Research On Overburden Rock Breaking Law In Shallow Coal Mining

Shallow buried coal seam mining cause serious mine geological environment problems,such as ground collapse disaster,fissure and landslide are widely distributed. The research objects are all kinds of geological hazard body. Strata breaking law,surface collapse mechanism and mining-induced slope activity mechanism have been systematically analyzed by field observation,indoor geotechnical testing,computer simulation calculation, theory analysis and field testing,which could guide engineering practice initially.Innovative achievements of this dissertation have been displayed as follows:(1) Similar material model testing, the high density electrical prospecting and borehole flushing fluid experiments show that strata movement spread to the surface,which crack zone is divided into two zone features. Strata and the thick loose bed form the "falling loose body" structure. Tensile stress and shear stress weak-field control the structure’s breaking and caving.(2) Overburden rock tensile failure happens in the first place,and then shear failure rupture. The loess covering layer also has the similar laws. The tensile stress intensity weak-point is the initial craze position of rock beam.The tensile stress weak-field is the root cause of the strata rock destruction.(3)It set up a analysis model about the slip angle of collapse pit and know the characteristic of collapse pit is not only related to rock mechanics properties of gob, but also closely related to the space form of gob.Slip angle,rise span ratio,ratio between depth and span are inversely proportional relationship.(4) Considering key rock beam movement influence factor, it establishes the analysis model of the collapse pit. The periodic collapse type fracture can be characterized with fracture lagging and lag angle.Collapse type lag distance and angle can be characterized with crack growth characteristics of periodic collapse type fracture.(5) Based on the under rock beam fracture characteristics, The loess breakage fracture penetration degree concept is proposed. It found the structure model, which is about the fracture penetration degree of the loess beam. Shear stress on the loess section can over its ultimate strength when degree is greater than a certain threshold,also can lead to the collapse of loess fracture.(6) It simulates the tension fracture law of overburden strata and thick loose bed geological body by the tensile fracture finite element method. The results show that the tensile stress intensity weak-point is the initial craze position of rock beam. The consolidation weak-points form tensile stress weak-field. The tensile stress weak-field is the root cause of the overburden rock breaking. The tension fracture of loess cover is controlled by the tensile stress weak-field. The periodic cracks in ground have a coupling relationship with the main roof periodic breaking.