Effects of Strain Rate and Stress-State Dependence on the Mechanical Behavior of Calcareous Sand

Abstract The impact behavior of calcareous sand is critical in geotechnical and protective engineering. This study investigates the response of calcareous sand under triaxial stress conditions using an improved actively confined split Hopkinson pressure bar (SHPB) apparatus. The microscopic mechanism was revealed through the finite difference method-discrete element method (FDM-DEM) coupled numerical model. As the initial confining pressure decreases from 10.5–0.5 MPa, the axial stress-strain curve transitions from four stage to three stages. This is because the deformation states transition from being dominated by compression to those dominated by shear, causing the disappearance of the hardening stage. This also exacerbates the hysteresis of peak bond fracture, translation, and rotation on yield stress, resulting in an increasing strain rate effect. An index is defined as the ratio of dynamic increase factor for the rate dependent material to that for an ideal rate independent material to quantify the strain rate effect, which changes from 5.1–20.9 as the confining pressure changes from 10.5–0.5 MPa. The increase in density and nonuniformity coefficient reduces the strain rate index by 21.4% and 8.7%, respectively. The main factor leading to the increase in strain rate index is the confinement state.