Evolution laws of hysteresis loops of frozen soil under cyclic loading

Uniaxial cyclic compression tests on frozen soil at -1℃ under 5 Hz are carried out. The evolution laws of hysteresis loops are studied. The results show that the changing curves of accumulated strain with cyclic number can be divided into failure type and stable type. For failure type curves, the hysteresis loops change from sparse to close and then slightly sparse; the opening degree and the area of the hysteresis loops change from big to small and then slightly larger with the cyclic loading. For stable type curves, the hysteresis loops change from sparse to close; on the whole, the opening degree and the area of the hysteresis loops are quite small and gradually decrease with the cyclic loading. For both the failure type and the stable type curves, the strain lags the stress at the unloading stage. For the failure type curves, in the initial loading cycles, the strain lags the stress; after a certain number of cycles, the strain and the stress are almost synchronized, and the shape of the hysteresis loops is willow leaf. For the stable type curves, the strain and the stress are almost synchronized in the initial loading cycles; after a certain number of cycles the strain goes in advance of the stress, and the shape of the hysteresis loops is crescent. With the increasing maximum dynamic stress, the area of the hysteresis loops will increase, which means that the energy dissipation will increase and the sample will be damaged more easily.