Abstract: Through the dynamic triaxial test of the saturated silt in the unloaded state of Hangzhou metro line 5, the dynamic characteristics of the lateral unloading saturated silt under long-term cyclic loading are studied, and the influence of unloading stress path on dynamic characteristics of such soil is summarized. The test results show that the saturated silt has critical dynamic stress under the lateral unloading, and the critical dynamic stress of the soil which is under the unloading and reloading stress path is the smallest. When the dynamic load does not reach the critical dynamic stress, the cumulative dynamic strain and cumulative dynamic pore pressure of the soil appear to be stable. When the dynamic load exceeds the critical dynamic stress, the cumulative dynamic strain of the soil appears to be a destructive type. However, in the single lateral unloading stress path, the cumulative dynamic pore pressure development curve of soil samples does not show a steep increase stage. The results show that when the soil sample is under the lateral unloading and reloading stress path, the increase of excess pore water pressure caused by the reloading process will produce larger dynamic pore pressure and accumulated dynamic deformation, and reduce the critical dynamic stress of the soil sample, which is also a risk factor for the settlement and vibration settlement of the soil around the subway tunnel.

Key words: long-term cyclic loading, lateral unloading, saturated silt, dynamic characteristics