Research On The Mechanism Of Sudden Structural Instability Of Coal And Rock With Faults Under Dynamic And Static Load

Fault slip rockburst is a serious coal-rock dynamic disaster in coal mines.The mechanical properties near the fault zone are complex,and when disturbed by mining earthquakes,it is easy to induce fault slip and instability to generate stress waves,resulting in serious damage to the roadway.In this paper,laboratory tests,discrete element numerical simulation,field monitoring,and other means are used to study the characteristics of fault sliding and instability under dynamic and static load,the mechanism of fault sliding type rock burst,precursor information,and supporting means from the perspectives of stress,displacement,crack,energy,acoustic emission,and microearthquake.The research results are as follows:(1)Based on the indoor structural surface shear test with the combination of dynamic and static loads,the effects of structural surface roughness,normal dynamic load amplitude,tangential dynamic load amplitude,and tangential dynamic load loading time on the structural surface shear slip instability were investigated to reveal the characteristics of structural surface slip instability under dynamic loads.The results show that the shear force,friction coefficient,and normal displacement all change periodically under the normal dynamic load shear condition,which is consistent with the normal dynamic load period.With the increase of normal dynamic load amplitude,both the peak shear strength and dynamic friction coefficient of sandstone show a trend of first increasing and then decreasing.The effect of cyclic shear on the structural surface can be divided into contact and damage effects.An increase in the number of cyclic loading causes the peak shear strength of rock joints to show an increasing trend followed by a decreasing trend.At the same number of cyclic shear,the greater the amplitude of the cyclic load before the peak,the higher the degree of nodal damage,the more obvious the damaging effect,and the more obvious the decreasing trend of the peak shear strength.(2)Through theoretical analysis,the fault slip law and destabilization criterion were studied.The viscous slip instability model combined with the energy equation is used to analyze the viscous slip characteristics exhibited by the fault in the slip process and the seismogenic mechanism of the fault releasing large amounts of kinetic energy in the slip.Slip destabilization analysis was performed on the faults under the disturbance of upper and lower disc mining,and it was found that the faults were more prone to slip when the lower disc was mined.By appropriately simplifying the rough fault and combining it with the key layer theory,the fault of the lower plate mining model is analyzed in depth,and the slip form of the rough fault and the criterion is obtained.(3)The "mechanical parameter plunge method" was developed using Fish language to simulate fault slip,and the mechanism of fault slip rockburst was studied from the perspective of slip-type stress waves,revealing the evolution characteristics of cracks,stresses,and energy in the roadway.The geometric characteristics of the fault determine the intensity and radiation area of the slip stress wave,and the most unfavorable velocity load is the dominant factor in determining the severity of the rockburst.(4)Using the time-dependent damage model combined with the sharp-angle mutation model,the mutation destabilization mechanism of coal-rock structural assemblies under dynamic and static load combinations was analyzed,and the mathematical expression of the damage criterion of coal-rock assembled systems under two-dimensional dynamic and static loads were obtained.In the coal-rock combination system,the larger the height ratio of the rock sample and coal sample,the smaller the ratio of elastic modulus of the rock sample and elastic modulus of coal under dynamic and static load,the more likely the combination system is to have abrupt destabilization.Finally,the theoretical results are verified by combining the numerical model proposed in the paper,and they agree well.(5)Using acoustic emission monitoring,PFC numerical simulation,and UDEC numerical simulation,we analyzed the precursor information of fault slip rockburst,explored the acoustic emission characteristics and fine view damage law of the sawtooth structural surface under normal dynamic load,and monitored the characteristics of various mechanical parameters of the fault under mine seismic disturbance and in slip.