Analysis and Experimental Verification of Damage and Failure Characteristics of White Sandstone Based on Discrete Element Method

To investigate the damage evolution mechanism, meso-crack propagation law, and strain rate effect of white sandstone under static and dynamic loads, fine-grained white sandstone was selected as the research object. Taking fine-grained white sandstone as the research object, a three-dimensional discrete element model based on the parallel bond model (PBM) is established using PFC3D software to numerically analyze the mechanical behavior of white sandstone under three loading conditions: uniaxial compression, Brazilian splitting, and three-dimensional split Hopkinson pressure bar (SHPB). Meanwhile, corresponding laboratory experiments are carried out to conduct a comparative analysis of the macroscopic mechanical characteristics and failure modes of white sandstone under static and dynamic loads. The macroscopic mechanical characteristics and failure modes of white sandstone under static and dynamic loads were compared and analyzed. The process of crack initiation, propagation, and coalescence, the evolution law of force chains, and the energy transformation characteristics were explored from a mesoscopic perspective. The dynamic increase factor (DIF) was introduced to quantitatively characterize the strain rate strengthening effect. The results indicate that the established discrete element model effectively represents the macroscopic mechanical behavior of white sandstone, with relative errors of compressive strength and tensile strength between numerical analysis and laboratory results both below 2%, and the failure modes are in good agreement. Under uniaxial compression, Brazilian split, and dynamic impact, the crack propagation patterns of white sandstone differ, but all share a common basis: shear cracks initiate the fracture, tensile cracks guide the propagation, and the coupled development of the two types of cracks forms the fracture surface. The proportions of shear cracks are 61.8%, 52.7%, and 54.5%, respectively. The initiation and propagation of cracks are closely related to the breakage, reorganization, and concentration of force chains, with the concentrated regions of tensile force chains serving as the main paths for crack propagation. Under different strain rate loading conditions, the crack propagation mode and fragmentation morphology of white sandstone do not change significantly. Under high strain rate impact conditions, it can absorb more energy and exhibit better load-bearing capacity. This is because the number of internal cracks in the specimen increases significantly under high strain rate impact, and the penetrating crack zone becomes more pronounced, resulting in the white sandstone absorbing more energy under high strain rate impact conditions. The research findings can provide a theoretical reference for stability evaluation and disaster prevention in deep rock engineering under coupled static-dynamic loads.