Haoyu Han

In underground engineering, the dynamic failure mechanisms of rock masses containing openings under impact loading are of vital importance. This study systematically investigates the effects of opening shape, size, and orientation on the dynamic behavior of red sandstone. Dynamic impact tests are first performed using a split Hopkinson pressure bar together with high-speed photography and digital image correlation for full-field strain and crack monitoring. A two-dimensional combined finite–discrete element (FDEM) model is then developed to reproduce the dynamic failure process. It is found that the opening size significantly affects the dynamic compressive strength, while the opening shape dictates crack initiation and propagation. Circular openings induce symmetric cracking, square openings cause corner-dominated cracks, and horseshoe-shaped openings produce asymmetric failure whose dominant side depends on the rotation angle. The FDEM model established in this study successfully reproduces the main crack paths and failure modes observed in experiments, which provides a powerful tool for the analysis of rock dynamic failure. Moreover, the results in this study also provide practical engineering guidance for the reinforcement and support measures for different opening shapes.

Finite–discrete element method (FDEM) has become a widely recognised numerical method for simulating the fracturing behaviour of materials under various loading conditions. However, the substantial computational cost of three‐dimensional (3D) FDEM has led to a marked imbalance: extensive research exists on two‐dimensional (2D) FDEM, while studies on 3D FDEM remain limited. This study investigates the dynamic fracture behaviours of rocks under multiaxial static and dynamic coupled loads, utilising a self‐developed 3D FDEM parallelised based on a general‐purpose graphics processing unit (GPGPU). The 3D FDEM incorporates both intrinsic and extrinsic cohesive zone models (ICZM and ECZM) as well as various contact interaction algorithms to facilitate robust simulation of a full‐scale triaxial Hopkinson pressure bar (Tri‐HB) testing system. Dynamic uniaxial and biaxial compression (UC and BC) tests within the Tri‐HB framework are modelled with different combinations of cohesive zone models and contact algorithms, and the results are compared against each other and against laboratory experiments reported in the literature. The simulations demonstrate that the 3D FDEM with all these models and algorithms can reasonably capture the stress wave propagations in both metal bars and rocks as well as the primary dynamic fracturing behaviours of rocks under the coupled static and dynamic loads. However, computing accuracy and efficiency vary across model combinations. Overall, the 3D FDEM with the ECZM achieves the highest accuracy and efficiency.