
bottom of the bore hole by too much difference in the water levels
between the ground water table and in the hole are other sources of
error.
The original standard penetration Test was developed for sand.
However, at present it is commonly used for all types of soils.
Alluvial silt deposits are mixtures of medium dense fine sand and silt
with a small percent of clay. In some cases, layers of stiff soil are
encountered at depth of 6 to 10 meters. Delhi silt has about 20 35%
sand, 50-65% silt and upto 15 percent clay.
b) Cohesive soils
Due to very low permeability, highly cohesive soils in their natural state posses shearstrength due to cohesion only and are prone to time dependant settlement. Particles
of clay being very small in diameter (less than 0.002 mm), grain size analysis of the
soil fraction passing 75 micron is determined as per I.S. 2720 (Part IV) 1985.
Except when the soil is nonplastic (indicated by the inability to perform the test to
determine plastic limit), it is essential to determine the percentage of clay and silt
separately. Natural clay deposits may contain upto 70% or even more of material
belonging to sand and silt grades. Such clayey soils, when saturated, behaves as if
they are purely cohesive under normal loading conditions from the building. Silt
with even 25% clay behaves as clay. Apparent angle of internal friction is low in theun-drained condition since no water is expelled from the soil initially when the load is
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applied. This is the accepted basis for calculating ultimate bearing capacity of
saturated clays. Only in the case of very slow rate of loading, or with very silty soils,
drained condition persists during loading, producing increase in effective pressure on
soil due to decrease in pore water pressure. Consequently shear strength is increased
due to increase in the angle of internal friction from apparent to true value.In most cases, allowable bearing pressure is dependant on permissible
total settlement but in every case the foundation is checked against
shear failure. Tri-axi al tests on undisturbed samples in the laboratory,
in situ vane shear test to determine the shear strength and static cone
test for bearing capacity of predominantly cohesive soils are reliable.
Shear strength of soft sensitive clays are measured by in-s itu vane
shear test as per I.S. 4434 1978 since laboratory tests on disturbed
samples of such soils are not reliable.
In cohesive soils, apart from static tests, in situ compressive strength
tests are routinel y made using a Pen/Pocket pentro -meter. It is usual
practice to take thin walled tube samples for laboratory testing and
compare the field and laboratory test results.
Alluvial clay deposits consist and clay deposited in river valleys and
estuaries (on the bed of the sea). They are normally consolidated.
Stiff surface crust is due to exposure to the effects of weather and
vegetation. Load bearing structures with very shallow and narrow
foundation in the surface crust are constructed which do not transmit
stresses to the underlying soft and highly compressible deposits. In
the case of wide or deep foundations, it is necessary to adopt low
bearing pressures or use a raft or piles. Alluvial clays, especially
marine clays, are sensitive to dis turbance. If they are disturbed in
sampling or in construction operations (such as in piling) they show a
marked loss in shear strength.
1.2 Anticipated problems in construction due to soils characteristics.
In sandy/alluvial soils, if ground water table is lowered, ground
subsidence in the area surrounding the construction site may occur due
to consolidation of underlying clayey layers. In such a case, it may be
necessary to provide a water retaining barrier around the site if
structures exists adjacent to the excavation (since pumping to dewater
may produce 30 to 50 mm settlement within a short period of time).
When pore water in the soil is just enough to moisten sand but not
saturate it , the surface tension makes it possible to pr ovide shallow
excavations with near vertical sides. With continued drainage andevaporation or vibration, the sides collapse. Near vertical excavation
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in a cohesive soil may collapse due to rainfall softening the clay and
creating excess pore water pressure.
Excavation in sands below the water table may result in a slumping of
the sides and boiling of the bottom, unless a properly designed groundwater lowering system is adopted.
If excavation goes below the firm surface crust of alluvial clay,
support by timbering or sheet pilling is and stiffened trenches are
prone to failure by heaving of the bottom and bulging of the side
supports.
1.3 Programme of detailed soil investigation
In planning the Programme, full advantages should be taken of
available information from preliminary investigation, geo technical
consultants data base and soil Investigation reports for the nearby
sites and their correlation with actual performance of buildings and
load tests on piles. If rock is encountered in a bore hole, boring must
extend at least 2 meters to differentiate a boulder from bed rock. If
rock is encountered in different bore holes near about the proposed
foundation level, adequate number of bore holes are required to plot
the rock contour. On the basis of preliminar y borings or prior site
knowledge, details of in situ tests and laboratory tests are worked out
keeping in view the limitation of each.
Current methods of subsoil exploration are outlined in Appendix A of
IS 1892 1979 and the tests generally required are indicated in Table
3 and Appendix A of this Code of Practice.
A.S.T.M. suggests that when more than 15% of gravel or sand is
present in any type of soil , the description should include with. For
fine grained soils (with more than 50% passing 75 micron sieve )
with sand or gravel is written for percentages between 15 and 29
and gravelly of sandy for larger percentages.
Sands or gravels may be classified by the standard penetration tests
into broad groups as follows:
No of S.P.T. blows N
Loose Le ss tha n 10
Medium Dense 10 to 30
De nse ( o r c ompa c t ) More tha n 30Based on un-drained shear strength, clayey soils may be classified as follows
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Soft (0.2 to 0.4 kg/cm)
Medium (0.4 to 0.75 kg/cm)
Stiff (0.75 to 1.5 kg/cm)
After establishing correlation on the basis of other reliable tests,
standard penetration test results have been in use for many years for
relative density, angle of internal friction, un-drained compressive
strength, settlement and modules of sub grade reaction. Some of these
are of questionable value unless corroborated by adequate calibration
data for the locality since many were originally proposed without
extensive study of the large number of variables affecting the N
values.
A . Tests required for classification of soils
1) Classification as per IS 1498 1970 based on particle sizeanalysis as per IS 2720 (Part 4) 1985 and index properties
of the soil as per IS 2720 (part 5) 1985. On the basis of
index properties, if the soil is classified as clay of
intermediate or high compressibilit y, It is necessary to
determine the clay and silt percentages separately. Hence in
addition to sieving, pipette or hydrometer test is necessary to
determine the percentage of clay.
2) In assessing the engineering behavior of a cohesive soil, it isnecessary to determine in situ water content in addition to
liquid limit and plastic limit of re- moulded soil.
B. Tests required to determine safe bearing capacity of shallow
foundations ( including raft)as per I.S. 64031981.
Apart from ascertaining the highest level ever reached by the ground water
table and tests for classification of soil as per I.S. 14981970 based on grain
size analysis as per I.S. 2720 (part iv)1985 index properties of the soil asper IS 2720 (Part 5) 1985, the following tests are required to determine
safe bearing capacity based on shear strength consideration:
1) Standard penetration test as per I.S. 2131 1981 for coarse grained /finegrained cohesion less soils and semipervious clayey soils (i.e. c
soils with clay upto about 30 percent).
2) Direct shear (controlled strain) test as per I.S. 2720 (Part 13) 1986.Consolidated un-drained test for cohesive and for C soils and
consolidated drained test for cohesion less soils. The results may be
compared with standard penetration test/static cone penetration test
results. Since there is escape of pore water during box shear, partial
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drainage vitiates the consolidated un-drained test. Hence this test is not
exact for semi pervious soils such as clayey sands/silts (i.e. with clay
more than 15% but less than 30%). For such soils , Tri-axial Tests are
required if shear strength is the critical criterion.
3)
Static cone penetration test as per I.S. 4968 (part 3)1976 for foundationson non stiff clayey soils such as fine grained soils (i.e. more than 50%
passing 75 micron sieve). In fine and medium coarse sands such tests are
done for correlation with S.P.T. and to indicate soil profiles at intermediate
points.
4) Unconfined compressive strength test as per I.S. 2720 (part 10)1973 forhighly cohesive clays except soft/sensitive clays.
5) Vane shear test for impervious clayey soils except stiff or fissured clays.6) Tri-axial shear tests for predominantly cohesive soils. If shear strength is
likely to be critical.
C. Tests required to determine allowable bearing pressure for shallow
foundations on settlement consideration.
1) Standard penetration test as per I.S. 2131 1981 for cohesion less soils andsemi pervious clayey soils (i.e. c soils with clay upto about 30 percent)
2) Consolidation test as per I.S. 2720 (part 15) if the settlement of clayeylayer/layers calculated on the basis of liquid limit and in-situ void ratio
indicates that settlement may be critical. Consolidation test is not required if
the superimposed load on foundation soil is likely to be less than pre-
consolidation pressure (assessed from Liquidity Index and sensitivity or fromunconfined compressive strength and plasticity index).
3) Plate load test as per I.S. 18881982 for cohesion less soils and c soilswhere neither standard penetration test now consolidation test is appropriate
such as for fissured clay/rock, clay with boulders etc.
D. Test specially required for raft foundations (Refer para 3 of I.S. 2950
(Part I )1981.
Apart from other tests for shallow foundations, the following tests are required
especially for raft foundation :1) Static cone penetration test as per I.S. 4968 (part 3)1976 for cohesion
less soil to determine modulus of elasticity as per I.S. 18881982.
2) Standard penetration test as per I.S. 2131 1981 for cohesion less soilsand c soils to determine modulus of sub grade reaction.
3) Unconfined compressive strength test as per I.S. 2720 (part 10)1973 forsaturated but no pre-consolidated cohesive soil to determine modulus of
sub grade reaction.
4) As specified in I.S. 2950 (part I)1981, plate load test as per I.S. 18881982 where tests at sl. 1 to 3 above are not appropriate such as for
fissured clays/ clays boulders.
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5) In case of deep basements in pervious soils, permeability is determinedfrom pumping test. This is required to analyze stability of deep
excavation and to design appropriate dewatering system.
E. Tests specially required for deep foundations
1) While the composition and depth of the bearing layer for shallowfoundations may vary from one site to another, most pile foundations in a
locality encounter similar deposits. Since pile capacity based on soil
parameters is not as reliable as from load tests, as a first step it is essential
to obtain full information on the type, size, length and capacity of piles
(including details of load settlement graph ) generally adopted in the
locality. Correlation of soil characteristics ( from soil investigation reports)
and corresponding load tests (from actual projects constructed) is essential
to decide the type of soil tests to be performed and to make a reasonablerecommendation for the type, size length and capacity of piles since most
formulae are empirical.
2) If information about piles in the locality are not available or reliable, itmay be necessary to drive a test pile and correlate with soil data.
3) Standard penetration test to determine the cohesion (and consequently theadhesion based on or methods) to determine the angle of friction ( and
consequently the angle of friction & between soil and the pile and also the
point resistance) for each soil stratum of cohesion less soil or c- soil.
4) Static cone penetration test to determine the cohesion ( and consequentlythe adhesion based on or methods ) for soft cohesive soils and to check
with S.P.T. result for fine to medium sands. Hence for strata encountering
both cohesive and cohesion less soils, both S.P.T. and C.P.T. are required.
5) Vane shear test for impervious clayey soils.6) Un-drained Tri-axial shear strength of undisturbed soil samples (obtained
with thin walled tube samplers) to determine c and for clayey soils
(since graphs for correlations were developed based on un-drained shear
parameter). In case of driven piles proposed for stiff clays, it is necessary
to check with the c and from remoulded samples also. Drained shear
strength parameters are also determined to represent in situ condition ofsoil at end of construction phase.
7) Self boring pressure meter test to determine modulus of sub grade reactionfor horizontal deflection for granular soils, very stiff cohesive soils, soft
rock and weathered or jointed rock.
8) Ground water conditions and permeability of soil influence the choice ofpile type to be recommended. Hence the level at which water in the bore
hole and the level at which water in the bore hole remains are noted in the
bore logs. Since permeability of clay is very low, It takes several days for
water in the drill hole to rise upto the ground water table. Ground watersamples need to be tested to consider the possible chemical effects on
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concrete and the reinforcement. Result of the cone penetration test for the
same soil show substantial scatter. Hence, they need to be checked with
supplementary information from other exploration methods. Pressure
meters are used to estimate the in situ modulus of elasticity for soil in
lateral direction. Unless the soil is isotropic, the same value cannot beadopted for the vertical direction. A list of tests required for soil
investigation is given in Table 3.
2) Recommendation in the soil investigation Reports:
Due to the difficulty in assessing the contact pressure on the foundation soil
by individual columns/wall. And variation in soil properties, it is common
practice to provide an adequate factor of safety while making
recommendation for the foundation based on results of soil investigation.
However, we may have a problem if the investigating firm recommends, say,a special type of foundation with a safe bearing pressure of 8 tones per sq.
meter and it turns out that the safe bearing pressure is 12 tones per sq. meter
which would permit spread footings resulting in substantial economy.
Similarly, suggestion of a pile foundation without considering other economic
types of foundation is inappropriate. Hence, it is necessary to examine the
report to ensure that the recommendations flow from the data which have been
correctly interpreted.
2.1 Bearing capacity
For shallow foundation, the current practice is to use an average N value in
the zone affecting soil behavior. For a spread footings, the effective zone
extends to a depth equal to twice the width below the footing. For a square
footing, the effective zone extends to a depth equal to one and a half times the
width (if the effective zones of adjacent footings do not overlap). Weighted
average is used. For piles, average N for each stratum is used.
It is undesirable to place a footings on soil with a relative density
less than 0.5 in such cases, the soil should be compacted by drainage and / or
preloading prior to placing footings on it.
The effect of ground water table on settlement is considered as per
I.S. 8009 (Part 1)1976 and I.S. 64031981.
Recent geo technical studies indicate that prediction of
consolidation settlements are satisfactory when compared with actual
measurements. The predictions are better for inorganic insensitive clays than
for others. The predictions require great care if e Vs log p curve is curved
throughout or the clay is very sensitive. Much care is also required if the clay
is highly organic as the creep component of settlement is substantial.
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If required, settlements can be computed for various point such as corner,
centre or beneath lightest or the heaviest parts of a building.
Differential settlement can be computed as the difference between thesettlements of columns with maximum and minimum settlement.
Alternatively, it may be estimated at 3/4th of the computed maximum total
settlement for spread footings for columns /walls.
Limiting the total settlement and the differential settlement to that permissible
as per I.S. 19041986, the allowable bearing pressure on the foundation soil
is recommend for various sizes of footings, based on equal settlement
consideration.
If after applying the empirical rules, or computing settlements of the structure
at various points based on the assumption of a flexible foundation, it is shown
that the total and differential settlements exceed safe limits for spread/ strip
footings and the structure itself does not have sufficient rigidity (i.e. unlike a
well tied building with adequate cross walls and reinforced concrete bands at
intermediate levels) to prevent excessive differential movement with ordinary
spread foundations, provision of a rigid raft foundations either with a thick
slab or with deep beams in both directions may be considered.
If a tall building with basement is founded on clay, the base of the excavationwill initially heave to a convex shape. As superstructure is constructed floor
by floor, the soil will be consolidated and the bottom will finally deform to a
concave (bowl) shape.
The critical factor for framed buildings is the relative rotation (or angular
distortion) whereas the ratio of deflection to length is critical in load bearing
walls which fall by sagging or hogging of the centre length of the wall.
In view of excessive cost of a raft foundation, adequate soil investigation must
be done and the report should clearly bring out by proper analysis of results
that it is not possible to provide spread footings including combined footings.
In some cases of alluvial deposits, there may be a variation in characteristics
of soil deposit beneath a large raft. A stiff crust of variable thickness and
extent.
Precautions may be indicated to avoid the lateral yield of soil if loose sand is
encountered beneath the edges of raft at depths less than 2.5 to 3.0 meters
below the ground level.
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The immediate settlement calculated on the basis of theory of elasticity is
strictly applicable to flexible bases only and is used to determine the contact
pressure distribution under the raft. In practice most foundations are
intermediate between rigid andflexible. Even very thick ones deflect when
loaded by the superstructure. If the base is rigid, the settlement is uniform (butraft may tilt) and the settlement is about 7% less. In the equation for
settlement, the weighted average of the modulus elasticity is adopted in place
of a single value for the entire depth below foundation. If N values are used
to calculate the modulus of elasticity, which generally increases with depth,
weighted average of the modulus is calculated and used in computing
immediate settlement.
3. Shear strengthIn some cases, consolidated Drained Test on cohesion less soils (i.e. soils
containing less than 5 percent clay) may give a small value of cohesion, of theorder of 0.10 to 0.15 kg/cm2. This is attributed to test inaccuracy and surface
tension. Hence this small value of c being unreliable, is neglected in
analyzing field conditions (such as stability of slope etc.). Generally, deep
cuts in clayey soils are designed for short term stability based on total stress
analysis in consolidated un-drained condition. These are analyzed for long
term stability if the cut slope is to exist even when consolidated drained
conditions may occur.
4.0 Pile Foundation
A pile foundation is recommended only when a raft foundation cannot be
recommended due to excessive settlement (which must be calculated from
consolidation test) when the shallow foundation is on a loose filled up soil or
is under lain by a highly compressible soil stratum. The base level of the piles
is determined considering the end resistance of the stratum and settlement
behavior of the soil under the pile groups.
A slip of 5 to 10 mm of the soil is enough to develop full skin resistance along
the pile whereas a displacement of the order of 10 percent of diameter of piletip is necessary to mobilize full end bearing resistance.
Driven piles compact loose and medium dense cohesion less soils and hence
are preferable. For such piles, pile driving formulate are more reliable for
cohesion less soils than for cohesive soils. Large surface cracks are formed
by driven piles in stiff clay. Hence the skin resistance may be neglected upto
about 1.8 meters at top. Capacity of driven cast in-situ concrete piles is
determined as per Appendix A of I.S. 2911 (part 1/Sec 1)1979.
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Capacity of bored piles is more dependent on the construction technique than
for driven piles. Soil is loosened as a result of boring operations. Shaft friction
values for bored piles in sands may be only half of that for driven piles. This
ratio is about one third for end bearing resistance. If concrete is placed ( but
not mechanically compacted ) while withdrawing the shell tube, thesurrounding cohesion less soil may be considered to be in loose condition.
Capacity of bored cast in situ concrete piles is determined as per Appendix B
of I.S. 2911 (part 1/Sec 2)1979.
If piles encounter shrinkable clays near the ground, due allowable may be
made for loss of frictional resistance and also for uplift due to swelling.
In stiff fissured clays, bored cast in situ piles or low.
Displacement driven piles are usually recommended. Dense silts
cause high penetration resistance for driven piles but the
capacity of the pile remains low due to disturbance of the soil
during driving.
Normally consolidated clays cause down drag on bored cast
in situ piles due to consolidated on account of drainage
occurring as a result of boring.
Point resistance and skin friction of pile in sand increases as
the length of the pile increases upto the critical depth equal to10 times the pile diameter for loose sand and 20 times for
dense sand, Beyond this length, the values remain constant.
Point resistance of piles longer than 15 to 20 times the diameter,
driven through weak strata into thick firm sand deposit
increases with depth of embedment in this stratum upto a
maximum value corresponding to 8 to 12 times the diameter of
the pile.
Except for bored piles in sand capacity of a group of piles
equals the sum of the capacities of individual piles in the group.
In case of bored piles in sand, the capacity is about two thirds
the sum of capacity. Check is necessary for failure of the pile
group as a single block.
Pile capacity may be calculated by several appropriate methods
so as to establish upper and lower bound values. Errors are very
high when results from one type of soil deposit in one locality or
valid for one year of pile are extrapolated to derive the value for
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different deposits in another locality or another type of pile
involving a different construction technique.
With a view to limit the number of piles in each group to the
minimum, the recommendation should indicate the highestpossible capacity of the pile considering the soil parameters,
the bore log and the appropriate type of pile.
5. Conclusion:
Technical sanction of a project is based on sound engineering practice. It is
thus of utmost importance to evolve and acceptable practice for planning of
soil investigation and appropriate recommendation for foundation. Every soil
investigation report should be examined at an appropriate level before
acceptance of the recommendation regarding the type of foundation and theallowable bearing pressure. This is essential in view of the high cost of
foundation and that any error in foundation is difficult to rectify or may have
disastrous consequence.
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LIST OF VARIOUS FOUNDATION
ENGINEERING CODES
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SP 36 : Part 1 : 1987 Compendium of Indian standards on soil engineering: Part 1 Laboratory testing of soils for civilengineering purposes
SP 36 : Part 2 : 1988 Compendium of Indian standards on soil engineering: Part 2 Field testing
IS 1080 : 1985 Code of practice for design and construction of shallow foundations in soils (other than raft, ring andshell)
IS 1498 : 1970 Classification and identification of soils for general engineering purposes
IS 1725 : 1982 Specification for soil based blocks used in general building construction
IS 1888 : 1982 Method of Load Test on Soils
IS 1892 : 1979 Code of practice for subsurface investigations for foundations
IS 1904 : 1986 Code of practice for design and construction of foundations in soils: general requirements
IS 2131 : 1981 Method for St andard Penetration Test for Soils
IS 2132 : 1986 Code of practice for thin walled tube sampling of soi ls
IS 2720 : Part 2 : 1973 Methods of test for soils: Part 2 Determination of water content
IS 2720 : Part 3 : Sec 1 : 1980 Methods of test for soils: P art 3 Determination of specific gravity Section 1 fine grainedsoils
IS 2720 : Part 1 : 1983 Methods of Test for Soils - P art 1 : Preparation of Dry Soil Samples for Various Tests
IS 2720 : Part III : Sec 2 : 1980 Test for Soils - Part III : Determination of Specific Gravity - Section 2 : Fine, Mediumand Coarse Grained Soils
IS 2720 : Part 4 : 1985 Methods of Tes t for Soils - P art 4 : Grain Size Analysis
IS 2720 : Part 5 : 1985 Method of Test for Soils - Part 5 : Determination of Liquid and Plastic LimitIS 2720 : Part 6 : 1972 Methods of test for soils: Part 6 Determination of shrinkage factors
IS 2720 : Part 9 : 1992 Methods of test for soils: Part 9 Determination of dry density - moisture content relation byconstant weight of soil method
IS 2720 : Part 10 : 1991 Methods of test for soils: Part 10 Determination of unconfined compressive strength
IS 2720 : Part 11 : 1993 Methods of test for soils: Part 11 Determination of the Shear Strength Parameters of aspecimen tested in inconsolidated, indrained triaxial compression without the measurement of pore water pressure
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IS 2720 : Part 12 : 1981 Methods of t est for soils: Part 12 Determination of shear strength parameters of soil fromconsolidated undrained triaxial compression test with measurement of pore water pressure
IS 2720 : Part 13 : 1986 Methods of Test for Soils - Part 13 : Direct Shear Test
IS 2720 : Part 14 : 1983 Methods of Test for Soils - Part 14 : Determination of Density Index (Relative Density) ofCohesionless Soils
IS 2720 : Part XV : 1965 Methods of Test for S oils - P art XV : Determination of Consolidation Properties
IS 2720 : Part VII : 1980 Methods of Test for S oils - Part VII : Determination of Water Content-Dry Density RelationUsing Light Compaction
IS 2720 : Part 8 : 1983 Methods of Test for Soils - P art 8 : Determination of Water Content-Dry Density Re lation UsingHeavy Compaction
IS 2720 : Part 20 : 1992 Methods of test for soils: Part 20 Determination of linear shrinkage
IS 2720 : Part 22 : 1972 Methods of test for soils: Part 22 Determination of organic matter
IS 2720 : Part 23 : 1976 Methods of test for soils: Part 23 Determination of calcium carbonate
IS 2720 : Part 25 : 1982 Methods of test for soils: Part 25 Determination silica sesquioxide ratio
IS 2720 : Part 16 : 1987 Methods of Test for Soil - Part 16 : Laboratory Determination of CBR
IS 2720 : Part 17 : 1986 Methods of Test for Soils - Part 17 : Laboratory Determination of Permeability
IS 2720 : Part 18 : 1992 Methods of test for Soils - P art 18 : Determination of Field Moisture Equivalent
IS 2720 : Part 19 : 1992 Methods of Test for Soils - Part 19 : Determination of Centrifuge Moisture Equivalent
IS 2720 : Part XXI : 1977 Methods of Test for Soils - Part XXI : Determination of Total Soluble Solids
IS 2720 : Part XXIV : 1976 Methods of Test for Soils - Part XXIV : Determination of Cation Exchange Capacity
IS 2720 : Part 27 : 1977 Methods of test for soils: Part 27 Determination of total soluble sulphates
IS 2720 : Part 28 : 1974 Methods of test for soils: Part 28 Determination of dry density of soils inplace, by the sandreplacement method
IS 2720 : Part 30 : 1980 Methods of test for soils: Part 30 Laboratory vane shear test
IS 2720 : Part 33 : 1971 Methods of test for soils: Part 33 Determination of the density in place b y the ring and waterreplacement method
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IS 2720 : Part 35 : 1974 Methods of test for soils: Part 35 Measurement of negative pore water pressure
IS 2720 : Part 26 : 1987 Method of Test for Soils - Part 26 : Determination of pH Value
IS 2720 : Part XXIX : 1975 Methods of Test for Soils - Part XXIX : Determination of Dry Density of S oils In-place bythe Core-cutter Method
IS 2720 : Part 31 : 1990 Methods of Test for Soils - Part 31 : Field Determination of California Bearing Ratio
IS 2720 : Part XXXIV : 1972 Methods of Test for Soils - Part XXXIV : Determination of Density of Soil In-place byRubber-balloon Method
IS 2720 : Part 36 : 1987 Methods of test for soils: Part 36 Laboratory determination of permeability of granular soils(constant head)
IS 2720 : Part 37 : 1976 Methods of test for soils: Part 37 Determination of sand equival ent values of soils and fineaggregates
IS 2720 : Part 38 : 1976 Methods of test for soils: Part 38 Compaction control test (hilf method)
IS 2720 : Part XL : 1977 Methods of Test for Soils - Part XL : Determination of Free Swell Index of Soils
IS 2720 : Part XLI : 1977 Methods of Test for Soils - Part XLI : Measurement of Swelling Pressure of Soils
IS 2720 : Part XXXIX : Sec 1 : 1977 Methods of Test for Soils - Part XXXIX : Direct Shear Test for Soils ContainingGravel - Section I : Laboratory Test
IS 2720 : Part XXXIX : Sec 2 : 1979 Methods of Test for Soils - Part XXXIX : Direct Shear Test for Soils ContainingGravel - Section 2 : In-Situ Shear Test
IS 2809 : 1972 Glossary of Terms and Symbols Relating to Soil Engineering
IS 2810 : 1979 Glossary of terms relating to soil dynamics
IS 2911 : Part 1 : Sec 1 : 1979 Code of practice for design and construction of pile foundations: Part 1 Concrete piles,Section 1 Driven cast in-situ concrete piles
IS 2911 : Part 1 : Sec 2 : 1979 Code of practice for desi gn and construction of pile foundations: Part 1 Concrete piles,Section 2 Bored cast-in-situ piles
IS 2911 : Part 1 : Sec 3 : 1979 Code of practice for design and construction of pile foundations: Part 1 Concrete piles,Section 3 Driven precast concrete piles
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IS 2911 : Part 1 : Sec 4 : 1984 Code of practice for design and construction of pile foundations: Part 1 concrete piles,Section 4 Bored precast concrete piles
IS 2911 : Part 2 : 1980 Code of practice for desing and construction of pile foundations: Part 2 Timber piles
IS 2911 : Part 3 : 1980 Code of practice for design and construction of pile foundations: Part 3 Under reamed piles
IS 2911 : Part 4 : 1985 Code of practice for design and construction of pile foundations: Part 4 Load test on piles
IS 2950 : Part I : 1981 Code of Practice for D esign and Construction of Raft Foundations - Part I : Design
IS 2974 : Part 2 : 1980 Code of practice for design and construction of machine foundations: Part 2 Foundations forimpact type machine (hammer foundations)
IS 2974 : Part 3 : 1992 Code of practice for design and construction of machine foundations: Part 3 Foundations forrotary type machines (Medium and high frequency)
IS 2974 : Part 4 : 1979 Code of practice for design and construction of machine foundations: Part 4 Foundations forrotary type machines of low frequency
IS 2974 : Part 5 : 1987 Code of practice for design and construction of machine:foundations Part 5 Foundations forimpact machines other than hammers (forging and stamping press, pig breakers, drop crusher and jolter)
IS 2974 : Part I : 1982 Code of Practice for D esign and Construction of Machine Foundations - Part I : Foundation forReciprocating Type Machines
IS 4091 : 1979 Code of Practice for Design and Construction of Foundations for Transmission Line Towers and Poles
IS 4332 : Part 1 : 1967 Methods of test for stabilized soils: Part 1 Methods of sampling and preparation of stabilizedsoils for testing
IS 4332 : Part 3 : 1967 Methods of test for stabil ized soils: Part 3 Test for determination of moisture content-dry densityrelation for stablized soils mixtures
IS 4332 : Part 4 : 1968 Methods of test for stabil ized soils: Part 4 Wetting and drying, freezing and thawing tests for compa ctedsoil-cement mixtures
IS 4332 : Part 5 : 1970 Methods of test for stabil izd soils: Part 5 Determination of unconfined compressive strength of stablizedsoils
IS 4332 : Part II : 1967 Methods of Test for Stabilized Soils - Part II : Determination of Moisture Content of Stabilized SoilMixtures
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IS 4332 : Part 8 : 1969 Methods of test for stablized soils: Part 8 Determination of l ime content of l ime stablized soils
IS 4332 : Part 10 : 1969 Methods of test for stabil ized soils: Part 10 Test for soil /bituminous mixtures
IS 4332 : Part VI : 1972 Methods of Test for Stabilized Soils - Part VI : Flexural Strength of Soil-cement Using Simple BeamWith Third-point Loading
IS 4332 : Part VII : 1973 Methods of Test for Stabilized Soils - Part VII : Determination of Cement Content of CementStabilized Soils
IS 4332 : Part IX : 1970 Methods of Test for Stabilized Soils - Part IX : Determination of the Bituminous Stabilizer Content ofBitumen and Tar Stabilized Soils
IS 4434 : 1978 Code of practice for in-situ vane shear test for soilsIS 4968 : Part 1 : 1976 Method for subsurface sounding for soils: Part 1 Dynamic method using 50 mm cone without betoniteslurry
IS 4968 : Part 3 : 1976 Method for subsurface sounding for soils: Part 3 Static cone penetration test
IS 4968 : Part II : 1976 Method for Subsurface Sounding for Soils - Part II : Dynamic Method Using Cone and Bentonite Slurry
IS 5249 : 1992 Method of test for determination of dynamic properties of soil
IS 6403 : 1981 Code of practice for determination of bearing capacity of shallow foundati ons
IS 8009 : Part II : 1980 Code of Practice for Calculation of Sett lement of Foundations - Part II : Deep Foundations Subjected toSymmetrical Static Vertical Loading
IS 8009 : Part I : 1976 Code of Practice for Calculation of Sett lements of Foundations - Part I : Shallow Foundations Subjectedto Symmetrical Static Vertical Loads
IS 8763 : 1978 Guide for undistrubed sampling of sands and sandy soils
IS 9198 : 1979 Specification for compaction rammer for soil testing
IS 9214 : 1979 Method for determination of modulus of sub-grade reaction (k-value) of soils in the fieldIS 9259 : 1979 Specification for l iquid l i mit apparatus for soils
IS 9456 : 1980 Code of practice for design and construction of conical and hyperbolic paraboloidal types of shell fou ndations
IS 9556 : 1980 Code of practice for design and construction of diaphragm walls
IS 9640 : 1980 Specification for split spoon sampler
IS 9669 : 1980 Specification for CBR moulds and its accessories
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IS 9716 : 1981 Guide for lateral dynamic load test on piles
IS 9759 : 1981 Guidelines for de-watering during construction
IS 10042 : 1981 Code of practice for site-investigations for foundation in gravel boulder deposits
IS 10074 : 1982 Specification for compaction mould assembly for light and heavy compaction test for soils
IS 10077 : 1982 Specification for equipment for determination of shrinkage factors
IS 10108 : 1982 Code of practice for sampling of soils by thin wall sampler with stationery piston
IS 10270 : 1982 Guidelines for design and construction of prestressed rock anchors
IS 10379 : 1982 Code of practic for field control of moisture and compaction of soils of embankment and subgradeIS 10442 : 1983 Specification for e arth augers (spiral type)
IS 10589 : 1983 Specification for equipm ent for determination of subsurface sounding of soils
IS 10837 : 1984 Specification for moulds and accessories for determination of densit y index (relative density) ofcohesionless soils
IS 11089 : 1984 Code of practice for design and construction of ring foundation
IS 11196 : 1985 Specification for equipment for determination of liquid limit of soils cone penetration method
IS 11209 : 1985 Specification for mould assembly for determination of permeability of soils
IS 11229 : 1985 Specification for shear box for testing of soils
IS 11233 : 1985 Code of practice for design and construction of radar antenna, microwave and TV tower foundations
IS 11550 : 1985 Code of practice for field instrumentation of swelling pressure in expansive soils
IS 11593 : 1986 Specification for shear box (large) for testing of soils
IS 11594 : 1985 Specification for t hin walled sampling tubes and s ampler heads
IS 11629 : 1986 Code of practice for installation and operation of single point hydraulic over -flow setting gauge
IS 12023 : 1987 Code of practice for field monitoring of movement of st ructures using tape extensometer
IS 12175 : 1987 Specification for rapid moisture meter for rapid determination of water content for soil
IS 12208 : 1987 Method for measurement of earth pressure by hydraulic pressure cell
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IS 12287 : 1988 Specification for consolidometer for determination of consolidation properties
IS 12979 : 1990 Specification for mould for determination of linear shrinkage
IS 13094 : 1992 Guidelines for selection of ground improvement techniques for foundation in weak soils
IS 13301 : 1992 Guidelines for vibration isolation for machine foundations
IS 13468 : 1992 Specification for apparatus for determination of dry density of soils by core cutter method
IS 14893 : 2001 Non-Destructive Integrity Testing of Piles (NDT) Guidelines
IS 15284 : Part 1 : 2003 Design and Construction for Ground Improvement - Guidelines - Part 1 : Stone Columns
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Questions
1. Explain Density index of soil?
2. Explain the different divisions in which the soil is broadly divided in Indian
standard of soil classification system?
3. Explain in brief sub division of soil on the basis of arbitrarily selected liquid limit
of fine grained soils?
4. Define Void ratio, Porosity and Degree of saturation of soil?
5. Explain in brief the different types of failure in soil?
6. Define Liquid Limit, Plastic Limit and Shrinkage Limit in Plasticity Characteristicsof Soils?
7. List the different Tests which are specially required for deep foundations?
8. Explain the effect of water table on bearing capacity of soil?
9. Define Ultimate bearing capacity and Gross safe bearing capacity of soil?
10. When Pile foundation is recommended?