Penetration Migration Of Suspended Particles In Porous Media:Pore Structure And Particle Scale Effects

The transport and deposition of suspended particles in saturated porous media have become the key issues of environmental and geotechnical engineering with many researches in contaminated aquifer remediation,nuclear waste disposal,petroleum extraction,inverted filter design,groundwater recharge and grouting reinforcement.Based on the convection-dispersion equation(CDE)of steady state,CDE of unsteady dispersion along uniform flow was derived in this research,the analytical solution of two different boundary conditions were then obtained.The influence and the specific mechanism of pore structure,seepage velocity,gravity,particle size distribution on the transport and deposition behavior were discussed.Moreover,a temperature controlled soil column penetration test device was developed to investigate the influence mechanism of temperature on the migration and deposition of suspended particles in saturated porous media.Finally,strength of the polyacrylamide modified cemented soil was studied and the influence of polyacrylamide on the leaching and seepage of Pb2+ in the modified cemented soil was also investigated.The main contents include:(1)Based on the convection-dispersion equation(CDE)of steady state,CDE of unsteady state was derived in this research,the analytical solution of two different injection methods were then proposed,and the parameters in the equations were discussed.It can be concluded that with the increase of time,deposition coefficient and migration distance,the peak particle concentration decreases.(2)For particles with specific size and shape,particle turbidity can be tested to explain the changes of concentration.Soil column penetration tests were conducted to study the behavior of particles and tracers in two different porous media(glass beads and quartz sand)under 5 seepage velocities,the migration parameters of particles and tracers were obtained based on the analytical solution of the first order particle dynamic dispersion equation.The intrinsic mechanism of the effect of the pore structure and the flow velocity on the migration of particles in saturated porous media is presented;and the physical mechanism of the accelerating effect of the particles in the two kinds of media is revealed.According to the results,a critical seepage velocity can be found in the acceleration process in both media but with different values,beyond which the movement of particles is faster than tracers.(3)The effect of particle size,distribution and gravity on the migration and outflow concentration of particles in porous media was studied based on the soil column test with 4 different gradations,5 different seepage velocities and 2 different seepage directions.It is showed that the breakthrough curves were well described with the analytical solution of a corrected convection-dispersion model that takes into account dispersive flux on the deposition kinetics.The influences of particle size,particle size distribution and seepage velocity on the particle outflow concentration were given.The effect of gravity on the concentration and transport parameters of the particles was studied.The relationship between dispersion coefficient and pore water velocity was discussed and an empirical formula was proposed to illustrate the relationship between dispersion coefficient and mean particle diameter.(4)A temperature controlled soil column penetration test device was developed and to study the influence of temperature on the migration of particles and tracers under 4 different temperatures and 3 different seepage velocities,in the tests particles(larger than 10?m)with 6 typical mean diameters were selected,which have the most obvious influence on the water source heat pumping process.The migration parameters were proposed based on the theoretical analytical solution,the empirical equation of temperature and migration parameters was also proposed.Moreover,the influence of measuring condition on the turbidity of silicone particle and fluorescence value of fluorescein sodium were discussed respectively.(5)The strength of the polyacrylamide modified cemented soil was studied and the influence of polyacrylamide on the leaching and seepage of Pb2+ in the modified cemented soil was also investigated.The influence of temperature on the migration of Pb2+ was investigated,and Freundlich absorption model can be used to demonstrate the isothermal absorption of Pb2+.With the addition of polyacrylamide,the migration behavior of Pb2+ can be changed.