Structural Rehabilitation of a Critical 54-in. Force Main in Downtown Tampa

The City of Tampa's Harbour Island Force Main was constructed in 1951. This 54-in. sanitary force main conveys an average of 20 MGD of wastewater to the Howard F. Curren Advanced Wastewater Treatment Facility. In 1984, a portion of the original main was relocated to facilitate the construction of the Tampa Convention Center. As part of the relocation project, a critical air release valve (ARV) was constructed at a high point near the northeast corner of the Convention Center. At some time later, the ARV was paved over and lost. In 2018, the City determined that installing a combination surge protection/air release facility on the 54-in. force main in proximity to the paved over ARV would improve the resiliency of the force main. Two attempts to tap into the pipe in different locations failed; it was evident that crown corrosion was an issue. Collaboration between the City, an engineering consultant, and a local contractor determined that the best option was to perform a new tap, 100 ft upstream of the old ARV. This 36-in. outlet would serve as an accessway for inspection and rehabilitation and accommodate the future surge protection assembly. In January 2019, the contractor installed a 36-in. gate valve and performed a hot tap of the force main. The following week, the City organized a nighttime shutdown of the force main. The pumping station was turned off, and the force main was dewatered. A CCTV-mounted robotic pipe crawler used to investigate 750 LF of the force main interior showed areas of crown corrosion went further and was more severe than anticipated. Rehabilitation of approximately 500 LF of the force main was required. The carbon fiber wrap liner that the City planned to use for the rehabilitation requires a prolonged shutdown. However, the force main could not be offline for more than a few hours at a time. The team solved the issue with a bypass plan that kept the pump station in service while the pipe was rehabilitated. The bypass approach meant stringing 36-in. diameter HDPE pipe along the Hillsborough Riverbed 2,500 LF across the Garrison Channel to an existing manway installed on the 54-in. force main on the Harbour Island Bridge. Preventing the HDPE from floating while in operation and transitioning from the channel to the top of the Harbour Island Bridge were hurdles associated with this approach. The rehabilitation included two test layers of FRP Composite lining.