Reseach On The Mechanism Of Water-conducted Fractures In Rock And Coal Near The Goafs

From 2000 to 2020,1079 coal mine water disasters occurred in China,with 4391 deaths.Among them,527 accidents occurred about goaf and 2936 people died.The goaf water disaster in Shanxi is the most typical.Based on the hydrogeological structure of the coal mine area,the most serious water disaster of the same floor type is selected from the roof type,the same floor type,the floor type and the isolated type.A series of methods,such as microstructure characterization technology,water quality detection,immersion test,seepage test,physical model excavation test and so on,are adopted,combined with theoretical analysis,Comprehensive Geophysical Monitoring and numerical simulation.The weakening law of coal pillar and seepage characteristics of fracture are clarified,and the formation mechanism of water channel of surrounding rock(coal)in Gob with accumulated water is revealed.The main understandings obtained are as follows:(1)The water-filled water source and water-filled channels are classified and analyzed.According to the characteristics of the aquifer and structure affected by the cracking range of the mined-out area,the water supply relationship based on the point,line and plane cross-section is summarized,and the result is The view that the goaf will be filled with water as the water level of the aquifer recovers within a certain period of time after coal mining.(2)In the water inrush simulation test,the microseismic detection technology was introduced to locate the crack expansion position of the coal body during the test.The results showed that the most dense area of microseismic coincides with the fractured water inrush position of the model.Microseismic can be used in the formation of water channels Study on the evolutionary law of micro-cracks in China.(3)Transient electromagnetic method and direct current method are used as auxiliary detection means.From the change of the resistivity of the coal pillar between the heading head and the front water body in different stages,it can be judged that the region has experienced the original state stage,the stage of producing cracks,the stage of crack expansion and the stage of connecting the water body.In the stage of fracture formation,the resistivity increases because there is no rich water;when the fracture is full of water,the resistivity decreases rapidly.It can be used for real-time dynamic monitoring of the evolution of water channel in practical engineering,and for formulating and implementing water disaster prevention measures in the process of fracture development.(4)The immersion test of coal lump and coal powder in different acidity aqueous solutions showed that the surface change characteristics of the coal sample before and after immersion were obvious,and honeycomb-shaped small holes were observed on the surface of the coal sample under 2000 times.Through the water chemical analysis of the soaked water samples,the water chemical components of 7groups of water samples were obtained,the Piper three-line diagram and the ion ratio diagram were drawn,and the causes and changes of the ions dissolved in the acid water soaked coal were analyzed and summarized.(5)The study on the seepage characteristics of fractured coal samples found that the permeability may increase suddenly during the seepage process,and pressure will “close” the fractures of the coal sample and reduce the permeability.Under the same confining pressure,some coal samples also showed varying degrees of permeability reduction,and the fluctuations were large.Coal particles can be observed in the water flowing out of the test.It can be basically judged that a small particle flow has occurred at this stage.The fine particles of the coal sample migrate through the seepage channel,and the overall permeability decreases during the blockage process.It also gains momentum for a sudden increase in permeability.(6)The crack size in the water channel has a controlling effect on the seepage characteristics.When the crack size is 0.09 mm,the pressure reduction strength can reach 1.33 MPa,and the crack size is 0.2mm.The compression strength is 0.2MPa.Combining the characteristics of velocity distribution,it can be known that when there are one or more fissures smaller than 0.2mm in the fissure channel,the corresponding water permeation symptom is that the coal body becomes wet,but it is difficult to observe water gushing on the coal wall.(7)Based on the above research results,the calculation model of the critical failure thickness of the water-proof coal pillar was deduced,and the simulation results were optimized through large-scale indoor tests and numerical simulation methods.The scale of fracture development has a controlling effect on seepage.When there is a crack with a width of less than 0.2mm in the crack,it is considered that the coal pillar is less affected by the leakage effect,which is manifested in the overall destruction;when the minimum crack width is greater than or equal to 0.2mm,the coal pillar instability failure is a seepage-stress coupling effect.The model results have been effectively tested in the water inrush accident case.The research on the formation mechanism of the water channel in the goaf of water accumulation supplements and extends the theory of water inrush in coal mines,and is of great significance to coal mine safety.The paper has 108 figures,27 tables and 274 references.