Physical modeling of floor failure above confined water: a case study in China

Abstract

Coal mining in areas with deep confined water is very dangerous; to ensure safety, it is necessary to clarify the damage characteristics of the working face floor. To directly reflect the failure characteristics of the working face floor under the coupled effects of mining stress and confined water pressure, this study considers the mining above confined water in the deep coal seam of the II633 working face of the Hengyuan coal mine in the Huaibei mining area as the engineering background. With the use of the similar material simulation experimental method and a self-designed monitoring system for confined water diversion and a confined water loading system and a confined water lifting system that can directly reproduce the floor confined water lifting characteristics affected by floor failure during coal mining, the mining stress distribution patterns, deformation and failure characteristics of the overburden, and diversion characteristics of the confined water in the working face floor are investigated. The results show that the floor undergoes three stages of deformation in the horizontal direction: premining stress concentration-related compression (10–15 m ahead of the working face), postmining floor pressure relief-related expansion, and roof collapse-related stress recovery (the distance from the lagging working face is 15–20 m). In the vertical direction, a soft rock layer blocks the continuous transfer of mining stress to deeper layers and produces an important cushioning effect. In the process of coal mining, shear cracks easily develop in the coal wall in front of and behind the working face. After the coal seam is excavated, the length of the fractures that develop in the physical model is 27 cm. The confined water loading system can visually reproduce the hydraulic characteristics of the confined water during the mining process; that is, the confined water easily bursts at the front and back ends of the coal wall in the goaf. The error, as determined by comparison between the field measurement results and the theoretical calculation results, is only 0.617 m, verifying the reliability of the similar simulation method.