Characteristics of solid–liquid phase transformation of saturated coral sand subjected to various patterns of cyclic loading

This study conducts a series of undrained cyclic shear tests on saturated coral sand with different initial relative densities ([D.sub.r]) subjected to a 90[degrees] jump rotation of the principal stress with various initial orientations. Considering liquefiable coral sand as a fluid, an important finding is that the variation in the apparent viscosity with the number of cycles is significantly affected by [D.sub.r], the effective mean principal stress ([p'.sub.0]), cyclic stress ratio, cyclic loading path, and cyclic loading frequency. The average flow coefficient ([kappa]) is introduced to describe the fluidity of saturated coral sand under cyclic loading by considering the variation in the shape of the stress-strain rate curve. A positive exponential correlation is observed between [kappa] and the excess pore water pressure (EPWP) ratio ([r.sub.u]) under the given cyclic loading modes. Another significant finding is that the solid-liquid phase change time is the turning point of the apparent viscosity and the average flow coefficient gradients with [r.sub.u]. The inversion point's EPWP ratio is approximately 0.9, defined as the EPWP ratio during the solid-liquid phase transformation ([r.sub.uth]). The [r.sub.uth] value is not affected by cyclic loading mode, [p'.sub.0], and [D.sub.r].