Cyclic failure mechanisms of saturated marine coral sand under various consolidations

Abstract

The undrained cyclic response of coral sand in earthquake is an important issue that must be considered in ocean engineering. A series of undrained cyclic triaxial tests was conducted on saturated coral sand using GDS dynamic triaxial apparatus. This study discusses the influence of consolidation ratio (kc), cyclic stress ratio (CSR), and relative density (Dr) on the undrained cyclic response of saturated coral sand. The characteristics of excess pore water pressure (EPWP), axial strain (εa), effective stress path, and undrained cyclic resistance of saturated coral sand are analyzed. The test results show that two axial strain generation modes exist in saturated coral sand: cyclic mobility and plastic strain accumulation. The EPWP (ue) generation modes are quite different subjected to various CSRs under isotropic consolidation, while that is consistent under anisotropic consolidation. Suitable models are selected to describe various EPWP generation patterns. Consolidation condition can significantly affect the development of effective stress path. The residual effective stress becomes large with the increase of kc. A new index called stress parameter (λ) is introduced to consider the effect of kc and CSR on undrained cyclic resistance comprehensively. The critical line to distinguish the failure point from non-failure point of coral sand specimens can be clearly found in the correlation between λ and the relative density after consolidation (Drc). The existence of the critical line in the relationship between stress parameter and relative density is also verified by using the literature data.