Design, construction and performance of seepage barriers for dams on carbonate foundations
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ORIGINAL ARTICLE
Design, construction and performance of seepage barriers for dams on carbonate foundations Donald A. Bruce
Accepted: 5 June 2012 / Published online: 11 December 2012 Springer-Verlag 2012
Abstract 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. Keywords Drilling Grouting Karst Cut offs Diaphragm walls Composite walls Introduction As documented by Weaver and Bruce (2007), grout curtains have been used in the USA to control seepage in rock masses under and around dams of all types since the 1890s.
This article has been granted an exception from the standard measurement scale of the International System of Units for scientific publishing as utilized by this journal. D. A. Bruce (&) Geosystems, L.P., P.O. Box 237, Venetia, PA 15367, USA e-mail: [email protected]
For a variety of understandable, if not always laudable reasons, the long-term performance of many of these curtains has not been satisfactory, especially in lithologies containing soluble and/or erodible materials. Foundation remediation in such instances traditionally involved regrouting, often of course using the same means, methods and materials whose defects were the underlying cause of the inadequacy in the first place. Disillusionment on the part of owners and engineers with the apparent inability of these traditional grouting practices to provide a product of acceptable efficiency and durability led to the chorus of ‘‘grouting doesn’t work’’ voices in the industry from the mid-1970s onward. The fact that effective and durable grout curtains were being installed successfully elsewhere in the world, using different perspectives on design, construction and contractor procurement processes, largely escaped the attention of the doubters who, for all their other and obvious qualities, exhibited technological xenophobia. Partly as a result of the anti-grouting lobby, equally in response to indisputable geological realities and challenges and building on technical advances in ‘‘slurry wall’’ techniques, the concept and reality of
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