Development Mechanism Of Mining-Induced Water Flowing Fractures In Different Overburden Structure Of Coal Seam

With the shift of the coal production capacity center from the eastern region to the western region in China,the roof water damage of Jurassic coal seam in thewestern mining area has become a great threat to coal mining.The water flowingfracture as one of the most important water inflow path has the key influence on roof water damage measurement.The overburden structure plays an important role in the development of water flowing fractures in coal mining,so it has important theoretical significance and practical application value to carry out relevant research.On the basis of a large number of literature research and field investigation,this paper analyzes and summarizes the typical strata formation and its combinationcharacteristics of the Jurassic coal seam roof,and proposes four types of overburden structure:soft-hard-soft-hard,soft-soft-hard-hard,hard-soft-hard-soft and hard-hard-soft-soft.Using two-dimensional discontinuous numerical calculation softwareUDEC,the development characteristics of mining induced water flowing fractures of12 models of geological mining models in four types of overburden structure under three mining heights is studied;the mechanical mechanism of mining deformation process of different overburden structure is studied by using the basic principle of material mechanics and rock beam structure model.Taking two working faces of Guojiahe coal mine and Cuimu coal mine as examples,the effect of overburdenstructure on the development height of mining-induced water flowing fracture zone in Huanglong coalfield;and the characteristics of roof water damage of different overburden structure is analyzed.Main deliverables of this dissertation have been displayed as follows:（1）The control mechanism of overburden structure on the development height of mining water flowing fracture is revealed.It is concluded that the development height of mining water flowing fracture and mining height are not linear relationship,but step mutation characteristics according to different overburden structure（2）The maximum height of mining-induced water flowing fractures and its occrence time of different overburden structure is analyzed:soft-hard-soft-hard type overburden structure has the least development height of water flowing fracture while the occurrence of the maximum height is relatively early;hard-hard-soft-soft typeoverburden structure has the greatest development height while the occurrence of the maximum height is latest;soft-soft-hard-hard type overburden structure has themiddle height of water flowing fractures while its occurrence of the maximum height is the earlist;both the maximum height and its occurrence time of the water flowing fractures of the hard-soft-hard-soft type overburden structure is in the middle.（3）In the process of coal seam mining,the overburden is deformedincongruously in the mode of reconstruction composite rock formation;whetheroverburden produces layer separation is related to the elastic modulus,thickness and stress state of the upper and lower strata,according to the theoretical calculation,if the upper and lower strata are separated,the elastic modulus must meet⁰)₇0))>⁰)₇0))?（?）.（4）The layer separation between the mudstone of Anding formation and the glutenite of Yijun-Luohe formation is easily produced in the process of coal seam mining of the typical overburden structure in Huanglong coalfield.The prevention and control of the roof water damage is mainly the layer separation water damage.（5）Based on the analysis of the location relationship between different overburden structure and aquifers,the characteristics of roof water damage of different overburden structure are put forward.