Study On Mechanism Of Fine Particle Migration And Filter Clogging Effect In Drainage System Of Expansive Soil Channel Slope

Expansive soil is greatly affected by environmental changes,and it is very difficult to maintain a relatively stable environment in actual engineering.Therefore,it is necessary to start from the expansion mechanism of expansive soil and carry out relevant research combined with different environmental factors for the expansion problem in engineering construction.The first section of the middle route of the South-to-North Water Diversion Project is located above the expansive soil layer in the Taocha area of Nanyang.During the operation of the channel,it is affected by expansive soil.The efficiency of the drainage system in some sections has been reduced,and cracking and bulging phenomena have appeared on the slope surface of the channel section.In order to explore the reasons and process of siltation in the drainage system of expansive soil channels,after analyzing the action mechanism of soil and drainage filter layer in drainage engineering,expansive soil collapse tests and multiple sets of geotextile siltation tests were carried out.By analyzing the test parameters such as collapse test indicators(collapse amount,mass concentration,particle size distribution)and siltation test indicators(gradient ratio GR,permeability coefficient K and geotextile unit volume contentμ),this paper studied the influence of initial water content of soil samples on collapse characteristics and particle size distribution characteristics of collapsed flow loss,and analyzed initial water content of soil samples,hydraulic gradient and experimental geotextile specifications.The influence of factors such as geotextile permeability siltation characteristics.According to the collapse characteristics and particle characteristics of expansive soil,this paper analyzed the mechanism of geotextile siltation and determined the siltation evaluation index and predicted the effective period of geotextile.This paper draws the following conclusions:(1)The collapse process of expansive soil can be divided into three stages:the rapid collapse stage,the collapse development stage,and the collapse stable stage.The corresponding mass concentration of the suspended liquid during collapse can be divided into three stages:concentration increase stage,concentration decrease stage,and concentration stable stage.The mass concentration of the collapsed suspended liquid will eventually tend to a stable value.The change process of the collapse amount has a certain lag time with the change process of the mass concentration.(2)During the rapid collapse stage,the particle size distribution curve of the lost particles is bimodal,and the main lost particles have particle sizes of 1-4μm and 10-12μm;during the collapse development stage,the bimodality of the particle size distribution curve disappears,and its particle size characteristics are similar to those of the original soil,mainly 1-10μm;during the collapse stable stage,the bimodality of the particle size distribution curve is restored,and the lost particles are mainly 1-3μm in particle size.(3)An increase in hydraulic gradient will drive larger particles to move and increase the seepage velocity of particles.In the soil-geotextile composite system,an increase in local hydraulic gradient will enhance its permeability capacity,drive some deposited fine particles to move again,change the seepage environment,release some hydraulic gradient and cause gradient ratio fluctuations.(4)Particles that continue to seep after collapse stabilization are prone to cause siltation in geotextiles.With an increase in initial water content of soil samples,the mass concentration of suspended liquid decreases after collapse stabilization,and(9of fine particles in suspended liquid increases,indicating that the amount of fine particles in suspended liquid after collapse stabilization is proportional to its initial water content.(5)The seepage siltation process of drainage systems can be divided into three stages:soil seepage stage,initial siltation stage and stable siltation stage.During soil seepage stage,the composite system’s seepage coefficient fluctuates and decreases.During initial siltation stage,the composite system’s seepage coefficient continues to decrease and drainage efficiency begins to decrease.During stable siltation stage,fine particles continue to deposit in composite system and geotextile performance gradually deteriorates with increasing usage time until it cannot meet drainage requirements.(6)The service life of geotextiles with a unit area mass of 150g/m~2 is longer than that of geotextiles with a unit area mass of 200g/m~2 or 300g/m~2.In expansive soil slope engineering projects,drainage holes that are below groundwater level throughout the year should use geotextiles with a unit area mass of 150g/m~2 as much as possible for drainage work.It is recommended that they be replaced every 2.8 years as one cycle to ensure normal drainage inside slopes.