Abstract
The shape of the gasifier cavity and the high temperatures induced by underground coal gasification (UCG) have a significant influence on the failure characteristics of the surrounding rock. In this study, the variations in the mechanical properties of the surrounding rock in gasifier cavities subjected to different temperatures (20–700°C) were obtained experimentally, and the results were used to establish numerical models. FLAC3D was used to analyse the failure of the surrounding rock in drop-shaped and traditional rectangular gasifier cavities. The mechanical parameters of the surrounding rock in the numerical model were assigned a gradient distribution based on the temperature propagation law and the experimental results. The results revealed that the temperature of the surrounding rock has a significant influence on the coal pillar stability, and the surrounding rock primarily undergoes shear failure. As the temperature of the surrounding rock increases, the width of the stable coal pillar increases exponentially; the reasonable widths for coal pillars between adjacent drop-shaped gasifier cavities are 12 m (room temperature), 17 m (700°C and 850°C), 18 m (1000°C), 19 m (1150°C), and 20 m (1300°C). In contrast, the reasonable width of coal pillars in traditional rectangular gasifier cavities is approximately 21 m, which is significantly higher than that for drop-shaped gasifier cavities.
Highlights
Underground coal gasification mining is a safe, efficient, and green mining technology, and offers better safety, environmental protection, and adaptability than traditional mining methods [1,2,3,4]
The physical and mechanical properties of the surrounding rock of the gasifier cavities are altered by the high temperature, and the characteristics of the resulting deformation and failure of the surrounding rock are fundamentally different from those of traditional mining processes. ese characteristics have a significant effect on the reasonable width of the coal pillars between two gasifier cavities. erefore, the failure characteristics of the surrounding rock in coal gasifier cavities must be studied, and a method to determine the reasonable coal pillar width between adjacent gasifier cavities with different temperatures and shapes must be developed
The physical and mechanical properties of the surrounding rock in a coal gasification project in a coalfield in western China are experimentally studied at different temperatures (20–700°C). e experimental results are incorporated into a numerical model that addresses the stress field, displacement field, and failure characteristics of the surrounding rock in traditional rectangular and drop-shaped gasifier cavities at room temperature. e differences in the failure characteristics of the surrounding rock with different coal pillar widths are analysed at different temperatures, and a reasonable coal pillar width is determined
Summary
E shape of the gasifier cavity and the high temperatures induced by underground coal gasification (UCG) have a significant influence on the failure characteristics of the surrounding rock. The variations in the mechanical properties of the surrounding rock in gasifier cavities subjected to different temperatures (20–700°C) were obtained experimentally, and the results were used to establish numerical models. FLAC3D was used to analyse the failure of the surrounding rock in drop-shaped and traditional rectangular gasifier cavities. E mechanical parameters of the surrounding rock in the numerical model were assigned a gradient distribution based on the temperature propagation law and the experimental results. The reasonable width of coal pillars in traditional rectangular gasifier cavities is approximately m, which is significantly higher than that for drop-shaped gasifier cavities
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