Volumetric strain generation of saturated coral sand subjected to various stress paths of cyclic loading

The accumulation of volumetric strain in saturated sandy soil with a drained or partially drained state during earthquakes and waves can significantly distress the surface, seabed and nearby structures. A quantitative correlation exists between the tendency of the volumetric strain in drained and the generation of the excess pore water pressure in undrained saturated sand. The effects of the initial relative densities (D_r), cyclic stress paths and stress levels (CSR) on the tendency of the volumetric strain for saturated coral sand are studied by a series of undrained cyclic shear tests under isotropic consolidation conditions. The results show that a positive correlation exists between the residual volumetric strain (ε_{vd, ir}) with the minor-to-major ratio and the inclinations of the elliptical stress path shape under the same D_r and CSR. The generation of ε_{vd, ir} with the cyclic number (N) of saturated coral sand under various D_r, cyclic stress paths and CSR obeys the relationship of arc-tangent function. D_r, cyclic stress path and CSR have significant effects on the ultimate volumetric strain ((ε_{vd, ir})_u) and the convergence speed of ε_{vd, ir} versus N. By introducing a unit cyclic stress ratio (USR), a positive linear correlation exists between (ε_{vd, ir})_u and USR under the same D_r. The convergence parameter C_N1 of ε_{vd, ir} versus N has a positive linear relationship with USR, and C_N2 has a negative power function relationship with USR. The convergence rate of ε_{vd, ir} versus N slows down with the increase of USR. Another significant finding is that (ε_{vd, ir})_u decreases with the increase of D_r, and the convergence speed of ε_{vd, ir} versus N becomes faster with the increase of D_r. The proposed volumetric strain formulation provides new insights into the mechanics of residual volumetric strain generation under drained cyclic loading conditions.