FSSD Digester Post-Tensioning Repair
Owner: Fairfield-Suisan Sewer District
Specialty Contractor: PULLMAN
Safety concerns from corrosion and spalling at the Fairfield-Suisun Sewer District digester tank were resolved by using innovative external post-tensioning as temporary shoring during repairs, restoring the structure’s integrity and long-term reliability.
PROJECT DETAILS
The Fairfield-Suisun Sewer District (FSSD) Wastewater Treatment Plant serves over 135,000 residents in Solano County, California, providing wastewater treatment, recycling, and stormwater management. The plant’s digester tank was originally constructed with reinforced concrete and both the core wall and dome ring band are circumferentially prestressed using high-strength steel wire wrapped around the tank in a continuous helix. The mild steel and post-tensioning reinforcement had visible spalling and corrosion, raising safety concerns.
Tstrata conducted a structural analysis to determine the best repair strategy. Due to access limitations and a sloping interior floor, traditional shoring methods were not feasible. The team designed temporary shoring utilizing external post-tensioning tendons that were installed on the ring beam before de-tensioning the existing tendons.
PULLMAN, an exclusive licensee of Tstrata, executed the repairs. The scope of work included removal and installation of shotcrete as well as de-tensioning and installation of post-tensioning. The successful completion of this project enhanced the safety and reliability of this critical tank.
