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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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Soil Stiffness

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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