Experiment study of coupling effect of initial shear stress and loading rate on pore water pressure model of soft clay

The pore water pressure of saturated soft clay under cyclic loading is researched by GDS cyclic triaxial system. The effects of cyclic stress ratio, initial shear stress and vibration frequency on pore water pressure are analyzed. It is observed that the pore water pressure increases with the increase of cyclic stress ratio. There is critical cyclic stress ratio of soft clay under cyclic loading. The value of critical cyclic stress ratio can also be obtained by pore water pressure curves. At the beginning of cyclic loading, the pore water pressure rate is larger and then it decreases with the progressive of time. With the increase of cyclic stress ratio, the pore water pressure rate increases. The vibration frequency influences the relationship between pore water pressure ratio and cyclic number significantly; and the pore water pressure ratio decreases with the increase of frequency. However, the effect of vibration frequency on pore water pressure ratio-time and pore water pressure rate-time curves is indistinct at the frequency larger than 1Hz. With the increase of initial shear stress, both the pore water pressure ratio and pore water pressure rate increases. It shows linear relationship between pore water pressure rate and time at log-scale. Based on the test results, the empirical equation between pore water pressure rate and time is obtained. The pore water pressure model of soft clay under unidirectional cyclic compressive loading is obtained by integration.