| With the transfer of the emphases of the coal development in our country step towards the Midwest gruadually, situations that use longwall top coal caving in steeply inclined thick coal seam is increasing. However, as the law of overlying strata movement in steeply declined longwall fully mechanized top coal caving face is different with which in horizontal fully mechanized top coal caving face, theoretical study should be strengthen to guide the surrounding rock control and the overlying strata movement law. With the steeply inclined three-soft coal seam of Dayuan coal mine in the background, this paper researched the law of surrounding rock control and coal-rock movement in longwall fully-mechanized top coal caving face. Tthis paper did a comprehensive study of the physical and mechanical properties of roof and floor, law of overlying strata movement and mine pressure behavior in steeply inclined mining, relationship between support and surrounding rock and analysis of stability of roof. The following achievements were obtained.(1) Conducting rock mechanics experiment to rock sample which came from the core drilling in roof and floor through the method that combined the uniaxial compression test and point load. The physical and mechanical parameter of roof and floor in steeply inclined surrounding rock control has been obtained, which made foundations of numerical calculation and similar simulation tests.(2) In the mining progress of steeply inclined three-soft coal seam fully mechanized top coal caving, stress concentrated area appeared in the front of the working face. Meanwhile, the peak value of lead abutment pressure in the middle of working face is higher than that in the two ends. With the increasing of advancing length, the pressure relief range in goaf is increasing, and the influence range and concentrate extent of lead abutment pressure in the front of working face is increasing either. While the advancing length is 80m, pead value of abutment pressure in the lower part along the inclined direction did not change, which indicated that the lower part of goaf become compaction first and the caving rock shows the phenomenon of strain hardening. So the caving rock start to undertake overlying strata load and overlying strata movement has lower influence to abutment pressure. Meanwhile, stress recovery appears in goaf. However, in the upper working face, because of insufficient filling, the degree of stress concentration is increasing with the increasing of advancing length.(3) At the beginning of working face advancing, as the small range of the exposing of overlying strata in goaf, rock strata which is influenced by mining is relatively low, the largest displacement of the lower part of working face could reace to 11cm. Meanwhile, roof subsidence of the upper part is relatively small but the influenced strata range of the upper part is relatively big. While the advancing length is rather big, the area of goaf is increasd, overlying strata above the goaf reached its limit span and failed. With the influence of mining, roof subsidence of working face could reace to 14cm at the time.(4) In the foundation of similar simulation test and numerical calculation results, non uniform load model of steeply inclined roof has been established. Stress condition along the incline direction, deformation behavior and failure law of the roof have been revealed. "Three sections " hypothesis of characteristics of inclined overlying strata has been proposed. Compared with gently inclined mining, after the mining of steeply inclined coal seam, peak vertical displacement moved toward the lower part of working face. This in not only caused by non uniform pressure, but also caued by the downward force along the seam. In gently inclined mining, horizontal displacement of rock strata shows as the side strata of goaf move toward the middle part of goaf. However, because of the force which is vertical to the strate, in the steeply inclined mining the strata moved toward the side horizontal direction of the upper end.(5) Through the analysis of coal wall spalling of steeply inclined "three soft" coal seam fully mechanized top coal caving working face, this paper found that roof pressure intensity q is the key reason of the failure of coal wall. The higher is the cohesion c, internal friction angle φ and coal wall protection height HI, the higher is the applied force of the force guard q0 and the safety factor. The relatively small value of c is the internal cause of the shear failure of coal wall. Relatively speaking, internal friction angle, applied force of force guard and the guard height has little influence to coal wall stability. The force guard could only provent the fractured coal wall from falling, it cannot provent the coal wall from fracturing.(6) As the overlying strata movement characteristics of inclined fully mechanized top coal caving working face is different, bearing characteristics of the support is different. Three kinds of interaction model of "support-surrounding rock", upper part, middle part and lower part along inclined direction of working face respectively, has been established. Study shows that the top coal and roof in upper part is soft and would fall with advancing. Meanwhile the fallen rock and coal would slide downwards and fill the lower part of goaf. After the top coal caving, especially, empty space of the upper part would be larger and space above the support would be empty. At this time, the fracture of roof would hit the support and formed the dynamic load. In the lower part, the fallen rock and coal fill the empty space and undertake the pressure from overlying strata with support, so the load applied on support is relatively small. In the middle part, the load applied on the support is between the other two situations. Therefore, during the advancing of working face, protection of the upper part of the roof is emphasis.(7)Through the medium top-coal similar simulation experiment, steep thick coal seam fully mechanized top-coal develops towards to end development obviously and the area near the top beam develops faster. Analysis of top-coal recovery characteristics of distribution was carried out and the conclusion is got that along the strike of coal seam dip angle has little influence on the recovery rate distribution; Due to the difference of the working face end up and down coal loss along the inclined top-coal recovery rate of coal seam is "π" glyph distribution; distribution characteristics is low> high>Along the vertical direction(8) By using DEM numerical simulation and it found that in the steeply inclined fully mechanized process, the coal and rock medium move to approximate linear path to caving window, and the migration path to the plumb line particles are easy to be released; Fastest discharge path along the tendency of coal seam and the plumb line between a fixed Angle; Coal rock interface shows obvious characteristic of "asymmetry".(9) By using PFC2D numerical simulation, the three kinds of coal seams were studied under the order of top-coal recovery rate, release the contact force field, coal rock interface, and the different characteristics of coal time, put forward the rational coal sequence. The coal technology is optimized to improve the recovery rate. By using the tracker in steep 1201 fully-mechanized top coal caving face was studied through on-site observation, the measured values and anastomosed with the laboratory test results verified the repose of the correctness of the similar simulation experiment conclusion. |
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