Dynamic Response Analysis Of Coarse Particle Packing In Existing Heavy Haul Railway Based On PFC3D

Coarse-grained soil is widely distributed in nature and rich in reserves,and is often used as a filling material for heavy haul railway roadbeds.With the increase of axle load,vehicle speed and transportation frequency of heavy haul railways,the mechanical characteristics of coarse-grained fillers under cyclic loading have attracted the attention of many scholars.At present,research on coarse-grained soil is mainly divided into two methods: indoor dynamic triaxial test and numerical simulation.It is difficult to obtain the evolution process of internal displacement and crack failure of coarse-grained soil from the meso-level.The macro-mechanical properties of coarse-grained soil are inherent.The mechanism cannot be well revealed.As a kind of discrete element method,PFC is one of the main methods of meso analysis.In the PFC dynamic triaxial numerical simulation,the establishment of a numerical model with the same macromechanical response as the laboratory test is the basis of the dynamic triaxial numerical simulation.Selecting the appropriate contact model and calibrating the mesoscopic parameters are the key to the dynamic triaxial numerical simulation.Different meso-analysis methods revealing the intrinsic mechanism of macro-mechanical properties of coarse-grained soil is the ultimate goal of dynamic triaxial numerical simulation tests.Therefore,based on the research results of indoor dynamic triaxial tests,this paper conducts PFC dynamic triaxial numerical experimental research,proposes a method of meso-analysis,and analyzes the effects of meso-parameters on macro-mechanical characteristics.The main research work and results of this article are as follows:(1)Based on the existing laboratory dynamic triaxial test data of coarse soil,the PFC2 D dynamic triaxial numerical model was established,and the numerical simulation parameters were calibrated.The final simulation results were well fitted to the laboratory test results.By comparing the simulation results of the PFC3 D model and the PFC2 D model,the feasibility and correctness of the two-dimensional model to represent the three-dimensional force is verified.(2)Analyzed the evolution of the contact force,porosity,coordination number and the distribution of displacement field within the sample.It is found that the normal and tangential contact forces increase with the increase of dynamic stress,but when the dynamic stress is higher than the critical dynamic stress,it does not increase.The porosity and coordination number can reflect whether there is damage inside the sample.When the porosity increases and the coordination number decreases,damage occurs inside the sample.With the increase of the dynamic stress amplitude,the shear band inside the sample is formed and developed.The shear band angle gradually increases from 0 ° to 45 °.The greater the confining pressure,the smaller the shear band width of the sample.The water-containing conditions changed the failure mode of the sample.The saturated sample showed shear failure,but a certain tensile failure occurred in the unsaturated sample.(3)Analyze the variation law of saturated sample pore water pressure under different confining pressures and different dynamic stress amplitudes from a meso point of view,and obtain: for saturated samples,the maximum pore size of the sample under different confining pressure and dynamic stress amplitudes The pressure ratio has not reached 1.0,and the sample will not liquefy,but bed defects such as mud and mud may occur.The larger the dynamic stress amplitude and the closer the maximum pore pressure ratio to 1.0,the more likely to be diseases such as mud turning and mud slumping.The greater the confining pressure,the smaller the pore pressure ratio is,and the less likely it is that mud-turning and mud-sucking diseases will occur,which means that mud-turning and mud-sucking diseases are more likely to occur on the bed.(4)Analyze the influence of each meso-parameter on the macro-deformation characteristics,provide ideas for the calibration of the meso-parameter,and provide suggestions for subgrade filling and improvement.It is finally concluded that the stiffness ratio has little effect on the results.The greater the linear effective modulus and bond strength,the less likely the sample is to break.When improving or filling the subgrade,layered filling should be adopted to increase the linear effective modulus between the particles,and the earth-rock mixed filler should be selected or the subgrade geomaterials should be set to increase the bonding strength between the particles.