DEM Numerical Simulation Study On The Evolution Process And Influencing Factors Of Internal Erosion Of Soil

The seepage deformation of poorly graded coarse grained soil is an important reason affecting the impermeable safety of sandstone rockfill dam and gravel dam foundation.The only case of failure of high earth-rock dam in China,Gouhou dam,is closely related to the seepage deformation of the dam body.In recent years,China will build a number of high face sand and gravel dams,such as Aertashii dam,Dashixia dam,etc.In addition,there are also a lot of high earth-rock dams built on sand and gravel and other coarse soil overburden dam foundation,such as Luding dam,Pubugou dam,Huangjinping dam,Changhe dam,etc.,seepage deformation control is of great significance to project safety.It is found that seepage failure is one of the two main causes of earth-rock dams.The study on the mechanism,process and influencing factors of the seepage deformation of coarse grained soil is of great significance to the construction and operation safety of the project.Many scholars have studied the influence mechanism of total hydraulic gradient,soil material density and particle gradation on seepage deformation through laboratory tests.It is difficult to monitor microscopic phenomena such as particle migration and local hydraulic gradient in laboratory tests,so numerical tests have become an important supplement to the research methods of seepage deformation.Based on discrete element software PFC3D and external CFD fluid solver,for single particle size of coarse and fine particle groups mixture of bad gradation of coarse grained soil,considering the interaction of solid particles and pore water,this study simulating seepage deformation of soil under a certain hydraulic gradient,and analysis the initial content of fine particle,relative density,the hydraulic gradient of seepage deformation process,and observe the movement of specific fine particles.The development of soil permeability stability was also studied.Under the effect of a certain hydraulic gradient,the fine particle migration in soil sample goes through two stages,initial stage,the velocity of particles is low,only the fine particles near the seepage exit part move relatively quickly,then with the development of seepage deformation,seepage channel and migration channel gradually open,the fine particles near the entrance and central of soil sample will be speed up.The particles near the wall move faster,while the particles far away from the wall move slower,which is related to the higher local porosity of soli near the wall.During the development of seepage deformation,the fines content at the outlet and inlet of the soil sample and the local hydraulic ratio decreased,while the fines content in the middle of the soil sample increased and the local hydraulic gradient decreased slowly.When the initial fines content in the soil sample reached 40%,the fines content in the middle of the soil sample will increase and silting layer gradually appeared.The soil seepage deformation depends on the permeability stability of the entire seepage path,and the internal stability determined by the geometric relationship of the soil particle size cannot fully represent the soil permeability stability.The protection conditions of seepage outlet will also affect fine particles transport in the process of seepage deformation.In the case of the same fines content of soil sample,the higher the compactness of soil sample,the less the loss of fines.The increase of hydraulic gradient can obviously accelerate the movement of fine particles,but it is not possible to drive the destruction of soil samples with small hydraulic gradient if the gradation meets the unstable conditions.Because the particle not only needs to move in the direction of the water flow,but also needs to overcome other resistance,and also needs to move horizontally to find the pores.