Research On The Microscopic Characteristics Of Deep Fault Zone And Simulation On Evolution Law Of Seepage Water Inrush

In recent years,the rapid development of China’s national economy requires sufficient energy as a guarantee.Coal accounts for more than 50% of the primary energy consumption structure and still plays a leading role in fossil energy.At present,the depth of coal mining in China is gradually increasing,and the threat from deep high confined water is becoming more and more serious.Most of the water inrush accidents are related to the structure,especially the fault as a natural water channel.Based on the deep geological conditions of Nos.5&7 mining area in Dongtan coal mine of Yanzhou mining area,this paper studies the evolution law of seepage and water inrush in fault zone by means of micro test analysis,indoor model test and numerical simulation.(1)The fractal theory is applied to evaluate the distribution characteristics of fault structure in Nos.5&7 mining area of Dongtan coal mine.The analysis shows that the geological structure in this area is complex.Combined with the pumping test results,it is concluded that the water conductivity of Beigongcun No.1& No.2 faults in is poor,and the Ordovician limestone aquifer,the sandstone aquifer of No.3 coal roof and the Jurassic red bed do not have hydraulic connection through the fault.According to the Beigongcun No.2fault zone revealed by boreholes,the lithologic characteristics of different layers are quite different.Therefore,the fault zone is divided into three sections.The fault samples are tested and analyzed by XRD,SEM and cast thin section observation under orthogonal polarized microscope.It is found that there are different contents of clay minerals in the samples of the fault zone.In addition,cracks with large opening and extension length exist in the upper and middle samples.According to the structural characteristics and composition of the three samples,the stability of the fault zone was tested by using water samples from different aquifers,and the disintegration characteristics and conductivity data of the three samples were obtained.The results show that the water-rock interaction strength of fault zone samples increases with the increase of clay mineral content and fracture development.(2)According to the microstructure characteristics of natural fault samples in the study area,three fault simulation samples were prepared for permeability test.The experimental results show that the seepage process of samples with similar fault materials has obvious segmentation,that is,slow growth,rapid growth and saturation stage.Through the model test of fault water inrush under high pressure,it is concluded that the permeability resistance of fault similar materials with large coarse particles is weak,while the permeability resistance of fault similar materials with fine particles is strong.Through the multi-layer similar material combination test,it is found that the water flow in the fault zone will first form a dominant seepage channel,which will erode away the fine particles between the pores and further expand the channel.(3)By coupling the time-varying equations of permeability and porosity with the builtin module of COMSOL,the numerical simulation results show that the changes of hydraulic parameters in the seepage model are positively correlated with the initial porosity and permeability of the model.Through the water inrush simulation of many kinds of non-linear faults,it is found that under the condition of a certain flow rate,if there is a compression part in the fault,the water flow section will be reduced,and then the flow velocity will be increased.The velocity in the narrow compression section(compression ratio s= 0.1)is about10 times of that in the non compression section.By simulating the velocity of each flow field under high water pressure of 5MPa,6MPa,7MPa,8MPa and 9MPa,it is found that the velocity of confined water in the compression section of fracture zone is larger,and the velocity differentiation of each flow field is obvious,and the overall velocity increases with the increase of water pressure.By changing the permeability and porosity of the filling media in the fault compression section,the blocking effect of four filling media with different permeability resistance properties on water flow is simulated.There are 57 figures,8 tables and 122 references in this paper.