Deformation Mechanism And Control Of Thick Coal-seam Roadway Under Thick Loose Layer With Fully Mechanized Sub-level Caving Mining

With the strategy of China’s energy development moving west, the coal mining isfacing more challenges due to special geological conditions in the western areas, andthe researches on the deformation mechanism and control of the surrounding rock ofroadway which is formed through full-mechanized caving mining of thickunconsolidated formation and super high seam have become one of the currentresearch hot spots and difficulties. As the existing ordinary fully-mechanized theoryhas been difficult to guarantee the safe and efficient mining of the coal resource underthe complex geological conditions, such as thick unconsolidated formation, super highseam, large mining height, large caving ratio, etc., so an urgent task to implement theresearch on the deformation mechanism and control of the surrounding rock ofroadway under the conditions of the whole space and many factors. This papercombines the physical&mechanics test, theoretical analysis, similar material test,numerical calculation, field industrial test and other means and methods, and makes asystematic research on the deformation mechanism of the surrounding rock of the fullcoal roadway under the conditions of thick unconsolidated formation and super highseam and obtains the mechanics analysis model of the surrounding rock of theroadway and the change laws of the displacement, stress and energy and otherparameters. The innovation work and research results in this paper include thefollowing aspects:(1) This paper has established the structure mechanics model of the basic roofand overlying rock, determined the structure parameters of the overlying rock massand the fracture line position on the gob side, given the buckling criteria of the sliding,rotation, cutting down of the overlying rock mass; at the same time, this paper hasbuilt the "internal and external structure" cantilever structure model based on thecoupling of the length of the non-coal-caving interval, coal seam thickness, coal pillarwidth and other multiple factors so as to obtain the bending moment combinationequation under the coupling of the multiple factors, and the energy criterion of thestructure destruction.(2) Based on the limit equilibrium theory, this paper has amended the mechanicsequilibrium equation of the coal body edges, studied the mechanics model of the coalmass on the edge of the coal pillar on the roadway side and the gob side; besides, ithas also derived the relation between the internal stress and the width of the plasticity zone of the coal pillar edges and the calculation formula of reasonable width B of thestage coal pillar.(3) This paper has built the similar simulation experiment model of thefully-mechanized mining of the special high seam, analyzed the distribution laws ofdisplacement, stress and vector and studied the stability of the fracture structure of theoverlaying rock and the structure of surrounding rock of roadway. Besides, theresearch has found that the deformation of the roof and overlying rock mass hassomething to do with the thickness of coal seam. The fracture line location of themain roof is affected by the width of coal pillar. In addition, it has obtained theregression equation, that is, the inbreak, displacement and stress of the single keystratum and the compound key strata change with the pushing distance and the stressof the roadway surrounding rock changes with the width of coal pillar.(4) With the discrete element numerical calculation method, this paper has madethe research on the deformation characteristics of the surrounding rock of roadwayunder the conditions of the different combinations of the coal pillar width, thenon-coal-caving length, coal seam thickness and other parameters and obtained thelaw that the bending ad sinking curvature of the overlying rock changes with thethickness of coal seam. In addition, it has verified that the non-coal-caving interval atends is the cantilever beam structure. It has also found that the deformation of theright support is equal to the sum of the deformations of the roof, baseplate and leftsupport; the destruction points of the exceeding roof stress are about17.5m awayfrom the roof tensile fracture location; the length of the non-coal-caving interval at theoptimal end is7m; the reasonable width of the stage coal pillar ranges from25to30m.(5) This paper has designed the supporting scheme for the surrounding rock ofroadway which is formed through the full-mechanized caving mining of the thickunconsolidated formation. It has made a comparative analysis of the deformation ofroadway with FLAC3D so as to determine the optimal supporting parameters.Through the field industrial test and actual measurement, it has obtained thedeformation law of surrounding rock of roadway under the mining influence, andverified the deformation mechanism and the effect of the control technology of thesurrounding rock of roadway which is formed through the fully-mechanized cavingmining of the thick unconsolidated formation and the super high seam.