Enhancing recovery efficiency during the final mining phase of fully mechanized caving mining under thick-coal hard-roof conditions:countermeasures and strategies
To address the challenges of high mining stress concentration and low mining efficiency caused by large-area suspended roofs during the final mining phase of thick coal hard-roof working faces,comprehensive research methods including similar simulation tests,theoretical analysis,numerical simulations,and in-situ experiments were employed.The study set the 61304 working face of Tangjiahui Coal Mine as an engineering background and focused on the final mining phase of the 16.8 m extra-thick coal seam overlaid by 15.8 m thick hard main roof,taking into account factors such as the collapse pat-tern of overlying rock,mechanical transfer mechanism of the cantilever structure,characteristics of stress evolution,and other influential factors.In response,a roof collaborative control technology characterized by blasting roof-cutting was proposed to enhance the recovery rate.The findings of this study revealed that the cantilever structure of overlying rock caused stress concentration during the mining process,re-sulting in reduced top coal recovery during the final mining phase and necessitating the increase of stop-ping-protection coal pillars.By employing blasting roof-cutting,the cantilever structure was destroyed during the final mining phase,thereby reducing the stress transmission path of abutment mining-induced stress and weakening the transmission stress originating from the thick and hard main roof above the working face.Consequently,the caving distance of the working face could be extended.It was observed that the cantilever angle exhibited a negative correlation with the peak abutment stress,while the cantile-ver length showed a positive correlation.Shortening the cantilever length through the destruction of the cantilever structure helped reduce the peak stress.The average peak abutment stress was reduced by ap-proximately 5.76 MPa through blasting roof-cutting during the final mining phase,leading to a 20-meter reduction in the width of the stopping-protection coal pillar and an improved coal recovery efficiency.Engineering practice demonstrated that blasting roof-cutting could mitigate mining-induced stress concen-tration resulting from roof suspension during the final mining phase and effectively control the deforma-tion of surrounding rock in the entry.This significantly improved the coal recovery rate while ensuring safety and efficiency during the final mining phase.
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