Experimental Study On Piping Erosion Mechanism Based On The Flow Character Of Cohesionless Soil

Seepage failure is a main reason of the hydraulic structure accidents such as embankment and earth-rock dam.Piping is the most popular failure mode.There are many potential erodible pores in the dams due to the construction technology,design,defects of the soil.the direction,size and distribution of the pore is stochastic and the flow direction could be the different directions.The motion path of the fine particles which situate in the different direction pores are different due to drag force direction and the process of piping are different.The paper which is based on the financial supports from the National Natural Science Foundation of China “Researchs on movable porous media phase transition mechanism and the influence on preference flow path development in piping(No.51409129)”,through indoor experiment,the piping progress which is related influencing factors of piping progress were studied.Based on experimental research,it discussed the piping progress and critical condition r,in the influence of the grain size distribution,hydraulic condition and density,etc.The paper research results are as follows:(1)the piping testing system at different flow direction:The system consists of flow direction adjust gear,axially pressure loading device,and-water isolating-gathering device,data collection system,water level control system,etc.This system can adjust the flow direction from 0°to 180°by flow direction adjust gear and monitor the progress of piping at different flow direction.Axially pressure loading device can provide 0KPa-400 KPa and simulate the progress of soil piping located in different elevation.The variation of fine particle accumulated amounts,the flow velocity,the processing head,etc are monitored by the system.(2)Soil seepage failure critical condition:The soil seepage failure critical condition could be divided two categories that soil self-conditions and hydraulic condition.Self-conditions are particle size gradation and soil compactness,etc.Hydraulic condition mainly refers to the critical hydraulic gradient.This article mainly analyze the relationship between Soil seepage failure critical hydraulic gradient and flow direction,particle size gradation,compactness,stress state,etc.Beyond that,the international relationship among the factors were also analyzed.(3)The preference flow zone development in piping:Driving force of the fine particle movement stems from the drag force which caused by seepage flow.Motion law of the fine particles will change with the force direction.Based on it,the coloured sand are utilized as tracer which could show the position of the fine particles.The particles' location and motion path,the sources of the particles and the preference flow zone development are observed and recorded.(4)Reveals the variation of the loss of fine particles: Piping process is the foundation of the piping danger warning and working out countermeasures.The influence of the seepage direction,grain size distribution,density and stress state on the piping process is studied.On this basis,the empirical formula of the moving particle loss percentage changing with the time of piping is obtained.In the meantime,the loss of fine particles when specimens are damaged in the varies stress state by the seepage is studied.