Research On Mesomechanical Parameters Of Graded Macadam Based On Triaxial And CBR Test

Graded crushed stone is widely used in pavement engineering as a rock-soil material.Its mechanical properties and deformability in the compacted state have an important influence on the bearing capacity of the pavement base layer.In the past,when studying the mechanical properties and deformability of graded crushed stone fillers,they were usually regarded as continuous media.However,as a typical loose material,grading crushed stone ignores its non-continuous characteristics when studying its mechanical properties and deformation laws,which will lead to some deviations in the results.Discrete element theory and methods start from the constitutive relationship of the bulk material,consider the discontinuity of the bulk material,and establish a mechanical model of the bulk particles contacting each other,thereby realizing the study of their stress behavior.In this paper,the discrete element method is used to establish the particle flow model using the relevant test parameters of grading crushed stone,and the triaxial compression and the California bearing ratio(CBR)test are performed on it.Under the premise of using laboratory test results to calibrate,explore the effect of particle mesoscopic parameters on the mechanical properties of the graded crushed stone model.In addition,using the triaxial compression numerical model of graded crushed stone,the difference between the two particle contact models in discrete element software PFC was studied.It provides a reference for the research on the bearing performance of pavement base with graded crushed stone as filler.The thesis focuses on the mechanical properties of graded crushed stone.The triaxial test results are used to analyze the effects of particle contact model and meso-parameters on the shear strength and Poisson’s ratio of the material.First,the linear contact key model is used to generate the triaxial test sample,and the mapping relationship between k_n/k_s,μ,T_σ,S_σand the values of c andφis established,and the influence of each parameter on the deformation of the sample is studied through the change of Poisson’s ratio;Secondly,restrict the particles to only slide or rotate,and investigate the mechanical properties and shear strength changes of coarse-grained soil under the two movement forms;Finally,a linear model of rotational resistance was selected for the triaxial test,and compared with the test results obtained by the linear contact key model.The characteristics and applicable objects of the two models were obtained,and the linear contact key model was confirmed to be suitable for grading gravel.With the help of the force chain model in the discrete element software PFC,the internal force evolution of the specimen during the CBR test was observed and measured,and the influence of the contact model parameters on the test results and the boundary force was discussed.Observation shows that with the increase of penetration,the particle contact force chain expands like a vertical football,and the displacement field grows in a triangle in the sample.It can be seen from the displacement field that a cone-shaped compaction body gradually appears at the bottom of the sample.Adjust the contact parameters and conduct experiments to determine the influence of each parameter on the CBR value.The results show that the CBR value increases linearly with increasingμ,and the increase of S_σcauses the CBR value and its rate of change to decrease simultaneously.Record the changes in the force at the sample boundary,thus realizing the quantitative observation of the shape of the contact force field in the sample.It is found thatμhas a great influence on the shape of the contact force field,which has a positive correlation with the vertical development of the contact force field.