| The fault is a common geological structure in coal mining and mining engineering,and it is also one of the most important geological conditions for geological disasters that can easily be induced in deep mining of coal mines in China.The presence of the coal rock interrupting layer will seriously affect the normal underground mining operations,especially in the case of relatively large faults,which will make the original layout of the wells difficult to sustain and must be further explored,and the mechanical and electrical equipment has to be relocated.In the case of an extra amount of manpower and material resources,it also greatly slows the progress of mining.On the other hand,the presence of fractured structures in the coal seam is also very likely to cause local coal and rock structural mechanical properties,gas occurrence characteristics,and water conductance characteristics,especially when the faults undergo sliding deformation due to the disturbance of mining operations.The original balance of mechanics was broken,and the coal and rock bodies were very easy to destabilize and destroy,forming a coal-rock dynamic disaster,and the water-conducting fissures could easily be turned on to cause the permeability of the mine.It can be seen that the distribution of the downhole fault structure and its sliding deformation due to mining influence have greatly increased the occurrence probability and risk degree of various disasters such as underground coal and rock power disasters,mine water disasters,gas disasters,roof accidents,etc.The study of the sliding deformation characteristics and regularity of coal-rock fault structures under dynamic conditions will be helpful for a deep understanding of the mechanical characteristics of the fault zone and will help to correctly understand the mechanism of disasters in the fault zone area,as well as reasonably arrange the mining operations and safety in the fault zone.Protective measures,which effectively prevent and control the occurrence of underground mine dynamic disasters induced by faults,have important theoretical and practical values.At present,there are relatively few researches on the evolutionary features of fault sliding deformation and the mechanism of faults in the country,and no unified understanding has been formed yet,resulting in the limited effectiveness of existing regional fault prevention and control measures in some complex mines.For the forecasting and warning of fault-related disasters,the current warning methods mainly rely on traditional methods such as stress monitoring.The accuracy of prediction is low and the impact on mining operations is great.The acoustic emission/microseismic monitoring method has already been introduced,However,there is a general lack of corresponding early-warning index systems,which have poor operability and general applicability.The results obtained by different people are quite different,and it is difficult to accurately predict and predict the relevant geological disasters induced by faults.Based on this,in theory,this paper combines the related knowledge of rock mechanics,material mechanics and other related knowledge,starting with the relationship between the traditional fault friction sliding force and displacement,analyzes the law of friction coefficient change in fault sliding process,friction sliding constitutive relationship and its parameter changes.The law of stability is based on the increase of the steady friction coefficient as an indicator,and the stability of fault friction sliding is analyzed.At the same time,the Mohr-Coulomb criterion is adopted to determine the mechanical activation criterion of the fault and the influence factors are analyzed.In order to verify the correctness of the previous theoretical analysis results,a fault double-shear friction sliding experiment system was designed on its own.Combined with the digital speckle correlation method(DSCM),the temporal evolution characteristics and regularity of the sliding displacement of the fault friction interface were studied.During the fault friction sliding process,the time evolution characteristics and regularity of strain energy density,the characteristics and laws of the magnitude and actual stress drop of fault friction sliding,and the dynamic monitoring technology of acoustic wave and stress wave,and studied the sound of fault friction and sliding at different loading rates.The characteristics of spatio-temporal evolution of parameters such as ringing count,acoustic emission energy,acoustic emission event rate,germinal growth,and primary frequency are transmitted.The ABAQUS finite element software was used to establish and solve the fault sliding numerical model under mining conditions.The influence rule of fault dip angle,roof thickness,mining intensity,fault friction coefficient,etc.on the fault sliding law under mining conditions was studied.The criteria of fault activation and activation criteria under mining conditions were put forward,and the corresponding disaster prevention measures were put forward.At the same time,the combination of numerical simulation and the microseismic evolution feature is used to numerically simulate the evolution law of stress and deformation in the fault sliding area of the fault,combined with the characteristics of on-site microseismic evolution,to preliminary analyze the evolution process of fault friction sliding under mining conditions in a coal mine.Application Discussion.The research results have important research significance for further improving the formation mechanism and prevention methods of fault-induced sliding geological disasters.Through the above research,this paper has obtained the following main research results and conclusions:(1)According to the analysis of the relationship between fault shear force and displacement,the evolution of fault friction sliding displacement includes three stages of elasto-plastic deformation,creeping and stick-slip,among which the shear shear and displacement of the stick-slip stage show three corresponding relationships.It is a linear relationship between shear force and displacement,that is,the shear force decreases linearly with displacement,and secondly,the shear force and displacement have a segmented abrupt relationship.That is,the constant shear displacement increases,the shear force decreases the displacement,and the third is the shear force.The displacement shows a piecewise linear relationship,that is,as the displacement increases,the shear force appears to increase linearly and decrease linearly.Initially applying directional pressure to the fault,the rough surfaces of the fault contact with each other.When the normal pressure is small,the fault contact surfaces are in elastic contact with each other,and the real contact area is small.When the normal pressure is large,plastic contact may occur.The real contact area increases.With the shear force applied to the contact surface of the fault,when the shear force is small,the stress at the contact surface is lower than the strength of the rock material,and the overall connection mode of the contact interface is not affected.The friction sliding of the fault is in the elastic stage,and when the shear force continues to increase,the shear force reaches a certain amount.Values,the contact surface stress reaches the rock material strength,the contact surface material plastic deformation,the real contact area of the fault increases,the fault connection mode changes slightly,and the fault friction sliding is in the plastic stage.As the shear force continues to increase,the rock material at the contact surface of the fault is sheared and destroyed in a different manner,affecting the creep characteristics of the fault,ie,the creep stage is mainly reflected in the shear failure of the contact surface of the fault,if no shear failure occurs.The creep stage of the corresponding fault friction sliding is not obvious.The dynamic friction coefficient of the stick-slip stage is characterized by:first,the law of the influence of the loading rate on the friction coefficient is not obvious,but the magnitude of the overall friction coefficient is relatively close.Second,the coefficient of friction during the creep stage is less than the corresponding coefficient of static friction during the creep stage.For the same normal pressure at different loading rates,the static friction coefficient of the stick-slip period of the stick-slip stage presents the following characteristics:First,the effect of the loading rate on the friction coefficient is not obvious,but the magnitude of the overall friction coefficient is relatively close.Second,the coefficient of static friction between the stick-slip stages is greater than that of the corresponding stick-slip stage.From the overall trend of fault sliding evolution,the stability of the fault friction sliding increases or the stability decreases,which can be judged by the steady-state friction coefficient increment ??ss.That is,as the sliding speed increases,if the friction coefficient increases,that is,the speed increases.The stability of the frictional sliding increases;if the frictional coefficient decreases,that is,the velocity weakens,the frictional sliding stability decreases.It can be judged by the change of the parameter(ab)in the constitutive model.When(ab)>0,the velocity is strengthened,which shows that the stability of the fault friction sliding increases;when(ab)<0,the velocity weakens,and the fault The friction sliding stability is reduced.From the four experimental results presented in this paper,the fault friction sliding is in the slip-slip state of stick-slip,but overall,as the sliding speed increases,the speed increases,and the stability of the fault friction sliding increases.The stability and stress ratio of the fault are related to the cohesion and internal friction angle of the contact surface of the fault.When the stress ratio of the fault is between the minimum stress ratio corresponding to the normal fault and the maximum stress ratio corresponding to the reverse fault,the fault is in a stable state.When the stress ratio is smaller than the minimum stress ratio of the normal limit equilibrium equilibrium state,or the stress ratio is greater than the maximum stress ratio of the limit equilibrium state of the reverse fault,the fault will activate and induce fault instability.(2)Through the above analysis of the deformation field of the fault friction sliding process with different loading rates,it can be concluded that the process of fault friction sliding to stick.slip is mainly divided into three stages.The first stage is the initial non.uniform deformation stage.The deformation value of the stage is smaller,the local area of the fault is concentrated in the deformation,and the overall deformation concentrated area shows the trend of expanding from the loading end to the free end,but the defonnation concentrated area shows a non-uniform distribution in the entire fault zone.In the second stage,the overall deformation of the fault is concentrated,and the magnitude of deformation at this stage is relatively large.Under normal circumstances,the load is greater than 90%of the peak strength.The third stage is the fault stick-slip,and the deformation field reflects the overall sliding characteristics.By analyzing the time evolution characteristics of the sliding displacement of the fault interface at different loading rates,the results show that under the same loading rate,the sliding displacement of the fault interface has a good correspondence relationship with the loading evolution of the specimen loading.According to the stick-slip state,the loading curve can be divided into three stages:stick-slip pre-slip stage,stick-slip stage and inter-viscous-slip stage.Before the stick-slip occurs,the loading curve evolution process includes the non-linear growth of the load in the early stage,and the mid-stage load linearity.The three stages of the increase and the non-linear growth of the load in the later stage correspond to the compaction stage of the fault interface sliding,the elastic-plastic deformation stage of the fault interface and the creep stage of the fault interface.During the stick-slip period,the load curve shows a sudden drop in stress,corresponding to the sudden displacement of the sliding interface at the fault interface.During the period of stick-slip,the loading curve increases linearly(partial curves include linear and non-linear segments),corresponding to the small sliding displacement of the fault interface.It is considered that the fault interface is mainly in the elastic deformation state at this stage.Through the analysis of the spatial evolution characteristics of the sliding displacement of fault interfaces at different loading rates,the results show that the overall trend of sliding displacement evolution at different positions of the fault interface is consistent.However,the sliding displacement values at different positions on the fault interface are different,reflecting the experiment.The process breaks the deformation transfer characteristics of the layer interface from the loading end to the free end.After multiple stick-slips,the defonnation evolution of the fault interface tends to be even,which reflects the overall uniform sliding characteristics.The sliding displacement and sliding start-up time difference at each monitoring point of the fault show that the displacement value of each monitoring point of the fault interface is consistent with the viscosity.The sliding events increase and gradually converge,and the stick-slip start-up time difference at each monitoring point of the fault interface gradually decreases as the number of stick-slip events increases.Based on the above analysis of the time evolution of strain energy density,the fault strain energy density has a good time-correlation relationship with the evolution process of the fault sliding displacement,that is,the fault sliding initiation coincides with the origin of fault energy release,but the fault strain energy density release value There is no correlation with the magnitude of sliding displacement at the fault interface;usually,in the initial stick-slip period,the release rate of fault strain energy density is slow.With the increase in the number of stick-slip events,the release rate of fault strain energy density is accelerated.It is considered that due to the fault interface Inhomogeneity,in the initial stick-slip period,there is an asynchronous non-uniformity in the energy accumulation and release at different positions of the fault interface.Therefore,the data processing in the average sense results in a slow release rate of strain energy density.With the increase of stick-slip event,the inhomogeneity of fault interface weakened,and the release rate of fault strain energy density showed rapid characteristics.At the same time,under the high loading rate,the increase of the strain energy density during the accumulation of fault energy density shows that the fault strain energy accumulation under the high loading rate instability characteristics.The initial stick-slip start-up time of the fault specimen decreases with the increase of the loading rate,and the stick-slip generation period decreases with the increase of the loading rate;at different loading rates,the fault-slip-slip-slip displacement field evolves similarly and presents a uniform displacement evolution.,Inhomogeneous evolution and overall sliding characteristics;there is no correlation between the slip-slip sliding displacement and slip velocity and the loading curve stress drop and loading rate.The magnitudes corresponding to different loading rates are related to the actual stress drop.The overall manifestation is that with the increase of the actual stress drop,the magnitude of the increase in the magnitude of the approximately linear evolution trend;magnitude and actual stress drop and load rate relationship overall performance,with the magnitude The loading rate increases and decreases;the actual stress drop decreases with increasing loading rate.(3)In the pre-viscous stage of the fault,as the load increases,the fault interface undergoes random initial distribution of micro-defects during initial loading,evolution of elasto-plastic deformation and creep of the fault,among which the random distribution at the initial loading The amount of acoustic emission ringing count during the initial compaction of the defect is small,and the density distribution on the time axis is sparse.The number of acoustic emission ringing counts during the evolution of elasto-plastic deformation has a small increase,and the density on the time axis increases.The magnitude of acoustic emission ringing counts during the creeping process of the fault is generally increasing,and it shows fluctuations,and the density on the time axis further increases.In the stick-slip period of the fault,the occurrence of stick-slip events generally corresponds to a sudden increase in the number of acoustic emission ringing counts,and there is no corresponding relationship between the increase in the count of the acoustic emission ringing count and the amount of load reduction.During the period of inviscid slip,the load generally increases linearly.This stage is mainly the elasto-plastic deformation evolution of the fault interface.The ringing count is at a relatively small level,and there is a pre-sliding period before stick-slip.The common feature of the acoustic emission energy during fault friction sliding is that the acoustic emission energy increases sharply when the stress suddenly drops,and the small-scale and local-area sliding velocity changes under the influence of the overall structural load cause the acoustic emission energy to increase rapidly.At the time,the stress does not necessarily drop abruptly;in the pre-tight stage of the fault,the acoustic emission energy value is small and there is a wave phenomenon;during the stick-slip of the fault,the acoustic emission energy generally has a sharp increase in magnitude,and both There is a "quiet period before sliding";as the loading rate increases,the total amount of ringing energy and the magnitude of the increase in the excitation energy before the first sticking and sliding of the fault are gradually increased;the change of the sliding speed of the fault interface has a great influence on the acoustic emission energy;The magnitude of the surge in launch energy is independent of the amount of load reduction.Before the occurrence of fault stick-slip,the slower growth of the load can be used to reduce the incidence of the start of the acoustic emission event as the precursor of the creeping sliding of the fault;after the fault stick-slip event,the acoustic emission event rate increases with the increase of the load.Increase;When the fault occurs sticky slip,the sudden decrease in the rate of acoustic emission events,the rapid increase in the rate of acoustic emission events can be seen as a precursor to stick-slip in inviscid slipperiod.The main frequency of acoustic emission events in the fault friction sliding experiment is mainly distributed in the range of 0.250 kHz.Before the first stick-slip event,the number of acoustic emission events within the main frequency distribution range of each acoustic emission event is in the range of 0.250 kHz.More.After the stick-slip,the acoustic emission events in each frequency range increased.In the stick-slip period,the acoustic emission events in each frequency range decreased,and the number of acoustic emission events in the low-frequency range decreased more significantly.(4)According to the data of the eight monitoring points A and A',B and B',C and C',D and D',the displacement of the relative monitoring point is analyzed along with the change characteristics of the fault-to-fabrication thrust.The change of fault dip angle under mining conditions has obvious influence on fault slippage,and the smaller the fault dip angle relative to the fault footwall,the farther the working surface is from the fault plane when the corresponding displacement difference between the two points changes,and the fault is more likely to occur-slide.As the thickness of the overlying roof on the working surface increases,the displacement difference at the monitoring point changes.The corresponding working surface is further away from the fault distance.At the same time,as the thickness of the overlying roof over the working surface increases,the fault slips from the top of the model and gradually shifts towards the working surface.The change of friction coefficient of the fault plane has no obvious effect on the advance or lag of the fault sliding in the mining state,but the friction coefficient of the fault plane has influence on the sliding distance of the fault,and the larger the friction coefficient,the smaller the sliding distance.The size of the fault surface friction coefficient also affects the slip speed of the fault,and the impact relationship is that the larger the friction coefficient,the smaller the slip speed of the fault.(5)Taking the influence of a working face mining on the F-fault frictional slippage as the engineering background of the research,through the numerical simulation of stress and displacement evolution of the fault friction sliding during the mining process of the working face,the on-site microseismic monitoring data of the fault friction slip is determined.Analyze the area.Combined with the typical acoustic emission energy and loading relationship of the fault friction sliding test,the on-site monitoring of the micro-seismic energy data of the fault,and the numerical simulation results of the shear stress/normal stress of the fault,from the analysis of the microseismic energy and the time evolution curve,it is possible to initially judge the mining period of the working face.Corresponding faults are in the stage of random fissure development.No load reduction occurs in the load curve of the corresponding point of the fault,and the magnitude of the microseismic energy is increased sharply,but the increase is small,indicating that the local area of the fault slips and the sliding rate changes greatly. |
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