Stress Optimization And Structure Stability Control For The Surrounding Rock Of Gob-side Entry Retaining

Gob-side entry retaining supplies the essential space for pillarless-continuousmining, pillarless-simultaneous extraction of coal and gas, and continuousde-stressing mining of coal seams, which provides a pretty important safeguard fordecreasing dynamic disasters of methane, boosting coal recovery ratio, reducingroadway drivage ratio and is one of key technologies for performing scientific miningof coal. However, both surrounding rock structure stability and space maintaneanceare under threat due to the fact that position of gob-side entry retaining is near the gob,which will suffer mining activity for many times during its service period.Through physical simulation, numerical simulation and theoretic analysis, thisdissertation analyzes systematically roof weighting mechanism by investigating roofstrata movement characteristics of lateral roof beside gob. Besides, on the basis ofstress evolution and distribution of the surrounding rock of gob-side entry, an idea thatapplying lateral roof presplitting technology optimizes region stress of surroundingrock is proposed, which indicates fracture stability mechanism of lateral block.Ultimately, region stress control technology is formed and structure stability controltechnology system for surrounding rock of entry is presented, from which it can beconcluded as follows:(1) Roof of gob experiences orderly fractionated collapse and once collapse incoal mining effect, which indicates after insulation of separation space from fracturedroof strata. Roof stresses are under distributary and impose pressure on thesurrounding rock of entry by transmiting effect from lateral wedge area. Subsidencevalue of roof consistes of deflection subsidence before fracture, rotation subsidence infracture period, and compression subsidence after fracture, which means givendeformation to low location rock mass continues a long time. Roof of gob-side entrypresents multi-weighting property and long term gradual deformation characteristicduring fractionated collapse, while it presents fierce weighting and short term severedeformation.(2) Mining stress for surrounding rock of mining panel presents T-shapedistribution and stress-ring distribution in a plane and in the space respectively, whilegob-side entry is located between valley point and peak point of T-shaped area.Surrounding rock of gob-side entry will become weaker under the condition of longterm movement of roof, which makes entry in low stress area and deep bolting support can exert the bearing capacity of deep rock mass and restrict rock massdeformation of shallow low-stress area.(3) Presplitting de-stressing can accelerate fracture movement of main roof,which can release pressure from entry roof. On this basis, abutment pressure willmove towards shallow area and there is a small decrease of peak point of stress. Theimprovement of de-stressing to deformation of entry surrounding rock, from high tolow, is roof, filling wall, floor and rib. It is noticed that fractured blocks will form newrock arch structure by attaching other blocks. Mechanics relationship betweenstructures determines stress release degree, which means optimization space ofcantilevel length is objective. Therefore, a new optimization methodology ofcontilevel length, with stress release criteria for lateral roof, is proposed in thisdissertation.(4) Impact factors about surrounding rock stability of gob-side entry are analyzedand these show that system stiffiness of “roof-wall-floor”structure, which is formedby gob-side supporting wall, roof and floor of entry, determines the bearing efficiency.Strength development of filling wall should be in accord with roof pressuredynamically and roadway maintaneance is hard when blind area of bolting andequivalent span increase.(5) An idea that district control technology for surrounding rock of T-shape areaof gob-side entry is proposed, which forms structure stability control technologysystem for surrounding rock of entry. Firstly, there are presplitting de-stressingtechnology for lateral roof, optimization techonolgy for span-depth ratio of roadwayand width-height ratio of wall in structure aspect. Secondly, there are three heightbolting technology, height-span reducing technology, and deep-bolting andshallow-grouting technology in supporting aspect. Thirdly, there are plaste-concretefilling technology, masonry structures filling technology, steel cylinder prop fillingtechnology and high-water material filling technology in filling aspect. Ultimately,there are full-length and stage gob-side entry retaining technology in entry lengthaspect.Combining with gob-side entry retaining engineering cases which contains10mthick hard limestone roof of entry in154307mining panel of FenghuangshangCoalmine, superposition main roof with1.45m thin direct roof in E1403mining panelof Xiaoqing Coalmine, and over10m compound roof in1205mining panel ofZhongxing Coalmine, these above technologies are tested and verified in this dissertation.