Experimental study on development patterns of volumetric strain and predictive modeling for saturated coral sands

The coral sand has better drainage conditions, and the drainage deformation of the saturated coral sand under earthquake and wave loads can easily cause damage to the seabed and nearby structures. Focusing on the properties of the saturated coral sand and by investigating the effects of fines content FC, relative density D_r and cyclic stress ratio CSR on its deformation characteristics, a series of cyclic drainage loading tests are carried out on the specimens of Nansha islands using the GDS dynamic triaxial instrument. The test results show that the development rate and the degree of deformation of cumulative volumetric strain ε_vp of the coral sand increase with the increase of FC and CSR, and decrease with the increase of D_r. The ε_vp-N relationship curve of the saturated coral sand shows two development modes, cyclic smoothness and cyclic creep. The potential damage factor DP is introduced to characterize the influences of FC on the development pattern of ε_vp, and a DP×CSR-D_r framework is established to evaluate the development patterns of its volumetric strain. To characterize the effects of FC and D_r on its ε_vp-N relationship curve, the equivalent skeleton void ratio e_sk^* is introduced, and it is found that there is a good correlation between ε_vp-s and e_sk^* under both development modes, thus, a model for the development of volumetric strain in the saturated coral sand under drainage cyclic loading conditions is established, which can well predict the development patterns of volumetric strain in the saturated coral sand.