Design, Construction, and Performance of Seepage Barriers for Dams on Carbonate Foundations

The design, construction and performance of concrete cut-offs, and grout curtains, as dam seepage remediations in carbonate foundations are reviewed. Recent experiences when attempting to build concrete cut-offs through hard and highly permeable rock masses have led the author and associates to develop the concept of “composite cut-offs” for seepage control. A campaign of high-quality drilling, permeability testing and grouting is first conducted to pretreat the very permeable and/or clay-filled zones, to seal the clean fissures and to provide an extremely detailed geological basis upon which to design the location and extent of the subsequent concrete wall (if in fact needed). Bearing in mind that the average cost of a concrete wall is many times that of a grouted cut-off, and that there is currently a shortfall in industry capacity to construct the former, the concept of a “composite wall” is logical, timely and cost-effective. Following presentation of the basic concepts, the paper provides details of a recent case history in Alabama.