Rehabilitating and replacing aging infrastructure is one of the largest and most complex issues facing municipalities today. With urban growth and densification, infrastructure managers, engineers, and contractors must find innovative ways to rehabilitate infrastructure while minimizing impact to businesses, the public, and the environment. The City of Edmonton faced these issues in rehabilitating the Groat Road Stormwater Trunk, which had begun to degrade after more than 60 years in service.
The Groat Road Trunk is a corrugated metal plate storm sewer originally built in 1953 by hand tunnelling. The trunk travels along 118th Avenue and Groat Road, discharging into the North Saskatchewan River. It consists of 4 kilometres of 1.7 metre and 2.3 metre diameter pipe, and manholes varying in depth from 7 metres to 17 metres. During an inspection, the City discovered areas of significant pipe wall loss along the pipe invert, as well as on the side walls. Voids, some as deep as 1 metre, were identified under the trunk, as well as on its sides.
The City of Edmonton Drainage Group tendered a $35 million project to rehabilitate the storm trunk as a design-build project. Associated Engineering supported Shanghai Construction Group during the request for proposal stage, developing the design of the rehabilitation works using trenchless construction methods.
As the City’s selected proponent team, Associated provided design and advisory services to Shanghai Construction, and collaborated with Shanghai Construction, their subcontractors, and consultants in weekly meetings for over three years. Our civil engineering scope included fibreglass pipe design, sliplining design, 3D modelling for the segmental design of the fibreglass installation, void/annular space grouting design, construction inspection, and quality assurance. We also completed structural engineering of deep manhole design and structural shaft reviews.
Project Manager, Jason Lueke, tells us, “The City has seen a number of sinkholes due to degraded infrastructure. With the location of the Groat Road Trunk, the voids and potential sinkholes were considered a major risk under this major roadway. These voids are more likely found around drill drops, which this storm trunk used beneath the deepest and busiest sections.”
Chris Lamont, Lead Civil/Sliplining Design and Construction, says, “A major challenge was the degraded condition of the pipe. Void grouting outside of the pipe was a problem, as the grout would shoot back into the storm trunk due the corroded holes in the pipe. To resolve this issue, we had to redesign the tendered grouting plan.”
To install the slipline pipe through small shafts, the team employed 3D modelling to assess feasible pipe lengths.
We also considered the weight and ability of pipes to be transported within the tunnel itself for placing, blocking, and grouting. Shafts were excavated down to the storm trunk to install new structures to replace the drill drop manholes.
Chris tells us, “Working in a live storm sewer, we designed custom, perched manhole foundations, independent of the new fibreglass pipe, eliminating the need for a large bypassing pump systems.” This included over excavating onto undisturbed ground outside of the shaft structure to cast the new support for the manholes, which were up to 17 metres deep.
The project was successfully completed in December 2020. Key personnel on this project were Jason Lueke, Chris Lamont, Linda Chacko, Sam Saunders, Keyton Thompson, Caitlin Luo, and Dusanka Stevanovic.