Experimental investigation of cyclic failure mechanism of saturated coral sand under various consolidation conditions

This study reports a series of undrained cyclic triaxial tests that were conducted on Nansha coral sand by using the dynamic triaxial apparatus of the GDS to investigate the effects of the consolidation ratio (Kc), cyclic stress ratio (CSR), and relative densities (Dr) on the characteristics of liquefaction of saturated coral sand. The results indicated the presence of two modes of generation of axial strain (εa) in saturated coral sand: cyclic mobility (without initial shear stress) and the accumulation of plastic strain (with initial shear stress). By considering liquefiable coral sand as a fluid, the coefficient of average flow (κ¯\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\overline{\kappa }$$\end{document}) was introduced to determine the characteristics of flow of saturated sand under cyclic loading. Under isotropic consolidation, the value of κ¯\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\overline{\kappa }$$\end{document} of saturated coral sand was not sensitive to the CSR but decreased with an increase in Dr, indicating that its fluidity had weakened. The fluidity of saturated coral sand decreased with an increase in the initial shear stress. Under anisotropic consolidation, ue2.5% (excess pore water pressure, EPWP, corresponding to εa = 2.5%) decreased with an increase in Kc and Dr, but was not sensitive to the CSR. We established an empirical formula for the value of ue2.5% of saturated coral sand based on Kc and Dr. Furthermore, a two-parameter modified stress model was formulated to represent the ratio of EPWP with different values of Dr, CSR, and Kc. The results of experiments on different types of sands reported in the literature independently verified its applicability.