| It is easy to cause mine water disaster under high intensity and complex mining conditions such as slicing and multi-seam mining in extra-thick Jurassic coal field in Xinjiang.Jurassic coalfield in Xinjiang contains ultra thick coal seams and complex overburden geological conditions with high proportion of argillaceous rocks.The water-conducting fractures can highly develop under the condition of remining.It is of great significance to research on the evolution regulation of water-conducting fracture height to ensure the safety of mining and to protect the environment.Taking Liuhuanggou Coal Mine as the research target,this thesis analyzes the engineering geological and hydrogeological conditions of the working face(9-15)08overburden.Combining methods such as in-situ measurement,numerical simulation and machine learning together,the development law of overburden fractures in layered comprehensive mining of extra-thick coal seam is researched in this thesis,the linear prediction formula and nonlinear prediction method are established.The structural evolution mechanism of mining overburden roof is revealed in this thesis.Furthermore,the thesis predicts water flow amount during the working face extraction and puts forward the waterproof barrier pillar design,providing a basis for the mine water prevention.In the thesis,the heights of water conducting fractures are measured by core engineering geological catalog combining methods such as observation of borehole water level change,hole flushing fluid leakage and borehole TV log.According to insitu measurement,the water conducting fracture height is influenced by factors including the size of the working face,mining thickness,lithological combination characteristics and caving zone existence.The measured results show that multiple mining influence increases the height of the water-conducting fracture zone,and the development height of the overburden water-conduction fracture in the layered and comprehensive mining of extra-thick coal seam is positively correlated with the mining size of the working face,the strength of the overburden,the mining thickness,and the spacing between the upper goafs.The results show that under the circumstance the upper layer mining at the top of extremely thick coal seam,without goaf,the height of the water-conducting fracture develops rapidly in the early and middle stage of mining,and increases slowly and keeps stable in the middle and late stage.The re-mining disturbance of overburden rock by the lower layer mining makes the height of the water-conducting fracture zone further develop,but the failure degree of the overburden rock is lower than that of the first layer mining.Under the influence of the upper goaf,the height of the water-conducting fracture zone increases during the first slice mining,and the height of the water-conducting fracture zone is proportional to the distance between the working face and the goaf.Parameters are selected as the main control factors of the PSO-SVM prediction model such as mining height,Mining depth,the diagonal length of the working face,hard rock proportion coefficient,distance from caving zone to working face and slice numbers.Based on that,the nonlinear prediction model for water conducting fracture heights is established.There are three periods of water conducting fracture zone developing including rapid development period in early-middle stage;slow development period in middlelate stage and stable period in late stage.After the working face mining,‘M’ type microstructure,masonry beam structure and pressure arch macro-structure are formed in sequence upper ward.According to the development regulation of water conducting fracture height of the working face,the working face is divided into different sections for water flow amount prediction under different mining conditions.Waterproof barrier design is also put forward near goaf zone,fault belt and coalfield burning zone for water prevention of the coal mine.There are 113 Figures,26 Tables and 90 references in this thesis. |
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