The mechanism of rock-breaking using disc cutter assisted by pre-slotting

Abstract

To reveal the rock-breaking mechanism under the pre-slotting assisted disc cutter, an experimental study on rock breaking was conducted based on a disc cutter linear cutting test bench. The relationships between the cutting force, specific energy consumption (SE), rock debris distribution parameters (roughness index CI, uniformity coefficient n_b, characteristic particle size r_e, and fractal dimension D_f) and the pre-slotting depth were analyzed. Additionally, the relationship between SE and rock debris distribution parameters was further investigated. Meanwhile, a two-dimensional discrete element model for the pre-slotting assisted disc cutter rock breaking was established. The rock-breaking mechanism under the presence or absence of pre-slotting was revealed from the perspectives of crack number, crack propagation trend, and internal stress distribution within the rock. The results show that as the pre-slotting depth increases, the rock-breaking force of the disc cutter first decreases and then increases. The SE exhibits a trend of first decreasing and then increasing with the increase in pre-slotting depth. The presence of the pre-slotting can effectively reduce the rock-breaking force on the cutter (up to 58 % reduction in the normal force, and 51 % in the rolling force) and significantly decrease the SE required for rock breaking (up to an 88 % reduction in SE). SE decreases following a power function trend with the increase in CI and r_e, while it increases with D_f and n_b, following power and linear growth trends, respectively. From the strength of the correlation between SE and rock debris (CI > n_b > r_e > D_f), it can be seen that CI is a reasonable debris distribution parameter, which can be used to assess the SE and rock-breaking efficiency of the disc cutter. The distribution trend of crack number can effectively reflect the variation of the cutter’s cutting force. The larger the ratio of tensile cracks to shear cracks, the smaller the cutting force required for rock breaking by the disc cutter. An appropriate pre-slotting depth can effectively guide the crack propagation direction and reduce the number of cracks, thereby improving the fragmentation size of the rock debris. Under the condition without pre-slotting, rock fragmentation is primarily dominated by shear failure driven by compressive stress, while under the condition with pre-slotting, rock fragmentation is mainly dominated by tensile failure driven by tensile stress.