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

To investigate the influences of cutting cavity depth on subsequent rock breaking properties in driving sections, driving sections with different depths of cutting cavities were simplified as sandstone specimens with different depths of cavities. A series of dynamic compression tests were conducted using the split Hopkinson pressure bar (SHPB) testing system. Then, the dynamic mechanical properties, 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 that for sandstone specimens with cavity diameters of 10 mm 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 fragmentation size of the specimens gradually decreases. These findings indicate that increasing cutting cavity depth could reduce the rock mass's 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. In the field, the cutting blasting technique with hole-inner and hole-outer composite delays is adopted, which can increase the cavity depth and diameter to provide sufficient free surfaces for subsequent borehole blasting, thereby increasing the hole utilization rate of the full section blasting to 96.1%, and ensuring uniform and reasonable rock fragmentation degree.