Tensile-shear collaborative fracturing in hard rock induced by a controllable free surface: Mechanism and application

In deep hard rock mining, high confining pressure inhibits tensile failure, leading to low efficiency and severe tool wear in conventional mechanical rock breaking methods. To solve this problem, we propose a Controllable Free Surface Induced Tensile-Shear Collaborative Fracturing (CFS-TSCF) method. The method pre-forms an engineered controllable free surface (CFS) to reconfigure the local stress field, enabling a specialized device (FIPFD) to apply directional tensile-shear loads for low-energy breaking. A multi-scale approach integrating lab AE tests, DEM simulations, and field verification investigated the fracture mechanism and performance. Results revealed a predominantly tensile-driven (>50%) process. The CFS transforms the rock’s triaxial compression into a specific stress path. This path, dominated by directional tension and constrained by lateral compression, guides the fracture along a low-energy channel. This also dictates the micro-mechanism’s evolution from central quasi-tensile to peripheral tensile-shear failure. Field trials in hard rock (>200 MPa UCS) validated the method, demonstrating controllable, blocky spalling and achieving an average mining efficiency of 52.03 t/h. This research validates the CFS-TSCF method, offering a new technical paradigm for safe, efficient, continuous hard rock mining.