Research On Force Chain Evolution Characteristics Of Surrounding Rock And It's Key Physical

In this paper,by using theoretical analysis,numerical simulation and laboratory experiment,the distribution characteristics of force chain and the measurable physical quantity of surrounding rock are systematically studied.The distribution of the force chain of the surrounding rock of the stope and its evolution rule are analyzed,and the visualization of the force chain in the surrounding rock of the stope is realized.On the basis of the distribution of the force chain and its evolution rule,The acoustic emission numerical simulation model is established,and the law of time-space-strong response of the force chain and acoustic emission is obtained.The key physical information which can characterize the lithology of different rocks is obtained by means of laboratory acoustic emission and mathematical calculation.Based on the comprehensive study of numerical simulation and laboratory experiment,the mechanics mechanism of rock mass fracture of overlying strata is revealed,and the key physical measurable quantity of coal rock force chain is obtained,and the force chain of surrounding rock is realized.Can be measured.The main research results are as follows:1.The distribution characteristics and temporal-spatial evolution law of the force chain of the surrounding rock are simulated by using the discrete element method for the first time,and the visualization of the force chain of the surrounding rock is realized.Based on the engineering geology and mining technology of 21116 working face in Xieqiao Coal Mine,the distribution and evolution law of the force chain of the surrounding rock are fully reconstructed by using PFC3 D,and the mechanism of force chain formation and the mechanical properties of macro.The main conclusions are as follows:(1)There is a force chain system composed of a large number of force chains in the surrounding rock of the stope.The force chain represents the size and direction of the force transfer between the particles.The strong chain plays a major supporting role in the force chain system.Chain system stability play a supporting role.The force chain can bear larger normal force,the tangential force is more stable,the tangential force can bear is smaller,more than its tangential load limit force chain fracture.(2)For the first time,the discrete element method is used to simulate the distribution and evolution of the force chain of the surrounding rock.It is found that with the excavation of working face,the concentration of the force chain around the working surface is different,the upper and lower corners and The force chain at the inner side of coal wall is obviously stronger than that at other locations.(3)With the advance of the working face,the force chain arch consisting of the strong chain bundle is formed in the direction of the strike and the direction of inclination,and the strong chain-like beam is formed in the overburden layer.Stress shell is the main bearing capacity of overlying strata.The strength chain in the stress shell is stronger than that in the shell,and the stress shell is evolving along with the advance of the working face.The main mechanical characteristics of the shell are that the strength chain in the shell is the strongest and the strength of the force chain inside and outside the shell is relatively low.2.Based on the moment tensor theory,the time-space-strong response laws of force chain and acoustic emission are revealedBased on the theory of moment tensor,the macroscopic mechanical response,force chain evolution,crack evolution law,force chain and acoustic emission response law of rock specimen under axial loading are studied by numerical simulation and laboratory experiment.,Reveals the time-space-strong response of the force chain and acoustic emission.The main conclusions are as follows:(1)Under the action of axial stress,the strong chains formed inside the granular material are distributed in the form of "dendritic",and the direction of the strong chain is controlled by the direction of axial stress.As the axial stress increases,,Slip,slip and other forms of change,resulting in the direction of the force chain deflection.(2)There is a negative correlation between the number of internal force chains and the maximum contact stress between particles.Before the peak stress,the number of fissures is increased under the condition of the external load increasing continuously.The fissure between particles is less,but the internal force chain is more concentrated and the stronger chain is formed.(3)Based on the theory of moment tensor,numerical simulation of rock material under uniaxial compression is carried out by using particle material numerical simulation method.The stage of acoustic emission is divided into compaction stage,elastic deformation stage,stable expansion stage,Unsteady expansion stage and macroscopic destruction,and show the spatial distribution and intensity of AE at various stages.(4)The force chain,the crack and the acoustic emission are synchronous in time,showing the same region in space,and the strength is consistent.The mechanics essence of fracture formation and acoustic emission is the transfer and fracture of force chain.Under the condition of continuous loading of axial stress,the energy released from the unbalanced force chain breaks off the coal and rock particles on the force chain,resulting in the damage of the force chain and the formation of microcracks.Some unabsorbed energy is released Acoustic emission phenomena.3.Key chain of physical information acquisitionIn order to obtain the key physical information which can characterize the force chain during rock loading process,acoustic emission experiments of the same lithology and different rock are carried out on the stope,and the general eigenvalues and dominant frequency characteristics of acoustic emission are compared and analyzed.The acoustic emission characteristics of different lithology can be distinguished.The main conclusions are as follows:(1)The acoustic emission amplitude and energy of different rock samples of the same lithology are similar with the loading of stress.The same acoustic emission characteristic values of different lithologies are similar to the evolution laws of loading process,But the eigenvalues of different sizes,indicating that the acoustic emission amplitude and energy characteristics can not be used as a distinction between the upper strata of different lithological information.(2)The fast Fourier transform method was used to transform the acoustic emission waveform data obtained in the experiment,and the main frequency values of different lithological rocks were extracted.The main frequency values of various lithological rocks are 300 KHz for fine sandstone,95 KHz for siltstone,245 KHz for medium sandstone,130 KHz for limestone,310 KHz for magmatic rock,and 88 for raw coal,using the normalization method.KHz.The results show that the distribution of acoustic emission spectrum of rock materials is not only able to monitor the fracture evolution characteristics of rock in real time,but also reflects the characteristics of rock fracture.The lithology of the rock.4.The numerical simulation and the laboratory experiment method are used to study the characteristics of the measurable physical quantity of the force chain in the stopeBased on the numerical simulation and laboratory experimentation,the shear mechanism,the evolution of the surface strain field and the destabilization of the force chain were analyzed.The mechanism of the force chain during the loading process of the composite rock mass was revealed.The measurable physical quantities of the force chain are studied.The main conclusions are as follows:(1)Using the digital speckle calculation and numerical simulation,the breaking rule of the composite rock mass is revealed.The shear failure process of the rock mass is firstly occurred in the soft rock layer,followed by the thin hard rock layer and the hard rock layer.The existence of the soft rock layer on the one hand to ease the combination of rock damage caused by the impact,on the other hand also makes the combination of rock layer breaking rule is more complex.(2)The evolution of force chain and the development of fissure have mutual promotion effect.The combination of the rock mass bearing load causes the local force chain to concentrate locally,which leads to the formation of the fissure and further the concentration of the force chain,The Micromechanical Nature of Dynamic Disasters.(3)The comparison of force chain and acoustic emission spectrum shows that the frequency value of each rock layer remains unchanged and the magnitude of magnitude of the main frequency value increases abruptly when the fracture of the rock strata breaks,Ie the amplitude of each lithologic frequency is the key measurable physical quantity which characterizes the force chain.