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Precast system helps solve stormwater challenges

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delivering precast stormwater retention tank components
delivering precast stormwater retention tank components

Above-ground stormwater retention ponds — whether temporary or permanent — consume valuable real estate and create impediments to construction vehicles during the building phase of large projects.

An expansion project at the >University of Western Ontario (UWO) in London solved this problem by employing a modular pre-cast concrete stormwater detention system.

The construction project, near the university’s >Richard Ivey School of Business, required an underground system that could retain significant volumes of stormwater, while supporting surface construction traffic.

The solution chosen for the project was the StormTrap precast concrete modular storm water detention system.

The U.S. company has partnered with Hanson Pipe & Precast in Canada to supply the product to the Ontario and Quebec construction markets.

The product is delivered complete with inspection access points and connectors.

The 50 precast sections that would be assembled in London to create the retention tank were manufactured at Hanson Pipe & Precast’s Whitby facility.

Once assembled, the reinforced high-strength concrete detention system would stand about three metres tall and retain about 600 cubic meters of stormwater.

The system was installed last year by Blue-Con Construction of London, a contractor specializing in earth moving and excavation.

Blue-Con performed a considerable portion of the expansion project’s groundwork, including site grading, site servicing, parking lot grading, excavation and backfill on sub-contract to EllisDon Corporation, the project’s construction manager.

“We were able to work with Hanson Pipe & Precast and StormTrap to ensure quick and efficient installation that was crucial for this project,” said Brandon Haasen, project manager with Blue-Con.

“The job was the first one we’d taken on of this type. It was essentially a giant puzzle cube made of 50 pieces that needed to be assembled in order.”

Excavators first prepared the site and a firm foundation for the base of the tank, creating a stone bedding that would orient the finished tank to the proper grade and elevation.

“Once I received the plans for the retention tank, I told the Hanson plant in Whitby, Ont. which section I wanted to start with, and they strategically delivered the parts in the order we asked for,” said Haasen.

“We didn’t want to stockpile the tank segments on the construction site. We were working from a sketch of all of the components. The trucks would arrive every 15 minutes, ready to be unloaded in the order needed for each piece to be set in place as we called for them.”

The contractor began with a row of bottom tank sections, which were moved into place with an excavator.

The bottom of the tank was completed, row by row, before the next section was begun.

“For the base units, the components were just lifted on cables by excavator and we butted them up flush against each other in parallel,” he said.

“You get them as tight as possible and create something like a concrete floor or a slab-on-grade. The upper sections are dropped on top of the lower row into a notch that holds them into place.”

The project moved along swiftly.

“We started setting at 7:30 in the morning and assembly was completed by 2 p.m.,” said Haasen.

“When assembly was finished, we wrapped the structure in a membrane that was heat-applied to seal the tank along the joints. Once installed, and covered with earth, the tank is designed to be strong enough to support construction equipment passing overhead, or the construction of a parking lot.”

Blue-Con also installed pre-cast concrete manholes and catch basins supplied by Hanson.

“We were able to supply the school with a high quality storm water management system that has easily solved multiple needs without adding extra expense or time,” said Bob Christensen, senior vice president, Hanson Pipe & Precast, East Region.

Work on the three-storey school expansion project should wrap up soon.

The stormwater detention system will be part of the university’s application for LEED Gold Certification for the project.

by Peter Kenter

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