New technology for controlling large deformation in soft rock mining roadways based on deep and shallow dense drilling and its engineering application

This study investigates the control of large deformation in extraction roadways, a critical issue for safe coal mining. While conventional dense drilling offers moderate effectiveness, it provides limited capability for targeted treatment of roof strata at varying depths. To overcome this limitation, an innovative pressure relief technique employing both shallow and deep dense drilling is proposed and applied to the mining roadway of the New Shanghai No. 1 Coal Mine, China. Through a synergistic pressure relief mechanism, the method effectively reduces the magnitude and propagation range of front abutment stress ahead of the mining face. Key design parameters—including borehole length, spacing, and angle—were optimized through an integrated approach combining theoretical calculations, numerical simulations, and field validation. Field measurements demonstrate that after implementing this technique, the average stable axial force in roof anchor cables decreased from 173.3 kN to 141.0 kN, representing a reduction of 18.6%. The average support resistance of hydraulic supports # 210 and # 212 dropped from 34.82 MPa and 29.15 MPa to 22.16 MPa and 14.88 MPa, respectively, corresponding to reductions exceeding 35%. Total cumulative convergence was reduced by more than 40%. These findings confirm the substantial deformation control performance of the proposed method, offering a practical reference for managing large deformations in tunnels under similar geological conditions.