An experimental investigation of the mechanical behavior and a hyperplastic constitutive model of frozen loess

For the engineering construction in cold regions, it is essential to understand the mechanical properties of frozen soil. In order to investigate the mechanical characteristics of frozen loess, three kinds of laboratory tests were carried out at −6 °C. These included constant-confining pressure triaxial compression tests, isotropic compression tests, and constant-slope stress path tests. The test results show that the direction of the plastic strain increment is influenced by stress path. The influence of the mechanism of the confining pressures on the strength and deformation of frozen loess is investigated in detail. An analytical method to determine pressure crushing and melting of the ice in frozen soil is proposed. In order to apply the hyperplasticity theory to modeling constitutive behavior of frozen soil, a new systematical approach to derive the yield criterion and flow rule from dissipation function is proposed based on the properties of homogenous function. From the mechanical characteristics of frozen loess, Gibbs free energy function and dissipation function of frozen loess are established by applying the hyperplasticity theory. An elasto-plastic incremental constitutive model for frozen loess is derived from the two thermodynamic functions and a method of determining the corresponding parameters is also given. Simulated results show that the constitutive model, proposed in this paper, describes well the deformation behavior of frozen loess under different stress levels and stress paths.