The New Mississippi River Bridge: Water Utility Relocations

Abstract

This paper is intended to cover some of the challenges associated with designing and overseeing the construction of various antiquated large diameter water mains to meet scheduling deadlines and expectations as set by the client and the DOT. Subjects touched upon include: • Overall project scope • Conflict identification, • Project design/construction phasing, • Existing/proposed utility location, • DOT coordination, • Contractor coordination, • Large water main taps on antiquated existing water mains, • Reliability of valves in older systems for shut-downs, and • Line stops on large water mains, and The design and construction contracts were necessary to make plans to relocate existing water mains to avoid potential identified conflicts with work that was being planned by the DOT for the New Mississippi River Bridge (MRB) project and associated highway improvement projects. The DOT’s proposed work included the approach to the new MRB consisting of aerial portions of highway as well as portions to be constructed on compacted fill at elevations up to approx. 20’ higher than the existing grade. Proposed work also included the construction of new bridges over an existing highway interchange as well as the reconstruction of the existing interchange. The biggest challenge for the water utility was that there were two (2) existing large water main crossings at the existing interchange that was scheduled to be reconstructed. One crossing consisted of an underground 24-inch lock joint concrete water main and another crossing consisted of dual 30-inch steel water mains that crossed the highway on a steel truss bridge structure approximately 18 feet above the highway across four (4) spans supported by reinforced concrete piers. These crossings would need to be eliminated to allow for the planned DOT construction work, however, these mains served as the primary source of water for many cities and