Compression and critical-state behaviors of calcareous sand–diatom mixtures

Calcareous sand–diatom mixtures are found naturally in the coral reef sediments, where the diatom potentially affects the mechanical behaviors of the mixtures. We performed a series of isotropic compression and triaxial drained shear tests to investigate the effect of diatom on the compression and critical-state behaviors of the mixtures. We found that the diatom and effective confining pressure can considerably affect the compression index, swelling index, coefficient of volume compressibility, compression modulus, secant modulus, peak-state deviatoric stress, peak-state axial strain, and peak-state frictional angle. In addition, the critical-state friction angle is independent of the diatom content, while the critical-state line (CSL) in the compression plane is affected significantly by the diatom content. We proposed modified equations for compression modulus and CSL considering the influence of diatom content, and the two equations could reasonably predict the compression deformation and critical-state behaviors of the mixtures. This study provides experimental basis for understanding critical-state behavior for the calcareous sand–diatom mixtures.