Effects of confining stress on crack propagation and energy evolution during rock indentation: Insights from 2D-DEM simulations and implications for mechanized mining

Non-explosive mechanized rock breaking technology is being increasingly adopted for deep rock excavation. The complexity of stress conditions in deep rock can significantly affect the efficiency of non-explosive mechanized rock breaking. However, the limited understanding of the rock breaking performance of conical picks under complex stress conditions constrains the application of this technique in deep rock engineering projects. In this study, the rock breaking characteristics associated with rock indentation under varying confining stress levels were investigated through numerical simulations using discrete element modelling software (MatDEM). The results indicate that tensile fractures predominantly occur during vertical indentation. As the confining stress increases, the length and quantity of radial cracks generated within the rock decrease. When the confining stress exceeds 9 MPa (16.6 % of the uniaxial compressive strength of rock), discrete distributions of tensile cracks form within the rock during the indentation process. Moreover, the evolution of rock energy exhibits a nonlinear double-peak trend with increasing confining stress, whereas the system heat evolution demonstrates a “decrease–increase–decrease” pattern. Additionally, the rock cuttability is evaluated by analysing the indentation force and specific energy during the initial leap process. The findings reveal that the rock is more easily fractured under low- or no-stress conditions. As the confining stress increases, the rock cuttability initially decreases but subsequently increases. This study reveals the nonlinear mechanism of confining stress on controlling crack propagation and energy evolution during rock indentation, providing a theoretical basis and technical pathway for non-explosive mechanized mining in deep hard rock.