Study On Stability Of Surrounding Rock Of Roadway Next Goaf With Small Pillar In Tashan Coal Mine Fully Mechanized Caving Face

The method of fully mechanized coal mining was used for mining the extra-thick coal seam of carbonic in Tashan mine of Datong mining area,lots of problems caused by leaving 38 to 45 meters of coal pillar to protect roadways,such as the low coal mining rate,high strength of roadways supports and strong pressure,which were seriously affecting to the mine safety and efficient production.Therefore,from the perspective of resource efficient recovery and safety production,according to the Tashan mine coal seam characteristics and mining conditions,using theoretical analysis,similar simulation experiment,numerical calculation and field observation and other methods to study technology of small coal pillar along gob and stability of surrounding rock.The main research results were as follows:Structure model of the overlying strata of gob stability before and after of fully mechanized top coal caving face with large mining height in extra thick seam was established,movement law,breaking structure characteristics of high and low key strata of end overlying strata was analyzed.Before the gob was stable,the low key layer existed in the form of cantilever beam structure and high key layer existed in the form of masonry beam structure before the mined out area is stable;the triangle slip area with an angle of 70°was formed in the end overlying strata which was divided into slip rupture zone,tension and compression fracture zone and pressure fracture zone after the cantilever beam structure broken.Simplified analysis model of the end lateral abutment pressure about the stability of gob before and after was established,and evolution mechanism of lateral abutment pressure dominated by the movement of triangle slipping area was revealed,the root reason of the lateral abutment pressure peak value reduced and influence scope expanded was the load distribution changes caused by triangle slipping area breaking movement.From the perspective of the block stability after low key strata cantilever beam breaking,block motion model of triangle slipping area was established,the stability after the cantilever beam breaking mainly decided by the high-length ratio of broken fault block body,the breaking angle and the rubbing surface friction coefficient.There were the remarkable influence to the end overlying strata structure and the lateral abutment pressure caused by mining thickness and length of unexploited end coal.As thickness increasing,the plastic area gradually increased,the lateral stress decreased,which were in favour of tunneling roadway with small pillar along gob;The smaller of the length of the unexploited end coal,the more favors to the stability of roadway along gob,once the length of unexploited end coal surpassing a step distance of the low key strata,the roadway along gob would be in the high stress area all the time.Comprehensive the above varieties of factors,the width small coal pillar of roadway along gob was determined 6 m,the optimal time of roadway tunneling was 9 months after the end of the adjacent panel mining.The reasonable supporting scheme of roadway along gob with large cross section was put forward,which used of combined supporting of bolts,anchor cables,w-type steel bands,anchor composite beams and metal meshes.Surface displacement of roadway was observed using crossing method during preliminarily mining period,square period and after fully mining;the stress of the anchor cables and displacement of deep surrounding rock of roadway with small pillar were monitored by anchor dynamometers and multi-point displacement meters.Displacements of two sides and roof and floor of roadway with big pillar were 5 times and 6.5 times as much as roadway with small pillar comparing to the deformation of surrounding rock of roadway with big pillar.The numerical calculation model of surrounding rock crush and fracture development of roadway along gob with small pillar was established,physical and mechanical parameters of rock strata and parameters of soft body in gob filling were inversed combining with ground deformation monitoring data,broken feature and its variation law of small coal pillar was analyzed quantitatively during the roadway along gob tunneling period and fully mechanized top coal caving panel mining period;The internal crack of small coal pillar is relatively developed whereas the whole was still in good condition.