Research On Comprehensive Partition Characteristics And Stability Of Stope Floor Under Water-rock Coupling Action

The mechanism of the interaction of physical、chemical or mechanical between groundwater and rock which not only changes the quality and state of rock and groundwater, but also the mechanical state and the mechanical properties of both sides constantly. Mining activities undermine the balance of the original stress and make stope rock stress redistribute, and stope surrounding rock will produce deformation and failure under new stress field. Meanwhile, the effects of press water splitting, squeeze and soften dissolution make rock mass splitting extension, shear deformation and displacement and increase rock structural plane porosity and connectivity, which increase the permeability of rock mass, be easy to form water inrush channel and make floor water inrush if connecting to stope face. By taking the stope floor stress field, displacement field evolution as the research object, the thesis is done to systematically analyze the stress, deformation and failure partition characteristics and the corresponding relationship between the systematic research on the floor, reveals depth of destroyed floor and its stability of different facial length mining thickness, pressure under the Water-Rock coupling, using comprehensive study methods of similarity simulation test, computer numerical simulation, theoretical analysis and example analysis, etc. The detail research contents are as following:(1)According to the elastic mechanics theory, the floor of coal seam was regarded as a homogeneous and isotropic half-infinite body and its boundary stress was simplified to the form of Weibull distribution, which can obtain arbitrary stress analysis of the floor space.(2)Based on the principle of the water-rock interaction, the force of end position and intermediate position of working face floor was comparatively analyzed with water pressure or not, and results showed that floor stress with pressure is higher than the one without pressure near confined aquifers, stress in end position presents two peaks change shape and stress in intermediate position presents one peak change shape.(3) Water-Rock numerical analysis shows that:With the aquifer water pressure and face length increasing, the maximum principal stress in intermediate position of aquifers tended to increase and gradually reduced to the sides; vertical stress of the floor in stress decreasing zone rises again at the action of pressure, fully uninstall range decreases with the increase of pressure; pore water pressure distribution showed that the two ends of working face were concentrated area of water inrush, it is prone to water inrush if shear failure area cracks at the two ends which are caused by shear stress develop fully after coal mining.(4) Based on the stope surrounding rock stress distribution, partition characteristics of surrounding rock stress was obtained:①Load slowly increased area;②End stress reduced area;③Arched stress concentration area;④End key bearing area.(5) Fissure production and development evolution law of stope floor under the stress and pressure were obtained by similar simulation test of coal mining above aquifer. Rock exceeds its tensile strength and vertical tensile cracks occur under the horizontal stress when early mining; bearing capacity of the rock increases and then its overall bending resistance reinforces in mining metaphase, a certain amount of interlayer fissure occur at the same time in vertical cracks occurring; after the mining activities, pressure and overlying rock which has a certain capacity clamps the rock near aquifer and integrity of rock was further enhanced, bedding fissure forms because of the deflection caused by the different rock layers mutual dislocation.(6) The analysis using digital image correlation method to the movement and deformation laws of the floor shows that:The floor appears relative compression deformation by advanced pressure influence at35cm～40cm ahead of the stopping line, the displacement value is2mm～4mm lower than the one in unaffected zones of coal mining; deformation of the floor gets to the maximum by press at5cm～10cm behind the stopping line towards gob in which is called the formation of the compression zone; Floor displacement restored to the level of mining influence unaffected at more than30cm～40cm behind the stopping line in which is called the compression tympanites transition zone, the separation zone is at65cm～75cm behind compression tympanites transition zone where floor heave deformation peak point appears, the maximum of floor heave reaches about12mm of which the peak point is located10cm～20cm behind the middle position; floor heave deformation decreases from the peak point to10cm～20cm behind the cut in coal body in which is called the restoration of compaction zone.(7) Floor heave value is analyzed by pressure uninstalled in differential pressure to 0.5MPa from4.5MPa in simulation process, the highest point of floor heave falls7mm when pressure is1.5MPa, it is shown that:As far as the comprehensive force of mining stress and pressure is concerned, floor strata deformation dominated by three gray water pressure.(8) The entire floor space is divided into two obvious zones by displacement characteristic, most of floor space range corresponded with gob was floor heave zone, floor heave value declines or trend slows down in the central by obvious gangue compaction effect where is formed floor heave deformation reduction zone; with increase of distance to the floor, floor heave form was gradually increased to the central from both ends of the stope by carrying capacity of the lower rock enhanced and influence degree of gangue compaction effect weaken in which is called floor heave stability development zone;the area from the upper boundary of aquifer to the depth not affected by mining in the floor is called floor heave deformation weakening zone, in this area, floor heave is further lower than the one mining without confined water by the region boundary due to hydraulic pressure and the overall is also high in the middle and low in both ends of form.(9)Measure the floor’s failure depth using parallel electrical method in similar material simulation process, the results indicate that the most significant region of roof strata destruction is located at48cm above the roof, and the most significant region of floor strata destruction is located at19cm below the floor. For the mining conditions like face length(120m、160m、200m)、pressure(11MPa、3MPa、5MPa) and mining thickness(1.0m、2.0m、3.0m、4.0m、5.0m), floor failure depth fitting formula can be obtained with analyzing mining floor failure modes and failure dept, which is suitable for face length of more than300and about the above three factors. y=57.11n((?))+0.09M2+0.0644eP-127.727(10) Stope floor damage divided from the failure point which are A--full damage zone; B--potential water damage zone; C--plastic failure zone. Three areas form band in the full destruction, mining new shear failure of the original field central tension failure basis, called repeated failure zone; two ends of the central area is controlled by the compressive stress and the mechanical contact interval decreased, further aggravating the damage depth and pull stress range, called the destruction area. Three dimensional stress increases in the middle of③zone, despite the formation of plastic damage, but still have the capacity which called the damage zone; both sides of shear surface④form the two ends from failure to shear failure, stress increase is not large compared with③zone, as a potential water inrush area, called the potential permeable failure zone.(11)Have compressive and tensile strength of conventional testing of the rock group A coal seam and obtain the corresponding intensity value. Have creep test of standard with MTS-815hydraulic servo system and get the specimen axial and lateral creep parameters under different stress levels.(12)The mechanics analysis model of the floor viscoelastic rock beam is established and the variation tendency of the deflection plate intact rock beam and tensile stress is obtained by the principle of virtual work and energy functional variation condition under the influence of the viscoelastic rock beam flexural capacity decreased in different action time with mining stress and pressure. Analyze influence degree of rock beam elastic modulus, coefficient of viscosity and pressure to the deformation and obtain the result that reinforcement floor can improve the mechanical properties of rock beam, on the one hand, modulus increasing is helpful to strengthen the floor deformation resistance, on another hand, the water area of rock viscous coefficient of destruction improving can slow down the intact rock beam deformation and strength; drainage can effectively reduce the rock beam boundary stress and improve the stability.(13) For the Panbei Mine A3coal geology and hydrogeology conditions, combining with the stope floor failure depth calculation formula, calculating floor failure depth under the conditions as pressure (4.5MPa) and face length (120m、160m、200m), prevention measurements for safety production are obtained.(14) In order to ensure the safety mining of11113working face, the working face length is decided to120m, the thickness of higher slice is decided to2.8m-3.2m, mean3.0m and pressure is reduced to0.50MPa using water drainage project. In view of the existing mining conditions and hydrological conditions, calculate inrush coefficient to meet requirements of the regulations and analyze long-term stability of face floor. The results shows that it is likely to occur hysteresis water inrush in face under the existing mining hydrological conditions. For pressure monitoring field to the work surface, the field experiment shows that the first weighting interval is38m and the periodic weighting step distance is18m, there are no water inrush and abnormal underground pressure behavior when advance distance reaches100m.