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Determination of Soil Stiffness
Parameters
Short Course on Computational Geotechnics + Dynamics
Boulder, Colorado
January 5-8, 2004
Stein Sture
Professor of Civil Engineering
University of Colorado at Boulder
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Contents
General concepts and stiffness of sandHooke’s law
E-moduli from triaxial testing
E-moduli from oedometer testing
Examples on the estimation of E
Stiffness of claysUndrained clay behavior
Drained clay behavior
Examples on the estimation of EComputational Geotechnics Determination of Soil Stiffness Parameters
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Idealized and real stress-
strain behavior of soils
Idealized types of stress-strain behaviors: (a) nonlinear elastic
Model, (b) linear elastic model, and (c) elastoplastic model
Computational Geotechnics Determination of Soil Stiffness Parameters
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Idealized and real stress-
strain behavior of soils
Various types of elastoplastic behaviors: (a) strain hardening, (b)
perfectly plastic, (c) strain softening, and (d) combination of a to c.
Computational Geotechnics Determination of Soil Stiffness Parameters
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Hooke’s Law of Isotropic
Elasticity
Computational Geotechnics Determination of Soil Stiffness Parameters
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Hooke’s Law of Isotropic
Elasticity
Computational Geotechnics Determination of Soil Stiffness Parameters
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Standard Drained Triaxial Test on
Sand
Computational Geotechnics Determination of Soil Stiffness Parameters
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Standard Drained Triaxial Test on
Sand
Computational Geotechnics Determination of Soil Stiffness Parameters
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Oedometer Test on Sand
Computational Geotechnics Determination of Soil Stiffness Parameters
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Oedometer Test on Sand
Computational Geotechnics Determination of Soil Stiffness Parameters
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Oedometer Test on Sand
Hooke:
Loose:
Dense:
oed oed E E E 3
2)21(
1
1
( 13
)
ref
y
ref p p
E
3
2150
ref
y
ref p p
E
3
2500
Computational Geotechnics Determination of Soil Stiffness Parameters
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Oedometer Test on Sand
y' x
'
K 0 2 x
'
ref x
ref x
ref p p p E
150232150
ref
x
ref
x
ref p p p
E
50023
2500
E E 50
Loose:
Dense:
This implies:
Computational Geotechnics Determination of Soil Stiffness Parameters
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Summary on Stiffness Parameters:
Sand(Laboratory based experience)
E E 50 2
3 E oed
13
E pref
150 x'
pref
E pref
500 x'
pref
E E ref x
'
pref
E 15 MPa x
'
pref
E 50 MPa
x
'
pref
pref 100kP
Loose:
Dense:
Loose:
Dense:
Unloading: About 4 times stiffer. smallComputational Geotechnics Determination of Soil Stiffness Parameters
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Selection of Moduli for FEM-Computation
E 50
ref 15 MPa
y0
/ 70kPa
y' 50kPa
y' 95kPa x
' 50kPa
E 50 15000 0.5 10000 kP
Layer 1 (extremely loose sand
Layer 1:
Average
Mohr-Coulomb model:
Example 1 (loading):
Computational Geotechnics Determination of Soil Stiffness Parameters
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Selection of Moduli for FEM-ComputationExample 2 (unloading):
E 50
ref 45 MP
E 50
ref 30 MPa
15.0,4 50 ref ref
ur E E
y' 2 1.5 ' 55kPa
x' 27.5kP
E 4 45000 27.5100 95000 kPa
x'10kP kPa E 3800010.0300004
Layer 1 (dense): Layer 3 (medium):
Unloading: for both layers
Mohr-Coulomb model: Layer 1:
Layer 3:
Computational Geotechnics Determination of Soil Stiffness Parameters
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E oed
from Cone Penetration Test in
Sands
qc
E oed qc
= 1 to 3
= 3
ref
coed pq E )1030(
Cone Resistance:
Correlation:
Literature NC-Sand:
Vermeer’s Experience:
Alternatively:
Computational Geotechnics Determination of Soil Stiffness Parameters
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Undrained Triaxial Test on
Clay
E u50
15000 C u
I p%
E u50 3G50
Normally consolidated clay:
Cu = undrained shear strength (or Su)
Computational Geotechnics Determination of Soil Stiffness Parameters
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Idealized and real stress-strain
behavior of soils
Computational Geotechnics Determination of Soil Stiffness Parameters
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Idealized and real stress-strain
behavior of soils
Computational Geotechnics Determination of Soil Stiffness Parameters
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Plate Loading Tests
Duncan & Buchignani (1976)
Computational Geotechnics Determination of Soil Stiffness Parameters
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Plate Loading Tests
Computational Geotechnics Determination of Soil Stiffness Parameters
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Drained Behavior for Clays
Computational Geotechnics Determination of Soil Stiffness Parameters
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