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Determination of Soil Stiffness ParametersShort 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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ContentsGeneral concepts and stiffness of sand Hooke’s law E-moduli from triaxial testing E-moduli from oedometer testing Examples on the estimation of E Stiffness of clays Undrained clay behavior Drained clay behavior Examples on the estimation of E

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Idealized and real stress-strain behavior of soilsIdealized types of stress-strain behaviors: (a) nonlinear elastic Model, (b) linear elastic model, and (c) elastoplastic model

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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.

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Hooke’s Law of Isotropic Elasticity

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Hooke’s Law of Isotropic Elasticity

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Standard Drained Triaxial Test on Sand

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Standard Drained Triaxial Test on Sand

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Oedometer Test on Sand

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Oedometer Test on Sand

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Oedometer Test on Sand

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Oedometer Test on SandLoose:Dense:This implies:

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Summary on Stiffness Parameters: Sand(Laboratory based experience)Loose:Dense:Loose:Dense:Unloading: About 4 times stiffer. n small

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Selection of Moduli for FEM-ComputationLayer 1 (extremely loose sandLayer 1:AverageMohr-Coulomb model:Example 1 (loading):

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Selection of Moduli for FEM-ComputationExample 2 (unloading):Layer 1 (dense):Layer 3 (medium):Unloading:for both layersMohr-Coulomb model:Layer 1:Layer 3:

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Eoed from Cone Penetration Test in Sandsa = 1 to 3a = 3Cone Resistance:Correlation:Literature NC-Sand:Vermeer’s Experience:Alternatively:

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Undrained Triaxial Test on ClayNormally consolidated clay:Cu = undrained shear strength (or Su)

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Idealized and real stress-strain behavior of soils

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Idealized and real stress-strain behavior of soils

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Plate Loading TestsDuncan & Buchignani (1976)

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Plate Loading Tests

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Summary on Stiffness Parameters: ClayUndrained ConditionsDo not use empirical relationships only. Get good quality experimental data from lab tests, cone penetration tests and vane tests

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Drained Behavior for Clays

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Drained Behavior for Clays