A Case Study on Design, Testing, and Installation of One of World's Largest Subaqueous Pressure Pipelines

摘要

The Bay Aqueduct, a 144-inch diameter, 3600 ft. long reinforced concrete cylinder pipe (RCCP) subaqueous pipeline installed in 2000 under Lake Mead's Boulder Harbor near Las Vegas, Nevada, is one of the largest subaqueous pressure pipelines in the world. The Bay Aqueduct was designed for a nominal flow of 600 MGD with a peak flow of 800 MGD, an internal pressure of 160 psi under working conditions, a maximum pressure of 300 psi, 80 ft. of external water head, and up to 20 feet of soil cover at the banks. The 144-inch diameter RCCP was designed in conformance with the AWWA C300 standard and the AWWA M9 manual with modifications to meet project requirements; the reinforcement of the 12 inch thick concrete pipe wall consisted of a 5/8-inch thick steel cylinder and three reinforcing cages: an inner circular, an intermediate circular, and an outer circular cage. The design procedure and special design features of the pipe and its joints, including the specially designed corrugated grout bands, will be discussed and presented. Since the Bay Aqueduct is one of the most critical elements of the Southern Nevada Water Authority's Lake Mead Intake No. 2 Project, qualification testing was required before full-scale pipe production began. The qualification tests, which will be briefly summarized and discussed, included hydrostatic joint testing and structural testing of the pipe to verify the flexural, radial tension, and diagonal tension and shear performance of the pipe, and to compare the observed performance with predictive analytical models. The project also required placing precast concrete saddles over the pipe to counteract buoyancy since the subaqueous pipeline was dewatered after installation to grout the external joint spaces with cement mortar from inside through small grouting nozzles for corrosion protection and also to install an internal welded steel butt-strap across the joints. This paper will also discuss the installation procedure in 90 ft. deep water. This procedure consists of joining three 144-inch diameter RCCP pipe sections on shore to form a 50 ft long assembly weighing 180 tons which was floated and transported to the installation site tugged to a laying barge.