San Jose / Santa Clara Digesters Upgrade
Location: San Jose, CA
Owner: City of San Jose
As part of San Jose’s biosolids upgrade, four digesters were structurally modernized by replacing corroded external prestressing with a value-engineered post-tensioning and shotcrete system that met seismic and AWWA standards while reducing cost and construction time.
PROJECT DETAILS
Four prestressed digesters located in San Jose, CA were a part of the city’s first phase of upgrades to their biosolid processing facilities. The project involved converting the digestion process from mesophilic to temperature-phased anaerobic digestion (TPAD).
With a conventionally reinforced core wall and an external bar-wrapped prestressing system, the original digesters were covered with three inches of shotcrete. The phase one project included structural wall upgrades as well as roof and floor replacements of the original digesters.
Tstrata’ crews performed the demolition and removal of the external wall shotcrete. Each digester was de-tensioned and the pre-existing bar-wrapped systems removed. For the repairs, crews installed a new external post-tensioning system as well as new seismic restraint connections at the floors and roofs. An external layer of shotcrete was then applied over the post-tensioning systems. The walls were upgraded to withstand seismic loads as well as provide the 200 psi residual compression required by the AWWA D115 Standard.
The structural design initially required three separate layers of external post-tensioning and shotcrete to wrap each tank. Tstrata was able to value engineer a solution that only required 1.5 layers of post-tensioning by spacing strands tighter at two inches on center, thereby maximizing spacing efficiency. This value engineering approach provided a more cost efficient solution as well as a shorter construction schedule for the city without jeopardizing tank performance.
