Cyclic response of calcareous sand seabeds to extreme wave loading in the South China Sea

In the South China Sea (SCS), the structural stability of offshore marine structures near calcareous sandy seabeds is significantly threatened by the accumulation of excess pore water pressure (Δ u ) and plastic strain induced by extreme wave loading with restricted drainage. To investigate the dynamic response of calcareous sand under such conditions, a series of undrained cyclic triaxial tests was performed on saturated coral sand, using the wave characteristics of Typhoon Hato as a reference. The effects of the cyclic stress ratio ( CSR ), relative density ( D r ), frequency ( f ), initial confining pressure ( σ ' 3 ) at constant CSR , and σ ' 3 under constant initial dynamic stress ( σ d ) on the liquefaction resistance of saturated calcareous sand were systematically examined. Increasing CSR, f , as well as rises in σ ' 3 under constant CSR , or reducing D r and σ ' 3 under constant σ d , increased the potential for liquefaction. As an engineering approach to enhance the liquefaction resistance of calcareous sand, low-energy tamping to increase D r is recommended. Placing protective bags filled with coral fragments on the shallow calcareous sand seabed may improve its liquefaction resistance and thus its stability under extreme wave loading.