| With the construction and planning of the South-to-North Water Diversion Project,dams and highway networks in China,there is a growing concern about the migration of particles and its hazards in the field of geotechnical engineering.Most of the existing investigations on particle migration consider the influence of single factors such as hydraulic head or static load,ignoring the external dynamic load disturbances existing during the construction and operation of the project(such as filling,excavation,vehicle driving,construction of structures,etc.).Therefore,in this thesis,the effect of coupled waterhead-cyclic load on sandy soil particle migration is investigated by developing particle migration test apparatus,and a coupled DEM-CFD simulation program is constructed to investigate the microscopic characteristics of particle transport in porous media.The influence law of coupled waterhead-cyclic load on sand-soil particle migration and the related mechanism were investigated from both experimental studies and numerical simulations.The main research contents are summarized as follows.(1)The particle migration test device was developed and the particle migration test of saturated sandy soil-gravel bilayer soil structure was carried out.The effect of changing hydraulic conditions on the development of particle vertical migration and pore water pressure accumulation was investigated.The basic conditions of particle initiation were analyzed.The study shows that the change of water head has a significant effect on the migration pattern of particles in sandy soil layer,the accumulation of pore water pressure is an important factor for the migration of particles,and the degree of liquefaction can effectively discriminate the degree of particle migration.(2)Using the improved particle migration test system,the particle migration test was carried out in sandy soil.The effects of cyclic load frequency and water head on particle migration were investigated.The laws of pore water pressure,water flow and particle migration were analyzed.The effects of particle migration on hydraulic parameters such as hydraulic gradient and permeability coefficient inside the soil were studied.The experimental results show that increasing the loading frequency and raising the water head can significantly induce particle migration.Particle migration causes changes in hydraulic parameters such as permeability coefficients and pore structure,while changes in soil permeability properties and continuous disturbance by cyclic loads intensify particle migration.There is a significant difference in the degree of particle migration at different depths,and the migration of fine particles decreases with the depth of the specimen.(3)Using the coupled DEM-CFD method,the migration-blockage process of fine particles was simulated and analyzed.The effects of hydraulic conditions,particle size and composition on particle transport were investigated.The spatial and temporal development pattern of particle migration and its influence on the microscopic properties of the structure were investigated from the perspective of numerical simulation.It was found that particle size and water pressure magnitude are important influencing factors for particle migration distance and migration quantity.The particle transport interacts and influences with the hydraulic properties of porous media.By analyzing the particle transport trajectories,the classification criteria of particle transport in porous media are proposed.The research results of this thesis deepen the understanding of particle migration characteristics and provide theoretical and experimental support to complete the research on the development mechanism of related diseases.This thesis includes 45 figures,6 tables and 105 references. |
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