Damage evolution of sandstone under cyclic impact loading and its influence on triaxial compression behavior

The degradation of rock mass mechanical properties induced by cyclic dynamic disturbances is a key factor leading to engineering failures. To investigate this mechanism, cyclic impact tests were performed on cylindrical sandstone specimens with varying initial stress conditions using an improved Split Hopkinson Pressure Bar (SHPB) system, thereby producing rock specimens with different levels of impact-induced damage. Subsequently, triaxial compression tests on these damaged specimens were carried out with a TYJ-2000M electro-hydraulic servo testing machine to examine their static mechanical responses. Results show that cyclic impacts cause significant nonlinear deformation characteristics in the stress–strain curves and an evident unloading response following the peak. At an initial stress of 5 MPa, the dynamic strength, secant modulus, and unit-volume absorbed energy progressively decrease with increasing impact numbers, while the damage degree rises. In contrast, specimens with an initial stress of 15 MPa show negligible damage. When the dynamic damage exceeds a critical value (D > 0.118), the specimen initiates the release of accumulated elastic energy, which eventually surpasses the absorbed kinetic energy. During triaxial loading, specimen with 5 MPa confining pressure fails along diagonal shear bands, whereas those with 15 MPa confining pressure develop a localized shear surface. Overall, cyclic impacts substantially reduce rock cohesion but have little influence on the internal friction angle. • Cyclic impact and triaxial compression tests were conducted on sandstone under varying stress conditions. • The three-dimensional stress state of rock before and after cyclic impact was first considered. • After damage, more cyclic impacts lower strength and stiffness but raise strain rate, strain, and damage. • Cyclic impacts greatly reduce sandstone cohesion but have little effect on friction angle.