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Soil Stiffness
Determination of Soil Stiffness ParametersShort Course on Computational Geotechnics + Dynamics Boulder, Colorado January 5-8, 2004Stein Sture Professor of Civil Engineering University of Colorado at Boulder
ContentsGeneral concepts and stiffness of sandHookes 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
Idealized and real stressstrain 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
Idealized and real stressstrain 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
Hookes Law of Isotropic Elasticity
Computational Geotechnics
Determination of Soil Stiffness Parameters
Hookes Law of Isotropic Elasticity
Computational Geotechnics
Determination of Soil Stiffness Parameters
Standard Drained Triaxial Test on Sand
Computational Geotechnics
Determination of Soil Stiffness Parameters
Standard Drained Triaxial Test on Sand
Computational Geotechnics
Determination of Soil Stiffness Parameters
Oedometer Test on Sand
Computational Geotechnics
Determination of Soil Stiffness Parameters
Oedometer Test on Sand
Computational Geotechnics
Determination of Soil Stiffness Parameters
Oedometer Test on SandHooke:
1 + 2 E= (1 2 ) Eoed Eoed 1 3
( =1 ) 3
Loose:
E 2 150 ref p 3E 2 500 ref p 3
y ref py ref pDetermination of Soil Stiffness Parameters
Dense:
Computational Geotechnics
Oedometer Test on Sand'y = 'xK 0 2 'xx x E 2 150 2 150 p ref 3 p ref p ref
Loose:
Dense:
x x E 2 500 2 500 ref ref ref p 3 p p
This implies:Computational Geotechnics
E E 5 0Determination of Soil Stiffness Parameters
Summary on Stiffness Parameters: Sand (Laboratory based experience)2 E=E E 5 0 o e d 3
=1 3' x re f
Loose:
E =1 5 0 re f p p
E=E
ref
'xpref
5M P a Loose: E=1
'xr e f p
Dense: E =5 0 0 re f p pr e f p = 1 0 0 k P aComputational Geotechnics
' x re f
0M P a Dense: E=5
'xre f p
Unloading: About 4 times stiffer. smallDetermination of Soil Stiffness Parameters
Selection of Moduli for FEM-ComputationExample 1 (loading):
Layer 1 (extremely loose sand Mohr-Coulomb model: Layer 1: Average/ 7 0 k P a y 0
r e f E 1 5 M P a 5 0=
' 5 0 k P a y=
' 9 5 k P a y=
' 5 0 k P a x
E = 1 5 0 0 0 0 . 5 1 0 0 0 0 k P a 5 0Computational Geotechnics Determination of Soil Stiffness Parameters
Selection of Moduli for FEM-ComputationExample 2 (unloading):
Layer 1 (dense): Unloading:
r e f E 4 5 M P a 5 0=
Layer 3 (medium): for both layers
r e f E 3 0 M P a 5 0=
ref ref Eur 4 E50 , 0.15
Mohr-Coulomb model: Layer 1:' ' ' = 2 + 1 . 5 = 5 5 k P a 2 7 . 5 k P a y x7 . 5 E = 4 4 5 0 0 02 9 5 0 0 0 k P a 1 0 0
Layer 3:Computational Geotechnics
' 1 0 k P a x
E = 4 30000 0.10 38000kPaDetermination of Soil Stiffness Parameters
Eoed from Cone Penetration Test in SandsCone Resistance:
qc
Correlation: E q o e d c Literature NC-Sand: = 1 to 3 Vermeers Experience: = 3 Alternatively: Eoed = (30 10) qc p ref
Computational Geotechnics
Determination of Soil Stiffness Parameters
Undrained Triaxial Test on Clay
Normally consolidated clay: Cu = undrained shear strength (or Su)Computational Geotechnics
1 5 0 0 0 C 5 0 u E = u Ip%5 0 E 3 G u = 5 0Determination of Soil Stiffness Parameters
Idealized and real stress-strain behavior of soils
Computational Geotechnics
Determination of Soil Stiffness Parameters
Idealized and real stress-strain behavior of soils
Computational Geotechnics
Determination of Soil Stiffness Parameters
Plate Loading Tests
Duncan & Buchignani (1976)Computational Geotechnics Determination of Soil Stiffness Parameters
Plate Loading Tests
Computational Geotechnics
Determination of Soil Stiffness Parameters
Summary on Stiffness Parameters: Clay Undrained 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
Drained Behavior for Clays
Computational Geotechnics
Determination of Soil Stiffness Parameters
Drained Behavior for Clays
Computational Geotechnics
Determination of Soil Stiffness Parameters