Study On The Damage And Subsidence Effect Of Surface Under Mining-induced Tremor

Mining-induced tremor is a local earthquake induced by mining.It has the characteristics of shallow source,small magnitude,high intensity and strong destructiveness.The impact of mining-induced tremor on surface damage has attracted more and more attention.Therefore,it is of great significance to explore the effect of mining-induced tremor on surface damage.In this paper,the influence of mining-induced tremor on surface damage and deformation is studied by means of theoretical analysis,numerical simulation and statistical analysis of measured data.The main results are as follows:(1)During the mining process,due to the overburden hard roof breaking and vibration effect,the strata will sink after the roof breaking suddenly.At the same time,the vibration will change the compactness of the fractured rock and soil medium,and the surface subsidence will be affected when the mining-induced tremor is involved.Based on the method of surface damage predicted by the influence function method,the influence factor K_s of mining-induced tremor is introduced,and the calculation model of surface damage parameters due to mining-induced tremor disturbance is established,and the subsidence displacement of surface after mining-induced tremor disturbance is obtained as follows:(?)Horizontal displacement is obtained as follows:(?)Tilt displacement is obtained as follows:(?)That is to say,in the case of mining-induced tremor disturbance,the subsidence displacement,horizontal displacement and tilt displacement of the surface are different from those without mining-induced tremor disturbance.(2)Using UDEC numerical simulation,the peak value of particle vibration velocity and the law of subsidence displacement of rock and soil layer directly above the source are simulated.The results show that the shallower the depth of tremor source and the higher the tremor energy level is,the greater the damage to the surface will be;the shallower the depth of tremor source is,the lower the peak velocity of the particle and the smaller the subsidence displacement will be;the closer the tremor source is to the surface,the higher the peak velocity of the particle and the greater the surface displacement will be;the harder the rock layer is,the smaller the attenuation amplitude of the tremor wave will be,and the higher the peak velocity and the greater settlement displacement of the surface particle will be.The tremor with source depth of 250 m,when the energy level is 10~2~10~7 J,the peak value of the tremor velocity changes from 0.38 m/s to 1.01 m/s,an increase of165.8%,and the peak value of the tremor acceleration changes from 19.5 m/s~2 to 37.5m/s~2,an increase of 92.3%,the radius of influence increased from 450 m to 550 m.When the energy level of the mining-induced tremor is 10~4~10~7 J,the peak velocity is greater than 0.5 m/s,which meets the damage standard of surface civil buildings.When the energy level is 10~6~10~7 J,the peak value of vertical velocity and subsidence displacement increases sharply when the depth of tremor source is 250 m,and the peak value of velocity and acceleration is 1.01 m/s and 37.5 m/s~2.Compared with the impact of no tremor,the increment of vertical displacement is 0.509 m,the increase ratio is 163.7%,the influence radius is 550 m.When the source distance is less than 300 m,the peak value of vertical velocity will be greater than 0.5 m/s,which meets the damage standard of surface civil buildings.When the energy level is 10~6~10~7 J,the peak value of subsidence displacement of surface particles in hard rock strata(defined rock stratum coefficient is 1)is 0.643 m,which is much larger than that in weak rock strata(rock stratum coefficient is 0.2)when the peak value of settlement displacement is 0.245 m..The simulation results show that the damage degree of the surface caused by the tremor is related to the depth of the tremor source,the energy level of the tremor and the properties of the overburden,which are determined by the three factors together.(3)Statistical analysis is made on the occurrence regularity of mine tremor during mining in a working face of Dongtan Mine.Mining-induced tremors in this mine are mainly small energy release shocks between 10~2~10~3 J and 10~3~10~4 J,and strong shocks above 10~5 J are relatively few.Tremors often occur in geological structures,periodic faults on the basic roof and overlying high-level"red beds"sandstones with focal depths ranging from 200 m to 660 m.According to the analysis of the depth and energy level of the tremor source in Dongtan Mine,it is concluded that the higher energy level tremor of 10~4 J or more in Dongtan Mine will have a certain impact on the surface damage and subsidence.(4)In the actual mining process of a working face in Dongtan Mine,two large-energy tremors,9.0×10~6 J and 1.45×10~7 J,were detected by ground monitoring stations,with focal depths of about 500 m and 400 m.According to the actual geology and mining conditions of the mine,the numerical simulation method is used to analyze the surface subsidence value of mining face in the case of no tremor.The predicted maximum subsidence value is 0.436 m and 0.453m.The measured results of surface subsidence show that the maximum subsidence values are 0.653 m and 0.878 m respectively after two tremors,which are 0.217 m and0.425 m higher than the predicted values without tremors.The results show that the tremors in the mining process will increase the surface damage and subsidence.