Determination of Soil Stiffness Parametersceae.colorado.edu/~sture/plaxis/slides/Soi… · PPT...
Transcript of Determination of Soil Stiffness Parametersceae.colorado.edu/~sture/plaxis/slides/Soi… · PPT...
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Determination of Soil Stiffness Parameters
Short Course on Computational Geotechnics + DynamicsBoulder, ColoradoJanuary 5-8, 2004
Stein StureProfessor of Civil EngineeringUniversity of Colorado at Boulder
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Contents
General concepts and stiffness of sandHooke’s lawE-moduli from triaxial testingE-moduli from oedometer testingExamples on the estimation of E
Stiffness of claysUndrained clay behaviorDrained clay behaviorExamples on the estimation of E
Computational 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 elasticModel, (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:
oedoed EEE32)21(
11
( 13)
refy
ref ppE
32150
refy
ref ppE
32500
Computational Geotechnics Determination of Soil Stiffness Parameters
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Oedometer Test on Sand
y'
x'
K0
2 x'
refx
refx
ref pppE
150232150
refx
refx
ref pppE
500232500
E E50
Loose:
Dense:
This implies:
Computational Geotechnics Determination of Soil Stiffness Parameters
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Summary on Stiffness Parameters: Sand
(Laboratory based experience)
E E50 23Eoed
13
Epref
150 x'
pref
Epref
500 x'
pref
E E ref x'
pref
E 15MPa x'
pref
E 50MPa x'
pref
pref 100kPa
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
E50ref 15MPa
y0
/ 70kPa
y' 50kPa
y' 95kPa
x' 50kPa
E50 15000 0.5 10000kPa
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):
E50ref 45MPa
E50ref 30MPa
15.0,4 50 refrefur EE
y' 21.5' 55kPa
x' 27.5kPa
E 4 45000 27.5100 95000kPa
x' 10kPa kPaE 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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Eoed from Cone Penetration Test in Sands
qc
Eoed qc
= 1 to 3
= 3
refcoed pqE )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
Eu50
15000CuIp%
Eu50 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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Summary on Stiffness Parameters: ClayUndrained Conditions
Do not use empirical relationships only. Get good quality experimental data from lab tests, cone penetration tests and vane 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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Drained Behavior for Clays
Computational Geotechnics Determination of Soil Stiffness Parameters