Abstract
The narrow pillar mining method is widely adopted for working faces in coal mines. However, in cases of an overlying hard roof, a suspended triangle roof plate or a cantilever will be formed near the goaf. At this point, the coal pillar extrusion and serious deformation will occur in the gob-side roadway. In order to mitigate the problem, the roof-cutting technology with a chainsaw arm and its equipment have been developed. In this paper, based on the analysis of deformation and failure characteristics of 2312 roadway, which is close to the goaf of 2311 working face in Tashan Coal, the roof-cutting technology with a chainsaw arm was chosen to be applied in 2311 roadway. Then, the roof-cutting process and the load acting on the coal pillar were discussed and analysed. A numerical model was established to analyse the stress releasing effects after roof cutting. Moreover, the roof-cutting height and the support parameters of the roadway were optimized through numerical analysis and the results manifested that the roof cutting was the most effective when the roof-cutting height was 6.4 m. After roof cutting, the vertical stresses within the coal pillars were lowered by about 25.0%. Finally, the roof-cutting experiment was carried out in the 2311 roadway in Tashan Coal Mine. The on-site roof-cutting depth was 6.4 m and the roof-cutting width was 42 mm guided by the numerical analysis. To verify the stress-relieving effects, the borehole stress meters were applied to monitor the peak advancing stresses of narrow pillars at various depths. The measured results indicated that the peak advancing stresses decreased by 22.8% on average, and therefore, roof cutting and stress releasing effects were achieved.
Highlights
In order to isolate the mined-out areas of adjacent working faces, the coal pillars with a certain width are usually reserved [1,2]
The coal pillars will directly lead to the waste of mine resources and reduce the service life of coal mines
Singh et al [1] analysed the effects of surrounding rock stress on pillar stability during the mining process by the theoretical calculation; Renani et al [9] analysed the failure laws of the pillar owing to size and shape; Elmo et al [10] analysed the influence of joints and fractures on the pillar stability by an integrated numerical modelling–discrete fracture network approach; Zhou et al [11] studied the dynamic process of coal pillar deformation and failure by the physical simulation method; and Bertuzzi et al [12] gave the strength calculation equation of the coal pillar by the empirical formula, and the numerical simulation was used for verification
Summary
In order to isolate the mined-out areas of adjacent working faces, the coal pillars with a certain width are usually reserved [1,2]. Singh et al [1] analysed the effects of surrounding rock stress on pillar stability during the mining process by the theoretical calculation; Renani et al [9] analysed the failure laws of the pillar owing to size and shape; Elmo et al [10] analysed the influence of joints and fractures on the pillar stability by an integrated numerical modelling–discrete fracture network approach; Zhou et al [11] studied the dynamic process of coal pillar deformation and failure by the physical simulation method; and Bertuzzi et al [12] gave the strength calculation equation of the coal pillar by the empirical formula, and the numerical simulation was used for verification. The industrial experiment was carried out in the 2311 roadway in Tashan Coal Mine
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