Constitutive Model For Static Liquefaction Of Sand And Parameters Determination

Static liquefaction failure usually takes place in loosely packed, water saturated granular deposits, such as soil or tailings. Undrained triaxial compression tests on loosely prepared and fully saturated sand specimens show a peak in shear strength when the strain is very small, then the shear strength decrease sharply to a steady value.This thesis discusses the mechanical characteristics of sand systematically, including undrained characteristics, drained characteristics and the mechanism of liquefaction, makes deeply study of state depending theory, analyses the function of different dilative equation on the constitutive model and point out the field of application of different dilative equation to the mechanical characteristics of sand.Based on the theory of critical state, the model proposed by Boukpeti et al. is refined using the theory of state dependent, by simplifying the hardening rule and leading a state parameter in the plastic potential function, a new constitutive model for static liquefaction of sand is developed. The model can represent sand deformations over different densities and confining stresses with only one set of model parameters, moreover, the number of parameters are less than the original model.The model parameters are determined using the modified particle swarm optimization method. Numerical tests for undrained triaxial tests over different initial densities and confining stresses and a set of drained numerical test both illustrate the capability of the model.Using the orthogonal test method, regard the parameters as influencing factors and the computing results as examined indexes, the sensitivity analysis is made, then the signify parameters and the less important parameters are departed. Then the author discuses affects of model parameters.