Design and Logistical Concerns Rehabilitating Twin 1,100-Ft Long Inverted Siphons under the Fox River in De Pere, Wisconsin

摘要

For Green Bay Metropolitan Sewerage District, Michels Pipe Services, of Brownsville, WI, rehabilitated 1,100-foot inverted siphons of 24-inch and 30-inch diameters. The siphons were immediately upstream of the treatment plant, and the logistics of operating the system during the rehabilitation was crucial to the client. Design considerations included excessive external hydraulic force. The siphons dropped nearly 30 feet in elevation from the upstream manhole invert, and then rose 24 feet back to the tail manhole. Of the 1,100-foot inversion distance, 1,000 feet was under water. Consideration was given to high inversion pressures at the inverting face during installation, particularly as the tubes inverted through the deepest sections of the siphon. Care had to be taken not to exceed design limits. Finally, each siphon would carry the entire flow of the system while the other was being worked on, requiring precise calculations for gravity flow capacity. Hydraulic jetting was the original plan for pipe cleaning, but was changed to a method of using air to propel cleaning pigs to finally get the pipe to acceptable standards. Due to the heat-sink effect encountered in underwater siphons, Michels pumped enough cure water to raise the Reynolds number into the turbulent flow regime that would assure cure of the bottom of the pipe. As a Quality Assurance measure, two dedicated thermocouples were pulled 600 feet to the lowest portion of the siphons. The tubes were given extended cure times as a final measure of assurance, and these precautions resulted in a high quality installation.