Experimental Study on Direct Shear Mechanical Characteristics of Warm Frozen Silty Clay

Received: 15 August 2019 Accepted: 28 November 2019 The strength of the warm frozen soil is the key to the design of buildings and structures in the permafrost region, laying the basis for the safe operation and stability evaluation in the later stage of building/structure projects. In this paper, the frozen red silty clay is collected from Wudaoliang section of Qinghai-Tibet Highway, and prepared into samples for direct shear experiments. During the experiments, the direct shear properties of the samples were observed under different densities, normal stresses, water contents, temperatures, etc. The results show that, with the growing density, the cohesion of the frozen silty clay continues to increase, while the internal friction angle decreases first and then increases; with the growth in water content, the cohesion and internal friction angle show the same trends, but the angle increment is small; with the increase in normal stress, the internal friction angle exhibits a declining trend; the shear strength of the frozen soil has a linear relationship with temperature. Through theoretical analysis, the author established an expression for the relationship between shear strength and temperature of warm frozen soil at 0~-2°C, and confirmed that the shear stress-strain relationship of the frozen silty clay belongs to the strain hardening type, which obeys the hyperbolic model proposed by Clough and Duncan. The research findings lay a solid basis for the building/structure design in permafrost regions.