An inside view of the pre-cast pipe sections during construction of the Davis Brook Storage Facility.Click here to enlarge imageCity staff discussed solids deposition at great length. The tunnel was eventually designed with a v-shaped bottom to maintain velocity over a wide range of flows.
Flow control, when required, is by SCADA operated modulating sluice gates at the inlet and outlet of the tank. Generally, control is not expected to be needed, with operation relying on the outlet capacity of the structure under most conditions. The existing 42-inch interceptor was retained for additional storage capacity and to allow the tank to be taken out of service if necessary.
Construction of the project began in early September 1998. The pre-cast sections were manufactured by American Concrete Industries. The company procured three sets of custom designed forms to construct the individual sections. The sections were reinforced for H-20 wheel loading, used 5,000 psi concrete, and had steel bolt pockets cast into each corner. ACI provided 1 inch thick by 4 inch wide flexible butyl resin sealant and 3/4 in. stainless steel threaded rods, nuts and washers to join the sections. Each section was five feet in length and weighed 21,000 pounds. They were delivered to the site on flatbed trailers.
Construction was by Lou Silver Inc. On a typical day, an excavator dug the trench slightly ahead of the pre-cast installation. Clean excavated materials were used for backfill of the pre-cast sections already installed. Other materials, such as rocks, logs and materials otherwise not suited for backfill, were stockpiled on site for other uses.
Once subgrade was reached, the excavator placed 12 inches of crushed stone in the bottom of the trench. Workers adjusted the grade using lasers.
While these activities were taking place, another crew was attaching lifting bolts to a pre-cast section. Then a crane lowered the section into the excavation where workers placed strips of sealant against the face of the tongue end. Once the sealant was in place, the crane placed the section against the previously installed section. Workers used hand-operated hydraulic jacks and a custom designed apparatus that fit into the bottom bolt pockets to pull the sections together.