Calibration Method And Sensitivity Analysis Of Micromechanic Parameters For Limestone Based On Particle Flow

The PFC particle flow numerical simulation method has been widely used in the geotechnical engineering,such as constitutive model of rock and soil,geological disaster analysis,foundation pit and foundation treatment and other fields.However,due to the lack of a clear relationship between the meso-level parameters of the numerical simulation and the macroscopic parameters of the rock and soil,there are many problems such as control factors,blindness of the calibration,and uncertainty of the results,which results in low efficiency and poor accuracy of the numerical simulation.The calibration method for determining the meso-parameters of rock and soil mass is a problem to be solved in the PFC numerical simulation.In this paper,based on the discrete element method and particle flow theory,the PFC numerical simulation program was used to align the geotechnical materials on the site of Yueshan Tunnel and successfully calibrated.Based on the calibration results,the influence of microscopic parameters of the particle flow on the macroscopic mechanical parameters of the material was studied by the control variable method.Through the normalization of macroscopic parameters,single factor sensitivity analysis,factor.analysis of variance,and regression analysis,A meso-parameter calibration method suitable for parallel flow model of particle flow is proposed.The results show that:(1)Through meso-parameter optimization and limestone calibration analysis of Qiyueshan tunnel,it is concluded that the elastic modulus and Poisson's ratio gradually decrease with the increase of particle size,and the larger the particle size,the greater the change in elastic modulus with particle size.Obviously,the Poisson's ratio changes little and tends to be flat;the particle size has a direct relationship with the number of particles.The smaller the particle size is,the more obvious the number of particles changes,and the decrease in particle number with particle size is similar to The increase of multiples;the smaller the particle size,the more pronounced the failure mode of uniaxial compression,and the closer the failure characteristics of the sample are to the actual destruction of the actual rock mass.(2)Based on numerical simulation,using the control variable method,the slopes of the stress-strain curve and the load-displacement curve increase with the increase of the effective modulus,decrease with the increase of the stiffness ratio,and show the overall peak of the curve.With the increase of the stiffness ratio,the trend decreases;the peak value of the stress-strain curve and the load-displacement curve increase with the increase of the normal strength,and the pre-peak curves under different normal intensities are coincident in the figure.The post-peak curves are approximately parallel to each other;changing the tangential strength,the stress-strain curve and the load-displacement curve are similar to the curves under different normal strength conditions,but the post-peak patterns are obviously different;the larger the tangential strength,the more brittle characteristics of rock failure.obvious.(3)Based on numerical simulation studies,the effect of effective modulus on macroscopic physical parameters is:elastic modulus>tensile strength>compressive strength>Poisson's ratio;the effect of normal/tangential stiffness ratio on macroscopic physical parameters Sensitivity is:Poisson's ratio>tensile strength>elastic modulus>compressive strength;the effect of normal bond strength on macroscopic physical parameters is:tensile strength>compressive strength>elastic modulus>Poisson's ratio.The sensitivity of the parallel bond tangential strength to macro physical parameters is:compressive strength>tensile strength>Poisson's ratio>elastic modulus;the effect of particle friction coefficient on macro physical parameters is:tensile strength>mooring Loose>compressive strength>elastic modulus.(4)The elastic modulus E is positively correlated with the effective modulus Ec,and has a negative correlation with kn/ks;the Poisson's ratio is positively correlated with kn/ks The uniaxial compressive strength ?c is negatively correlated with the Ec&kn/ks,and is positively correlated with the normal bond strength ?c and the parallel bond tangential strength ?c.The tensile strength is negatively correlated with the effective modulus Ec and the kn/ks,and is positively correlated with the ?c,and ?c;the?c/?t is positively correlated with Ec,kn/ks,and ?c.(5)The multi-factor variance analysis method was used to analyze and rank the meso parameters with significant influence on the macro parameters.The results are as follows:elastic modulus E,Ec>kn/ks;Poisson's ratio,kn/ks;uniaxial compressive strength,?c,?c>?c>Ec>kn/ks;tensile strength ?t,?c>?c>Ec>kn/ks The tensile strength ratio,Ec>kn/ks>?c.(6)A meso-parameter calibration method for the parallel flow model of particle flow is proposed.The method reveals the influence of meso-parameters and macro-parameters through normalization,single-factor sensitivity analysis,multi-factor analysis of variance,and regression analysis.The law further defines the nonlinear relationship between the two,improves the efficiency and accuracy of parameter calibration,and compares the numerical simulation and the indoor test by calibrating the meso-parameters of the rock sample in the pit mining and water control project of Pingnan limestone mine.This verifies the reliability of this calibration method.