Research On The Fracture Mechanism Of Overburden And Control Technology Of Surrounding Rock Of Long Wall Repeating Workface

The longwall mining method of residual coal resources after old coal mining method is one of the important direction of coal mining technology.Among related problems,surrounding rock control problem in fully mechanized mining face crossing roadway,especially parallel roadway,is the emphasis and difficulty of the subject.Mining face and parallel roadway situation is the most difficult to control in pillar old mining area of residual coal mining.Current research on mine pressure law of mining working face crossing parallel roadway does not develop deep enough,and research on the migration of overlying strata and the overlying rock breaking off during mining over parallel roadway has not yet reached a quantitative degree.The Shenghua colliery 3101 mining working face as the research object,through field investigation,data analysis,theoretical analysis and similar simulation method,this thesis studies surrounding rock stress distribution and transfer rules,the movement rule of overlying strata,surrounding rock breaking off and surrounding rock control technology in mining working face crossing parallel roadway,and provides a scientific basis for mining working face surrounding rock control.The contents and conclusions of the research are as follows:(1)By applying RST stope mining pressure analysis software,in theory,we calculated the mining face pressure strength and pressure step distance of Shenghua fully mechanized coal mining.Calculation results show that:under the surrounding rock environment,the initial pressure strength is 7482.4?7646.2 kN each frame,the initial pressure step distance is 48.75?56.29 m,and periodic pressure strength is 7315.6?7514.8 kN each frame,and cycle pressure step distance is 11.97?14.2 m.(2)We established the mining working face crossing parallel roadway mechanical model,comparatively analysed the working face parallel abandoned roadway and mining rock force transfer and migration of overlying strata.Through the contrast analysis,we pointed out the mechanism of the overlying rock rupture in advance during mining working face crossing gob:as coal pillar width decreases with the mining,coal pillar compression deformation increases and the roof starts bending and sinking.When the width of coal column is less than the critical critical instability width,the stability of coal column is lost.If the coal column compression is severe or overlying strata cantilever is longer during instability,the overlying strata will be bending and sinking severely,and the overlying rock breaking off position is at the top of the gob.The breaking position of the overlying rock is located way in the front of the coal wall of the working face,and the broken fault is called the lead fracture.(3)By analysis of force transfer and migration of overlying strata of mining working face surrounding rock stress,we points out the three main factors that cause the overlying rock rupture in advance:width of coal pillar,the basic roof hanging roof length,parallel abandoned roadway width.Study on the coal pillar width and basic roof hanging roof length,parallel abandoned roadway width,technology parameters of mining face and support of mining working face roof fracture mechanism in advance guard of technique or measure is made.The research shows that:1.with the coal pillar mined,the size decreases,there is always a moment of coal pillar instability.2.the instability of coal column will not necessarily cause the basic rock strata occur ahead of the fracture,rather,the occurrence of lead fracture is caused by many factors.Therefore,smaller width of the gob may also lead fracture,pressure strength is greater than that of the solid coal winning the periodic pressure strength.3.according to the existing theory we get the working face mining coal pillar stability calculation formula of critical width loss.4.Theoretical calculation get 3#coal seam in fully mechanized top coal caving on mining in front of the working face there is bigger than the width of the gob of about 6m,inevitable rupture in advance exists.And critical abandoned roadway width is used to judge the advance broken sufficient conditions,we cannot make conclusion that the abandoned roadway width less than this value does not appear to lead fracture of judgment.(4)By two-dimensional physical similar simulation method,we study force distribution and movement in two stages of mining coal pillar and surrounding rock of roadway.The research shows that the deformation and failure of coal pillar are the core factors causing the lead fracture.With the compression and deformation of coal pillar until the instability,the basic roof and its control of the weak rock bending and sinking and rotary.When the overlying strata load is over the coal pillar bearing capacity,plastic damage of coal pillar happens,and basic roof breakage and basic roof overlying strata load is transferred to the abandoned roadway of coal body in front of(column),the basic roof and immediate roof and top coal weight gradually by the front of the gob into the plastic zone of coal body,a bracket and plastic damage of coal pillar bear.(5)The theory of mechanics model analysis pointed out that the mining working face surrounding rock control mainly developed from two aspects.One is control of advanced great fracture,which is due to the advanced control key fault block slide instability required resistance varies with the hanging roof length exponentially larger than 1 even parabolic growth.Two is the stability control of the breaking of basic roof key block.Mechanical calculation shows in the process of mining crossing gob,working resistance of support needed for the most dangerous situation is 1452.55 kN each frame.(6)We put forward the technical measures to control surrounding rock mining working face.By filling empty roadway and roadway support,lane control can be achieved ahead of the break.The top coal caving process or supporting coal pillar reinforcement can reduce the compressive deformation of coal pillar,roof subsidence slowing down.Reducing working surface length can use coal pillar(or entity coal)on the working face to support the roof,sharing the load on the coal pillar,controlling the occurrence of advanced fracture.Reasonable planning or oblique crossing gob decreased roadway in parallel with the working surface,and improved the stress condition.Take "pressure" means or by using good scaffold with cutting top ability or water injection softening roof,can control hanging roof length and avoid fracture rock size greater.