Studay On Coal Wall Stability In Fully Mechanized Mining With Large Mining Height Of Extra-thick Coal Seam Under Goaf

According to the large mining height fully mechanized caving face,especially in the special geological conditions which under goaf with theextremely thick coal seam large mining height fully mechanized caving faceeasy happening phenomenon of coal wall slip caving and outstanding problemsof existing method for assessment coal wall caving depth and control measures,this paper which based on the engineering background of Xiegou coal mine23103working face aimed at systematic analysis and research the groundpressure behavior of workface, the risk of coal wall caving, the prediction ofcaving depth and the control methods by using field measurement, theoreticalanalysis and numerical simulation on the basis of detailed analysis and summarythe existing research of predecessors, finally got the following conclusions:（1）Under the influence of stress concentrate on the legacy trend coalpillar of goaf in the overlying8#coal seam, the additional vertical stresscoefficient in the middle of23103working face of13#coal seam reached0.40~0.55, and the vertical stress peak in the coal wall anterior is13Mpa whenthe working face advance100m, and the stress concentration factor is2.36. Themaximum load, average load and the proportion of high load in the middle of working face were greater than the upper and lower of the working face.(2) Established mechanical model of coal wall slip caving while working face advance along trend, uphill and downhill by using Bishop slice method based on the coal wall stress characteristics in working face, and derived the safety factor solving formula: Analysis the coal wall slip risk of23103working face and predict the largest coal wall caving depth is1.48m by using the safety factor solving formula. The result that the max slip caving depth based on Bishop is closer to the measure results and it has very important scientific significance and engineering practical value for the selection of control method and parameters.(3) Through established an improved mechanical model of support sprag plate-coal wall interaction, further to derive the solving formula of the slip face safety factor under the action of the sprag plate: Simulated the vertical stress distribution in the anterior of the coal wall by using FLAC3D when the support working resistance P is8000-13000kN. Calculates the coal wall slip minimum safety factor under the effect of different combination of the support sprag plate thrust p and the distance r from the roof according to the safety factor solving formula, and concluded that the coal wallstability is positively related to p and r. The result showed that with theincreasing of sprag horizontal thrust p and the distance r from roof to its actionpoint when the hydraulic support working resistance have no change, the coalwall stability increases, and with the increasing of hydraulic support workingresistance when the work way of sprag have on change, the coal wall stabilityincreases too. With the increasing of value of p×r, the sensitivity of coal wallstability to the support working resistance falling. It can not only providetheoretical basis and technical reference for the parameter selection in the fieldof using support to control coal wall caving in the large mining height workingface, but also can help to the selection of the hydraulic support and optimizationdesign for sprag structure. Introduce the reliability coefficient that when giventhe support sprag plate thrust p and the distance r from the roof can beconcluded the coal wall stability（reliability）.On the other hand, according to thestability requirements of working face coal wall while given the reliabilitycoefficient can help optimal design the structure of the hydraulic support spragplate.