Study on rock fragmentation and vibration response characteristics in hard rock formations using high-pressure gas expansion method

Low-disturbance excavation constitutes a critical technology for rock mass engineering in environmentally sensitive areas, exerting decisive impacts on environmental protection and construction efficiency. This study employs a combined methodology incorporating small-scale model tests, field measurements, and numerical simulations to systematically investigate multi-parameter borehole layout schemes in limestone strata. Through PVDF piezoelectric sensors installed on small-scale model borehole walls, this research precisely captured the dynamic borehole wall forces during high-pressure gas expansion for the first time, establishing reliable design parameters with peak expansion tube forces reaching 581 MPa and validating its hard rock fracturing capability. The field-calibrated FLAC3D numerical model systematically compared the dynamic response patterns of rock mass plastic zone and near-field vibrations to three controlling parameters: burial depth, horizontal borehole spacing, and expansion tube density, identifying the optimal parameter combination of horizontal borehole spacing at 1.5 m × 2.0 m and a borehole depth of 1.5 m (burial depth of 1.3 m). Field application has verified that this optimized drilling pattern significantly enhances hard rock fragmentation efficiency, induces dense fracture networks, and substantially reduces mechanical rock-breaking losses.