Test Study On Surrounding Rock Deformation Mechanism And Control Method Of Automatically Formed Gob-Side Entry Retaining With No-pillar

When traditional longwall mining roadway driving along goaf,the stress environment of roadway is complex,the surrounding rock is difficult to control,and safety accidents are easy to occur during driving.When the reserved coal pillar width is small,the coal pillars along the gob are fragmented and have poor bearing capacities.If the reserved coal pillar width is increased,the resource waste can be severe.Filling-based methods of gob-side entry retaining reduce resource waste,but the cost of the filling materials is high,and many fillings cannot conform to the deformation properties of the roof surrounding rock,which can lead to splitting failure.Currently,large deformation-induced coal mining accidents frequently occur near roadways.Specifically,coal mine working face accidents account for 85%of all accidents,and roadway accidents account for over 90%of the working face accidents.The majority of these accidents occur during roadway excavation.Cutting roof and no-pillar mining technique with automatically formed gob-side entry retaining.Mining technology of self-formed roadway without coal pillar with roof cutting and pressure relief can reduce periodic weighting,gas in goaf,spontaneous combustion tendency of coal seam.And it can greatly reduce the excavation rate of mining roadway,increase the recovery rate of coal resources,reduce the cost of coal mining.In this technique,pressure is offloaded via directional roof cutting,and a roadway is automatically formed via the ground pressure and rock breaking expansion.These processes permit the implementation of a new longwall mining process in which there is no mining roadway and no reserves of coal pillars.Many researchers have conducted extensive research on no-pillar mining technique with automatically formed gob-side entry retaining.But their research are concentrate on theoretical analysis,numerical simulation and field test.Previous model tests were mostly planar models.It cannot accurately simulate the stress state of surrounding rock.Therefore,to carry out three-dimensional geomechanically model test which is based on no-pillar mining technique with automatically formed gob-side entry retaining and clarify the failure mechanism of surrounding rock can provide guidance for the design of self-formed roadway support in the field,and is of great significance to the safe and efficient production of coal mines.Based on the engineering background of Ningtiaota Coal Mine,a large-scale geomechanically model test has been independently developed and carried out,and the stress and displacement evolution law of surrounding rock of no-pillar mining technique with automatically formed gob-side entry retaining has been studied in combination with numerical simulation and field test.The main research work and results are as follows.(1)Research on key parameters of no-pillar mining technique with automatically formed gob-side entry retaining.According to the field working conditions,the numerical simulation of key parameters such as different cutting roof,cutting angle,anchor cable spacing,anchor cable row spacing and coal seam thickness is carried out,and the deformation control mechanism of surrounding rock of self-formed roadway under the influence of different factors is clarified.(2)Development of model test device of no-pillar mining technique with automatically formed gob-side entry retaining.A large-scale geomechanically model test device is constructed,which consists of reaction device,high-pressure loading and hydraulic control system,mining sliding device and pulling power device,and high-precision monitoring system.The developed test device is easy to assemble and has the advantages of high pressure,stable loading and long-term pressure retention.The hydraulic pump station can control each row of cylinders independently,and the model opening can realize multi-specifications interchange,and the overload damage experiment can be realized.(3)Research and development of similar materials for model test of no-pillar mining technique with automatically formed gob-side entry retaining.Based on the physical and mechanical parameters of raw rock and the similarity theory of model test,a large number of test tests of model similar materials have been carried out.Coal seam,roof and floor rock seam and blasting slit similar materials have been prepared according to the ratio of materials.The largedeformation anchor cable and hydraulic support specimens which conform to the geometric similarity ratio and stress similarity ratio of model test were developed.(4)Research of model test of no-pillar mining technique with automatically formed gob-side entry retaining.Based on the site engineering geological conditions of Ningtiaota coal mine,the geomechanically model test of the mining process of roof-cutting and pressure-relieving and no-pillar mining technique with automatically formed gob-side entry retaining was carried out.The evolution process of the rotary subsidence of the key blocks of the basic roof during the advancing process of the working face was analyzed,the law of the basic roof breaking and instability was determined,the law of the movement of the overlying strata was defined,and the deformation law of the surrounding rock of the no-pillar mining technique with automatically formed gob-side entry retaining.