Site preparation is an essential first step in the process to ensure a successful construction project. Every project poses its own challenges that can be addressed and even mitigated through some prep work. But sometimes, the prep work is so extensive, it feels like a project all on its own, with its own set of challenges. Such was the case for Vogel Bros. on the Krause Pump Station project recently completed for the City of Tampa.
Complete emergency repairs for two of the Krause Pump Station’s influent lines.
This station collects the flows from the downtown Tampa area around the convention center and all flows from Davis Island, so it needs to remain operational.
Create a flow bypass plan.
This solution presented an additional challenge in that the temporary pipe line would need to extend across and along both sides the Hillsborough River. This required a fair amount of prep work, including collaboration from the Army Core of Engineers, US Coast Guard and the Port of Tampa Water Authority.
PROJECT BEFORE THE PROJECT:
Build a bypass to get the flow from the pumps on the west side of the river to the east side where it would empty into a manhole.
They bypass system cannot interrupt boat traffic on the river, so it would have to be submerged. The US Coast Guard required at least 8’ of draft available over the top of the submerged pipe at low tide. The river could only be closed from midnight to 8am to allow for the submerged pipe to be installed.
First, a bathymetric survey found the river to have 12.5’ of draft in the middle of the channel at low tide. The bypass required two 24” HDPE pipe lines to cross the river, so with only 12.5’ of draft, they would have to be sunk as close to the bottom of the navigable channel as possible.
Construction of the two bypass lines occurred on two consecutive nights. Each night, Vogel Bros. floated the north/south portion of the pipe into place and then swung the east/west portion across the river. The two portions were then bolted together by a 90 degree flanged connection. Once the two runs were bolted together, a 900 lb concrete ballast was connected every 8’ to keep the 120 lf section of the pipe submerged. Once the pipe was ballasted and neutrally buoyant, it was filled with river water and submerged in place. Divers then secured the submerged pipe to three 4,000 lb anchors that had been installed the day before. Once the pipe was in place and properly tested, turbidity booms and buoys were installed to keep boat traffic in the channelized portion of the river that had the 8’ draft above the submerged pipe.
With the bypass in place, repairs to the pump station were completed in 10 days. Upon their completion, the removal of the bypass was scheduled and completed in reverse order of the installation.