Strength Criterion And Hardening Parameter For Frozen Silty Clay Under Complex Stress Paths

Frozen soil is a kind of special geomaterial with ice in it,whose strength and deformation characteristics under complex stress paths are not only the basic problems faced by frozen soil engineering,but also the basis for developing strength theory and constitutive theory,two core problems of frozen soil mechanics.In order to deeply understand the deformation behavior of frozen soil under load and further develop the mechanical theory of frozen soil,this paper took frozen Genhe silty clay and frozen Lanzhou silty clay as research objects,performed a series of experimental and theoretical research:(1)Employing both global and local measurements of strains,a series of monotonic and cyclic triaxial compression tests under linear and polygonal stress paths in the meridian plane were carried out.Under the stress paths' condition in this paper,the influence of stress paths on the strength and deformation characteristics of frozen silty clay was investigate,and the coupling effect of initial confining pressure and stress increment direction angle on strength and deformation was revealed:The lower the initial confining pressure is,the stronger the influence of stress increment direction angle on strength and deformation is;The larger the direction angle of stress increment is,the stronger the influence of initial confining pressure on strength is.(2)An asymmetric strength criterion was proposed in the meridian plane,which can not only describe strength characteristics under complex stress paths but also be able to overcome the shortcomings of parabolic or elliptic function;In order to reflect the effect of the mean stress on the shape of strength loci in the deviatoric plane,a unified strength criterion in the ? plane was constructed,which utilized a shape parameter that is hyperbolic with the mean stress to linearly interpolate the Drucker-Prager criterion and the Matsuoka-Nakai criterion;and the three-dimensional form of frozen silty clay's strength criterion in principal stress space was established.(3)A method for determining elastic stiffness parameters was proposed based on transformation relations of isotropic linear elastic materials' elastic parameters as well as loading-unloading-reloading test results under the same control mode,which can consider the influence of strain level and confining pressure simultaneously.Employing this approach,the variation of Young's modulus,shear modulus,bulk modulus and Poisson's ratio of frozen Lanzhou silty clay with strain level and confining pressure during conventional triaxial shear process was ascertained,and the plastic flow law was revealed after decoupling elastoplastic deformation.(4)The geometric shape and evolution law for four kinds of plastic strain functions' contours under conventional triaxial shear as well as total conventional triaxial compression process for frozen Lanzhou silty clay were investigated;and the reasonable selection method of hardening parameter was discussed by considering the evolution of plastic strain increment direction and plastic potential.