Dynamic characteristics of a calcareous sand: Yongshu Reef, Spratly Islands, China

Calcareous sand, as a elastic coral reef sediment, is mainly distributed in atoll lagoons. It is characterised by multiple pores and broken particles. In this study, in situ flat dilatometer tests (DMT) and laboratory dynamic and static triaxial-torsional coupled shear tests were carried out to test the calcareous sand found along the Yongshu Reef located in the small lagoon of the Spratly Islands. Meanwhile, pore pressures, deformations, and liquefaction characteristics of this calcareous sand were analysed under different test conditions. Data showed that this calcareous, shallow sea, sand can liquefy under seismic intensities of the seventh degree: it was shown to be influenced by wave loading with its peak pore pressures, when saturated, corresponding to the constant adjustment of its pore structures, Crushing of grains of this calcareous sand varied with vibration time. Its state change process could be divided into four stages: parabolic growth, linear growth, exponential growth, and stability. The liquefaction mechanism of this calcareous sand was described as a flow failure under isotropic consolidation conditions.