Simulation Study on Ground Shock Convergence Effect of Multi-Point Explosions in Geomaterials for Underground Engineering

Underground simultaneous multi-point explosions are an efficient attack method against protective structures and critical infrastructure. The superposition and focusing of ground shock waves produce a convergence effect, which significantly increases peak pressure within a specific region and enhances destructive power. Seven-point convergent explosion model tests were conducted in a geomechanical model material, revealing that charge spacing markedly affects the convergence effect. A numerical model was established to investigate the explosion convergence effect and attenuation under different charge layouts, yielding the optimal charge spacing formula. Based on grey theory, grey correlation degrees were established between scaled charge spacing, charge mass ratio, initiation height difference, and peak pressures at various scaled distances. The optimal initiation parameters for a Grade III rock mass prototype were determined. With optimized parameters (scaled charge spacing: 0.326 m/kg1/3, charge mass ratio: 1.293, scaled initiation height difference: 0.0702 m/kg1/3), the best explosion convergence effect is achieved. At a scaled distance of 0.724 m/kg1/3, the peak ground shock stress is 3.05 times that of a single-point explosion with the same charge weight, and 71.35% higher than that before optimization. This study provides a reliable numerical and experimental framework for the optimization analysis of ground shock convergence effects induced by multi-point explosions, contributing to the safety assessment and resilience enhancement of underground infrastructures against extreme blast loads.