Study On Failure Mechanism And Coupling Control Of Coal Roadway With Mud Compound Roof Under The Dynamic Mining Pressure

The support problem of soft rock coal roadway with mud compound roof, which is considered complex in underground engineering, become the difficult problem in the coal roadway supporting due to adverse conditions such as poor surrounding rock lithology and high engineering deviatoric stress. The support in the form of a single object in this kind of coal is not feasible, and the combined support often trapped in the embarrassing situation that the front roadway is digging while the rear is repairing is not ideal. The reason why the single supporting is infeasible is that support strength is insufficient and the failure reason of joint support lies in uncoupling between mechanical properties of surrounding rock and that of support structure. Traditional combined support method, without considering the supporting mechanism of the support system, the release of internal savings ability of surrounding rock and the stability of surrounding rock to the fullest, will be just the combination of a variety of supporting structures in as simple a way as possible, thus making it hard to achieve the coupling effect on strength, stiffness and structure of support body and surrounding rock.Haulage entry of 20307 working face in Gao Jialiang mine 2 coal seam is selected as the research object. Such methods as on-site survey, indoor rock physical mechanics test, microscopic physical-chemical composition analysis, the theoretical analysis, numerical simulation and field industrial test are used to make comprehensive analysis on deformation failure mechanism under dynamic mine pressure and coupling control countermeasure research of surrounding rock stability in coal roadway. The main results are acquired as following:(1)This paper, in consideration of the coal roadway disturbance, discontinuous structural plane including the structure of the joint and crack discontinuous structural plane, groundwater and many other factors, on the basis of the fractal theory to predict loose circle radius of haulage entry ranging from 1600 mm to 2000 mm, determines the plastic loose circle radius from 1740 mm to 2020 mm by means of on-site hole wall method. Compared results show that the fractal theory which is applied to the prediction of plastic loose circle has certain reliability.(2)The fuzzy clustering analysis method is presented in this paper to identify overall stability classification of surrounding rock in coal roadway of 2 coal seam under dynamic mine pressure and clarify the clustering center, thus making sure 20307 haulage entry belong to third class of instability surrounding rock. Surrounding rock is classified once again according to the geological conditions of the specific coal roadway. Weak structure of soft rock coal roadway is differentiated based on the criterion——effective load coefficient S≥0.55.(3)Those sensitivity factors including high deviatoric stress, low mechanical strength of surrounding rock, the supporting structure and surrounding rock, through the indoor experiment and comprehensive analysis of engineering geological environment, which cause fast convergence rate as well as big deformation value on the surface of soft rock, which bring about serious sinking asymmetric deformation of mud composite roof, and which result in a serious crowded deformation with strong Theological properties in the two sides, are determined as the main factors influencing stability of mud composite roof.(4)The surrounding rock in 20307 haulage entry, through quantitative analysis of microscopic physical-chemical composition and qualitative analysis of the deformation mechanism, whose deformation mechanics principle is IabcIIBDIIIda model, is determined composite geological soft rock characterized by stress dilatation and scale expansion——high engineering deviatoric stress-joints-swelling (HJS).(5)Through qualitative research on the deformation mechanism conversion technology of engineering soft rock, "high strength bolt+metal mesh+high strength anchor cable +steel belt +the grouting in flood area" coupling support scheme that refers to "bolt mesh cable belt grouting" is adopted in 20307 haulage entry. Based on FLAC3D numerical simulation software, the reliability of the coupling support scheme is analyzed, the result showing that "bolt mesh cable belt grouting" coupling support structure system is effective.(6)This paper designing supporting parameters of "bolt mesh cable belt grouting" coupling support, conducting site industrial test and implementing such on-site monitoring as deformation on the surface of surrounding rock, bed separation of coal roadway and the actual stress of bolt (anchor cable), monitoring results show that coupling support structure system can effectively constrain the surrounding rock deformation in haulage entry and that verify the application reliability of coupling support theory together with FLAC3D numerical software in soft rock coal roadway support under dynamic mine pressure.