Abstract:A series of triaxial compression tests were carried out on frozen sand clay with confining pressures from 0.0 to 18.0 MPa at -6 ℃. The experimental results indicate that the strain softening exists in the stress-strain relationships of the studied frozen sand clay when the confining pressures is below 3.0 MPa;and the strain hardening phenomenon appears in the stress-strain relationships when confining pressures is greater than 3.0 MPa. Since the general hyperbolic model cannot describe the strain hardening behavior;and Duncan-Chang model cannot describe the strain softening behavior of frozen sand clay;an improved Duncan-Chang model is proposed. This model can describe not only the strain softening behavior but also the strain hardening behavior of frozen sand clay. Moreover,its modeling precision is better than those of Duncan-Chang model and the general hyperbolic model. Due to pressure melting,shear strength of frozen sand clay nonlinearly changes with increasing confining pressures. In order to solve the problem that linear Mohr-Coulomb criteria can not exactly reflect the shear strength of frozen sand clay,a nonlinear Mohr criterion of frozen sand clay is presented. The results calculated by the nonlinear Mohr criterion of frozen sand clay illustrate that it has higher precision and can more exactly describe the shear strength of frozen sand clay than the linear Mohr-Coulomb criterion.