Research On Mining Induced Fault Slip Dynamic Response And Rockburst Mechanism

Fault is the most common geological structure in coal mine,which has an important impact on panel layout and mine safety production.Production practice shows that the areas near fault structures where rockbursts frequently occur,and the occurrence of fault slip rockbursts is closely related to the large-energy microseismic events released by fault slips.In addition,the fault slip rockburst has the characteristics of high severity and large impact range.This paper comprehensively uses on-site investigations,theoretical analysis,rock mechanics tests and numerical simulations to analyze the characteristics and influencing factors of fault slip rockburst,the mechanism of rockburst induced by fault visco-slip and the dynamic respone of fault slip as well as the hazard of rockburst.The research results of this paper are as follows:(1)Based on the on-site data of the panels near the faults,the occurrence regularity of microseismic events and the appearance characteristics of rockburst near the fault are summarized and analyzed.The characteristics of fault slip rockburst and the main influencing factors that induce fault slip rockburst are summarized and refined.(2)Through theoretical analysis,the law of fault shear slip and the microseismic events induced by fault visco-slip,the law of fault slip instability under the influence of mining,and the energy conditions for the initiation of fault slip rockburst are studied.Finally,the dynamic mechanism of fault visco-slip induced rockburst under the influence of mining is proposed.The slip form of the fault during the mining of footwall and hanging wall panels through the faults and its criterion are derived.The slip form of the rough fault is affected by the horizontal force FN near the fault.When the horizontal force FN near the rough fault is large enough,incisor slip will occur in the rough fault,and the fault slip exhibits the characteristics of visco-slip and releases large-energy mine earthquake events.The possibility of fault slip rockburst on the working face is greater.The occurrence of fault slip rockburst is that the energy of the coal body static load and the fault slip dynamic load in the peak abutment stress area is greater than the minimum energy required for the destruction of the coal body,causing the coal body to suddenly fail in the peak abutment stress area and release a large amount of elastic energy and then induces rockburst.The greater the static load energy of the coal body in the limit equilibrium area as well as the greater the slip dynamic load energy of the fault,the greater the elastic residual energy when the coal body is destroyed,and the more severe the rockburst appears.(3)Based on direct shearing,acoustic emission,three-dimensional laser scanning and electron microscopy scanning techniques,the slip law of fault zone rough joints and the characteristics of shear damage under different normal stresses and shear rates are studied.Research shows that the shear strength,shear modulus,shear stress drop,acoustic emission number and energy in the shearing process of rough joints all increase with the increase of normal stress and roughness.The direct shearing process of rough joints can be divided into four stages:elasticity,crack initiation,peak failure and post-peak failure.The higher the normal stress,the smaller the elastic stage range,the larger the range of crack initiation,peak failure and post-peak failure stage,the earlier the joint convex damage,the longer the damage duration,and the higher the severity.The smaller the shear rate,the smaller the number of acoustic emissions and energy(within 1s)during the direct shearing process,and the greater the number of accumulated acoustic emissions and the accumulated energy released.The bumps are cut and worn during the shearing process of the rough joint,the significant reduction in roughness shows the characteristics of slip weakening,which is the direct cause of visco-slip release of a large amount of energy on the joints.And the greater the roughness of the joints and the higher the normal stress level,the more significant the visco-slip feature during the shear-slip process,the greater the energy released.Quantitatively study the roughness attenuation law of the joints after direct shear under the conditions of different roughness and normal stress levels.Under the same roughness condition,the roughness of the joints after direct shearing decreases exponentially with the increase of normal stress..(4)Based on the direct shear test results of the rough joints and the FLAC3D numerical simulation software,a Barton shear strength model considering the slip weakening effect of the rough joint of the fault zone is developed,and the fault slip process and its dynamic response under the influence of mining are calculated.The whole process of "mining-fault slip release dynamic load-mining space dynamic response" is realized,and the mining space dynamic response and rockburst hazard under the action of fault slip dynamic load are studied.It reveals the law of the influence of mining-induced fault slip dynamic load on the vibration velocity of coal and rock mass and abutment stress near the working face.When the working face advances to different positions,the size of the seismic source of the fault slip induced by mining is different,resulting in different vibration velocity of the coal and rock mass near the working face,and the abutment stress is also affected by the fault slip dynamic load to different degrees.When the working face advances to the vicinity of the fault,as the supporting effect of the fault coal pillar on the roof decreases,the fault occur a large area of slip and releases the strong fault slip dynamic load.Under the action of the strong fault slip dynamic load,the coal and rock mass near the working face is vibrated at a high speed and severely damaged,and the coal stress value in the peak area of the abutment stress is reduced and a large amount of elastic energy is released to induce the fault slip rockburst.(5)Based on the fault slip dynamic calculation model,a comparative analysis of the fault slip seismic source and its dynamic response characteristics under the conditions of different mining influences and fault characteristic parameters at the working face are compared.Considering the stress disturbance caused by the fault slip dynamic load on the coal and rock mass near the working face,an evaluation index for the rockburst potential of the working face under the fault slip dynamic load is proposed,and the rockburst potential of the working face under different influencing factors is compared and analyzed.The influences of mining the panel through the fault from the footwall on the fault is greater than when mining the panel through the fault from the hanging wall.The greater the roughness of the fault and the higher the level of ground stress,the more energy accumulated in the fault before the fault slips.Once the shear slip occurs on the fault,the shear stress drops suddenly,and the fault slip seismic moment M0 is larger.The degree to which the vibration velocity,stress and energy of the coal and rock masses near the working face disturbed by dynamic loads are generally positively correlated with the fault slip seismic moment M0.When the mining disturb is severe,the fault roughness is large,and the fault stress level is high,the rockburst potential of the working face is greater.