Research On The Effect Of The Mining Pressure Under The Influence Of Mining On The Face Passing Through The Conjugate Fault

The fault destroys the continuity of the rock layer,which affects the fracture and collapse patterns of the roof rock around the stope,the stacking structure of the collapsed rock and the redistribution form of the surrounding rock pressure after mining disturbance,destroying the stability of the surrounding rock and easily inducing dynamic disasters.This paper takes the geological condition of the presence of conjugated faults in the 12#coal seam in the 21 mining area of a coal mine in Guizhou.Conjugated fault composition and structure:F1 reverse fault?inclination angle 30°,drop 2m?,F2 normal fault?inclination 45°,drop 2m?,The two faults run through the 12#coal seam and are 62m apart horizontally.This article uses theoretical models,similar simulation experiments,FLAC^3Dnumerical simulation,on-site measurement and other means,Study the status of coal wall flank,mining pressure appearance law and the breaking form and movement law of overlying rock layer when 12#coal seam mining passes through conjugate fault area.The research results are as follows:?1?Through on-site inspection and data compilation,the morphology of the reverse and normal faults in the conjugate faults and the spatial relationship between the two faults and the 12#coal seam are determined.The rheological instability comprehensive model is used to analyze the mechanical effect of the fault model.?2?According to the geological conditions of the 12#coal seam,through the combination beam theory calculation,the key layer above the 12#coal seam is composed of two layers of fine sandstone and siltstone.The key layer has the characteristics of high strength and thick rock layer,and its thickness is determined.It is 26.5m;using the calculation formulas of falling zone and fissure zone,the height of"two zones"is calculated.According to the comparison between the height of fissure zone and the upper coal seam,the structural stability of the upper coal seam is destroyed by the mining of 12#coal seam.It is small and does not affect the mining work of the upper coal seam;the mechanical analysis of the broken rule of the old roof with the simple supported model at both ends and the fixed model at both ends,combined with the site conditions of the coal mine,based on the measured site roof breakage data,the old roof is obtained The initial breaking span is 36m,and the periodic breaking step is calculated as 14.19m.?3?Through similar simulation experiments,it can be concluded that there is a difference between over-conjugated faults and over-single faults.The experiment is divided into three stages:1)The coal mining face advances from the cut to the F1?reverse fault?in the 80m conjugated fault.During this process,the mining face is basically not affected by the F2?normal fault?in the conjugated fault.The characteristics of a single reverse fault are basically the same.2)The coal mining face advances from the F1 fault to the 142m F2 fault.During this process,the coal mining face is less affected by the F2 fault during the 80m to 110m advance,mainly affected by the F1 fault.In the process of advancing the F2 fault from 110 to 142m in the coal mining face,the effect of the F2 fault on the face began to increase.3)Coal mining face advances from F2 fault to 240m?protected coal pillar?.During this process,when the face advances to 160m?over fault 18m?,normal faults have a strong influence on the face.As the coal mining work continues to advance,the influence of the F2 fault on the coal mining face has weakened sharply.When the coal mining face passes the F2 fault by 30m,the F2 fault has basically no effect on the coal mining face.?4?Through similar simulation experiments,it is concluded that under the combined action of mining disturbance and reverse and normal faults,the roof of coal seam in the area affected by the conjugate fault is broken,the collapsed rocks are stacked closely,and the proportion of vertical filling space becomes smaller The supporting capacity of the overlying rock layer is weakened,resulting in the reduction of the roof breaking distance in the area,making it difficult to form a"masonry beam"structure.When the working face passes 50m of F2?normal fault?in the conjugate fault and advances to 190m,the roof sinking amount of the stope in the conjugate fault area reaches the maximum.The collapsed rock mass in the conjugated fault area is broken and lacks the support of the"masonry beam"structure,which results in a greater degree of settlement and fracture development of the overburden rock in the conjugate fault area than the non-conjugated fault area on both sides.?5?The FLAC^3Dnumerical simulation is used to analyze the rock pressure behavior of the surrounding rock of the stope in the mining face passing through the conjugated fault area.The study shows that the stress concentration of overburden rock during the mining process of the working face changes as the working face approaches the fault.more obvious.When the coal mining face crosses the F1 fault20m and advances to the middle area of the conjugate fault,the expansion range of the pressure relief area of the surrounding rock of the goaf becomes smaller,and the stress concentration area increases within 10m in front of the coal mining face,which is not conducive to work Fanggas pressure release;The coal mining face is in the process of advancing from 80m?F1 fault?to 142m?F2 fault?,The stress at the top of the F1 fault presents:Increase-maximum value-decrease-slow decrease-increase change process,It shows that under the influence of mining,the stress change of F2fault promotes the stress change of F1 fault;When the coal mining face advances to F2 fault,Due to the blocking effect of the fault,there is no strong stress concentration in front of the coal mining face,The stress concentration is transferred to the bottom of the fault of F2 fault,which is easy to cause the bottom drum of the coal mining face.?6?On-site research and analysis of the pressure measurement data of the hydraulic support in the area affected by the conjugate fault,According to the effective working resistance value of the hydraulic support,It is concluded that the pressure value in the affected zone of the conjugate fault is higher than that in the non-fault zone.The actual measurement of the scale and quantity of coal wall flank when passing through conjugate faults during coal mining,It is concluded that when the working face passes through the conjugate fault zone,The block size of the coal wall flank increases and the number of flank increases,The roof management in the fault area should be strengthened.