Abstract: The Long Term Performance of Geocomposite Drainage Materials Used as Capillary Break Layers

In arid regions, groundwater is often saline and the water table can be relatively close to the surface. Capillary rise above the water table brings dissolved salts near to the surface of the ground which can result in severe problems for both vegetation and the foundations of building structures.

For vegetation to survive, it is essential that there is a barrier between the saline ground and the clean ground and that this barrier also provides good drainage. A capillary break layer is installed above the highest level of the water table so that the void is never totally saturated by ground water and that the capillary break has high in-plane flow capacity to remove excess precipitation and irrigation water that enters through the clean ground above.

Chloride ions within saline moisture can be drawn into stone and concrete where the resultant chemical reaction causes expansion and weakening of foundations and the degradation of architectural finishes such as marble flooring. An effective barrier is to provide a capillary break layer between saline ground and clean ground. The capillary break layer creates a void across which capillary rise of saline moisture is prevented.

In both instances it has become common to use geosynthetic drainage layers to provide this capillary break. This paper introduces the application of capillary break layers and discusses in detail the need for ample understanding of the in situ and long term performance characteristics of the different types of drainage composite.