Integrated characterization methods for cuttability assessment of hard rock after hydraulic fracturing

Hydraulic fracturing can effectively improve the cuttability of hard rock and provide a novel approach for the non-explosive mechanized mining within hard rock. Considering the hydraulic-mechanical coupling, a hydraulic fracturing numerical model was developed based on the industrial-scale discrete element method in this study. The effects of Young's modulus, shear modulus, water pressure, cohesion, density and porosity on the number of cracks and the peak cutting force during hydraulic fracturing were examined. The results demonstrate that crack evolution exhibits three distinct stages under different influencing factors, including a rapid growth stage, a steady growth stage, and a slow growth stage. Four main controlling factors significantly impact the effectiveness of hydraulic fracturing: Young's modulus, shear modulus, water pressure, and cohesion. Additionally, the functional relationship between the number of cracks, peak cutting force, and the main controlling factors was established, and the weights of the four main controlling factors in the crack evolution process were determined. Consequently, an integrated characterization method for the peak cutting force after hydraulic fracturing was developed. The verification results demonstrate that the mean absolute percentage error calculated by the proposed integrated characterization method for peak cutting force ranges from 1.91 to 2.05%, indicating that the proposed method exhibits a high level of calculation accuracy. Finally, a calculation method for cutting indexes was proposed, and then a classification table for hard rock's cuttability was established. This study provides a theoretical basis for mechanized mining assisted by hydraulic fracturing techniques for hard rock cutting.