Fixed-axis shear characteristics of marine coral sand under various consolidation conditions

Abstract

Coral sand is commonly used to construct ports and other types of infrastructure in coral reefs, where soil elements within slopes and embankments are usually under anisotropic stress because anisotropy is inherent to coral sand. In this study, marine coral sand was subjected to undrained fixed-axis shear tests using a cyclic hollow-cylinder shear apparatus, and the results indicate that the undrained response of such sand is influenced significantly by the initial orientation angle of the major principal stress (α0) and the monotonic loading direction angle (αm). In all cases, the excess pore water pressure (ue) of the coral sand tended to increase and then decrease with increasing generalized shear strain (γg), implying that such sand exhibits shear shrinkage and then shear expansion under monotonic loading. Another finding was that in the case of isotropic consolidation, the phase-transition strength (SPT) and phase-transition internal friction angle (φPT′) of the marine coral sand tended to decrease and then increase with increasing αm, while those in the case of anisotropic consolidation were always maximum in the α0 direction. There is a linear relationship between the SPT of marine coral sand and a dimensionless parameter β, where β−1 varies cosinusoidally with α0 and αm.