| The research of this paper is based on the National Natural Science Foundation of China(51374216).The most important method of gas control is the gas extraction,and the most critical problem of gas extraction is the determination of reasonable extraction parameters.The crack field of the roof is the main channel for the upward movement of the gas in the goaf.Therefore,it is very important to study the evolution law of the roof fissure field under the influence of the mining face.It is determined that the roof gas drainage and high Laying the way and other means of arrangement of the main basis.In this paper,the evolution law of the fractured field under the influence of the surrounding rock of the working face is taken as the research direction.Through the laboratory mechanics experiment,the principle of macro-scale fissure distribution,the on-site drilling peep observation,the three-dimensional network reconstruction of the roof fracture,Under the condition of parametric conditions,the paper focuses on the evolution law of the fractured field in the surrounding rock of the working face under the influence of the mining stress of the working face.Through the research,this paper has obtained the following conclusions:(1)The experimental scheme of rock cycle loading and unloading with maximum stress increasing is proposed.The stress and unloading speed of the scheme are determined according to the characteristics of the roof roof stress,and the acoustic emission of the rock is monitored.It is found that the cyclic loading and unloading experiments of rock can be divided into three stages according to the characteristics of the acoustic emission signal,which are the acoustic emission phase,the development stage and the peak stage.The peak stage of the sudden increase of the number of acoustic emission events is the most important stage,which is about 60% ~ 70% of the peak intensity.In the peak phase,the high amplitude signal appears more,and the acoustic emission location is also concentrated,and the concentrated region corresponds to the final sample destruction position.The rock of the whole loading process more than 90% of the acoustic emission events are concentrated in this stage,can be considered within the rock cracks,porosity and other types of damage are mainly produced at this stage,so this is the most important stage of rock damage.(2)The acoustic emission signal has obvious Kaiser effect and Felicity effect.By calculating the Felicity ratio,it is found that the accuracy of the Kaiser effect decreases with the process of cyclic loading and unloading,and the acoustic emission is more and more with the Kaiser point prior to.After careful observation of the acoustic emission signal in the unloading phase of the latter cycles,it is found that when the stress is less than the maximum value of the coat cycle,the acoustic emission effect will be generated,but the amplitude and event rate are less than the cycle loading stage.After analysis,it is considered that the stress is less than the maximum of the upper cycle,the rock produced a certain degree of plastic recovery and produce a sound emission signal,and in the next cycle of the loading phase,the plastic recovery to reach the maximum stress before the cycle was destroyed,resulting in the Felicity effect,which is a good explanation of the causes of the Felicity effect.Since this phenomenon is also generated after the last cyclic stress maximum,it is defined as the post-Kaiser effect.(3)At the mesoscale scale,the amplitude of the acoustic emission reflects the magnitude of the signal energy to a certain extent,which in turn reflects the magnitude of the damage as an energy source.According to the acoustic emission amplitude distribution,it can be deduced that the small-scale damage of the rock is a random occurrence in the process of destruction.With the increase of the number of small damage,they are connected and penetrated,and the larger amplitude Acoustic emission signal;with the further expansion of the crack,eventually through the rock,leading to rock damage.On the macroscopic scale,the law of the crack field in the rock mass can be carried out according to the size distribution of the fractured surface.(4)In this paper,the equilibrium equation,geometric equation,deformation control equation and constitutive equation of the elastic phase of the rock loading process are analyzed on the mesoscopic scale.The damage ratio of the area of destruction,the molar pressure criterion and the tensile strength criterion are summarized.Ringing count and other parameters based on the different parameters of the definition of damage,and finally combined with the previous chapter under the conditions of rock cycle loading and unloading acoustic emission energy accumulation characteristics,defined by the acoustic emission cumulative energy as the parameters of the damage variable D,to better Reflecting the size of the rock at different times.(5)At the mesoscopic scale,the relationship between the total number of events corresponding to different amplitude values of acoustic emission and the total number of events corresponding to different energies is analyzed.It is found that small amplitude and small energy acoustic emission events dominate,and both show y The size of the macroscopic fissure surface of the geologic body is measured on the macroscopic scale,and it is found that the size of the fissure plane corresponding to a certain size is between the number of fissures in the logarithm On the straight line,the fitting law also shows a negative power relationship.It is consistent with the amplitude and energy distribution of the acoustic emission of the meso-scale rock.It can be concluded that the damage of the rock is consistent with the macroscopic fracture The self-similarity and fractal properties of rock materials.(6)On the macroscopic scale,the working principle of the front view drilling peers is analyzed,and the method of converting the video of the front view drilling into the panoramic image of the drilling hole and the principle of extracting the fracture information of the drilling hole are put forward.Using the proposed conversion method to convert the peephole video into a panoramic image of the hole and extract the fissure information in the picture.Furthermore,the parameters such as the strength,shape and size of the fissure group required for the three-dimensional reconstruction of the fissure field are extracted from these fissure information.(7)Based on the relevant parameters of fissure,based on the principle of 3D network reconstruction of discontinuities,the 3D simulation of spatiotemporal evolution of roof slabs on the basis of field drilling is carried out with the help of Mo Frac software,and the following rules are obtained: In the direction along the working surface,the mining distance is 25 m and before,the fissure is mainly concentrated in the distance of 60 m from the roadway,and the fissure is located in the direction of the goaf along the working surface.And more than 50 m in the direction of the direction becomes more even;in the height direction,mining 6m when the cracks in the height of 10 m range,with the face of the advance,cracks in the height range of distribution is growing,25 m when the height of about 15 m,75m and 100 m when the mining reached 35 m or so,the highest observed distance of only 35 m,so that the true distribution of the fissure field to more than 35m;(2)the initial mining face 6m,the resulting Roof fissure size is generally small,and with the face of the mining,the roof of the cracks in the area gradually increased,the old roof of the first and week The large fissure surface caused by the pressure is further cut and connected to the middle and small fissures before it is generated,and then the complicated and interconnected fissure network is formed,which becomes the main gas seepage channel in the roof of the goaf;(3)The inclination is mainly in the horizontal direction,and the tendency of the fissure is not too obvious.The density of the fissure plane can be seen to increase gradually with the mining of the working face and gradually stabilize after 50 m.(8)The choice of constitutive model and the assignment of material parameters are very important in numerical simulation,which is the key factor to determine whether the numerical simulation results are reasonable.In the FLAC3 D,considering the residual strength,the model coal and rock mass are defined as the strain hardening / softening model which is more in line with the actual situation.At the same time,the mined-out area is determined according to the parameters such as the coefficient of crushing and the mined-And the volume modulus K and the shear modulus G of the coal seam overlying 54 m roof are assigned according to the Weibull distribution.(9)Based on the analysis of the vertical stress and the failure zone of the plastic failure zone in the surrounding rock of the mining process,it is concluded that the plasticity of the coal body is within 12 ~ 14 m in the front face of the working face.The plastic damage in the roof is mainly found in the mined The top of the area,the recovery of more than 30 m after the beginning of the coal in the face of the coal body in the roof generated;working face recovery to 72 m before the propulsion,mineda above the emergence of a layer of plastic plastic damage area,which is the most stable fracture zone,While working in front of the front of the front position of a large number of plastic damage,which is a large range of roof pressure or damage related to the internal may generate a lot of cracks.The plastic deformation range of the roof can reflect the generation and evolution of the fissure plane in the roof.After comparison with the observation results,it is proved that the strain-based hardening / softening model,the double yield model and the Weibull distribution rock roof parameters are randomly assigned Sex.(10)This paper presents a method to obtain the key parameters of high efficiency gas drilling and extraction technology of roof roof by using the observation of roof slab drilling.Based on the characteristics of the aerial space of the roof fissure field and the main source of the gas,the gas seepage law of the roof fissure field is analyzed.Based on the formula of the roof collapse zone and the height of the fracture zone,the main parameters are arranged.Considering the effective length of drilling,the drilling scheme of N3-7 working face is optimized,and the arrangement scheme of high hole drilling in the inlet tunnel and the layout of the drilling group are obtained respectively.The scheme can provide a reference for the layout of the roof gas drainage in the N3-7 working face and its surrounding working surface. |
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