Experimental Study Of Transport Of Soil Particles In Porous Media

The transport and leaching of soil particles are the primary widespread soil-formingprocess, play an important role in pedogenic process and migration of soil materials. Also, ithave significant effects on the environmental behavior of nutrients and contaminant materialsin soil and porous media, and provide important foundation with and provide importantfoundation with evaluate soil quatility and contaminant behavior in water and soilenvironment. In this paper, the retention, outflow and migration of soil particles in porousmedia were investigated, such that we obtained the relationship between these processes andpacked bulk density, solution pH, soil suspension concentration and porou mediumcomposition through a lot of laboratory experiments with soil columns, and the mainconclusions were given as follows:1. The leaching of soil particles is subjected to packed bulk density of columns andsolution pH. Results illustrate that the leaching of＞50μm and＜1μm soil particlesdecreased as the packed bulk density increased, and the leaching of1~50μm soil particlesincreased when the packed bulk density increased, with the nonlinear dependency on thepacked bulk density. Moreover, the leaching of＞50μm soil particles decreased, and thenrapidly increased as solution pH value increased. However, the leaching of1~50μm soilparticles increased, and then rapidly discreased when solution pH increased. The changes inthis two leaching of soil particles are the parabolic curve trend with the changes in solutionpH value.2. The discrepancy in retention and migration of soil particles in different sandy porousmedia relative to concentration of soil suspension is significant. Results show that migrationof soil particle in sandy porous media was influenced by size and concentration of soilparticles as well as composition of the porous media. Retention dominated the transport ofsoil particles through porous media with retention rate increasing with the concentration ofsoil particles, and decreasing with the proportion of coarse sand in porous media. The outflowof total particles,>50μm particles and1-50μm particles increased with the input amount oftheir respective fractions in a power function, while the outflow of <1μm particles increasedlinearly with the input amount. The outflow of total particles increased linearly with the proportion of coarse sand in porous media. The results from this study suggest thatcomposition of porous medium and size and concentration of soil particles are major factorsaffecting migration of soil particles through sandy porous media, and factors that should betaken into full account in the study on fate of soil particles and contaminants in porous media.3. Experimental results show that soil particles transport in porous media wassignificantly influenced by porous medium and soil suspension concentration, and theinfluence mechanisms have significant discrepancy during injection of soil suspension andleaching. Soil suspension concentration play an important role in clay particle transport forLou soil, and porous medium and soil suspension concentration have important effects ontransport of clay particles during the initial stage of injection. When the pore space increased,thus the outflow of sand and silt particles is dominant process. But the outflow of clayparticles is dominant as the discreasing pore space of medium. Porous medium and soilsuspension concentration have not significant influence on the transport of sand particles forred earth. The transport of soil particles in porous media is subjected to the corporate effect ofporous medium composition and suspension concentration.4. The transport of clay and sand particles is dominant during initial stage of leachingand last stage of leaching, respectively. There are similar transport characteristics between theretention of particles in porous media of840μm and420μm. The outflow amount of calyparticles discreased with increasing time, the outflow of sand particles increased as timeextended. Porou medium and suspension concentration have significant effect on the outflowof soil particles for red earth, and the influences of the finer porous medium and highersuspension concentration on transport of sand and silt particles are not significant.These study results indicates that the retention, outflow and leaching of soil particles inporous media are subjected to diverse facters including porous medium composition, soilparticles size, packed soil bulk density, leaching solution pH value and the source of selectedsoil particles. Therefore, when the environment behavior of soil particles in porous mediumand relative nutrients materials and contaminant are analysed and investigated, these fatorsshould be taken into consideration.