Study On The Mechanism Of Acoustic Emission Relative Calming Period Of Polycrystalline Granite With Different Fabrics Based On Particle Flow

The relatively quiet period of rock acoustic emission is a phenomenon that the acoustic emission decreases significantly before the main fracture of rock.As a precursor of rock instability and failure,the relative calm period of acoustic emission can timely judge the stability and safety of rock mass in actual engineering,which is of great significance to the monitoring and warning of rock mass instability and earthquake disaster.In order to study the mechanism of rock acoustic emission relatively quiet period,based on the Granite as the research object,on the basis of indoor test,using particle flow program PFC2 D building Granite equivalent crystal GBM(Granite--based Model,referred to as the GBM)Model,considering the Granite abnormal distribution of crystal size,strength and different mineral content different fabric,such as simulation of acoustic emission of uniaxial compression test,to explore internal different rock fabric acoustic emission,has been relatively quiet period of effect and its mechanism.The main contents and conclusions are as follows:(1)In order to provide mechanical parameters for the establishment of particle flow model,uniaxial compression acoustic emission tests of granite were carried out on four specimens.The mineral composition was identified by XRD,and the content,meso-structure and dimensional characteristics of different minerals were obtained by digital image processing technology.Among them,the two specimens have a relative quiet period of acoustic emission,which lasts for 13 s and 17 s respectively.(2)Build equivalent granite crystal GBM model and write acoustic emission monitoring program.By analyzing the relationship between the elastic modulus,Poisson’s ratio,uniaxial compressive strength and the effective modulus,normal shear stiffness ratio and bonding strength in granular flow,the meso-parameters of GBM granular flow model of granite equivalent crystal were calibrated.The results show that the uniaxial compressive strength,elastic modulus,Poisson’s ratio,macroscopic failure mode and AE event rate of numerical simulation are in good agreement with the experimental results.(3)The simulation results of different fabric granites show that with the increase of crystal size,the duration and significance Z-value of AE during the relative calm period tend to decrease.When the intensity abnormal parameter b value is 2～6,the relative quiet period of AE is not obvious,and when b value is 8,there is a relatively obvious relative quiet period of AE.When the quartz content percentage is 5%～65%,the time and Z-value of AE relative calm period have a decreasing trend.(4)By analyzing the evolution law of Poisson’s ratio of different fabric granite,the change process of Poisson’s ratio can be divided into four stages: shock,stationary,obvious increase and exponential increase.Before the peak stress,the measured Poisson’s ratio increased significantly before and after the relative calm period,and increased exponentially when the peak stress was reached.