Large Diameter Feedermain Takes Advantage of Grooved Technology

With increasing pressure from the general public to provide safe, reliable, long-lasting infrastructure, large diameter feedermains that deliver potable water supply to large municipal populations are under scrutiny. Design decisions to provide robust long life infrastructure require proper evaluation of design loads and loading combinations. These often include internal pressure and external loads, environment conditions including seismic activity, soil types, and geotechnical hazards, and pipeline settlement concerns. Designers of large diameter feedermains often avoid large and costly cast-in-place reinforced concrete thrust blocks in favor of internally restrained field joints designed to transmit tension forces from one pipe to the next. Current technology for field joining of individual pipes includes field welding, flanging, and grooving. Welded and flanged connections provide a rigid connection at the joints, however many designers are uncomfortable placing flanged connections underground because of potential leakage that may go undetected. Grooved technology, pioneered in World War I to provide fuel and water to the battlefields of Europe is nearly 100 years old but, heretofore, has not been widely used until recently to join segments of large diameter feedermains. Both flexible and rigid joints can be supplied using grooved technology. This paper will provide a case study of a large diameter feedermain design and construction to include alternative analysis, material, and joint selection strategies with focus on grooved technology to provide thrust restraint yet flexibility at field connections. Geometric considerations for grooved technology will be presented. A typical AWWA Manual M11 harnessed joint design to provide flexibility will be compared to restrained flexible joint technology. Example problems will be presented.