Particle Breakage Characteristics of Marine Coral Sand under Cyclic Shear Loading Conditions

Coral sand is widely distributed in offshore oil and gas basins, and beneath the foundations of offshore wind turbines that are exposed to persistent cyclic loads, including wind, ocean waves, and seismic activity. Under these cyclic loads, coral sand is prone to particle breakage, resulting in unexpected differential settlements that potentially threaten the security of offshore structures. A series of cyclic simple shear tests were conducted in this study to investigate the process of coral sand particle breakage during cyclic loading. The findings revealed that the shear stress and shear modulus of coral sand significantly increase after the first cycle, and then increase moderately with the number of loading cycles. Particle breakage becomes more severe as the cyclic shear strain amplitude, vertical stress, and total cycles increase. There is a critical shear rate that induces significant particle breakage, leading to a more regular particle shape in coral sand. The detachment interlocking and mechanical grinding models are proposed for analyzing the mechanism of the particle breakage in coral sand under cyclic loading. The level of input energy that controls the particle breakage in coral sand is set based on analysis of the energy dissipation.