Experimental study of the mechanical behavior of calcareous sand under repeated loading-unloading

Understanding the mechanical behavior of calcareous sand under repeated loading-unloading is important to engineering design for island-reef underground caverns and pile foundation projects. In this study, we conducted conventional consolidated-drained triaxial shear tests on calcareous sand collected from the South China Sea under different effective confining pressures, and then, we performed multiple sets of triaxial repeated loading-unloading tests on calcareous sands with equivalent physical properties under different deviatoric stress levels and effective confining pressures. Based on the results, we conducted an in-depth investigation of the effects of the loading mode and effective confining pressure on the strain softening behavior and shear strength angle of calcareous sand. We studied the variation in the unloading rebound modulus as the effective confining pressure and deviatoric stress level changed, verified the applicability of the Dunkan-Chang model's estimation equation for the unloading rebound modulus to calcareous sand, and established the relationship among the volume contraction during unloading, the effective confining pressure, and the deviatoric stress level. The results of this study provide an important basis for selecting appropriate parameters for island-reef construction engineering.