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Published: 1991

Total Pages: 96

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The purpose of this study was to investigate methods of repairing stilling basins of hydraulic structures underwater, thereby eliminating costly dewatering operations, and to develop a plan to evaluate products or concepts. The effort focused on methods using precast concrete or prefabricated steel panels. This report reviews underwater repairs of the Old River Low Sill Control Structure, Upper St. Anthony Falls Lock, and Kinzua Dam. An overview of the required underwater construction tasks is presented (preplanning, mobilization, surface preparation, installation of field anchors and panel supports, installation of panels, concrete placement, and inspection). Construction methods for underwater repairs are discussed, including the use of divers, wall enclosures, caissons, cofferdams, above-water platforms, and submersibles. Panel design factors considered are abrasion resistance, uplift forces, joints, and weight. Other panels considerations include shapes, joints, bond, and supports. It is feasible to relay on divers in underwater repair projects, because most stilling basins have low-water depths of 40 ft or less. Steel panels or composite steel-concrete panels are preferred to concrete panels because of the abrasion resistance of steel. Design details become important to assure that the steel panels remain serviceable under vibration and uplift forces from high- velocity water flow and impact from rocks in turbulent flow.