Study On The Laws Of Strata Behavior And Breaking Feature Of Roof In The Large Mining High Fully-mechanized Face Under The Thick Sandstone Roof

Aiming at the thick coal seam mining with Large space and high strength under the thick sandstone roof in Shendong mining area,the strata behavior,changing rules of hydraulic support working resistance and characteristics of roof structure is studied by using the methods of field measurements,theoretical analysis,numerical simuLation and etc in the 52307 working face of the Da-liuta coal mine.Through the field measurement of hydraulic support working resistance and overburden subsidence in three different mining stages in the 52307 high mining face,the main features of strata behavior and changing rules of hydraulic support working resistance are obtained.The results show that the strata behavior is distinguishing in different positions in the working face.In the middle position of the working face,the periodic weighting has the obvious reguLarity,the pressure strength is the Largest,and there is a clear periodic weighting step distance,the average step distance is 18.7m,and the continuous pressure step is 3.3m.The periodic weighting of the upper part of the working face is not obvious because of the side of the solid coal.The structure and fracture characteristics of thick sandstone roof exert great influence on the mining pressure.When periodic weighting,the working resistance of the support increases rapidly to the rated working resistance or exceeds it,the dynamic load coefficient is 1.5.At the same time,according to the change of the working resistance of the hydraulic support,the curve of working resistance can be divided into 4 types: rapid growth,slow growth,stable and reduced.The results of CDEM numerical simuLation show that the part of the thick sandstone roof falls into the caving zone and becomes the equivalent direct roof.The working resistance of the hydraulic support increases rapidly because the periodic breaking of upper stratified sandstone act on the cantilever beam of lower stratified sandstone.The overlying rock movement that is affected by coal mining becoms more sensitive,the roof breaking step becomes shorter and the vertical dispLacement extended speed of overlying rock is quicker because of the lengthening of the working face.According to the key strata theory,changing rules of hydraulic support working resistance and characteristics of roof structure,the thickness of equivalent direct roof is analyzed and the mechanical model of roof control is established.At Last,the discriminant standard for the roof structure of thick sandstone and the calcuLation method of working resistance are determined.