Abstract: The strength for frozen silt soil increases with the increase of confining pressure at relatively low pressures, but decreases with the increase of confining pressure at relatively high pressures, which is different from unfrozen geomaterials such as metal, concrete, rock, sand and clay. To investigate the strength criterion for frozen soils and simulate the breaking process under different confining pressures, the strength criterion is derived from the modified slope M* of q-p strength curves in the meridian plane, and the formulation is deduced, which is related to internal friction angle and average normal stress on the basis of the Mohr’s circle and envelope theory. The strength criterion in the deviatoric plane is obtained from the assumption that the deviatoric stress is a combination of Mohr-Coulomb and Von-Mises strength criterion. A series of cryogenic triaxial compressive tests are conducted at three different temperatures, i.e. -6, -10 and -15 ℃, and different confining pressures of 0.3, 1.4, 3.0, 6.0, 10.0 and 15.0 MPa to determine the related strength parameters. Testing results are shown as follows: 1) the modified strength criterion in the meridian plane can simulate the strengthening effect at a relatively low confining pressure and the weakening effect at a high confining pressure; 2) the variation tendency of internal friction angle increases first and then decreases with the increase of normal stress; and 3) with the increase of parameters, the envelope shape of deviatoric stress is transformed from Mohr-Coulomb to Von-Mises criterion in the deviatoric plane, and its value corresponds to yield stress. Finally, the comparison between literature and experimental data demonstrates that the proposed strength criterion has a satisfactory applicability for frozen silt soils.

Key words: frozen silt soil, strength criterion, modified Mohr-Coulomb criterion, meridian plane, deviatoric plane