Analysis of Surface Cracking and Fracture Behavior of a Single Thick Main Roof Based on Similar Model Experiments in Wes
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Original Paper
Analysis of Surface Cracking and Fracture Behavior of a Single Thick Main Roof Based on Similar Model Experiments in Western Coal Mine, China Jianping Zuo,1,2,4 Meilu Yu,1,2 Chunyuan Li,1,3 Yunjiang Sun,1,2 Shunyin Hu,1,2 and Zhengdai Li1,2 Received 24 March 2020; accepted 23 August 2020
Surface subsidence over coal mines in western China is serious. Collapse pits, step subsidence, surface cracks, among others occur during coal mining. Based on data of surface subsidence in western mining area, this study analyzed the control of key strata on surface subsidence. The breaking mode of the main roof with different thicknesses was discussed based on self-designed simulation test device for the initial breaking of main roof. Through physical experiments, two types of breaking models of the main roof, namely horizontal ‘‘X’’ type and vertical ‘‘X’’ type, were obtained. With the increase in the thickness of the roof, the roof was more prone to sliding instability. Based on ReissnerÕs thick plate theory, mechanical model of the initial breaking of the main roof was established, and the parameters such as thickness, step distance, PoissonÕs ratio, and burial depth were introduced. Through theoretical analysis, the fracture critical condition and breaking mode partition of main roof were obtained. According to the characteristics of surface subsidence of shallow coal seam, the mechanism of strata movement controlled by layered hydraulic fracturing technology was analyzed in the western coal mines of China. This study provides a theoretical reference for the prevention of main roof sliding instability and the control of surface subsidence. KEY WORDS: Shallow coal seam, Surface subsidence, Cutting down full-thickness of main roof, Breaking mode partition.
INTRODUCTION In western China, grass is the dominant plant functional type with biomes ranging from tall grasslands, short grasslands, dry and moist savannas to deserts. Vegetation coverage is low, as it belongs 1
School of Mechanics & Civil Engineering, China University of Mining & Technology (Beijing), Beijing 100083, China. 2 State Key Laboratory of Coal Resources and Safe Mining, China University of Mining & Technology, Beijing 100083, China. 3 Deep Mining and Rock Burst Research Institute, China Academy of Coal Science, Beijing 100013, China. 4 To whom correspondence should be addressed; e-mail: [email protected]
to arid or semiarid areas, and the ecological environment is extremely fragile. At the same time, coal reserves in the western region account for a large proportion of ChinaÕs total coal reserves, and coal seams are shallowly buried (less than 100–150 m deep). When the roof of shallow buried working face freely collapses or caves, sliding instability and step subsidence are easily induced (Yang 2010; Huang et al. 2017). Severe rock strata movements have caused ground subsidence, cracks, step subsidence, landslides, etc., causing loss in groundwater, decline in water level, degradation of surface vegetation, and desertification of land, making t
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