Influence of subgrade, temperature and confining pressure on GCL hydration

Geosynthetic Clay Liners (GCLs) are often used in waste disposal facilities. In order to act as a barrier as cover or bottom liner, GCLs must hydrate and swell under a confining pressure. According to the French Committee for Geosynthetics (Fascicule n 12, 1998), the gravimetric water content of the bentonite must be at least 100%. GCLs are commonly installed at their initial bentonite water content (around 10–15%), for practical reasons and ease of installation. Therefore, the duration of the hydration period (vapour and liquid migration from the subgrade) appears to be an important issue in terms of confining performance. This question was addressed during laboratory and field experiments performed on a natural sodium bentonite GCL and aimed at examining the influence of several parameters: subgrade (sand versus clay), temperature and confining pressure.Results illustrate the high influence of the subgrade permeability and water content on the bentonite final water content level and hydration kinetic. As could be expected, sandy soils allow a faster hydration and higher water content than clayey soils for a same period of observation. The hydration rate and the final gravimetric water content at equilibrium both increase significantly when temperature rises. But a low temperature, such as tested during the experiments (5 °C), drastically slows down the rate of hydration but also the final water content, whatever the material. The vertical stress also appears to influence the hydration rate by providing a better contact between the GCML and the soil. The water content at equilibrium appears to be not improved by that confining stress whatever the materials and the temperature.