Experiment study on hydraulic reaming in borehole fracture zone in underground coal mine

In order to solve the difficult problem of hole formation caused by drilling and collapsing in fracture zone of the complex strata in coal measure strata, the fracture zone hydraulic composite reaming technology was used to flush out the debris from fracture zone to reduce the risk of sediment sticking. In this paper, based on the principle of combining water jet reaming with guided mechanical reaming, the development of water jet reaming drills was carried out, and the jet erosion effect of the nozzle was tested to guide the structure design of jet sub nozzle of water jet reaming drilling tools through ground test of jet erosion effect of nozzle. Ground tests show that the influence of nozzle diameter on jet flow rate is much greater than jet pressure on nozzle jet flow. The failure pattern of the jet erosion of the ordinary and cavitation nozzles on the coal samples is elliptical and the ratio of the long and short axes remains unchanged. The erosion depth of cavitation jet is more than twice that of ordinary jet. The water jet reaming tool preferably uses a 3×2.8 mm cavitation nozzle structure for the jet sub-section. The mechanical reaming sub-section adopts a pilot reaming drill with a diameter of 89/120 mm, forming a hydraulic composite reaming technology for the crushing zone. In a mine in Huaibei, a directional drilling hole was drilled in the broken zone of 175 m to 195 m on the roof of the A2 of the air-suction connecting tunnel, the diameter of borehole was expanded from 98 mm to 173 mm to reduce the risk of sediment sticking and ensure the drilling construction to 420 m.