Study On Meso-parameter Calibration Of Chlorite Schist Particle Flow Based On Discrete Element Method

Particle flow discrete element technology has been widely used in various fields of geotechnical engineering,However,the relationship between macro and meso parameters is not completely clear,and macro parameters are more controlled by meso parameters,the calibration has high blindness and inaccuracy,which often results in a long calibration period,low efficiency and low accuracy.Determining a set of methods suitable for calibrating the meso-parameters of rock and soil materials is an urgent problem for particle flow software.In this paper,based on the discrete element method and the particle flow theory,PFC2D numerical simulation technology is used to calibrate the surrounding rock materials of no.5 tunnel in tangxian-shangshi,a water resources allocation project in northern hubei.Through the control variable method,the influence law of the micro parameters on the macro parameters is studied,the relationship between the macro and micro parameters is fitted on the basis of the single factor sensitivity analysis and the multi-factor orthogonal design range analysis,and the multiple linear regression is combined to propose a calibration method for the micro parameters of PFC2D.At the same time,the set of meso-parameters was used to simulate the excavation process of 5#branch tunnel under the support of pipe shed.The results show that:(1)Based on the control variable method,the influence of mesoscopic parameters on macroscopic parameters was studied.The slope of stress-strain curve increased with the increase of effective modulus of particles,and decreased with the increase of particle stiffness ratio.The poisson's ratio decreases with the increase of friction coefficient and increases with the increase of parallel bond stiffness ratio.The compressive strength,crack initiation stress,damage stress,tensile strength and cohesion increase with the increase of the normal strength of parallel bonding.The Angle of internal friction increases with the increase of tangential strength of parallel bonding.(2)Based on single factor sensitivity analysis and multi-factor orthogonal design,multiple linear regression analysis was used to fit the relationship between macro and micro parameters,which improved the efficiency and accuracy of parameter calibration.The surrounding rock of no.5 tunnel in tangxian-shangshi,north hubei water resources allocation project,was calibrated,and the results of numerical experiment and laboratory experiment were compared to verify the rationality and feasibility of the calibration method.(3)Based on the calibrated mesoscopic parameters,the excavation process of no.5 branch tunnel under the support of pipe shed was simulated,and displacement monitoring was carried out on the central axis of the tunnel and at different depths on both sides.Under this set of meso-parameters,the amount of subsidence of the arch top is 2.81mm;the horizontal displacements of the arch waist are 4.74mm and 4.28mm respectively;the displacements of the left and right sides of the arch feet and the arch bottom are also effectively controlled,and the maximum displacements are 5.59mm,2.30mm and 2.34mm.The overall displacement of the surrounding rock of the tunnel is small,achieving the expected support effect.