Stability Analysis Of Normal Fault Coal Pillar Outside The End Of Working Face

The geological conditions in China are complex,and faults are often encountered in the process of coal mining.When the working face is arranged along the fault,the fault pillar will be formed between the coal wall and the fault.Due to the remarkable benefit of stress barrier of coal pillar,a large peak of abutment pressure will be formed on the coal pillar of fault,which is easy to destroy and destabilize.Based on this,Taking the 3103 working face of Liangbaosi Mine as the engineering background,the theoretical analysis,and continuum of FLAC3D numerical stimulation and gray correlation analysis was employed to study the relationship between the stability of fault pillar and its width,mining height,fault dip Angle and mining depth and analyz under the condition of working face mining along fault.The main conclusions of the study are shown as follows:1)When the width of fault coal pillar is large,the effect of fault stress blocking is not obvious.With the decrease of the width of fault coal pillar,the effect of fault stress blocking becomes more and more obvious,and the degree of stress concentration of coal pillar becomes higher and higher.When the width of the fault coal pillar is more than 30m,the coal pillar is relatively stable,and when the width of the coal pillar is less than 30m,the coal pillar will lose stability and release elastic energy under high-concentration medium stress.The stress evolution characteristics of coal pillar in upper and lower face are consistent,but the stress concentration degree of fault coal pillar in upper face is greater than that in lower face.2)When the working face is mined along the hanging wall of the fault,the stress concentration degree of the fault coal pillar is positively correlated with the mining height.Under the mining height of 2m,4m and 6m,the ultimate bearing width of the coal pillar is 30m;When the mining height is 8m,the ultimate bearing width of the coal pillar is 40m.When the working face is mined along the footwall of the fault,when the mining height is 2m,the ultimate bearing width of the coal pillar is 20m;When the mining height is 4m,6m and 8m,the ultimate bearing width of the coal pillar is 30m.In the actual mining process,the mining sequence of upper and lower wall working faces is different,and different fault coal pillar widths should be designed.3)Under the same mining conditions,when the working face is mined along the hanging wall of the fault,with the increase of fault dip angle,the peak value of coal pillar support pressure gradually increases.Under the condition of different inclination angles,the stability law of coal pillar is consistent.The ultimate bearing width of fault coal pillar is 30m.When the width of coal pillar is less than 30m,the coal pillar will lose stability and release elastic energy under high support pressure.The greater the fault dip angle,the greater the energy release and the weaker the stability of the coal pillar.When the working face is mined along the footwall of the fault,the instability law is basically the same when the fault dip angles are 45 and 55.The ultimate bearing width of the coal pillar is 40m,and when the fault dip angles are 65 and 75,the ultimate bearing width of the coal pillar is 30m.When the fault coal pillar is less than the limit bearing width,the instability of the coal pillar releases elastic energy at the same time.The greater the fault dip angle,the greater the released energy,and the higher the stability of the coal pillar.4)Under the same mining conditions,when the working face is mined along the fault,the stress concentration increases obviously with the increase of mining depth.When the working face is mined along the hanging wall of the fault,the stability of the coal pillar is strongest when the mining depth is 400m,the ultimate bearing width of the coal pillar is 20m,when the mining depth is 500m and 600m,the ultimate bearing width of the coal pillar is 30m,and when the mining depth is 700m,the ultimate bearing width of the coal pillar is 40 m.When the working face is mined along the footwall of the fault and the working face is mined along the footwall of the fault,the instability rule of the coal pillar is basically the same as that of the hanging wall,but the overall stress concentration degree is less than that of the hanging wall,and the plastic damage area of the fault coal pillar is also less than that of the hanging wall.5)When mining along fault F32-1 on the upper working face of liangbaosi 3103,the stability of coal pillar is the weakest in the initial stage of mining.ln the case of the same coal pillar width,the main factor affecting the coal pillar property of the fault is the height of the coal seam,followed by the fault dip,and finally the coal pillar width and mining depth.