DYNAMIC DEVELOPMENT CHARACTERISTICS OF TWO ZONES OF OVERBURDEN STRATA UNDER CONDITIONS OF COMPOUND ROOF, HIGHLY GASSY AND THICK COAL SEAM IN FULL-MECHANIZED TOP COAL CAVING FACES
Taking Yuwu coal company as the experimental mine,by using the equipment which is sealed two ends by capsules in borehole,affused measurable water between the two capsules and borehole televiewer system,overburden two zones height of fully-mechanized top caving are monitored and analyzed through the digital relationship of fractures around mining such as change of dip angle,numbers and depth,numbers and width.At the same time,similarity model and numerical model experiment of fissure development evolution are carried out.The results show that:(1) Caving zone height changes from 27 m to 32 m and fractured zone height changes from 58 m to 61 m;(2) The fracture characteristics are mainly with high angle and low width before mining,with small angle and middle width after mining;with the mining of working face,the numbers of fractures increase with straight line;(3) The fractures cluster region mainly focuses near the coal wall,and the fractures density distribution curves of overlying strata are high at two ends and middle of working face,just like wave-shapes.