3/14/2011 1 Basic Soil Mechanics Basic Soil Mechanics: Basic soil properties, correlation between engineering parameters, geotechnical investigation, bore log. Pile foundation: Jacket main piles, skirt piles, driven piles, drilled and grouted piles, steel and concrete piles, axial capacity, point bearing and skin friction, factor of safety, lateral load on piles, p-y, t-z and q-z curves, pile group effect, scour around piles, seabed subsidence and design of piles against seabed movement, negative skin friction, cyclic degradation, main pile to jacket connections, skirt pile to jacket connections, API RP 2A provisions. Pile Installation: Minimum pile wall thickness, pile handling stresses, static and dynamic stresses, pile stickup, stresses during stick up, wave and current loads, hammer selection, pile driving stresses, wave equation analysis, pile driving fatigue, API RP 2A guidelines. Pile Testing: 27 June 2009 Dr. S. Nallayarasu Department of Ocean Engineering Indian Institute of Technology Madras-36 1 Pile Testing: Working load test, ultimate load test, pile monitoring during driving, pile integrity testing, high strain dynamic testing, rebound method. Special foundations: Mud-mats: bearing capacity, sliding stability, over-turning stability, short term and long term settlements, factor of safety; Bucket foundation; Suction anchors; Gravity foundation. Basic Soil Mechanics BASIC SOIL MECHANICS Basic soil properties Correlation between engineering parameters Geotechnical investigation Bore log 27 June 2009 Dr. S. Nallayarasu Department of Ocean Engineering Indian Institute of Technology Madras-36 2 Bore log
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Pile foundation:Jacket main piles, skirt piles, driven piles, drilled and grouted piles, steel and concretepiles, axial capacity, point bearing and skin friction, factor of safety, lateral load onpiles, p-y, t-z and q-z curves, pile group effect, scour around piles, seabed subsidenceand design of piles against seabed movement, negative skin friction, cyclic degradation,main pile to jacket connections, skirt pile to jacket connections, API RP 2A provisions.
Pile Installation:Minimum pile wall thickness, pile handling stresses, static and dynamic stresses, pilestickup, stresses during stick up, wave and current loads, hammer selection, pile drivingstresses, wave equation analysis, pile driving fatigue, API RP 2A guidelines.
Pile Testing:
27 June 2009 Dr. S. NallayarasuDepartment of Ocean Engineering
Indian Institute of Technology Madras-36
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Pile Testing:Working load test, ultimate load test, pile monitoring during driving, pile integritytesting, high strain dynamic testing, rebound method.Special foundations: Mud-mats: bearing capacity, sliding stability, over-turning stability,short term and long term settlements, factor of safety; Bucket foundation; Suctionanchors; Gravity foundation.
27 June 2009 Dr. S. NallayarasuDepartment of Ocean Engineering
Indian Institute of Technology Madras-36
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Basic Soil Mechanics
CLAY STRUCTURES
27 June 2009 Dr. S. NallayarasuDepartment of Ocean Engineering
Indian Institute of Technology Madras-36
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a) Dispersed, b) Flocculated, c) Book house, d) Turbostratic e) Example of a natural clay
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Basic Soil Mechanics
Soil type Term Field test
Sands, gravels
Loose
Dense
Can be excavated with a spade; 50 mm wooden peg can be easily driven Requires a pick for excavation; 50 mm wooden peg is hard to driveVisual examination; pick removes soil in lumps
BASIC CHARACTERS OF SOIL
Slightly cemented
Visual examination; pick removes soil in lumps which can be abraded
Silts Soft or looseFirm or dense
Easily moulded or crushed in the fingersCan be moulded or crushed by strong pressure in the fingers
Clays Very soft
SoftStiff
Exudes between the fingers when squeezed in the handMoulded by light finger pressureCannot be moulded by the fingers; can be indented by the thumb
27 June 2009 Dr. S. NallayarasuDepartment of Ocean Engineering
Indian Institute of Technology Madras-36
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Very stiff Can be indented by the thumbnail
Organic, peats Firm Spongy Plastic
Fibres already compressed togetherVery compressible and open structure Can be moulded in the hand and smears the fingers
Basic Soil Mechanics
Homogeneous Interstratified
Deposit consists essentially of one soil typeAlternating layers of varying types or with bands or lenses of other materials (an interval scale for bedding spacing or
BASIC CHARACTERS OF SOIL
of other materials (an interval scale for bedding spacing or layer thickness can be used)
Homogeneous Weathered
A mixture of soil typesCoarse particles may be weakened and may show concentric layeringFine soils usually have crumb or columnar structure
Fissured (clays) Breaks into polyhedral fragments along fissures (interval scale for spacing of discontinuities may be used)
Intact (clays) No fissures
27 June 2009 Dr. S. NallayarasuDepartment of Ocean Engineering
Indian Institute of Technology Madras-36
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Intact (clays) No fissuresFibrous (peats) Plant remains are recognizable and retain some strength Amorphous (peats)
Recognizable plant remains are absent
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Basic Soil Mechanics
Soil groups Subgroups and laboratory identification
GRAVEL and SAND may be qualified sandy GRAVEL and gravelly SAND, etc., where appropriate
Group symbol
Subgroup symbol
Fines (% less than 0.06 mm)
Liquid limit
GW GWof Slightly silty or clayey
British soil Classification System for Engineering Purposes
GWGGP
G-MG-F
G-CGM
GFGC
SW
GW
GPU GPg
GWM GPM
GWC GPCGML.etc
GCL, GCIGCH,GCVGCESW
0 to 5
5 to 15
15 to 35
CO
AR
SE
SO
ILS
35%
of
the
mat
eria
l is
fin
er
than
0.0
6 m
m
GR
AV
EL
S
Mo
re t
han
50%
of
coar
se m
ater
ial
is o
gra
vel
size
(co
arse
th
an 2
mm
)
%
Slightly silty or clayey GRAVEL
Slightly GRAVEL Clayey GRAVEL
Very stilty GRAVEL
Very clayey GRAVEL
Slightly silty or
27 June 2009 Dr. S. NallayarasuDepartment of Ocean Engineering
Indian Institute of Technology Madras-36
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SSP
S-MS-F
S-C
SPu SPg
SWM SPM
SWC SPC
0 to 5
5 to 15
CL
ess
than
3
SA
ND
S
Mo
re t
han
50
of
coar
se
mat
eria
l is
of
san
d s
ize
(mo
re t
han
2
mm
)
g y yclayey SAND
Silty SAND
Clayey SAND
Basic Soil MechanicsVery Silty SAND
Very clayey SAND
SMSFSC
SML, etc
SCLSCISCHSCVSCE
15 to 35
ll G G
SA
ND
S M
ore
than
50%
of
coar
se m
ater
ial i
s of
san
d si
ze
(mor
e th
an 2
mm
)
Gravelly SILTGravelly CLAYEY
Sandy SILTSandy CLAY
SILT (M-SOIL)
MGFGCG
MSFS
CSM
MLG, etc
CLGCIGCHGCVG CEGMLS, etc
CLS, etcML, etc
<3535 to 5050 to 7070 to 90>90
FIN
E S
OIL
S5
% o
f th
e m
ate
ria
l is
fin
er
tha
n 0
.06
mm
Gra
velly
or
sand
y S
ILT
S a
nd C
LAY
S
35%
to 6
5% fi
nes
27 June 2009 Dr. S. NallayarasuDepartment of Ocean Engineering
Indian Institute of Technology Madras-36
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( )
CLAY
MFC
ML, etc
CLCICHCVCE
<3535 to 5050 to 7070 to 90>90
Mo
re t
ha
n 3
SIL
TS
AN
D
CLA
YS
65%
to
100%
fine
s
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Basic Soil Mechanics
Main Terms Qualifying Terms
GRAVEL G Well graded W
SAND S Poorly graded uniform
PPu
gap-graded PgFINE SOIL, FINES F Of low plasticity (wL < 35) L
SILT (M-SOIL) M Of intermediate plasticity (wL 35 - 50) I
CLAY C Of high plasticity (wL 50 - 70)Of very high plasticity (wL 70 – 90)Of extremely high plasticity (wL > 90)Of upper plasticity range (wL > 35)
HV EU
27 June 2009 Dr. S. NallayarasuDepartment of Ocean Engineering
Indian Institute of Technology Madras-36
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Organic (may be a suffix to any group) OPEAT Pt
Basic Soil Mechanics
Name Group
symbols
Laboratory criteria Fines (%) Grading Plasticity Notes
Coarse grained (more than
Gravel (more than 50% of
Well graded GWGravels,
0 – 5 CU > 41 < CZ <
Dual symbols if 5 12%
UNIFIED SOIL CLASSIFICATION SYSTEM
(more than 50% larger than 63% um BS or No. 200 US sieve size
50% of coarse fraction of gravel size)
sandy gravels, with little or no fines
Poorly graded GPgravels, sandygravels, withlittle or no fines
Silty gravels, GM
0 – 5
>12
3
Not satisfying GW require-ments
Below A-line
5 – 12%fines. Dual symbols if above A-line and 4 < IP < 7
27 June 2009 Dr. S. NallayarasuDepartment of Ocean Engineering
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Silty gravels, GMSilty sand gravels
Clayey gravels GCclayey sandygravels
>12
>12
Below A line or Ip<4Above A-line and IP > 7
Contd…
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Basic Soil Mechanics
Name Group
symbols
Laboratory criteria Fines (%) Grading Plasticity Notes
Coarse grained
Sands (more than 50% of
Well graded GWsands,
0 – 5 CU > 61 < CZ < 3
Dual symbols if
UNIFIED SOIL CLASSIFICATION SYSTEM
(more than 50% larger than 63% um BS or No. 200 US sieve size
coarse fraction of gravel size)
sa ds,Gravely sands, with little or no fines
Poorly graded GPsands, gravellysands, withlittle or no fines
Silt sands SM
0 – 5
>12
C 3
Not satisfying SW require-ments
Belo A
5 – 12%fines. Dual symbols if above A-line and 4 < IP < 7
27 June 2009 Dr. S. NallayarasuDepartment of Ocean Engineering
Indian Institute of Technology Madras-36
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Silty sands SM
Clayey sands SC
>12
>12
Below A-line or Ip<4Above A-line and IP
> 7
Contd…
Basic Soil Mechanics
Name Group symbols
Laboratory criteria
Fine grained (more than 50% smaller than 63 μm BS or No.200 US sieve size)
Inorganic clays, silty CLclays, sandy clays of low plasticityOrganic silts and OL organic silty clays of low plasticity Inorganic silts of high MH plasticity In organic clays of CH plasticity Organic clays of high OH
Use plasticity chart
Use plasticity chart
Use plasticity chart
Use plasticity chart
U l ti it h t
27 June 2009 Dr. S. NallayarasuDepartment of Ocean Engineering
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Highly organic soils
Organic clays of high OH plasticity
Peat and other highly Pt organic soils
Use plasticity chart
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Basic Soil MechanicsPLASTICITY CHART : UNIFIED SYSTEM
27 June 2009 Dr. S. NallayarasuDepartment of Ocean Engineering
called SPT “N” Value It indicates relative strength of soil E i i l l ti b t th
27 June 2009 Dr. S. NallayarasuDepartment of Ocean Engineering
Indian Institute of Technology Madras-36
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Empirical correlation between other parameters available.
Basic Soil MechanicsSCHEMATIC DIAGRAMMS OF THE THREE COMMONLY USED HAMMERS
27 June 2009 Dr. S. NallayarasuDepartment of Ocean Engineering
Indian Institute of Technology Madras-36
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Basic Soil Mechanics
Description Very loose Loose Medium Dense Very dense
Relative density D 0 0 15 0 35 0 65 0 85
Empirical values for ø, Dr, and unit weight of granular soils based on the SPT at 6 m depth and normally consolidated
SPT N70: finemediumcoarse
1 – 2 2 – 33 – 6
3 – 64 – 75 – 9
7 – 158 – 2010 – 25
16 – 3021 – 4026 – 45
?> 40> 45
ø: finemediumcoarse
26 – 2827 – 2828 – 30
28 – 3030 – 3230 – 34
30 – 3432 – 3633 – 40
33 – 3836 – 4240 – 50
< 50
λwet, pcf
(kN/m³)
0-100†
(11 – 16) 90 – 115(14 – 18)
110 – 130(17 – 20)
110 – 140(17 – 22)
130 – 150 (20 – 23)
Relative density Dr 0 0.15 0.35 0.65 0.85
27 June 2009 Dr. S. NallayarasuDepartment of Ocean Engineering
Indian Institute of Technology Madras-36
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( )
† Excavated soil or material dumped from a truck will weigh 11 to 14 kN/m³ and must be quite dense to weigh much over 21 kN/m³. No existing soil has a Dr = 0.00 nor a value of 1.00 – common ranges are from 0.3 to 0.7
27 June 2009 Dr. S. NallayarasuDepartment of Ocean Engineering
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Basic Soil Mechanics
VANE SHEAR TESTS
Two types available Field Vane Shear Laboratory Vane Shear Laboratory Vane Shear
Principle is same but only the size of equipment different
Method based on shearing a circular soil surface and relating it with the torque applied
Gives the undrained shear strength of soil
27 June 2009 Dr. S. NallayarasuDepartment of Ocean Engineering
Indian Institute of Technology Madras-36
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Gives the undrained shear strength of soil, mostly clay based soils.
Basic Soil Mechanics
VANE SHEAR
27 June 2009 Dr. S. NallayarasuDepartment of Ocean Engineering
Indian Institute of Technology Madras-36
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Basic Soil Mechanics
VANE SHEAR TEST
32 dhd
lengthvaneh
width vaneoveralld
failureat Torque
62
32
t
dhdcT u
27 June 2009 Dr. S. NallayarasuDepartment of Ocean Engineering
Indian Institute of Technology Madras-36
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length vaneh
Basic Soil Mechanics
SHEAR TEST
27 June 2009 Dr. S. NallayarasuDepartment of Ocean Engineering
Indian Institute of Technology Madras-36
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Basic Soil Mechanics
DIRECT SHEAR APPARATUS
27 June 2009 Dr. S. NallayarasuDepartment of Ocean Engineering
Indian Institute of Technology Madras-36
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Basic Soil MechanicsPRINCIPAL LINE DETAILS OF TRIAXIAL CELL
27 June 2009 Dr. S. NallayarasuDepartment of Ocean Engineering
Indian Institute of Technology Madras-36
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Basic Soil Mechanics
THE MOHR-COULOMB FAILURE CRITERION
The shear strength of a soil at a point on a particular plane was originally expressed by Coulomb as a linear function of the normal stress on the plane at the same
StressNormal
StrengthShear
tan
f
f
ff c
function of the normal stress on the plane at the same point
27 June 2009 Dr. S. NallayarasuDepartment of Ocean Engineering
Indian Institute of Technology Madras-36
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ParametersStrength Shear c, f
Basic Soil Mechanics
THE MOHR-COULOMB FAILURE CRITERION
In accordance with Terzaghi,s fundamental concept that shear stress in a soil can be resisted only by the skeleton of solid particles, shear strength is expressed as a
in ParametersStrength Shear ,
tan,,
,,,
c
c ff
of solid particles, shear strength is expressed as a function of effective normal stress:
27 June 2009 Dr. S. NallayarasuDepartment of Ocean Engineering
Indian Institute of Technology Madras-36
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stress effective of terms
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Basic Soil Mechanics
expressedbealsocan soilaofstrength shear The
THE MOHR-COULOMB FAILURE CRITERION
2sin)(2
1
failure.at and stresses
principalminor andmajor effective of in terms
,3
,1
,3
,1
f
27 June 2009 Dr. S. NallayarasuDepartment of Ocean Engineering
Indian Institute of Technology Madras-36
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2cos)(2
1)(
2
1 ,3
,1
,3
,1
, f
Basic Soil Mechanics
σ΄1
σ΄1τ
Stress Conditions at Failure
σ΄1
σ΄3 σ΄3θ
τ1
τ1
27 June 2009 Dr. S. NallayarasuDepartment of Ocean Engineering
Indian Institute of Technology Madras-36
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σ΄σ΄3 σ΄1σ΄1
2θ
1
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Basic Soil Mechanics
major ebetween th angle al theoretic theis
245
hatapparent t isIt
failure.ofplanetheand plane principal
,O
27 June 2009 Dr. S. NallayarasuDepartment of Ocean Engineering
Indian Institute of Technology Madras-36
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2
Basic Soil Mechanics
:Now obtained. be alsocan parameters
strength shear theand failureat stresses
principal effective ebetween th iprelationsh The
Therefore,
)(21
cot
)(21
sin,3
,1
,,
,3
,1
,
c
27 June 2009 Dr. S. NallayarasuDepartment of Ocean Engineering