Experimental investigation on dilatancy behavior of frozen silty clay subjected to long-term cyclic loading

An interesting and common feature of frozen silty clay cyclic behavior is that the accumulation of shear strain is not significant after a critical number of loading cycles, whereas the volumetric strain accumulates continuously in cyclic triaxial tests of frozen soils. Under cyclic triaxial conditions, the deformation mechanism of a frozen soil is often considered as a combination of frictional sliding and volumetric compaction, and hence the accumulated plastic volumetric strain can be divided into a dilation component due to shearing and a compaction component due to mean stress. A series of cyclic triaxial tests are carried out on a frozen silty clay. The evolution of volumetric dilation in each test is investigated against the accumulation of plastic shear strain. Volumetric dilation in these tests is shown to start right from the beginning, without a clear initial compression phase that is typically observed in testing unfrozen dense sand or stiff clay. The dependence of volumetric dilation on stress measures including cyclic stress amplitude, confining pressure or initial stress ratio is not pronounced, whereas the nonlinearity between the volumetric dilation and accumulated plastic shear strain is apparent. The plastic shear strain is then employed as a state variable, and a state-dependent dilation law is proposed to explain the experimental results. The experimental data and the proposed dilation law can potentially be incorporated into some cyclic constitutive models, leading to new insights of the behavior of frozen soils.