Study On The Characteristics Of Activation And Catastrophe Induced Fault Filling In Mining Influence

Faults are natural defects produced by crustal movement,which destroy the continuity and integrity of rock strata.Fault fracture zone and fault filling body have the characteristics of low strength and poor cohesion,and their response to stress changes is obvious.Under the action of mining,the original in-situ stress is destroyed,and the stress concentration area near the fault fracture zone is easy to cause coal mine disasters such as fault activation and rock burst.Based on the theoretical analysis of rock failure and fault activation,this paper studies the similar material of fault breccia and designs the simulation test of similar material by using the principle of similarity ratio to simulate the change of displacement and stress of the working face.A numerical calculation model is established by using FLAC3D software to test the simulation test results of similar material and to monitor the normal stress and shear stress of the fault surface.According to the change of force,the fault activation index is deduced and the numerical values at different distances are calculated to analyze the fault activation status,and a reasonable method to prevent the fault activation is put forward.The main research results are as follows:(1)Based on the original geological data of mine and the requirements of similar material simulation test,the similar material of fault breccia is developed by using breccia as aggregate,rock powder as filling material,mudstone powder and clay powder as cementing material.Through uniaxial compression test and permeability test,it can be concluded that the increase of clay powder and mudstone powder content will not only increase the strength of the specimen.It also reduces the permeability of the specimen;the filling rock powder plays the role of aggregate and cementing agent;the aggregate content is the core material to control the similar material of fault breccia.(2)Based on the principle of similarity ratio and the size requirement of the test bed,the self-developed fault breccia similar material is applied to the simulation test of similar material.By observing the crack propagation paths and modes of overlying strata and near fault fracture zone under the influence of mining,the independent area of inverted trapezoidal formation of overlying strata above the coal pillar is analyzed,and the stress monitoring data can be divided into two parts.The stress of the precipitated fault plane is obviously affected by the distance between the working face and the coal pillar protected by the fault,and the slope of the overlying strata is larger when the caving velocity is closer to the coal pillar protected by the fault.(3)The numerical calculation model is established by using FLAC3D software to monitor the stress field,plastic zone and normal stress and shear stress of the model under mining.Through the cloud maps,it can be concluded that the Inining stress does not affect the vicinity of the fault fracture zone in the early stage of mining,and when the working face advances to 60 meters away from the fault protective pillar,the mining influence extends to the fault surface.With the advancing mining of coal pillars facing fault protection,the greater the impact on fault surface is,when the coal pillars reach fault protection,the stress on the upper wall is transmitted to the lower wall of fault through fault fillings;the normal stress and shear stress on the fault surface are related to the distance from the coal pillars facing fault protection and the advancing position of the working face,and the farther away from the coal pillars facing fault protection,the smaller the impact is,and the closer to the coal pillars facing fault protection.The increase of shear stress at monitoring point is larger than that of normal stress.(4)Fault activation index is deduced by simplifying the stress condition of fault surface,and the normal stress and shear stress of fault surface monitored by numerical calculation model are brought into the formula of fault activation index to calculate the relationship between advancing distance of working face respectively:the farther the coal seam is away from its fault activation index along the upward and downward directions of fault,the smaller the fault activation index is,that is,the closer the coal seam is,the more fault surface is broken.The risk of stratum activation;who works after monitoring data of fault activation index on the upper fault surface of coal seam to influence the advance of coal pillar facing fault protection downwards and finally form high value area of fault activation index above coal pillar facing fault protection;the methods to prevent fault activation include:setting protective coal pillar,blasting pressure relief in stress concentration area and grouting reinforcement in fracture zone.According to the specific geological conditions,the design and construction methods are carried out.For the small faults in coal seam geology,most of them adopt the methods of direct crossing:cutting the top,cutting the bottom and cutting the top and bottom.When crossing the faults at the working face,attention should be paid to the change of fault strike.