Abstract
Currently, shallow coal resources are being exhausted gradually, mining depth is continuing to extend downward, and hydrogeological conditions are becoming increasingly complex. Therefore, accurate determination of the failure floor position is necessary to perform multiple‐seam mining. In this study, the 7255 working face of the Renlou coal mine is regarded as the research object. Through a comprehensive measurement of ground penetrating radar detection and fixed‐point grating optical fibers, the law of floor deformation and failure is analyzed dynamically, and the characteristics of the floor rock deformation response are discussed. The results of on‐site monitoring indicate that the mining effect of the working face is greater than that of the tectonic stress. With the advance of the working face, the deformation of the shallow area (0–8 m) first increases gradually, then increases rapidly, and finally increases gradually again; the middle area (8–19 m) experiences three stages, from a gentle increase to temporary stability and then a rapid increase; the deep area (19–29 m) undergoes three stages, from being stable to increasing and then being stable again. After mining, the floor of the working face can be classified into four areas in the vertical direction: complete failure area (0–5 m), poor severe influence area (5–11 m), failure development area (11–19 m), and elastic deformation area (19–29 m). Mining‐induced stresses cause resistance at the interface of different lithologies and weaken the effect of downward propagation. Coal seams and the interface between different lithologies are more prone to deformation. The results can provide a certain reference basis for the advanced exploration scheme of the underlying seam mining under the multiple‐seam mining method, as well as provide a new approach for floor failure depth measurement.
Highlights
As the depth of coal mining continues to extend downward annually, the geological and hydrogeological conditions of coal mines are becoming increasingly complex
After mining the underlying 72 coal seam, the mining failure depth of the coal seam floor should be determined. erefore, ground penetrating radar detection and a fixed-point grating optical fiber were used in this study to dynamically monitor the deformation and failure of a coal seam floor, providing reference for the advanced exploration scheme of underlying seam mining
When approaching the working face, the deformation speed was initially high and decreased. e main part of the floor exhibited compressive strain, and a small part exhibited tensile strain. e 73 coal seam with weak lithology and its interface were easier to deform, and the interface of different lithologies could resist the downward transmission of rock deformation to a certain extent
Summary
As the depth of coal mining continues to extend downward annually, the geological and hydrogeological conditions of coal mines are becoming increasingly complex. Li et al used 3DFLAC to simulate the height development of a water-conducted fracture zone and the floor failure depth before and after coal mining [10]. E research object of this study is the 7255 working face of the Renlou coal mine, which adopts close-distance multiple-seam mining. Erefore, ground penetrating radar detection and a fixed-point grating optical fiber were used in this study to dynamically monitor the deformation and failure of a coal seam floor, providing reference for the advanced exploration scheme of underlying seam mining. E working face corresponds to a flat-terrain surface, with an average elevation of 25.6 m It is in the first stage of the south middle-five mining area. Using the data of the 7255 working face in equation (4), we obtain hmax 18.76 m; the theoretical floor failure depth of the 7255 working face was approximately 19 m
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