GEOTECHNICAL-ENGINEERING-2 module 1 module 2 module 3

M

1. GEOTECHNICAL
ENGINEERING -II

2. Soil Exploration –What is it and Why???
•Thefieldandlaboratoryinvestigationsrequiredtoobtainnecessary
dataregardingthesoil,forproperdesignandsuccessfulconstruction
ofanystructureatthesitearecollectivelycalledsoilexploration.
•Explorationinsoil-involvesasitevisit,quickvisualinspectionand
detailedteststodeterminethebehaviour

3. Objectives of Soil Exploration
Determination of the nature of the deposits of soil.
Determination of the depth and thickness of the various soil strata and their extent
in the horizontal direction.
The location of groundwater and fluctuations in GWT.
Obtaining soil and rock samples from the various strata.
The determination of the engineering properties of the soil and rock strata that
affect the performance of the structure
Determination of the in-situ properties by performing field tests.

4. Need for Soil Exploration
Todeterminethetypeoffoundationrequiredfortheproposedprojectatthesite,i.e.
shallowfoundationordeepfoundation.
Estimationoftheprobablesettlementofastructure.
Determinationofpotentialfoundationproblems(forexample,expansivesoil,
collapsiblesoil)
Establishmentofgroundwatertable.
Predictionofsoilpressureforstructureslikeretainingwalls
Establishmentofconstructionmethodsforchangingsubsoilconditions.

10. •Disturbed
In situ structure not retained
Water content, classification, compaction
•Undisturbed
Less disturbed
Shear strength, consolidation, permeability
SOIL SAMPLES

24. Indirect methods
kg

33. PLATE LOAD TEST

37. •Thetestpitshouldbeatleastfivetimesaswideasthetestplateand
thebottomofthetestplateshouldcorrespondtotheproposed
foundationlevel.
•Atthecentreofthepit,asmallsquareholeismadethesizebeingthat
ofthetestplateandthedepthbeingsuchthat,

38. (i)Afterexcavatingthepitofrequiredsizeandlevellingthebase,thetestplateis
seatedovertheground.
(ii)Aseatingpressureof7.0kN/m2(70g/cm2)isappliedandreleasedbeforeactual
loadingiscommenced.
(iii)Thefirstincrementofload,sayaboutone-tenthoftheanticipatedultimateload,is
applied.Settlementsarerecordedwiththeaidofthedialgaugesafter1min.,4min.,10
min.,20min.,40min.,and60min.,andlateronathourlyintervalsuntiltherateof
settlementislessthan0.02mm/hour,oratleastfor24hours.
(iv)Thetestiscontinueduntilaloadofabout1.5timestheanticipatedultimateloadis
applied.Accordingtoanotherschoolofthought,asettlementatwhichfailureoccurs
oratleast2.5cmshouldbereached.
(v)Fromtheresultsofthetest,aplotshouldbemadebetweenpressureandsettlement,
whichisusuallyreferredtoasthe‘‘load-settlementcurve’’,.Thebearingcapacityisdetermined
fromthisplot

40. •The plot between pressure and settlement usually consists of two straight
lines as shown in Figure. The point corresponding to the break gives the
failure point and the pressure corresponding to it is taken as the bearing
capacity.
•IS: 1888–1971 also recommends this method for use with plate load tests.

41. ALTERNATE METHOD FOR DETERMINATION OF BEARING
CAPACITY
Bearing capacity

42. Settlement of original foundation (S)
f

43. Ultimate bearing capacity (qu) for foundation

44. Limitations of Plate load test
Sizeeffectsareveryimportant.Sincethesizeofthetestplateandthesizeofthe
prototypefoundationareverydifferent,theresultsofaplateloadtestdonot
directlyreflectthebearingcapacityofthefoundation.
Consolidationsettlementsincohesivesoils,whichmaytakeyears,cannotbe
predicted,astheplateloadtestisessentiallyashort-termtest.
Resultsfromplateloadtestarenotrecommendedtobeusedforthedesignofstrip
footings,sincethetestisconductedonasquareorcircularplateandshapeeffects
enter.
Theloadtestresultsreflectthecharacteristicsofthesoillocatedonlywithina
depthofabouttwicethewidthoftheplate.Thiszoneofinfluenceinthecaseofa
prototypefootingwillbemuchlargerandunlessthesoilisessentially
homogeneousforsuchadepthandmore,theresultscouldbeterriblymisleading.

45. PRESSUREMETER TEST
•Thepressuremeterconsistsoftwoparts,theread-outunit,whichrestsonthe
groundsurface,andtheprobethatisinsertedintotheborehole.
•Theprobeconsistsofthreeindependentcells,ameasuringcellandtwoguard
cells.
•Theprobecanbeinstalledbypre-drillingaholeusinghollowstemaugerorhand
auger,orforcingtheprobeintothegroundanddisplacingthesoilbydriving,
jacking,orvibrating.
•Oncetheprobeisatthetestdepth,theguardcellsareinflatedtobracetheprobein
place.Thenthemeasuringcellispressurizedwithwater,inflatingitsflexible
rubberbladder,whichexertsapressureontheboreholewall.
•Asthepressureinthemeasuringcellincreases,theboreholewallsdeform.The
pressurewithinthemeasuringcellisheldconstantforapproximately60seconds,
andtheincreaseinvolumerequiredtomaintaintheconstantpressureisrecorded.
•Aload-deformationdiagram,asshowninFigure

49. •Thepressure-volumedataisplottedtodeterminethelimitpressure
(PL),cohesionandthepressuremeterdeformationmodulus(E).These
valuesareusedforfoundationdesign.

51. •The test is conducted in a predrilled borehole normally at intervals of
1m.
•The pressure of water in the measuring cell is increased in increments
until the soil fails.
•Usually failure is considered to have reached when the total expanded
volume of the test zone reaches twice the volume of the original
cavity.
•The asymptotic value of pressure corresponding to final point where
failure occurs is known as limit pressure (PL).

52. •Ultimate bearing capacity is directly proportional to the limit pressure
K is bearing capacity factor depending on type of foundation, depth and
soil type (0.8-0.9)
•Cohesion C= PL/9
•Pressure meter modulus is calculated as:
??????
�??????�=??????×????????????

53. SAMPLE DISTURBANCE

54. 10% ������??????��������������≤
= 0.5 to 3% ������??????��������������
= 0 to 2 % ������??????��������������
= 96 to 98 % ������??????��������������
L is the length of the sample obtained from the sampler and H is the penetration depth
Factors affecting soil disturbance while sampling

55. BORING LOG/ BORE HOLE LOG
•Informationonsubsurfaceconditionsobtainedfromtheboring
operationistypicallypresentedintheformofaboringrecord,
commonlyknownas“boringlog”.
•Acontinuousrecordofthevariousstrataidentifiedatvariousdepths
oftheboringispresented.
•Descriptionorclassificationofthevarioussoilandrocktypes
encountered,anddataregardinggroundwaterlevelhavetobe
necessarilygiveninapictorialmanneronthelog.

57. Subsoil profile from Bore log

58. SOIL EXPLORATION REPORT
Areportisthefinaldocumentofthewholeexerciseofsoilexploration.Areport
shouldbecomprehensive,clearandtothepoint.
1.Introduction,whichincludesthescopeoftheinvestigation.
2.Descriptionoftheproposedstructure,thelocationandthegeological
conditionsatthesite.
3.Detailsofthefieldexplorationprogramme,indicatingthenumberofborings,
theirlocationanddepths.
4.Detailsofthemethodsofexploration
5.Generaldescriptionofthesub-soilconditionsasobtainedfromin-situtests,
suchasstandardpenetrationtestandconepenetrationtest.

59. 6.Detailsofthelaboratorytestsconductedonthesoilsamplescollectedandtheresults
obtained.
7.Depthofthegroundwatertableandthechangesinwaterlevels.
8.Analysisanddiscussionofthetestresults.
9.Recommendationsabouttheallowablebearingpressure,thetypeoffoundationof
structure.
10.Calculationsfordeterminingsafebearingpressure,pileloads,etc.
11.Tablescontainingborelogs,andotherfieldandlaboratorytestresults.
12.Drawingswhichincludesite-plan,testresultsplottedintheformofchartsandgraphs,
soilprofiles,etc.

60. Geotechnical Engineering –II
Assignment No. 1
(Last date of submission- 19/01/2019)

1. Explain Standard Penetration test. Discuss the corrections applied to the observed N-
values.


2. Explain the pressure meter test with a neat sketch. Also write the limitations of this test.


3. With a neat sketch, explain the procedure for conducting a Plate load test. How do you
use the results of this test in designing foundations?


4. List the objectives of soil exploration. Describe the salient features of soil investigation
report. Explain with the neat diagram of a borelog.


5. With neat sketches explain the different boring methods.


6. Explain the factors affecting soil disturbance while sampling. During a soil exploration
programme, a soil sample of length 550mm was recovered using a split spoon sampler.
The penetration length of the sample was 610mm. Dimensions of the sampler is given
below:
Inside and outside diameter of the sample tube = 5 and 38mm respectively
Inside and outside diameter of the driving shoe = 35 and 51mm respectively
Determine inside clearance, outside clearance, area ratio and recovery ratio and make
comment about the degree of disturbance of the soil sample.

61. MODULE-II
STABILITY OF SLOPES
GEOTECHNICAL ENGINEERING-II

62. SLOPES
•Earth slope-an unsupported, inclined surface of a soil mass
•Formed for railway formations, highway embankments, earth dams, canal banks etc.

63. Slope Failures

69. NEED FOR STABILITY OF SLOPES
•Steepestsectionisthemosteconomicalsection
•Verysteepslopesarehowevernotstable
•Forsafetyandeconomy-slopesprovidedareneithertoosteepnorflat
•Thesteepestslopeswhicharestableandsafewouldbeprovided
•Failureofsoilmassoccursalongaplaneorcurvedsurfacewhenalargemassofsoilslides
w.r.t.remainingsoilmass
•Adownwardandoutwardmovementofsoilmassoccursduringfailure
•Failureoccurswhenforcescausingfailurearegreaterthantheshearingresistancedeveloped
alongacriticalplane

70. SLOPES OF EARTH ARE OF TWO TYPES
1.Natural slopes
slopes exist in hilly areas
2. Man made slopes
The slopes of embankments constructed for roads railway lines, canals etc.
The slopes of earth dams constructed for storing water.

71. THE SLOPES WHETHER NATURAL OR ARTIFICIAL
MAY BE
1. Infinite slopes
Theterminfiniteslopeisusedtodesignateaconstantslopeofinfinite
extent.
Example-The long slope of the face of a mountain
2. Finite slopes
Finiteslopesarelimitedinextent.
Theslopesofembankmentsandearthdamsareexamplesoffinite
slopes.

73. TYPES OF SLOPE FAILURE
Slope can fail due to one of the following methods
1.Rotational failures
2.Translational failures
3.Compound failures
4.Wedge failures
5.Miscellaneous failures

74. 1. Rotational failures
•Occurs by rotation along a slip surface by downward and outward movement of soil mass
•Slip circle formed is circular for homogeneous soil and non-circular for non-
homogeneous soils
a) Toe failure
•Occurs along surface that passes through the toe
•Most common failure
•occurs when the slope is steep and homogeneous.
Toe failure

75. b) Slope failure
•Failure surface intersects the slope above the toe
•This type of failure occurs when the slope angle
is large and when the soil at the toe portion is strong.
c)Base failure
•Failure surface passes below the toe
•Occurs when weak stratum lies beneath the toe
Slope failure
Base failure

76. 2. Translational Failure
•Occursininfiniteslopesalongalongfailuresurfaceparalleltotheslope
•Shapeoffailuresurfaceinfluencedbypresenceofhardstratumatashallow
depthbelowslopesurface
•Commoninslopesoflayeredmaterials

77. 3. Wedge Failure
•Plane failure, wedge failure or block failure
•Failure along an inclined plane
•Occurs when distinct blocks and wedges of the soil mass become
separated
•Similar to translational failure in many aspects
•Wedge failure can occur in finite slopes
•Having two different materials
•Homogeneous slopes with cracks, joints or any other specific plane of
weakness

78. 4. Compound Failures
•Combination of rotational and translational failures
•Failure surface is curved at both ends and is plane in the middle portion
•Occurs normally when a hard stratum is exists at a considerable depth below the toe

79. Infinite Slopes: Analysis
•Infiniteslopeshavedimensionsthatextendedovergreatdistancesand
thesoilmassisinclinedtothehorizontal.
•Failureisassumedtooccuralongaplaneparalleltothesurface.
•Analysiscases
Case(i)Cohesionlesssoil
Case(ii)Cohesivesoil
Case(iii)Cohesive-frictionalsoil

80. Infinite slopes in Cohesionlesssoils
Consider an infinite slope in
a cohesionlesssoil inclined
at an angle to the horizontal
as shown.
Consider an element ‘abcd’
of the soil mass.

83. “The maximum inclination of an infinite slope in a cohesionlesssoil for stability
is equal to the angle of internal friction of the soil”.

86. Infinite slope in pure cohesive soil

87. Infinite slope in cohesive frictional soil (C and φ)

88. Finite Slopes: Analysis
1.Swedish Circle/Arc Method/Method of slices/Standard
method
2.Bishop’s Simplified method
3.Taylor’s stability Number Method

89. Swedish method of slices
•Adoptedforacohesive–frictional(c-Ø)soil
•Thetotalstressanalysiscanbeadopted.

105. T
W

106. T
α

108. •Bishop’ssimplifiedmethod(BSM)considerstheinterslicenormal
forcesbutneglectstheintersliceshearforces.Itfurthersatisfies
verticalforceequilibriumtodeterminetheeffectivebasenormal
force(N’).

109. •Iftheslopeangleβ,heightofembankmentH,theeffectiveunit
weightofmaterialɣ,angleofinternalfrictionφandunitcohesionc
areknown,thefactorofsafetymaybedetermined.
•Taylor(1937)conceivedtheideaofanalyzingthestabilityofalarge
numberofslopesthroughawiderangeofslopeanglesandanglesof
internalfriction,andthenrepresentingtheresultsbyanabstract
numberwhichhecalledthe"stabilitynumber".Thisnumberis
designatedasN
TAYLOR STABILITY NUMBER METHOD

110. TAYLOR STABILITY NUMBER AND CHART
•StabilityNumberisdefinedasS
n=c/(F
cγH)=c
m/(γH)
•Mobilizedcohesionc
m=c/F
c
•ReciprocalofStabilityNumber-Stabilityfactor
•Stabilitynumber-dimensionlessquantity
•Foranalysisofsimpleofsimplesectionsandofhomogeneoussoils
•ChartspreparedindicatingStabilityNumberandslopeangleβfordifferentvaluesofΦ
50

111. TAYLOR STABILITY NUMBER AND CHART
51

112. TAYLOR STABILITY NUMBER AND CHART
52

113. •For cohesive soils, the stability number is related to parameter D
•D = Depth of hard stratum below the top of slope / Height of slope

114. TAYLOR STABILITY NUMBER AND CHART
•Stability number can be used to determine the factor of safety
F
c= c / c
m= c / (S
n* γ* H)
•Stability charts can be used to determine the steepest slope for a given factor of safety
54

120. Critical height of slope Hc
•It is the maximum height a slope can have assuming activation of full
cohesion
•Height after applying a certain factor of Safety
??????
??????=??????
??????×??????

121. Question-
What is the maximum unsupported height of a
vertical-cut in pure clay???

122. Submerged and sudden drawdown condition of slope
??????
′
=??????
�??????�−??????
??????

125. An embankment is 5.4 m high with side slopes of 1.5 H : 1V. The
soil has C= 20kPa, φ=50 and γ=15kN/m
3
. If the Felleniusangles
are α=26
0
and β=35
0
, determine the factor of safety of the slope
using Swedish method of slices.

127. Geotechnical Engineering –II
Assignment No. 2
(Last date of submission- 25/01/2019)

1. How a slope is analyzed using Swedish circle method and Bishop’s method of slices?
Derive an expression for the factor of safety for both?

2. An embankment is 5.4m high with side slopes of 1.5 H : 1V. The soil has C= 20kPa,
φ=50 and γ=15kN/m
3
. If the Fellenius angles are α=26
0
and β=35
0
, determine the factor
of safety of the slope using Swedish method of slices.
3. Explain the Taylor’s stability Number method to Analyze finite slopes. Determine the
factor of safety with respect to cohesion for a submerged embankment 10 m high and
having a slope of 40
0
. The properties of the soil are c = 40kN/m
2
, φ = 10
0
and γsat=18
kN/m
3
. Given stability numbers for different slope angles are as follows. Also find the
critical height of slope.



4. Explain different types of slope failures with sketches
5. An embankment of 10m high is inclined at an angle of 36°, to the horizontal. A stability
analysis by the method of slices gives following forces per meter.
Sum of Shearing forces=450kN
Sum of Normal forces=900kN
Sum of Neutral forces=216kN
The length of the failure arc is 27 m. Laboratory tests on the soil indicate the effective
values c′ and φ′ as 20 kN/m
2
and 18° respectively. Determine the factor of safety with
respect to a) Shear strength and b) Cohesion

6. A 5m deep canal has side slopes of 1:1. The properties of soil are C = 30kN/m
2
, φ =
20°, e = 0.7 and G =2.7. If Taylor’s stability number is 0.11, determine the factor of
safety with respect to cohesion when the canal runs full. Also find the same in case of
sudden drawdown, if Taylor’s stability number for this condition is 0.125.

7. Distinguish between finite and infinite slopes. Write the equation of factor of safety of
an infinite slope in a) Cohesionless soil b) Cohesive and Frictional soil (C-ɸ) soil.

128. MODULE-III
EARTH PRESSURE
GEOTECHNICAL ENGINEERING-II

129. Lateral earth pressure
Lateral earth pressure is the pressure that soil exerts in
the horizontal direction

131. Why We Study Lateral Earth Pressure?
•Thelateralearthpressureisimportantbecauseitisconsideredinthe
designofgeotechnicalengineeringstructuressuchasretainingwalls,
basements,tunnels,deepfoundationsandbracedexcavations.
•Earthretainingstructuresarecommoninamanmadeenvironment.

132. Lateral earth pressure is a function of:
Type and amount of wall movement-Wall flexibility
Shear strength parameter of soil
Unit weight of soil
Drainage conditions of the soil

133. •Soilmassisstable-slopeofthesurfaceofthesoilmassisflatterthanthe
safeslope.
•Whereslopeislimited-soilhastoberetainedatasteeperslope.
•Soilhastobesupportedbyretainingstructure.
•Soilsatdifferentlevelsaresupportedbyretainingstructuresoneithersides.
•Soilatthehigherlevelwillslideandultimatelyfailintheabsenceof
retainingstructure.
•Determinationofmagnitudeandlineofactionofforcecriticalfordesignof
earthretainingstructures.

134. Lateral earth pressures
AT REST-PRESSURE ACTIVE EARTH PRESSURE PASSIVE EARTH PRESSURE
Not subjected to any lateral yieldingor movementsOccurswhen soil tends to
stretch horizontally
Occurswhen soil tends to
compress horizontally
Firmly fixedat its top Notfixed at top Notfixed at top
Notallowed to move laterally or rotate freelyAllowed to rotatefreely or
move laterally
Allowed to rotatefreely or
move laterally
Inelastic equilibrium In plastic equilibrium In plastic equilibrium
1.Retaining walls with basement slab at top
2.Bridge abutment
1. Retaining wall 1. Retaining wall
7

135. 8
No Movement
At-Rest Pressure
Basement Slab
Active
Pressure
Passive
Pressure
Movement Towards Left

137. Rankine’s Analysis

163. Coulomb’s Theory of Earth Pressure

165. Θ= Batter Angle
δ= Angle of Wall friction
β = Surcharge angle
δ=Thisisanangleoffriction
betweenthewallandbackfillsoiland
isusuallycalled‘wallfriction’.

166. Culmann’sGraphical Method for Active Earth
Pressure of CohesionlessSoil

167. ɸ line
??????=????????????−??????−??????

170. TYPES OF RETAINING WALLS
•Gravity retaining walls
•Cantilever retaining walls
•Sheet pile retaining walls
•Counter-fort / Buttressed retaining wall

171. Gravity retaining walls

172. •Itisthattypeofretainingwallthatreliesontheirhugeweight
toretainthematerialbehinditandachievestabilityagainst
failures.
•GravityRetainingwallcanbeconstructedfromconcrete,
stoneorevenbrickmasonry.Gravityretainingwallsare
muchthickerinsection.
•Geometryofthesewallsalsohelpthemtomaintainthe
stability.

173. Cantilever retaining walls
•Acantileverretainingwallisonethat
consistsofawallwhichisconnectedto
foundation.
•Theyarethemostcommontypeusedas
retainingwalls.Cantileverwallrestona
slabfoundation.
•Thisslabfoundationisalsoloadedby
back-fillandthustheweightofthe
backfillandsurchargealsostabilizesthe
wallagainstoverturningandsliding.

174. Sheet pile retaining walls

176. •Sheetpileretainingwallsareusuallyusedinsoftsoilsandtight
spaces.
•Sheetpilewallsaremadeoutofsteel,vinylorwoodplankswhichare
drivenintotheground.
•Theyaremainlyusedastemporarystructures
•Taller sheet pile walls will need a tieback anchor for stability

177. Counter-fort / Buttressed retaining wall
•Counterfort retaining wall
consists of a stem, toe slab and
heel slab as in case of cantilever
retaining wall.
•It also consists of counterforts
are regular interval which divides
the stem.

178. Stability of retaining walls

181. Geotechnical Engineering –II
Assignment No. 3
(Last date of submission- 25/03/2019)
1. Differentiate active, passive and earth pressure at rest.

2. An unsupported excavation is made in a clay layer. The properties of clay are c =23
kN/m
2
, γ =19 kN/m
3
and Φ =15
0
.
Determine.
i. Depth of tension crack.
ii. Draw active earth pressure diagram.
iii. Determine the total thrust
Assume the depth of clay layer as 6m.


3. A retaining wall 6m high, with a smooth vertical back is pushed against a soil mass
having C= 36 kN/m
2
and Φ =15° and γ =18 kN/m
3
. What is the total Rankine passive
pressure, if the horizontal soil surface carries a uniform load of 35 kN/m
2
? What is the
point of application of the resultant thrust?

4. Describe the construction procedure for Culmann’s graphical method.


5. A smooth vertical wall 6 m high retains a soil with c = 2.5 kN/m
2
, φ = 28°, and γ = 20
kN/m
3
. Show a) Rankine passive pressure distribution, b) Rankine Active earth
pressure distribution and also determine the magnitude and point of application

6. Determine the active pressure on the retaining wall shown in Figure. Take ɣw=10
kN/m
3
.



7. Discuss the design principles of retaining walls.

182. MODULE-IV
BEARING CAPACITY
GEOTECHNICAL ENGINEERING-II

183. INTRODUCTION
Thefoundationshouldbedesignedsuchthat
Thesoilbelowdoesnotfailinshear,i.etheloadappliedto
soilshouldbesuchthattheinducedstressesinsoilislesser
thanitscapacity
Settlementiswithinthesafelimits
Nodifferentialsettlementshouldoccur
2

184. 3
Types of Foundations

185. Bearing Capacity of soil
4
Bearingcapacityistheabilityofsoiltosafelycarrythe
pressure/loadplacedonthesoilfromanyengineered
structurewithoutundergoingshearfailureand
excessivelargesettlements.

186. 5

187. 6

188. BASIC DEFINITIONS
Grosspressureintensity(q)
Totalpressureatthebaseofthefootingduetoweightof
superstructure,selfweightofthefootingandtheweightof
theearthfill/soil
NetPressureIntensity(q
n)
Differenceinintensitiesofthegrosspressureafterthe
constructionofthestructureandtheoriginaloverburden
pressure
q
n=q–γD
7

189. UltimateBearingCapacity(q
u):
Theultimatebearingcapacityistheminimumgrosspressure
intensityatthebaseofthefoundationatwhichsoilfailsin
shear
NetultimateBearingCapacity(q
nu):
Itistheminimumnetpressureintensityatthebaseof
foundationthatcauseshearfailureofthesoil
Thus,q
nu=q
u–γD(overburdenpressure)
8

190. Net Safe Bearing Capacity (q
ns) :
Net ultimate bearing capacity divided by a Factor of safety
Thus, q
ns= q
nu/ F
F -Factor of safety usually taken as 2.00 -3.00
Safe Bearing Capacity (q
s) :
It is the maximum pressure which the soil can carry safely
without risk of shear failure
It is equal to net safe bearing capacity plus overburden
q
s= q
nu/ F + γ D
9

191. Net Safe Settlement Pressure (q
np) :
It is the net pressure which the soil can carry without exceeding
allowable settlement
Net Allowable Bearing Pressure (q
na):
It is the net bearing pressure which can be used for design of
foundation
Thus,
q
na= q
ns; if q
np> q
ns
q
na= q
np; if q
ns> q
np
It is also known as Allowable Soil Pressure
10

192. TYPES OF BEARING CAPACITY FAILURES
Distinctfailurepatternsaredevelopeddependingonfailure
mechanism
Vesic(1973)classifiedshearfailureofsoilunderafoundation
baseintothreecategoriesdependingonthetypeofsoil&
locationoffoundation
GeneralShearfailure
LocalShearfailure
PunchingShearfailure
11

193. In low compressibility (dense or stiff) soils
Heaving on both sides of foundation
Final slip (movement of soil) on one side only causing structure
to tilt
12
BEARING CAPACITY FAILURES-GENERAL SHEAR
FAILURE

194. 13
Load vs. Settlement behaviour

195. Ithaswelldefinedfailuresurfacereachingtogroundsurface
Thereisconsiderablebulgingofshearedmassofsoiladjacent
tofooting
Failureisaccompaniedbytiltingoffooting
Failureissudden
Ultimatebearingcapacityiswelldefined
14
BEARING CAPACITY FAILURES-GENERAL SHEAR
FAILURE

196. In highly compressible soils
Only slight heaving on sides
Significant compression of soil under footing but no tilting
15
BEARING CAPACITY FAILURES-LOCAL SHEAR
FAILURE

197. 16
Load vs. Settlement behaviour

198. In soils of high compressibility and in sands having relative density
between 35 and 70 percent
Failure pattern is clearly defined only immediately below the
footing
Failure surface do not reach ground surface
Only slight bulging of soil around the footing
Failure is not sudden and there is no tilting of the footing
Failure is defined by large settlements
Ultimate bearing capacity not well defined
17
BEARING CAPACITY FAILURES-LOCAL SHEAR
FAILURE

199. Inloose,uncompactedsoils
Verticalshearingaroundedgesoffooting
Highcompressionofsoilunderfooting,hencelargesettlements
Noheaving,notilting
18
BEARING CAPACITY FAILURES-PUNCHING
SHEAR FAILURE

200. 19
Load vs. Settlement behaviour

201. Nofailurepatternobserved
Nobulgingofsoilaroundthefooting
Notiltingoffooting
Failureischaracterisedintermsofverylargesettlements
Ultimatebearingcapacitynotwelldefined
20
BEARING CAPACITY FAILURES-PUNCHING
SHEAR FAILURE

202. 21

203. 22
TERZAGHI’S BEARING CAPACITY THEORY
Surcharge stress/Overburden Stress

204. Terzaghi’sBearing capacity equation for
determining ultimate bearing capacity of
strip footing (Only)
23
C= Cohesion ɣ = Unit weight of soil
B= Width of foundation
Df= Depth of foundation

205. 24

206. 25

207. 26

208. 27

209. 28

210. 29

211. 30

212. 31

213. 32
??????
′
isthesubmergedoreffectiveunitweight(??????
�??????�−??????
??????)

214. 33

215. 34

216. Alternate Approximate method
35

217. 36

218. 37

219. Extension of Terzaghi’sEquation for
Local shear failure of soils
38

220. 39
(For Cohesive soils only)

221. 40
q=ɣ*Df

222. 41

223. 42

224. PLATE LOAD TEST

228. Thetestpitshouldbeatleastfivetimesaswideasthe
testplateandthebottomofthetestplateshould
correspondtotheproposedfoundationlevel.
Atthecentreofthepit,asmallsquareholeismadethe
sizebeingthatofthetestplateandthedepthbeingsuch
that,

229. (i)Afterexcavatingthepitofrequiredsizeandlevellingthebase,thetestplateisseatedoverthe
ground.
(ii)Aseatingpressureof7.0kN/m2(70g/cm2)isappliedandreleasedbeforeactualloadingis
commenced.
(iii)Thefirstincrementofload,sayaboutone-tenthoftheanticipatedultimateload,isapplied.
Settlementsarerecordedwiththeaidofthedialgaugesafter1min.,4min.,10min.,20min.,40
min.,and60min.,andlateronathourlyintervalsuntiltherateofsettlementislessthan0.02
mm/hour,oratleastfor24hours.
(iv)Thetestiscontinueduntilaloadofabout1.5timestheanticipatedultimateloadisapplied.
Accordingtoanotherschoolofthought,asettlementatwhichfailureoccurs
oratleast2.5cmshouldbereached.
(v)Fromtheresultsofthetest,aplotshouldbemadebetweenpressureandsettlement,whichis
usuallyreferredtoasthe‘‘load-settlementcurve’’,.Thebearingcapacityisdeterminedfrom
thisplot

231. The plot between pressure and settlement usually consists
of two straight lines as shown in Figure. The point
corresponding to the break gives the failure point and the
pressure corresponding to it is taken as the bearing
capacity.
IS: 1888–1971 also recommends this method for use with
plate load tests.

232. ALTERNATE METHOD FOR DETERMINATION OF BEARING
CAPACITY
Bearing capacity

233. Settlement of original foundation (S)
f

234. Ultimate bearing capacity (qu) for
foundation

235. Settlement in Soil
54
Immediate Settlement
Consolidation Settlement

236. 55

237. 56

238. 57

239. Allowable/Permissible Settlements
58

240. MODULE V
DEEP FOUNDATIONS

241. 2

242. PILE FOUNDATIONS-USES
Highlycompressibleorweakstratadirectlybelowthegroundsurface
Foundationsforirregularstructures-irregularrelativetotheplanandload
distribution
Transmissionofloadthroughdeepwaterstoahardstratum
Structureswithriskofsoilbeingwashedout-shallowfoundationsalmostimpossible
Inexpansivesoils-subjecttoswellingorshrink
Incollapsiblesoils
3

243. PILE FOUNDATIONS
PILES
END
BEARING
FRICTION
COMPACTI
ON
TENSION
ANCHOR
FENDER
PILE
BATTER
SHEET
4
BASED ON FUNCTION
PILES
STEEL
CONCRETE
TIMBER
COMPOSITE
BASED ON MATERIAL

244. PILE FOUNDATIONS
PILES
END
BEARING
FRICTION
COMBINED
END
BEARING
AND
FRICTION
5
MODE OF TRANSFER OF LOAD
PILES
DRIVEN
PILES
DRIVEN
AND CAST-
IN-SITU
BORED AND
CAST-IN-
SITU
SCREW
JACKED
PILES
BASED ON METHOD OF INSTALLATION

245. 6

246. 7

247. 8

248. 9 Compaction Piles

249. 10 Fender Piles

250. 11

251. 12

252. 13 Batter Piles

253. 14

254. 15

255. 16

256. 17

257. 18

258. 19

259. 20

260. 21

261. LOAD CARRYING CAPACITY OF PILE
22
•The following is the classification of the methods of determining pile
capacity:
(i)Static analysis
(ii) Dynamic analysis
(iii) Load tests on pile
(iv) Penetration tests

262. Static Analysis
•The ultimate bearing load of a pile is considered to be the sum of the
end-bearing resistance and the resistance due to skin friction:
23

263. 24
q = ɣ*Depth
Criticaldepthcanbetakenas
10*B-loosesands
20*B-densesands
Piles in sand
B is the diameter of the pile

264. 25
ca = adhesion
σ
h=K*σ
v[K=coefficientofearthpressure] Average vertical stress/ surcharge is considered for analysis
????????????=??????∗
????????????
�
∗????????????????????????

265. 26
Piles in Clay
N
c=bearingcapacityfactorfordeepfoundation
9-commonlyusedforpiles
Ultimateload(Q
u)=c*N
c*A
b+α*c*A
s

266. 27

267. 28

268. 29

269. DYNAMIC FORMULAE
•EngineeringNewsRecordFormulae
Q
u=
(W∗h∗η
h)
(S+C)
•S=penetrationofpileperhammerblow;obtainedfromtheaverageforthelast
fewblowsofthehammer
•C=constant
•2.54cm-drophammer
•0.254cm-steamhammer
•Q
u=
(En∗η
h)
(S+C)
E
n=energyofhammerinkN-cm
30

270. •EngineeringNewsRecordFormulae
•Efficiencyofdrophammer-0.7to0.9
•Singleacting -0.75
•Doubleacting-0.85
•Dieselhammer-0.80to0.90
•Factorofsafety-6(recommended)
•Formulanotdependable
31

271. Modified Engineering News Record Formulae
•P=weightofpile;e=coefficientofrestitution;η
h=hammer
efficiency
•Hammerefficiencydependenton
•Piledrivingequipment
•Drivingprocedure
•Groundconditions
32
Hammer Type Drop SingleActing DoubleActing Diesel
Efficiency 0.75 –1 0.75 -0.85 0.85 0.85 -1

272. Coefficient of Restitution (e)
33
Type of Pile Coefficient of Restitution
Broomedtimber pile 0.0
Good timber pile 0.25
Drivingcap with timber dolly on steel pile 0.3
Driving cap with plastic dolly on steel pile 0.5
Helmet with compositeplastic dolly and packing on
R.C. C. Pile
0.4

273. •Hiley’sFormulae
•Takesintoaccountthevariouslosses
•Q
f=ultimateloadonpile
•W=weightofhammer,inkg
•H=heightofdropofhammer,incm
•S=penetrationorset,incmperblow
•C=totalelasticcompression=C
1+C
2+C
3
34

274. DYNAMIC FORMULAE
•C
1,C
2,C
3=temporaryelasticcompressionofdollyandpacking,pileandsoil
respectively
•η
h=efficiencyofhammer
•η
b=efficiencyofhammerblow
=
=
P=weightofpile
e=coefficientofrestitution
35

275. 36

276. Group Capacity of piles
37

277. 38

278. 39

279. 40

280. 41
=

281. 42

282. 43

283. 44

284. 45
For Individual Piles
Individual capacity of pile
??????�??????�??????????????????????????????�??????�=൯??????
??????(??????
Group capacity of pile
??????�∗�
??????�=??????.??????×�??????×��×??????

285. 46

286. Pile Load test
47

287. 48
B=Diameter of Pile

288. 49

289. 50

290. 51

291. 52

292. 53

293. 54

294. Settlement of pile groups in clay
•Theequationforconsolidationsettlementmaybeusedtreatingthepilegroupas
ablockorunit.
•Theincreaseinstressistobeevaluatedappropriatelyundertheinfluenceofthe
loadonthepilegroup.
•Whenthepilesareembeddedinauniformsoil(frictionandend-bearingpiles),
thetotalloadisassumedtoactatadepthequaltotwo-thirdsthepilelength.
•ConventionalsettlementanalysisproceduresassumingtheBoussinesqor
Westergaardstressdistributionarethenappliedtocomputetheconsolidation
settlementofthesoilbeneaththepiletip.
55

295. 56

296. •Calculatethefinalsettlementoftheclaylayershownbelowduetoanincreaseinpressure
of30kN/m
2
atthemid-heightofthelayer.Takeγ
w=10kN/m
3
.
57
Sand γ= 20 kN/ m
3
Clay γ= 18 kN/ m
3
C
c= 0.22 e
0= 1.30
4.0 m
2.5 m

297. γ
w= 10 kN/ m
3
; γ
sand= 20 kN/ m
3
; γ
clay= 18 kN/ m
3
Height of sand layer = h
1= 4 m
Height of clay layer = h
2= 1.25 m
C
C= 0.22; e
0= 1.30
Additional pressure = 30 kN/ m
2
Pressure at the center of the clay layer = 20 * 4 + 18 * 1.25 = 102.5 kN/ m
2
Settlement ∆H = C
C* H * log
10((σ0’+ ∆σ’) / σ0’) / (1 + e
0)
= 0.22 * 2.5 * log
10((102.5 + 30) / 102.5) / (1 + 1.30)
= 0.0266 m = 2.66 cm
58

298. 59

299. 60

300. Well Foundations
•Wellfoundationisthemostcommonlyadoptedfoundationformajor
bridgesinIndia.
•Sincethenmanymajorbridgesacrosswiderivershavebeenfoundedon
wells.
•Wellfoundationispreferabletopilefoundationwhenfoundationhasto
resistlargelateralforces
•Theconstructionprinciplesofwellfoundationaresimilartothe
conventionalwellssunkforundergroundwater.
•Well foundations have been used in India for centuries.
61

301. Advantages of well foundation
62

302. 63

303. 64

304. 65

305. 66

306. Types of Well Foundation
67

307. 68

308. 69

309. 70

310. 71

311. 72

312. 73

313. Types of well shapes
74

314. 75

315. 76

316. 77

317. 78

318. 79

319. 80

320. 81

321. 82

322. Design aspects of well foundation
83

323. 84

324. 85

325. TerzaghiandPeckhavesuggestedtheultimatebearing
capacitycanbedeterminedfromthefollowingexpression.
86
u