Abstract:

Anisotropic consolidation significantly affects the liquefaction behavior of saturated sand. To investigate the evolution characteristics of anisotropically consolidated saturated coral sand under cyclic loading, undrained cyclic shear tests were conducted with a 90º jump rotation of the principal stresses under varying consolidation conditions. The test results indicate that consolidation conditions significantly affect the stress-strain response of saturated coral sand. The hysteresis curve evolves with unidirectional accumulation when the stress component is collinear with the consolidation stress, whereas alternating cyclic hysteresis responses are observed under misaligned stress orientations. Based on variations in the average flow coefficient and its gradient with the number of cycles, the mechanical evolution of coral sand can be classified into three phases. The initial phase corresponds to an elastic solid state, characterized by low excess pore water pressure and negligible mobility. This is followed by a phase of accelerated pore water pressure accumulation, leading to a solid-liquid transition with increased particle mobility. Finally, a sharp change in the average flow coefficient gradient signifies the onset of a transient viscous-liquid state. Under varying consolidation and cyclic-loading conditions, gradient shows an initial increase followed by a decrease with increasing excess pore water pressure ratio with a turning point at a critical excess pore water pressure ratio r_uth of approximately 0.9, which remains invariant across test conditions. Given the observed discrepancy between pore water pressure development and strain response in anisotropically consolidated coral sand, this r_uth may serve as a reliable triggering criterion for liquefaction in saturated sandy soils under complex static and dynamic loading.

Key words: solid-liquid phase transition, anisotropic consolidation, critical excess pore water pressure ratio, cyclic loading pattern, liquefaction criteria