Research Challenges Involving Coupled Flows in Geotechnical Engineering

Coupled fluid, chemical, heat, and electrical flows are common phenomena that arc relevant to a wide variety of applications in Geotechnical Engineering, including the use of engineered clay barriers for waste containment, electro-osmosis for soil consolidation, highly compacted bentonite buffers for high-level radioactive nuclear waste disposal, and electrokinetics for soil contaminant removal. among others. For all of these applications, a fundamental understanding of coupled flow phenomena is required, including the basis of the various phenomena. the potential effect of the phenomena on fundamental soil behavior, and the applicability of the phenomena in both natural and built environments. This chapter highlights some of the advances over the past approximate three decades, including the effects of osmotic phenomena (chemico-osmosis, electro-osmosis, and thermo-osmosis) on the mechanical behavior of clays, the formulations and measurement of coupled flow phenomena, the distinction between phenomenological and microscopic (physical-based) formalisms, and considerations with respect to both saturated and unsaturated soil conditions. Based on the description of these advances, research challenges pertaining lo the study of coupled flow phenomena for Geotechnical Engineering applications are identified

Bromide transport before, during, and after colloid mobilization in push-pull tests and the implications for changes in aquifer properties

Περίληψη: Bromide breakthrough curves from push-pull tests were obtained at two wells before, during, and after citrate injections to assess how citrate-induced colloid mobilization affected physical aquifer transport properties. Tailing and incomplete bromide recoveries (67–95%) could not be fit with a conservative advection/dispersion model, and the results of batch tests using aquifer solids implied bromide was not significantly sorbing. Thus we modeled the bromide returns considering advection, dispersion, and rate-limited diffusive mass transfer between mobile and immobile regions by fitting αr, the radial dispersivity; α, the rate-limited mass transfer coefficient; and β, the volumetric ratio of immobile-to-mobile domains. Statistical t-tests indicated that the changes in aquifer transport parameters at a well where colloid mobilization was limited were not significant at a 95% percent confidence level. However, the substantial colloid mobilization at a second well corresponded to significantly decreased αr and β, while increasing α between premobilization and both mobilization and postmobilization. The changes in aquifer parameters and their correlation to the recovered colloidal mass are consistent with the idea that pore-clogging colloids were mobilized and/or reorganized during citrate injections. The results suggest that flushing a site under the right conditions with citrate could open up immobile regions and substantially reduce remediation time and costs by liberating contaminants whose transport would otherwise be diffusion limited.Presented on: Water Resources Researc