Influences of cutting cavity depth on subsequent rock breaking properties of driving sections

Cutting blasting is a crucial step in underground blasting driving. To investigate the influences of cutting cavity depth on subsequent rock breaking properties, driving sections with different cutting cavities depths were simplified as sandstone specimens with different depths of cavities. A series of dynamic compression tests were conducted using a 50 mm diameter split Hopkinson pressure bar (SHPB) testing system. Then, the dynamic peak stresses, dynamic peak strains, energy dissipation characteristics, and fracture patterns of the specimens were analyzed as the cavity depth varied, and the field cutting blasting parameters were optimized accordingly. The results demonstrate significant trends for sandstone specimens with cavity diameters of 10 and 20 mm. As the cavity depth increases, the dynamic peak stress decreases by 17.69% and 39.05%, the dynamic peak strain increases by 7.58% and 18.56%, the dissipation energy increases by 22.87% and 45.92%, the dissipation energy density increases by 26.92% and 73.08%, respectively. And the specimens fragmentation size also gradually decreases with the extension of cavity depth. These findings indicate that increasing cutting cavity depth could reduce the rock mass resistance to failure, enhance its deformation capacity and energy utilization efficiency, and improve its fragmentation effects. When the cavity diameter is 20 mm, the dynamic mechanical properties and energy dissipation characteristics of the specimens change at a faster rate with the increase of cavity depth, and the fragmentation size is smaller. This indicates that increasing the cutting cavity diameter is also beneficial for rock breaking. The cutting blasting technique with inner-hole and outer-hole composite delays is adopted, which can increase the cavity depth and diameter to provide sufficient free surfaces for subsequent blasting process. This optimization achieved remarkable filed performance that increasing the cycle advance and hole utilization rate of the full-section blasting into 5.0 m and 96.1%, and ensuring uniform and reasonable rock fragmentation degree. The research findings not only effectively reveal the influences of cutting cavity depth on the full-section rock breaking effects, but also provide theoretical supports and practical references for the design optimization of actual cutting blasting projects.