Study of Failure Mechanisms and Mechanical Responses in Double-borehole Splitting via Plunger-type Splitters across Different Lithologies

Abstract

To study the influence of lithology on rock fragmentation during double-borehole splitting with a plunger-type splitter, the Discrete Element Method (DEM) was employed to simulate fracturing processes across various rock strengths. The results indicate that: (1) Rock splitting resistance enhances significantly with increasing strength, with the equivalent splitting force required for fragmentation rising from 329.2 kN for soft rock to 4316.1 kN for hard rock. Rock splitting resistance enhances significantly with increasing strength, with the equivalent splitting force required for fragmentation rising from 329.2 kN for soft rock to 4316.1 kN for hard rock. The force-displacement relationship transitions from a single-peak profile with a gradual slope in soft rock to a bimodal structure in medium-hard rock, eventually evolving into a multi-peak distribution in hard rock. This evolution is characterized by significantly higher pre-peak growth rates and accelerated post-peak strength declines. Correspondingly, the crack propagation rate rises substantially, with the expansion mode shifting from a slow, single-interval expansion to a rapid, multi-interval surge. (2) The double-borehole coalescence consistently forms a V-shaped fragmentation zone, characterized by a narrow loading side and a wide empty-borehole side. This failure mechanisms is dominated by macro-shear and follows a three-stage evolution: micro-crack initiation, main crack coalescence, and rock fragment spalling. The research results provide a theoretical basis for rock-breaking engineering under different geological conditions.