A review of research approaches to contaminant transport in saturated deformable clay under coupled hydro-chemico-mechanical processes

One way to manage municipal solid waste and control leachate leaking into the surrounding environment is to bury them inside an isolated compacted clay liner. Despite the low hydraulic conductivity of clay, there is a possibility of fluid flow or chemical species transport. Phenomena that lead to fluid flow are Darcian flow and chemico-osmosis flow which are respectively caused by hydraulic and concentration gradients. On the one hand, membrane behavior of clayey soils causes chemico-osmosis flow. On the other hand, diffusion and advection cause chemical solute to transport. Due to the importance of the subject, this article provides a comprehensive review of the coupled effects of these phenomena with different research approaches. After categorizing analytical approaches into three groups of experimental, theoretical, and numerical and discussing them in detail, the coupled governing differential equations are presented. These equations describe the hydro-chemico-mechanical processes that influence solute transport in landfills. More importantly, key assumptions and findings of selected research with implications for design of contaminant barriers are criticized and discussed. Eventually, a proposal is put forward for future research in this area based on the current shortcomings and research challenges.