| Due to the influence of the dip angle,the law of the bending,deformation and failure of the overlying strata after the mining of the steep seam are different from the mining of the near horizontal or gently inclined coal seam.Firstly,the collapse form of the overlying strata after mining is asymmetric along inclined direction,and the maximum height of the caving zone does not appear above the middle of the goaf,but appears in the upper part of the goaf.Secondly,after the excavation of the coal seam,along the inclined direction,the rock carving from the roof of the goaf is moved along the coal seam to the lower part of the goaf due to gravity,resulting in the lower part of the goaf filling more fully.The stress relief zone in the lower part of the goaf is smaller,while that in the middle and upper part of the goaf is larger,thus the stress distribution of the roof above the goaf is asymmetric.Moreover,due to the large dip angle,the weight of the overlying strata along the strata direction is larger than that along the vertical direction,which makes the overlying strata suffers from compression.The carving form of floor above the goaf is look like the word "chang".If the "three-zone" height formula used in the near horizontal or gentle inclined coal seam is applied to the steep coal seam to judge the "three-zone" range,it can be different from the real situation as the height of the caving zone,the fissure zone and the curved subsidence zone of the upper roof of the goaf are greatly different from that of lower goaf after the mining of the steep seam.Therefore,after the mining of steep seam,it is a difficult problem to study the structural characteristics,deformation and failure law,the maximum influence height and influence degree of overlying strata.Upward mining refers to a kind of mining method in reverse order,which is when there are two or more layers of coal seam in a certain distance,the coal seam in the lower level is mined before the coal seam in the upper level.Because of its great safety,technical and economic superiority under certain conditions,more and more experts at home and abroad tend to study and use this method.However,at present,the study on this field is mostly about near horizontal or gently inclined coal seam,and rarely about the steep seam both at home and abroad.After the mining of coal seam in lower level,the overlying strata movement mode and the strata behavior law of the steep coal seam are very different from that of the near horizontal or gently inclined coal seam,and whether the coal seam in the upper level can be mined is mostly influenced and decided by the movement of and failure state of overlying strata of the coal seam in the lower level.Therefore,it is very important for the determination of the layout of the roadway and the mining of working face to study and analyze the characteristics and regularities of the overlying strata after the steep seam mining,and take effective protection measures in the working face in time.In this paper,the theoretical analysis is used to analyze the stress of the coal seam roof,which is regarded to be a beam-column structure.Then,the deformation of the overlying strata and the moving area are regarded as wedge-shaped areas,and the moving deformation model is established.Then according to the No.1942 working face in Zhaojiaba coal mining,the model was established by the use of numerical simulation software Flac3 D,and the mining of No.1942 working face was numerically simulated.Finally,the deformation and failure modes of the overlying strata were simulated by similar simulation test.The main results are as follows:a、the maximum degree of disturbance and its position of the main roof of the steep seam.b、 Considering the characteristics of the bending deformation of the overlying strata with the increase of the height,the maximum influence height of the overlying strata after the mining of the steep seam is obtained by the wedge-shaped moving model.c、The correctness of the theoretical analysis is verified by numerical simulation,the deformation and stress distribution law of the overlying strata are analyzed,and the angle of the strata movement and the influence angle of the mining are obtained.Finally,the influence degree and influence range of No.7 coal seam is judged after the mining of No.9 coal seam.d、The height of the "three zones",the strata movement angle,and the height of the impact and the impact degree of No.7 coal seam after the mining of No.9 coal seam are obtained through the similar simulation test.e、Based on the comprehensive analysis of the results of theoretical analysis,numerical simulation and similar simulation test,the law of the deformation,movement and stress distribution of overlying strata in steep seam are obtained,and the feasibility of upward mining is verified.Through the numerical simulation,similar simulation and other research methods,the analysis of the law of overlying strata after the mining of steep seam is provided,which provides reference for the mining of steep coal seam and also provides reference for the study of upward mining. |
