Pre-Stressed Concrete Tank Replaces Four Steel Tanks using Design-Build Procurement
The City of Santa Cruz chose the design-build delivery method for the third phase of this reservoir replacement project to reduce costs and expedite the schedule. The Gateway Pacific Contractors and Bennett Engineering Services design-build team had redesigned the structural portion of the facility’s pump station during Phase 2 construction as a separate project.
The design team worked with the tank supplier, DN Tanks, to develop the six-million-gallon, pre-stressed concrete tank design. Design elements also included potable yard piping to connect to the Phase 2 improvements. Grading and drainage included a perimeter swale.
Due to the required hydraulic elevation of the tank to correspond with the other water tanks in the system—as well as provide space to run the piping under the slab and to the pump station—approximately seven feet of engineered fill was placed under the tank.
The tank was constructed on top of an existing concrete reservoir basin with some structurally weak areas. To bridge the weak spots, the design called for three layers of geogrid fabric to reinforce the engineered fill below the tank. Drainage challenges included creating an adequate slope on the flat site to drain stormwater. Concrete covered swales were constructed to collect runoff, increase the speed of drainage, and carry the stormwater to the carefully selected inlet locations.