Feasibility study on the principle of punching-shearing composite rock fragmentation mode of connecting holes in rock strata

Replacing roadway with borehole is an important research direction of underground coal mine drilling technology, which has the advantages of high efficiency and low cost. However, in the construction of large diameter connecting holes in rock strata, the multi-stage reaming method has such problems as long lifting and drilling time and low efficiency of hole formation. This paper proposes the principle of punching-shearing composite rock fragmentation through structural and technological innovation without changing the configuration of drilling equipment. It is a creative combination of punching rock fragmentation of high-pressure water-impactor-inner bit rock and shearing rock fragmentation of drilling rig-drilling pipe-outer PDC bit. The impact energy is used to pre-split stratum, destroying the overall tectonic stress of rock formations. In the meantime, the drilling rig drives the outer PDC bit to shear and break the outer rock after pre-splitting, thus realizing the application effect of "small horse-drawn cart". ø153 mm punching-shearing composite bit is developed, and ZDY3200S separated type small rig is adopted to drill hard sandstone formations, with the average penetration rate of 8.3 m/h and the maximum penetration rate of up to 10 m/h. And the rotation speed and weight on bit have minor impacts on the rate of penetration. The field experiment results show that, the principle of composite rock crushing by punching and shearing is feasible, providing a new research idea for the drilling of connecting holes quickly and optimally in underground coal mines.