An experimental study of the stress-strain characteristics of frozen silty clay with high moisture content

To study the stress-strain characteristics of the Qinghai –Tibet silty clay with high moisture content, triaxial shear tests were conducted on the silty clay under relatively high moisture contents (15%, 30% and 50%), different temperatures (-2 ℃ and -4 ℃) and confining pressures (0.5, 1.0, 2.0 and 4.0 MPa). The shape of the stress–strain curves and the strength characteristics of the frozen silty clay were analyzed and interpreted in mechanism. The test results show that the stress-strain curves of the frozen silty clay specimens are all of the strain-softening type. At high moisture content (50%), the initial tangential modulus of the specimen increases with the confining pressure in the form of power function. With the increasing moisture content, the failure process of the specimens tends to be brittle. The continuous increase in moisture content causes the strength of the frozen silty clay to decrease first and increase subsequently, that is to say, there exists an unfavorable moisture content for the shear strength. The existence of the unfavorable moisture content is mainly due to the “weakest mass structure” composed of soil skeleton and ice and to the transition of the leading role of each composition in bearing the external load. With the increasing confining pressure, the shear strength of the frozen silty clay decreases linearly, but the variation range is not large. The analysis based on the Mohr-Coulomb criterion shows that the cohesion is the main constituent of the strength of the frozen silty clay. The cohesion reaches a minimum at the most unfavorable moisture content, at which the weakening effect of the confining pressure on the strength is also strengthened.