Investigation of Stress Wave Interaction and Fragmentation in Granite During Multihole Blastings

Both stress wave superposition and dynamic response process of rock materials are complicated in rock engineering, especially the fracture behavior is difficult to described quantify in the multihole blast loading. The laboratory experiment and a numerical study were performed with granite material to explore stress wave superposition and crack growth in radial and tangential directions. A high-speed photogrammetric system and strain measurement were adopted to obtain the crack propagation and the strain field. The interaction and fragmentation of the stress waves under blasting were simulated. The circumferential tensile stress increased during multihole loading, and the radial cracks further expanded into macroscopic fracture in rock. The development of radial cracks between adjacent holes played a role in rock fracturing. The superposed stress increased nonlinearly with boreholes increased, and both the borehole number and the loading direction influenced the stress field process. The strain field also increased nonlinearly with multihole blasting, and the micro-cracks gradually accumulated. Because of the combined action of the incident and reflected tension waves, the outgoing cracks extended to the boundary along the polygonal path, and the crack branching became seriously around the specimen boundary.