Study Of The Overlying Strata "O" Letter Type Spatial Structures Of Longwall And Correlate Rock Pressure

Overlying strata spatial structures of longwall are three-dimensional structures that are formed by breakdown overlying strata that have important influence to strata behavior of longwall. Overlying strata spatial structures of longwall formed by working faces that is mined and four sides are substance coal are named "O" letter type spatial structures. This paper studied forming, evolution laws, the relation with abutment pressure distribution and main influence factors of "O" letter type spatial structure by similar simulation, field exploring, numerical simulation and theory analysis.Through similar simulation and field exploring, the author considers that overlying strata spatial structures have two big and small parts. Those are "plate-shell" big structures in whole overlying strata of goaf and "articulated rock plates half-arch" small structures at all round goaf. Forming progress of overlying strata spatial structures "plate-shell" big structures is evolution progress of two spatial structures. Abutment pressure of longwall transform elastic distribution into elastic and plastic distribution with evolution of big spatial structures Longwalls present periodic pressure with evolution of small spatial structures. Stage leap of "plate-shell" big structures makes longwall present dig periodic unusual pressure.Evolution laws of "O" letter type spatial structures and distribution laws are: The height of "O" letter type spatial structures is controlled by the length of short border of goaf. When goaf reaches "square", longwall is loaded dig pressure. Overlying strata is existed in clipping action effect of thick and hard rock strata during evolution progress. And clipping action effect is basic reason for attribute transformation of immediate roof and main roof. The breakdown scope and abutment pressure distribution laws of two sides substance coal of "O" letter type spatial structures are the basically same. When working face footage is L = 4H/π≈ 1.27 H, abutment pressure of around strata reach maximum.This paper analyses main facts that influence evolution of "O" letter type spatial structures, such as key strata, property of overlying strata, obliquity of coal and terrane, mining depth, height of stone head, shear height, repeat mining and span of goaf. Moreover, there are some other influencing factors such as: thick loose bed, surface mining degree, impel speed of working face, coal mining and roof manage methods, mining procedure and time.Based on the study on evolution laws of "O" letter type spatial structures, the author studies "O" letter type spatial structures of strip mining and its evolution laws and analyzes five instances of overlying strata spatial structures of strip mining and surface subsidence and control. The author thinks that it is practicable to apply viewpoint of "O" letter type spatial structures to design strip mining and control surface subsidence, and put forward design norm of strip mining.Some important and core results of the study have been published publicly.