Static Blasting Roof Cutting Surrounding Rock Control Technology for Narrow Coal Pillar Gob-Side Entry Driving in Thick Coal Seams

Abstract

Under the condition of wide coal pillar mining in thick coal seams, gob-side roadways exhibit a high dynamic pressure and large deformation. Taking the gob-side entry driving of the 11603 working face in the Heilongguan Mine as the engineering background, this study overcomes these issues by combining the use of narrow coal pillars and the static blasting roof cutting technology. An elastic mechanics model involving the rock strata and coal pillar was established, and the process of roof cutting reducing the deformation of the coal pillar was analyzed. A suitable coal pillar width was obtained based on the cusp catastrophe theory, and the optimum expansion pressure of the static blasting cracking agent was investigated experimentally. A fracture mechanics model was introduced to analyze the final length of the propagating crack under the effect of the cracking agent, and based on the crack propagation length, the optimal spacing between roof cutting boreholes was determined. The effect of roof cutting on the roadway and coal pillar was analyzed using FLAC3D (version 5.0). The results showed that the maximum expansion pressure of the cracking agent reached 83.3 MPa. By cutting the roof, the surrounding rock pressure and plastic failure of the roadway could be effectively alleviated. The 25 m coal pillar will cause a high stress concentration and significant wastage of resources. Before roof cutting, the interior of the 8 m coal pillar entered the full plastic state, and an elastic zone with a width of 3.4 m appeared after the roof cutting. Based on the serious situation of a side collapse of coal pillars, a surrounding rock control measure for bolt–mesh–cable–beam, combined with the grouting anchor cable, was proposed and later applied in engineering practice to ensure the stability of gob-side roadways.