Study on rack zone development law of medium and hard overburden strata above high intensive fully mechanized coal mining face

In order to study the crack zone development law of the hard overburden strata under the high intensive fully mechanized coal mining conditions,according to the mining and geological conditions of No.6206 coal mining face in Wangzhuang Mine of Lu'an Mining Area,the site measurement,numerical simulation,similar material simulation and other means were applied to comprehensively study and determine the development height of the water conducted crack zone in the hard overburden strata above the fully mechanized top coal caving full seam mining face.In the combination with the height observation information of the crack zone above the fully mechanized slice mining in Lu'an Wuyang Mine,the analysis showed that under the conditions of the high intensive fully mechanized coal mining with above hard overburden strata,the crack zone height of the overburden strata was in direct proportion to M/n and could fully meet the site actual condition.The crack height and mining thickness ratio would be reached at 20.2 times and the experience formula obtained could be applied to predict the failure height of the overburden strata under the similar mining conditions.The crack height obtained could be applied to the reference bases to prepare the protective coal pillars and water keeping mining plan under the water bodies in Lu'an Mining Area.