Experimental Study on Strengthening and Sealing Materials and Their Application in Coal Mines

To solve the problem of unstable sealing in the sealing section of a gassy, soft coal seam, a seal reinforcement material for gas extraction boreholes was developed, which was mainly made of ordinary Portland cement and blended with additives such as aluminium powder, quicklime, and gypsum. Firstly, in order to obtain the necessary expansion and compressive strength of reinforcement material, key factors affecting the material properties were determined. Key factors affecting the expansion properties and compressive strength of reinforcing materials were investigated by a single-factor test. Moreover, according to the central combination (Box–Behnken) experimental principle and response surface analysis (RSA), the interactions of various factors on the expansion and compressive strength were determined, and the optimal experimental conditions were acquired. The experimental results indicated that the optimum ratio of the material was 2% for gypsum and 0.52% for aluminium powder and quicklime at the experimental temperature of 20°C, and the ratio of water to material was 0.6. Finally, in the N1103 working face of No. 3 coal seam of Yuwu coal mine, Luan Group, China, the sealing property of the reinforcement material was validated, and the problem of hole collapse at the borehole orifice was solved (resulting in a gas concentration 2.48 times that measured before borehole reinforcement), and the gas drainage effect was enhanced.