"Three plies in top coal" theory and its application in top coal caving mining for ultra-thick coal seams

WANG Jin-hua; HUANG Zhi-zeng; YU Lei

doi:10.13225/j.cnki.jccs.2017.0250

Abstract：The authors studied the top coal's fracture process in fully mechanized top coal caving mining for ultrathick coal seams with some combined research methods of laboratory test,numerical simulation,analog simulation and theoretical analysis.According to the studies,front abutment pressure plays a key role to the cracks development and fracture in the middle and lower plies of top coal.Repetitive propping up from hydraulic supports intensifies the decomposition of the lower ply in top coal.During the roof caving phase,the fully crushed granular coal in the lower ply comes down easily with the operation of hydraulic supports;the coal in the middle ply comes down in big lumps following the lower ply coal;and the upper ply coal comes down periodically with some time lapses.Based on the different fracture and caving features of lower,middle and upper ply of top coal,the authors propose the "three ply" structure model.Specifically,the lower,middle and upper ply coal is called "granular ply"," bulk ply" and "cracked beam ply".The thickness of each ply can be estimated by analyzing their specific fracture mechanics and caving features.The field measurement on the forms of top coal caving in Tashan Coal Mine of Datong Coal Mine Group has improvedthe "three ply" structure model."Three ply" structure exists in the top coal caving of ultra-thick coal seams.But insome special conditions,there exists only one ply or two plies,and this is affected by some factors such as top coal'sthickness,strength,fracture development,and crustal stress.