Application of pneumatic DTH hammer in drilling rescue of mine accidents

As an efficient percussive rock breaking tool, pneumatic down-the-hole (DTH) hammer has played an important role in drilling rescue of mine accidents at home and abroad. Herein, the technical characteristics of pneumatic DTH hammer were described from the points of rock breaking mechanism, structure type, drilling method and specification, and the reverse circulation type and its characteristics of pneumatic DTH hammer were emphatically analyzed. Besides, the application of forward circulation drilling of pneumatic DTH hammer and the combined deviation correction drilling of pneumatic DTH hammer and mud screw in small diameter drilling, as well as the research progress of pneumatic DTH hammer measurement while drilling technology, were analyzed based on the successful rescue cases such as the water inrush accident of Shanxi Wangjialing Coal Mine, the collapse accident of Shandong Pingyi Gypsum Mine, and the collapse accident of Shanxi Hushan Gold Mine. For shallow small-diameter drilling, the pneumatic DTH hammer could directly hit the underground roadway with straight drilling technology. For deep small-diameter drilling, the combined deviation correction drilling of pneumatic DTH hammer and mud screw could be used to hit the underground roadway. Moreover, the promotion and application of pneumatic DTH hammer in forward circulation, downward slag discharge and reverse circulation were introduced with reference to the successful cases of large-diameter rescue drilling on the ground at home and abroad, and the typical cases of large-diameter engineering drilling in mines. The maximum drilling depth of pneumatic DTH hammer for downward slag discharge reaches 688 m, and that by reverse circulation reaches 654.1 m. Further, in view of the gradual development of mining in China towards the deep, the scattered and wide distribution of mines, multiple geological types and large differences, and the deep hole rescue in complex formations, the shortcomings of the pneumatic DTH hammer technology for small-diameter drilling were analyzed, focusing on the main problems faced by the forward circulation, downward slag discharge and reverse circulation technologies of pneumatic DTH hammer technology for large-diameter rescue drilling. Meanwhile, the essence of the technical defects for drilling in the complex strata was clarified, and further research on pneumatic percussive directional drilling technology and gas-liquid double circulation drilling technology of large diameter borehole was suggested.