Strata Movement Model Based On Laminated Beam Structure With Dislocation End Under The Mining Of Shallow Buried Thick Coal Seam

With the change of geological and mining conditions,different supporting structures are presented in the overlying strata.Literature [1-2] proposed a classification method for the balanced arch structure of the mining rock and soil,and built the structure type of mining rock and soil.This paper selected the Shendong mining area as the study area,and focused on the strata movement model based on laminated beam structure with dislocation end under the mining of shallow buried thick coal seam.Shendong mining area located in the northwest of China.Coal seam of this mining area has the characteristics of shallow buried,large thickness,good coal quality,simple resource occurrence,stable geological conditions and large reserves.And it is easy to implement a wide range of high intensity mining.Compared with the general geological mining conditions,the law of surface movement and deformation have certain particularity with the high strength mining of shallow buried thick coal seam.By means of data analysis,theoretical analysis,physical similar material simulation and numerical simulation research methods,we have done an in-depth study of the movement and deformation laws with the high strength mining of shallow buried thick coal seam.And based on the laws,we have set up a dual medium coupling overburden subsidence prediction model.The main contents and achievements of this paper are as follows:(1)Measurement and analysis of surface subsidence characteristics under the mining of shallow buried thick coal seam.Through the collection of geological and mining conditions of the high strength mining working face with shallow thick coal seam in Shendong mining area,we got the static and dynamic deformation parameters of the relevant working face,and analyzed the special surface subsidence law.a)The movement and deformation parameters of high strength mining of shallow buried thick coal seam has the characteristics of smaller boundary angle,larger major influence angle tangent and smaller subsidence coefficient.b)The surface discontinuous deformation is fully developed,mainly including collapse pit,stepped crack and tensile crack.The stepped cracks appears periodically,lags behind the working face,and the spacing between the cracks is correspond to the periodic weighting interval of the roof.The tensile cracks are characterized by small width and large density.c)The surface movement of high strength mining of the shallow and thick coal seam is violent,and the mining of single working face could cause a large extent of grade IV surface damage.d)From the time dimension,the surface points quickly enter the active stage after being affected by mining,and the duration of the active stage is about 1/2 of the duration of the total movement.e)From the space dimension,paper selected the 18mm/d of the subsidence velocity as the critical point,and the surface dynamic movement basin was divided into severe moving area and slow moving area.The scope of the severe moving area is large and the length of severe moving area is about(1.1-1.5)H.The working face lags behind the front end of severe moving area and the lag behind distance is about 1/5 of the severe moving area length.(2)Failure characteristics of laminated beam structure zone with dislocation end and the stacking zone of broken rock blockThe failure characteristics of laminated beam structure zone with dislocation end and the stacking zone of broken rock block were analyzed from vertical and lateral through similar simulation.a)From the vertical direction,under the condition of insufficient mining,rock damage height increases in the exponential growth trend with working face advance,the fragments of broken rock above gob increases linearly with the increase of distance between the broken rock layer and the gob,and the fragments of the same broken rock layer is basically the same.b)From the lateral direction,according to the failure degree of rock strata,the bedrock was divided into undisturbed zone,continuous moving zone of rock strata and the stacking zone of broken rock block.The end of rock beam gradually introvert from top to bottom and rock beam superimposed on each other together.There exist the laminated beam with dislocation end in the continuous moving zone of rock strata.The broken rock mass is stacked on the lower broken rock block in the stacking zone of broken rock block and rock blocks generally lack of horizontal load.(3)Simulation analysis of mining response characteristics of laminated beam structure with dislocation end and the stacking zone of broken rock blockThrough theoretical analysis and similar model test verification,the overlying rock response characteristics under the condition of mining in shallow buried thick coal seam were revealed.Under the condition of mining in shallow buried thick coal seam,there is no balance arch structure exist in the sandy loose layer.Sandy loose layer response in the form of following body to the underground mining.The dynamic development process of overlying rock balance structure is "rock arch-no arch".While the balance arch structure is easy to occur in the mucilaginous loose layer during the mining process.In the early stage of mining,the mucilaginous loose layer response in the form of flexural body to the underground mining.Later,it turns into the following body.The dynamic development process of overlying rock balance structure is "rock arch-soil arch-no arch".The overburden balance structure of high strength mining in shallow buried thick coal seam is eventually developed into the "no arching" structure.Combined with the similar model test results,the formation mechanism of surface stepped crack and ground sinkhole were analyzed.The high strength mining of shallow buried thick coal seam,the upper roof of the coal seam could be considered as the "step rock beam" and dislocation break in the form of sliding upward layer by layer.The vertical joint in the sandy loose layer is fully developed.After all the bedrock breaks,surface stepped crack occur near the top of the broken position of the bedrock surface.There is a big gap between the continuous moving zone of rock strata and the stacking zone of broken rock block.The gap connect the source(water sand mixture)and storage space(gob),and lead to the occurrence of sand inrush and surface sinkhole.(4)Numerical simulation analysis on the mining subsidence law of overlying rocka)Through numerical simulation,we got the relationship that the subsidence rate,major influence angle and the movement range of sandy loose layer are greater than the mucilaginous loose layer,while the horizontal movement coefficient of the sandy loose layer is less than the mucilaginous loose layer;b)By means of numerical simulation and theoretical analysis,it was found that the moving boundary in the bedrock is concave,the moving boundary in the loose layer is upside convex.(5)Construction and reliability analysis of surface subsidence prediction modelBased on the mechanism and law analysis of overburden subsidence,the prediction formula of bedrock subsidence was deduced from the partition firstly,then the coordinate system was transformed,and a unified prediction model for bedrock subsidence was established.Based on the subsidence relationship between bedrock and loose stratum,combined with probability integral method,a prediction model of dual medium coupling ground subsidence for high strength mining of shallow thick coal seam was constructed.Combined with the geological and mining conditions of working face 2407 in Halagou mine and the working face 2304 in Hanjiawan mine,the practical engineering application of the surface subsidence prediction model was carried out.The reliability of the prediction model is verified.