| The compaction and strength characteristics of soil-rock mixtures,a common material in the field of transportation infrastructure,significantly affect the stability of subgrades.Since the mixing degree is a key property of soil-rock mixtures,it is too bold to consider the soil-rock mixture as a homogeneous material considering the fact that in most cases the soil and rock are unevenly mixed.The study on the compaction effectiveness and strength characteristics of soil-rock mixtures under the varying mixing degree is helpful to understand the road performance of soil-rock mixtures.In this dissertation,the compaction and strength characteristics of the soil-rock mixtures under different mixing degrees were investigated based on laboratory tests and DEM(discrete element method)simulations.The main contents and achievements are as follows:(1)Aiming at the shortcomings of the existing mixing degree indices in geotechnical engineering,a new index based on the distribution curve of particles with depth was proposed.In the evaluation of geotechnical samples,the proposed index can avoid the statistical errors raised by the limitations of statistical methodology,and give a more reasonable evaluation result of mixing degree when compared with other previous indices.(2)The video instance segmentation(VIS)technology based on the spatial granular network(SG-Net)was proposed.The negative effects on visual processing were neutralized by adding a timing characteristic fusion module and introducing a tracking head with long sequence external storage.This technology can accurately capture particle motion information under vibration load,calibrate the main contact parameters of DEM models from the perspective of particle motion,expand the verification methods of DEM simulation,and improve the reliability of simulation results.(3)The influence of the mixing degree on the compaction effect was investigated based on the laboratory test and DEM simulation of vibration compaction.The final void ratio and the variation of void ratio decrease with the increasing mixing degree,and the higher the coarse particle content is,the more obvious the influence of mixing degree is.The influence mechanism of mixing degree on the compaction effect is explained by the evolution of mesoscopic parameters throughout the compaction process.In other words,as the mixing degree increases,the distribution of coordination numbers and strong chains becomes more uniform;thus,the transfer effect of force enhances,the void ratio gap between layers decreases,and the compaction effectiveness improves.(4)The evolutions of damping energy,slip energy,rolling slip energy,strain energy,particle kinetic energy,and potential energy were analyzed The damping energy dissipation is closely relevant to the variation of void ratio,which is not affected by the mixing degree in the early loading stage and the effect increases in the later loading stage.The slip energy dissipation and rolling slip energy dissipation increase with the increasing mixing degree in the early loading stage,while decrease with the increasing mixing degree in the later loading stage.The evolutions of slip energy dissipation and rolling slip energy dissipation indicate that not all particle sliding is beneficial to the decrease in void ratio,yet the particle rotation tends to decrease the void ratio.(5)The effect of mixing degree on the strength of soil-rock mixtures was investigated through the large-scale triaxial test and the corresponding DEM simulation.The strength of loose samples and the peak strength of dense samples increase with the increasing mixing degree,while the critical strength of dense samples is not affected.The variation mechanism of strengths is revealed by the number of contacts,the size of contact forces,and their distribution.With the increase in mixing degree,the number and spatial uniformity of coarse-fine contacts increase,and the uniform distribution of strong contacts is the main reason for increasing strength.Additionally,the quantitative relationship between force-fabric anisotropy coefficients and strength parameters further explains the strengthincreasing mechanism.Figures 110,Tables 8,References 231. |
