Experimental Study On Piping Erosion Mechanism Of Cohesionless Soil

Seepage failure is one of the important reasons that cause failure of the embankment and other geotechnical engineering.Piping is the most common type of seepage failure,According to incomplete statistics,nearly half of the dam accident is caused by the piping in the world.The development process of piping damage is a multi-field couping process of seepage field,stress field and strain field in internal soil,mainly related to particle composition,density,flow direction,hydraulic gradient,stress state and other factors.but at this stage the research on the laws of the piping is majority concentrating on the composition and density of the particles,other factors are considered less,it can't reflect the influence of the different conditions on the development of piping comprehensively,it is difficult to establish the relationship between the actual situation and the parameters of soil piping.Therefore,in order to determine the variation of piping parameter in the process of cohesionless soil piping failure,and to reveal the mechanism of cohesionless soil piping erosion,and to establish the mathematical model for the piping development,method of model test is used to explore the piping rule of the cohesionless soil in this project.The main results are as follows:? Develops a cohesionless soil piping erosion test system.The test system includes a lot of important parts,such as pressure chamber,pressure/volume controlling device,the upstream water supply device,sand-water separation device and data acquisition systems,it can simulate the process of piping under different stress states.And it can measure the critical hydraulic gradient and the erosion ratio.The relationship between particle loss and volume deformation during piping process can be determined.? Reveals the variation of the critical hydraulic gradient for cohesionless soil piping.The experimental research on cohesionless soil piping erosion is carried out by using the test equipment.The influence of stress state?hydraulic gradient?grain size distribution and density on the critical hydraulic gradient is studied.Based on cohesionless soil seepage experimental phenomena,and combined with seepage velocity changing with hydraulic gradient,the lower critical hydraulic gradient and the higher critical hydraulic gradient is proposed,these two kinds of types can describe the critical gradient for the cohesionless soil seepage failure.? Reveals the variation of the erosion rate for cohesionless soil piping.In view of the effects of stress state,hydraulic gradient,grain size distribution,density and other factors on the soil erosion rate,through the effective monitoring in the process of the test,clear the relationship between the cohesionless soil piping erosion rate and soil properties and the stress state.Loss of fine particles has a great impact on the strength properties of cohesionless soil,based on the experimental results,the critical loss amount is proposed to describe the soil collapsing phenomena.? Reveals cohesionless soil piping erosion-volume deformation coupling laws.By using the monitoring data of volume change during the experiment,the influence of particle size distribution,density and hydraulic gradient on the volume deformation for cohesionless soil piping is summarized under complex stress state,and obtain the law of interaction between the soil erosion rate and the volume deformation.Based on the variation law of the gushing sand,the experience formula of the moving particle loss percentage changing with the time of piping is obtained.This formula can describe the impact properties of the hydraulic gradient and the stress state for piping erosion rates effectively.