Study On Supporting Mechanism And Technical Foundation Of "Multi-arch Of Pier Column" In Goaf Of Shallow Coal Seam

For the treatment of goaf by filling method,domestic and foreign research is mainly carried out in two aspects:full filling and partial filling.Partial filling method can be divided into paste strip filling in goaf,separated grouting filling in overburden strata and grouting filling in caving area in strip mining according to different filling positions.Although the full filling goaf treatment method is simple and effective,it is difficult to popularize in a large area because of the high cost of filling per ton of coal and the serious consumption of filling materials,and the above partial filling method has been criticized for its complex technology and poor filling effect.In this paper,a "Multi-arch of pier column "filling support structure is proposed,that is,by injecting filling grouting material into the goaf through drilling holes on the ground surface,the goaf debris is cemented and solidified together and filled with separated layer(separated layer grouting),forming two or more types of "pier" structure,which is composed of "Multi-arch of pier column " stable structure together with key layer because of filling all the way to the key layer.To jointly maintain the surface layer,no new subsidence will occur.Firstly,on the basis of field observation and similar material simulation test,the evolution mechanism of overburden breakage in goaf is analyzed in depth;secondly,aiming at the blindness and inaccuracy of filling in goaf at present,the paper puts forward that "filling pier pillar is formed by drilling grouting on the surface of goaf,and a stable structure of " Multi-arch of pier column " is formed between pier pillar and key strata of overburden in goaf to jointly maintain the surface.Based on the idea of stability,the mechanism of filling and supporting structure with pier multi-arch is analyzed from the mechanical point of view,and the calculation formula of supporting load is deduced.Finally,based on LAC3D numerical simulation,the proposed " Multi-arch of pier column " filling method is simulated and verified.The main conclusions are as follows:(1)Based on the monitoring data of ground pressure and the geological conditions of coal seam in Gaojialiang Mine,similar material simulation test is designed to study the movement law of overburden rock and roof breakage characteristics in goaf after mining.It is proposed that the overburden rock fracture line of shallow coal seam is in the form of "Upper curve and lower line " Model and the evolution mechanism of overburden rock breakage in goaf is revealed.(2)In view of the shortcomings of the traditional full-filling and partial-filling methods for goaf treatment,a new method of goaf treatment by filling is proposed.A " Multi-arch of pier column " filling support model formed between filling piers and key strata is established,and its mechanical analysis is carried out to calculate the supporting load of piers and pillars,and the relationship between the size and strength of piers and pillars is explored.(3)The relationship between filling effect and filling density is obtained by numerical simulation.Based on the simulation test of similar materials,the settlement reduction effect of "Multi-arch of pier column " structure is evaluated by monitoring the surface settlement of the model.(4)According to the field industrial test,the development law of overburden fracture zone and subsidence of key strata under separation zone before and after filling,combined with theoretical calculation and field surface observation,the filling effect of " Multi-arch of pier column " is illustrated.