Cyclic stress-strain behaviour of soft clay under traffic loading through hollow cylinder apparatus: effect of loading frequency

摘要

Unlike the ground transportation, the underground road or subway are directly constructed in the soft soil layer without a subgrade and foundation system to reduce the influence of traffic loading. Therefore, their long-term post-construction settlement is a serious issue. In order to gain an insight into the soil behaviour under traffic loading, a series of cyclic tests with different frequencies through hollow cylinder apparatus were conducted in this study. A heart-shaped loading path was applied to consider the variation of cyclic stress amplitudes and principal stress rotation simultaneously. Since the frequency is the key parameter in this study, its effect on cumulative plastic strain, pore water pressure, and resilient modulus were examined, respectively. Generally, the low-frequency loading is more influential on the behaviour of clay than the high one. The results show that the frequency effect is significant at the early stage of loading. Once the soil reaches a steady variation phase, the frequency effect is minor. This phenomenon is even more distinct when time instead of cycle number is considered as the variable. It is concluded that the frequency effect is actually a combined effects of loading duration and loading rate. Because the loading rate effect gradually diminishes with the cyclic loading, the overlook of frequency effect on the long-term soil behaviour is considered acceptable as long as the soil behaviour at the early loading stage is clear.