Spatiotemporal Evolution Of Water Flowing Fractured Zone In Jurassic Weak Overburden In Zhaoxian Mine

With the development of coal resources moving to the west of China,the development scale and intensity of Jurassic coal fields in northwest China are increasing,and the problem of water damage is becoming more and more serious.The Jurassic weak overburden thick and extra thick coal seams in Huanglong coalfield are characterized by short diagenetic time,weak cementation and high muddy content.As the main channel to communicate the overlying aquifer,it is very important to study the evolution law of the water flowing fractured zone,whether from the factors of mine safety production or water resources protection.This paper takes Zhaoxian coal mine as the research object.Based on the analysis of the engineering geological and hydrogeological characteristics of the No.1307 working face thickness and extra-thick coal seam overburden(including and aquifer),field investigation,in-situ measurement,theoretical analysis,Numerical simulation and other methods are used to study the development law of the water flowing fractured zone of the overburden mining and the seepage law of the water flowoing fractured.The main-network fracture seepage model of the rock mass is established,and the spatio-temporal evolution mechanism of the water-crack fracture zone of the Jurassic weak overburden is revealed.The amount of water inflow during the mining process is predicted,which provides a basis for the development of mine water prevention and control scheme to achieve safe mining.Through the core engineering geological cataloging,drilling TV logging and drilling rinsing fluid leakage and water level change observation and other measured methods,the development height of the No.1307 working face water flowing fractured zone is 198.8 m;the calculated value based on the standard is 160.03 m,and the measured value error is about 19.4%.Based on the FLAC3 D numerical simulation,the development height of the water flowing fractured zone breaks through the Yan'an group and enters the Zhiluo group when the coal seam advances 125 m.When the coal seam advances 160 m,the development height of the water flowing fractured zone breaks through the Zhiluo group and enters the Anding group.When the coal seam is pushed for 600 m,the development height of the water flowing fractured zone reaches 200.1 m,and the error with the measured value is about 0.65%.The orthogonal test principle is used to study the influencing factors of the dynamic development of water flowing fractured zone of overlying rock under fully mechanized caving mining in thick and extra thick coal seam.The results show that with the increase of coal seam advancing distance,the development height of water flowing fractured zone increases gradually.The morphology of development is divided into four stages in turn: initial slow development stage,rapid development stage,slow development stage and steady development stage.As awhole,there is a positive correlation between the development height of water flowing fractured zone and mining thickness,mining width and coal seam buried depth,but from the influence effect,the influence effect of coal seam buried depth and mining thickness in the early stage is great,and the mining width gradually becomes the main control factor in the later stage.Based on the three-dimensional stress-seepage model relationship,the FLAC3 D numerical simulation of the output stress field is used to study the permeability change.The results show that the coal seam mining caused the movement of the overburden fracture,which led to the change of permeability.As it moved away from the goaf,its change gradually decreased.Small,the overall performance is that the permeability of the goaf and its top plate is significantly increased,the permeability coefficient around the goaf is greater than the permeability coefficient of the middle goaf,but the influence of the change of the permeability coefficient in the lateral direction around the goaf is far.Less than the vertical direction,that is,the increase in the permeability coefficient is significantly larger in the horizontal direction than in the vertical direction,but the former has a smaller increase range than the latter.According to the relationship between the working surface advancing distance and the development height of the water flowing fractured zone and the variation of the overlying rock permeability coefficient,the working face is segmented,so that the water inflow during the mining of the coal seam is predicted by segmental stratification.The predicted results indicate that the overlying layer is not considered.In the case of water inrush,the development height of the water flowing fractured zone did not break through the Yan'an group.The amount of water inflow was 21.32 m3/h,and the height of the water flowing fractured zone developed to the Zhiluo group was 75.61 m3/h.When the development height breaks through the Zhiluo group,the amount of water inflow is 335.06 m3/h.The expected results provide a basis for the design of water prevention measures on the working face.