Coupling effects of bidirectional cyclic loading and loading frequency on pore water pressure of saturated soft clay

A series of undrained cyclic tests with variable confining pressures are conducted on Ningbo saturated soft clay by using the GDS cyclic triaxial system. In this study, the coupling effects of cyclic deviatoric stress and cyclic confining pressure on the pore water pressure of Ningbo saturated soft clay in real traffic loading are simulated. The developments of pore water pressure of saturated soft clay subjected to bidirectional cyclic loading are investigated with different cyclic stress ratios, cyclic confining pressures and vibration frequencies. It is observed that the pore water pressure increases with higher cyclic stress ratios and cyclic confining pressure, but decreases with higher frequencies under bidirectional cyclic loading. The relationships between pore water pressure ratio and cyclic time are identical under different values of η and frequencies. The slope of stress paths η and cyclic stress ratios CSR affect the relationship between pore water pressure ratio and cyclic time significantly, and the pore water pressure ratio increases with the increase of η and CSR. However, the effect of frequency on the curves of pore water pressure ratio and loading time is indistinct. The observations imply that the coupling effects of cyclic confining pressure and loading frequency on the pore water pressure should also be considered to estimate the values of pore water pressure.