Large Diameter Welded Steel Pipe Deflection: Working Beyond the Traditional

In response to nearly 20 years of drought conditions and declining water levels in Lake Mead, the Southern Nevada Water Authority (SNWA) has constructed a new Low Lake Level Pumping Station (L3PS) and new discharge aqueducts to convey the water to their existing water treatment plants. The two 144-in. diameter discharge aqueducts needed to extend under a 45-ft high causeway embankment. Traditional analysis methods referenced from the American Water Works Association and the United States Bureau of Reclamation sources resulted in very costly trench and backfill methods for this deep pipe cover. A further analysis of external loadings beyond the traditional methods was warranted. To streamline the construction schedule, reduce risk, and reduce construction costs, a two-dimensional finite element analysis was preformed to better predict the deflection of the aqueducts through the causeway. Several simulations were run, along with sensitivity studies, to determine how the pipe zone material properties would impact the deflection and determine the best overall design. Detailed field measurements were taken during construction to assess the accuracy of the assumptions and calculations. This paper presents the traditional and non-traditional design of these 144-in. diameter pipe sections, with results of actual field conditions.