Liquefaction characteristics of saturated marine coral sand with different non-plastic fines content subjected to complex cyclic stress paths

Abstract

Coral reefs thrive in complex marine geological environments and are likely to suffer from dynamic marine disasters. The liquefaction characteristics of saturated marine coral sand subjected to dynamic loading, such as ocean waves, submarine earthquakes, storm tides, volcanic activities, and hurricanes, are key factors affecting the safety of coral reefs. A systematic study is conducted through a series of hollow-cylinder torsional shear experiments on the undrained response of saturated marine coral sand with different non-plastic fines contents (FCs) under cyclic linear stress paths with various cyclic loading direction angles (αd). An interesting discovery is that the cyclic linear stress paths with angles αd and 90°−αd have the same stress effect on liquefaction characteristics under isotropic consolidation condition. The test results show that if the near-zero effective stress state is defined as the criterion for initial liquefaction, then the liquefaction resistance of saturated coral sand decreases with increasing αd or FC. The generation of excess pore water pressure (EPWP) presents three modes: (1) “rapid–stable–fast,” (2) “rapid–stable,” and (3) “fast linear-like.” Moreover, an energy-based EPWP prediction method is established. A novel discovery is that the generalized shear strain amplitude (γga) is uniquely related to the EPWP ratio of coral sand for a given relative density and FC. In addition, by introducing unit cyclic stress ratio (USR) as a new index of liquefaction resistance, a common correlation between equivalent skeleton void ratio esk* and USR15 (required for initial liquefaction in 15 cycles) is established for all test cases considered. This is confirmed by the experimental data of five types of terrestrial siliceous sands reported in the literature.