Constitutive Modeling For Sand Based On Anisotropic Critical State Theory

In order to consider the influence of anisotropy on the deformation characteristics of sand,two different kinds of sand anisotropic description methods are respectively introduced into an existing multi-mechanism bounding surface model of sand in the three dimensional space.The main contents and results of this research are as follows:(1)Within the multi-mechanism framework,a constitutive model of anisotropic sand is presented based on the critical state,bounding surface plasticity,dilatancy and fabric tensor theories.A second-order symmetric fabric tensor is introduced to describe the inherent anisotropy of sand,and an anisotropic state variable A is defined in terms of a joint invariant of fabric tensor and stress tensor to quantitatively describe the influence of anisotropy.The expressions of critical state line and plastic shear modulus are redefined and be made functions of A.These modifications in the multi-mechanism constitutive model provide the successful simulations of sand responses on the conditions of undrained triaxial compression,triaxial extension,hollow cylindrical torsional shear and simple shear tests,which means that the model can accurately reflect the deformation characteristics of sand under undrained conditions.(2)In the modified multi-mechanism bounding surface model of sand,a new fabric tensor is introduced and its evolution is taken into account.Different from the first method,both the anisotropic state variable A and the elastic shear modulus are made functions of the evolving fabric tensor to describe induced anisotropy and elastic anisotropy.A dilatancy state line,which is also a function of A,is defined in the void ratio-pressure plane to better characterize the contracting or dilating trends of the current state.Numerical simulations are performed to be compared with test results and simulations in the undrained hollow cylindrical torsional shear and simple shear tests by the first method.