Steady flow in mechanically stabilised earth walls using marginal soils with geocomposites

Marginal soils, which possess suitable mechanical properties but fail to meet the fine particle content and plasticity index requirements for mechanical stabilised earth (MSE) walls, are of particular interest to the construction industry as a potential replacement for granular backfill materials. A numerical analysis of the unsaturated flow was conducted to assess the potential impact of each unsaturated flow parameter on the hydrological conditions in an MSE wall with a geocomposite. The studied results indicate that using marginal soil as the backfill material results in a widespread high-water-content area inside the backfill zone, even when the geocomposite was properly installed. The hydraulic conductivity of the soil at the upstream side has an important effect on the phreatic surface level inside the protected zone. Care must be taken when using a marginal soil with a high fine particle content as a backfill material since the high-water-content area could spread widely inside the protected zone. Moreover, for severe cases in which the upstream water flow rate is greater than the drainage capacity of the drainage medium, using a material with a low or intermediate hydraulic conductivity could result in a more severe increase of the phreatic surface level inside the protected zone.