Investigation of directional fracturing mechanism induced by instantaneous expansion in tunnel excavation
摘要
The operational risks and rock damage associated with explosive blasting in tunnel excavation necessitate the development of non-explosive alternatives. This study proposes a novel Instantaneous Expansion (IE) technology that integrates directional energy-focusing tubes and eco-friendly fracturing agents to achieve precise rock breaking. Through field experiments and RHT model-based numerical simulations, the performance of Conventional Blasting (CB), Shaped Charge Blasting (SCB), and IE in full-face excavation is systematically compared. Results demonstrate that IE generates directional tensile fractures along predefined paths, reducing over-excavation by 65% (shaping rate: 7.63%) and minimizing the excavation-induced damage zone (average depth: 1.7 m) compared to CB and SCB. In-situ stress analysis reveals that confining pressure suppresses radial crack propagation while guiding fracture orientation, as evidenced by a 10.3% reduction in fractal dimension under high lateral stress (k = 2). The proposed IE mechanism leverages gas-driven tensile stress concentration, aligning with the "strong-in-compression, weak-in-tension" behavior of rocks. These findings provide critical insights into low-damage excavation for deep energy/resource projects, such as underground gas storage and geothermal reservoirs, while highlighting the need for optimized charge configurations in anisotropic stress fields.