Comparing Performance Of Geocomposite Filter-Drains And Granular Filters Under Canal Lining

In many irrigation projects where the groundwater table is high part of the canals may be located below the water table. In this situation groundwater applies uplift pressure to the bottom and side panels of the canal lining. This phenomenon may cause deformation, displacement and or rupture of the concrete panels or other damage which results in high maintenance costs to the project. The most effective way to control the uplift pressure under the canal lining is to provide a filter-drainage system under the lining. Up to the present, granular filters have been the most common material in use. In some cases application of granular materials is not an easy task due to high costs involved and/or environmental impacts. In recent years geosynthetic materials (geocomposites) have been employed as replacement for granular filters. In the present study the behaviour of geocomposite material as a filter drainage layer under canal lining has been investigated using a physical laboratory model. The results of the experiments showed that a geocomposite layer of adequate thickness can fully relieve the uplift pressure and discharge the drained water effectively. Also the efficiency of the filter-drainage under bottom concrete panels only and both bottom and side concrete panels were studied. The results showed that providing a filter under the side panels has no significant effect on the drainage capacity of the system. As the weight of the concrete panel on a geocomposite layer would cause some deformation of the material its effect was also considered in the physical model. The results of this part of the experiments showed that by applying the weight of the concrete lining the effective thickness and thus permeability of the geocomposite is reduced and its effect should be considered in the design of geosynthetic filters.