Internal Erosion Of Soil:Particle Size Evolution And Constitutive Modelling

It is a common problem in engineering construction that seepage flow may lead to fine particle loss and internal erosion.This phenomenon will significantly change the particle size distribution of soil and affect its mechanical properties.Furthermore,it may cause potential harm to the strength and stability of geotechnical structures.At present,there is no unified standard for the classification of internal erosion at home and abroad.Researches on the particle size evolution caused by internal erosion were mostly focused on qualitative analysis,and the gradation of soil was not considered into the constitutive model as a model variable.In this thesis,the particle size evolution law of soil considering internal erosion is investigated.Combined with PFC numerical simulation test,the influence of internal erosion on the stress-strain characteristics of soil is studied,and a constitutive model considering the particle size evolution of internal erosion soil is established.The main work is summarized as follows:（1）The particle size evolution of soil is studied when internal erosion caused the loss of fine particles.Based on the research of particle size evolution in the field of particle breakage,a particle loss Markov gradation transfer matrix model is established to describe the particle size evolution law of soil in the process of fine particle loss.The model is simple in form,and only the effective loss rate,an index representing the loss degree of soil particles,is introduced.Compared with the classical Kenney loss index,it is found that the effective loss rate is approximately linear with the Kenney loss.（2）Based on particle flow discrete element software PFC^3D,a series of numerical simulation tests with different confining pressures and different erosion degrees are carried out to explore the influence of internal erosion on the pore ratio,stress-strain behavior,strength,contact force and other mechanical properties of soil.At the same time,the study shows that the critical state line in e-p’plane shifts upwards with the loss of fine particles in internal erosion.The influence of different particle contact types and erosion sample preparation methods on soil mechanical response is also investigated.（3）A constitutive model considering the gradation evolution of internal erosion soil is established,and the proposed constitutive model is verified by numerical simulation results.The results show that the constitutive model can describe the stress-strain characteristics of erosion soil well under different confining pressures and different erosion degrees,and the quantitative description between the loss amount of fine particles and stress-strain relationship of soil is given as well.This thesis includes 36 figures,11 tables and 119 references.