Triaxial Tests on Shanghai Soft Clay Under Cyclic Loading with Low-Frequency

Silos and storage tanks are filled and emptied periodically in operational period, which leads to the ground soil underneath these structures experiencing the long-term and low-frequency cyclic loading. Series of undrained triaxial tests were conducted on the intact Shanghai soft clay retrieved from a construction site at Pudong area. Monotonic load and cyclic load with low-frequency were applied to investigate the development of pore water pressure and accumulated axial strain in the test specimens.Test results illustrate that the stress-strain (sigma - epsilon) shows lightly softening characteristics, and the behavior is more pronounced, especially in the case of a higher confining pressure. The variation of axial strain epsilon(a) is similar to that of permanent strain epsilon(p) under different cyclic stress ratios, and the accumulated axial strain is not only related to the CSR, but also to the effective confining pressure and the deviator stress levels. the resilient modulus decreases with the increase of CSR. Compared with high-frequency cycle loading, the soft clay exhibits plastic deformation in advanced during low-frequency cycle loading. The normalized residual excess pore pressure is equilibrated fast with the decrease of effective confining pressure. The normalized residual excess pore pressure is almost equal at the different deviator stress levels. The experimental results show that the development of pore water pressure is a time dependent phenomenon, independent of frequency.