Study On The Mechanism Of Quiet Period Of Rock Acoustic Emission By Particle Flow Code

A phenomenon of acoustic emission quite period may appear in rock material's loading process.The acoustic emission quiet period highly resembles the earthquake quiet period,so revealing its mechanism is of great importance to forecast the geological disasters and to judge rock engineering stability.This paper intends to discover the mechanism of acoustic emission quiet period of rock material through analyzing heterogeneity and abnormal stiffness distribution of rock samples.The particle flow code(PFC^2D)is introduced to simulate and describe acoustic emission characteristics of rock material which is homogeneous or contains abnormal stiffness domain under uniaxial compression condition,and relationships between rock material heterogeneity,abnormal stiffness distribution and acoustic emission quiet period are established.Some conclusions are drawn from these research as follows:?1?Through a series of uniaxial compression tests,the macro mechanical parameters of a almost homogeneous granite deeply buried in a lead-zinc mine are obtained to standardize the meso-structure parameters of rock particle flow code model.Firstly,a analysis about parameter sensitivity is conducted to ensure underlying relationships between different parameters,according to those relationships,a standardizing method that the normal-to-shear stiffness ratio is adjusted to match the poisson's ratio,followed by the effective modulus adjusted to match the elastic modulus and bond tensile strength adjusted to match the uniaxial compressive strength is come up.Finally a set of meso-structure parameters of particle flow code model consistent with indoor test results is obtained.?2?Based on the particle flow code(PFC^2D),a series of heterogeneous rock samples with bond tensile strength values subjected to Weibull distribution are made on the basis of above-mentioned meso-structure parameters to simulate and analyze the acoustic emission under uniaxial compression condition.Through utilizing the Z test method in statistics,the significant level of rock acoustic emission abnormal quiet period is quantified.The results show that the acoustic emission quiet period levels of rock samples whose b value related to homogeneous degree vary from 8 to 12 are much more significant,on the contrary,the acoustic emission quiet period levels of other rock samples are not apparent except that one whose b value equals 14 is a little significant.?3?Based on the particle flow code(PFC^2D)and Z test method in statistics,a series of heterogeneous rock samples whose abnormal stiffness domain has a common total area but different lengths and widths are made to simulate and analyze the acoustic emission under uniaxial compression condition.The length of abnormal stiffness domain parallel to rocks' loading direction are used to distinguish different rock samples.The results show that the abnormal stiffness distribution has an effect on acoustic emission quiet period.The rock samples whose lengths of abnormal stiffness domain are more than 10L?L equals 0.00625m?have highly significant levels of acoustic emission quiet period,compared with the rock samples whose lengths of abnormal stiffness domain are less than 10 L almost having no acoustic emission quiet period.Besides,the longer the length of abnormal stiffness domain parallel to rocks' loading direction,the more acoustic emission events that appear in abnormal stiffness domain,and rock samples' failure modes are transformed from shear failure to tension failure with the length of abnormal stiffness domain increasing.