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

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 (& alpha;0) and the monotonic loading direction angle (& alpha;m). In all cases, the excess pore water pressure (ue) of the coral sand tended to increase and then decrease with increasing generalized shear strain (& gamma;g), 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 phasetransition strength (SPT) and phase-transition internal friction angle (& phi;& PRIME;PT) of the marine coral sand tended to decrease and then increase with increasing & alpha;m, while those in the case of anisotropic consolidation were always maximum in the & alpha;0 direction. There is a linear relationship between the SPT of marine coral sand and a dimensionless parameter & beta;, where & beta;- 1 varies cosinusoidally with & alpha;0 and & alpha;m.

Automated summary

Marine coral sand exhibits shear shrinkage and expansion under monotonic loading, and its stress-strain response is influenced by the initial orientation angle and the loading direction angle. The phase-transition strength and internal friction angle of the coral sand vary with the loading direction. There is a linear relationship between the phase-transition strength and a dimensionless parameter that varies with the orientation angles.