Determination of Soil Stiffness ParametersShort Course on Computational Geotechnics + DynamicsBoulder, ColoradoJanuary 5-8, 2004

Stein StureProfessor of Civil EngineeringUniversity of Colorado at Boulder

ContentsGeneral concepts and stiffness of sandHookes 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

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

Idealized and real stress-strain behavior of soilsVarious types of elastoplastic behaviors: (a) strain hardening, (b) perfectly plastic, (c) strain softening, and (d) combination of a to c.

Hookes Law of Isotropic Elasticity

Hookes Law of Isotropic Elasticity

Standard Drained Triaxial Test on Sand

Standard Drained Triaxial Test on Sand

Oedometer Test on Sand

Oedometer Test on Sand

Oedometer Test on Sand

Oedometer Test on SandLoose:Dense:This implies:

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

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

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

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

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

Idealized and real stress-strain behavior of soils

Idealized and real stress-strain behavior of soils

Plate Loading TestsDuncan & Buchignani (1976)

Plate Loading Tests

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

Drained Behavior for Clays

Drained Behavior for Clays