Study on Backfill Secondary Mining Technique in Failure Zone of Mini Coal Mine

According to the failure zone in a mini coal mine existed in many mining areas seriously affected to the mining of the coal resources,in combination with the certain conditions for the fully mechanized top coal caving mining face in an ultra thick seam passing through a goaf in a mini coal mine in No.2 Underground Mine,a Ruimi backfill material was applied to the grouting and backfill of the failure zone in the mini mine,thus the flowing grout could automatically flow into the bulk coal pile and the fallen coal rejects,the backfill material after consolidated would be effectively bound with coal pile and fallen coal rejects with a certain integrality.A mechanics model was established.A low limit of the regenerated roof thickness formed with the backfill material was theoretically analyzed and calculated and feasibility of the calculated results was verified by the project practices.The results showed that the secondary mining technology with the grouting and backfill would be an advanced method to treat the failure zone in the mini coal mine,could maximally recover the coal resources left in the failure zone of the mini coal mine and could be a achievements in the green mining orientation.