Study On The Hydrodynamic Characteristics And Particle Migration Mechanism Of Subgrade Soil-rock Mixtures

Transportation infrastructure construction has made great achievements in China,and the maintenance of existing lines is becoming the research direction in the future.Relying on the National Excellent Youth Science Fund,the High-speed Railway Joint Fund and other projects,the study on the hydrodynamic characteristics and particle migration mechanism of subgrade soil-rock mixtures were carried in this dissertation,including the theories,equipment development,experiments and numerical calculations.The moisture migration and the hydraulic response evolution of subgrade soil-rock mixtures under dynamic load were analysed.The driving mechanism of the particle suspension and migration induced by the pumping effect and the internal erosion and permeability evolution of subgrade soil-rock mixtures were revealed.The main results are as follows:(1)A tailor-made test system was independently developed to stimulate particle migration by applying vibration load,which could serve as a beneficial reference for developing particle migration testing circumstance.A mathematical model for predicting the moisture migration of the subgrade soil under dynamic load is established.The theoretical and experimental results show that increasing the loading frequency causes the pore water to migrate upwards and enrich,which promotes the generation of mud pumping.Based on the rescaled range(R/S)analysis method,the hydrodynamic response evolution of the subgrade soil-rock mixtures was discussed,and the effects of fine content,loading times and repetition period on the excess pore pressure and its gradient evolution were analysed.(2)Focusing on the hydrodynamic response and particle migration mechanism in rail embankments,a series of particle migration tests in layered gravel-sandy silt column were carried out,including the different soil properties,water supplement and loading conditions,etc.The test results show that increasing load frequency and load magnitude simulates more fine particles to migrate upwards into the gravel layer at a higher rate.The movement of particles with different sizes and the evolution of the physical parameters of the mud were analyzed.The hydrodynamic response and slurry turbidity evolution in the gravel layer were revealed,and the effects of gradation,water level and loading conditions on particle migration and permeability were obtained.The hydrodynamic response in the saturated gravel layer was investigated,and the pumping effect was proposed to account for the oscillating excess pore pressure gradient generated by liquid sloshing in track bed.An analytical model of the pumping effect under vibration field was established.Combined with laboratory tests and numerical simulations,the detachment,suspension and migration behaviour of particles in porous media during mud pumping were discussed.(3)Based on the above theories and laboratory tests,it is proposed that mud pumping in subgrade soil-rock mixtures is closer to internal erosion than soil liquefaction,that is,the non-skeleton particles are detached from the soil skeleton by hydrodynamic force and migrate under the entrainment of pore fluid.Considering the multi-field and multi-phase coupling effect,a mathematical model of the particle migration induced permeability evolution of the subgrade soil was established,and the effects of particle migration on the permeability evolution of the subgrade soil were revealed.139 figures,8 tables and 220 references...