Abstract: To investigate the porous and particle crushing characteristics of the coral reef debris (calcareous sand) from a small lagoon in Yongshu Reef of Nansha Islands, the insitu dilatometer tests as well as the laboratory static & cyclic triaxial and torsional shear tests are conducted. The liquefaction characteristics of the calcareous sand are analyzed. The test results show that the calcareous sand at the shallow waters would liquefaction under seismic loading with a magnitude of seven. Under the wave actions, the interand intragranular voids would experience a constant restructuring process and may results in the particle crushing. The peak pore pressure of saturated calcareous sand increases with the number of vibration cycles. The development of the pore pressure in the particles can be divided into four stages: parabolic growth, linear growth, exponential growth and stable state. Liquefaction of the saturated calcareous sand is likely to be streaming slide damage under the isotropic consolidation conditions.

Key words: coral reef, lagoon, calcareous sediments, liquefaction