Stiffness degradation of saturated coral sand under complex stress conditions

Abstract

Coral sandy soils are frequently employed as fill and construction materials for land reclamation projects, port facilities, and other infrastructure projects in coral reef ecosystems. Considering the susceptibility of coral sand to liquefaction when subjected to dynamic loads such as earthquakes and storm surges, this study evaluates the stiffness degradation characteristics of saturated coral sand under varying physical states and cyclic loading conditions. This analysis employed undrained cyclic hollow cylinder tests with 90° jumps of principal stresses. Test results demonstrate that the stiffness degradation curve of specimen is significantly affected by relative densities, fines contents, and the cyclic loading conditions. The equivalent intergranular void ratio (e*) was introduced to account for the effects of fines content, particle physical state, and inter-particle contact on the physical properties of specimens. A negative power function relationship was observed between the initial cyclic stiffness and e* under identical cyclic loading conditions. Besides, a predictive equation for the excess pore-water pressure ratio (r_u) was formulated based on the factor of safety. To further establish their close relationship, a correlation function between stiffness degradation and r_u accumulation is proposed. Consequently, a stiffness degradation model accommodating these multiple development modes has been established. The results of this experiment can provide effective references for the construction of islands and reefs.