Liquid migration in an encapsulated bentonite layer due to geomembrane defects

In some applications of geosynthetic clay liners (GCLs), the bentonite layer component of the GCL is encapsulated between two geomembranes. One of the benefits of this configuration is to decrease the risk of shear strength decrease due to bentonite hydration. The liner thus formed is typically used to contain a liquid, such as water or leachate. If there is a defect in the upper geomembrane, some of the liquid initially contained above the upper geomembrane migrates into the bentonite. Similarly, if there is a defect in the lower geomembrane, some of the liquid initially contained in the soil underlying the lower geomembrane migrates into the bentonite. The liquid that has migrated into the bentonite then migrates laterally in the bentonite between the two geomembranes. The analyses presented in this paper provide analytical solutions for the one-dimensional and axisymmetrical cases. In each of the two cases, two types of analytical solution are provided: an equation that gives the time required for the hydration front to reach a certain distance from the geomembrane defect, and an equation that gives the rate of liquid migration through the defect. It appears that the time required for the hydration front to reach a relatively small distance (e.g. a few meters) is very long (i.e. of the order of decades). Therefore a very long time is required for the development of a large hydrated area that could significantly impact shear strength. Also, a very long time is required for liquid migrating through a defect in the upper geomembrane to reach a defect in the lower geomembrane, thereby creating a leakage path from the medium overlying the upper geomembrane to the medium underlying the lower geomembrane. The analyses also show that the rate of liquid migration through the upper geomembrane defect is very small compared with the rate of leakage through the same defect in the geomembrane component of a typical composite liner where the soil component is clay or a GCL. The results of these analyses demonstrate the effectiveness of a liner that consists of a layer of bentonite encapsulated between two geomembranes, and provide a method to quantify this effectiveness.