Research On The Development Law Of Overburden Fractures Under The Hydraulic Coupling Effect Of Repeated Mining In Close-range Coal Seam

Based on the mining and exploration on the power and water comprehensive considering these two factors,the engineering background of a in shaqu coal mine,through field observation and theoretical analysis,physical analog simulation,numerical simulation and other research methods,research close distance coal seam group mining upper coal seam(a mining)and the lower coal seam(secondary mining)under the action of the hydraulic coupling law of rock fracture.The main conclusions are as follows:(1)The caving height of 3+4# coal seam in Shaqu No.1 Mine is 15.24 m by calculation.According to similar simulation,the caving height is 16 m,about 3.2 times of the mining height.The height range of the fracture zone is 39.62 ～ 67.92 m.(2)Through the observation of "anhydrous" and "water-bearing" boreholes by means of borehole peeping method,it is concluded that in the coal strata near the mining face,the internal fractures of the coal body within the range of the coal seam are extremely developed,and the fractures in the coal and rock mass are relatively less developed in the deeper and closer to the roof strata;At the same time,due to the existence of a small number of annular fractures,water will gradually penetrate into rock fractures over time.It can be found that water without source(continuous water)has little influence on coal and rock mass.(3)by comparison with similar simulation experiment to research,it is concluded that "no hydraulic coupling" model and "hydraulic coupling" model in the upper coal seam mining(a mining)cases have difference,concrete embodiment in the hydraulic coupling "model in mining upper coal seam(mining)at a time when changed the" no hydraulic coupling "model the distances of first weighting and periodic;When the"hydraulic coupling" model is excavated in the lower coal seam,its ore pressure behavior and overburden movement are the same as that of the "no hydraulic coupling" model in the secondary mining,which may be because when the upper coal seam is mined,the influence of water content in the overburden of the "hydraulic coupling" model is small,so it is difficult to cause too much influence on the secondary mining.(4)The repeated mining model of near-distance coal seam group without hydraulic coupling and the repeated mining model of near-distance coal seam group with hydraulic coupling model are simulated by numerical software,and the fracture development diagram,stress distribution change diagram and displacement evolution diagram of the two models are further compared and analyzed.It is concluded that in UDEC discrete element numerical simulation software,when the overburden strata contain 0.1mpa water pressure,the development of overburden fractures is more likely to be caused by the primary mining,while the "hydraulic coupling" and "no hydraulic coupling" are similar in the case of the secondary mining.(5)Based on the applied research methods,it is concluded that the overburden fracture development under the hydraulic coupling action of repeated mining in the near coal seam group is similar to that under the hydraulic coupling action of repeated mining in the near coal seam group,but the overburden fracture development under the water pressure effect of 0.1MPa is more prominent.With the continuous advance of the working face,the roof in the middle of the goaf gradually collapses and compacts,resulting in the occurrence and expansion of overburden fissures.There is a development area of fissures in the front and rear of the goaf,and it is easy to lead to the existence of cross-layer fissures,which makes the roof in the front of the working face collapse frequently with mining.At the same time,with the continuous advance of the working face,the overlying strata of the goaf sank and collapsed,and there were cracks on both sides of the goaf.(6)According to the field measurement data of roof and floor flow of double-end plugging leak detection method,the height of the fracture zone is 28.0m～53.5m,and the height of the fracture zone in the roof of 4502 working face in the Fifth mining area is about 38.5m,and 5.2m is the initial position of floor fracture development.