Stability monitoring and bearing pressure capacity of waterproof sealing wall in underground goaf

Underground water storage in goaf is one of the important means of water conservation and mining in the western ecologically fragile area. The stability of waterproof sealing wall is related to the safety of water storage in goaf. In view of the key problem that the stability of the waterproof sealing wall in the goaf is difficult to monitor and the water pressure resistance ability is difficult to predict, under the background of underground mining end sealing in Chahasu Coal Mine, by means of theoretical analysis, numerical simulation and field measurement, the mechanical properties of coal seam and roof and floor are tested, and the minimum compressive strength of coal body and roof and floor is obtained. Considering the stress characteristics of the sealing wall structure, the maximum bearing capacity of the waterproof closed wall without the influence of mining is calculated and deduced. The numerical model of waterproof sealing wall is established, and the stress state, deformation and damage of sealing wall under the influence of advanced mining and different water head heights (6, 9, 12 and 15 m) were analyzed. The stress and displacement monitoring systems of the waterproof sealing wall in the underground goaf has been developed. Based on the theoretical analysis, the monitoring points had been reasonably arranged and applied in the field. On this basis, combined with theoretical analysis and numerical simulation results, the maximum safe head height of the waterproof sealing wall and the head height of the warning water line are determined. The results showed that the advance mining has a certain impact on the damage of the waterproof sealing wall, and the water pressure increases the sliding range of the cracks between the sealing wall and the coal pillar contact surface. The maximum water head height borne by the waterproof sealing wall at the end of mining is 12 m, and the water head height of the warning water level line of the waterproof sealing wall is 9.6 m. The contact surface between the wall and the coal pillar as well as the top and bottom corners of the closed wall are structural weak surfaces, which are prone to damage. Attention should be paid to strengthening the monitoring or observation of the position of the sealing wall embedded in the coal and rock mass and the top and bottom corners of the sealing wall. If necessary, grouting and plugging can be used to reinforce the weak surface or leakage part of the structure. The research results can provide theoretical basis and application reference for stability monitoring and water pressure resistance evaluation of similar mine waterproof sealing walls.