Study On The Crack Development Law Of Overburden And Its Prediction Method In Shendong Mining Area

Shendong mine area,as the coal energy base of China,have thick unconsolidated layer(wind-blown sand),thin bedrock and thick coal seam,the geological mining condition is superior,it is necessary to study the development law of overburden crack and prediction method for reducing the ecological environment destruction by coal mining because of special natural environment,such as serious desertification,sparse vegetation and fragile ecological environment.Through the similar material simulation experiment,the primary and periodic collapse of overburden in Shendong mine when mining shallow depth seam were shown as the whole collapse of bedrock,many vertical cracks and separated cracks appeared thereupon too,the whole course of these cracks was ‘production,expansion,reduction,closure',the periodic collapse of key strata promoted the course to some extent.There were two producing ways of vertical transfixion crack,the first one was that upward crack run through surface by itself,the second one was that upward crack and downward crack mutually developed to run through surface.The reason of second producing way was that overburden failure was violent and strata movement transported rapidly from bottom to top so that upward crack and downward crack got a chance to lay in tensile deformation zone commonly.Based on analyzing the influencing factors of the height the fractured zone,combing with support vector machine and parameter optimization of genetic algorithm,mining depth,mining thickness,hard rock lithology proportional coefficient,dip length of working face and 47 sample data were selected to establish the model for predicting the height of overburden crack based on GA-SVR,and the accuracy of predicted height could meet the requirements of the practical engineering.