Keller’s crawler cranes putting the BC 40 Hydromill and Mechanical Clam Bucket in place
Photos: courtesy of Robert Vienneau, PhotographicMemories.ca
Located at the mouth of the Don River, Toronto’s Port Lands was created over decades by infilling what was once one of the largest wetlands on Lake Ontario. The area is one of the largest underdeveloped stretches of downtown waterfront in North America; long considered undevelopable due to its vulnerability to flooding from extreme weather events brought on by climate change.
The attempt to create value in the Port Lands is nothing new for the City of Toronto. Over the last decade, Waterfront Toronto, Toronto and Region Conservation Authority, the Toronto Port Lands Company and the City have all worked together to find a solution that could develop this underused waterfront property to generate significant economic opportunities, in addition to protecting southeastern portions of downtown Toronto from potential flood damage.
The result of this collaboration has been the ambitious, $1.25 billion Port Lands Flood Protection and Enabling Infrastructure Project (PLFPEI) that first broke ground in November 2018.
PLFPEI is one of the most intensive earth moving projects in recent history, requiring the excavation, movement and placement of more than one million cubic metres of soil and fill (more than enough to fill Rogers Centre) to raise the grade across much of the project area by an average of two metres.
“This is of one of the largest waterfront revitalization projects in the world and certainly one of the most ambitious and significant infrastructure projects in Toronto’s history,” said Toronto Mayor John Tory at the groundbreaking ceremony. “The project will unlock the potential of underutilized waterfront lands, protect the area from flooding and create new parks, natural areas and neighbourhoods where people will live, work and play.”
PLFPEI will completely transform approximately 290 hectares (715 acres) of underdeveloped industrial zone into a new and vibrant – and resilient – downtown neighbourhood called Villiers Island. The economic importance of this development cannot be overstated. A third-party economic impact study conducted by urbanMetrics in 2016 estimated that the project will generate approximately 51,900 full-time years of employment, $5.1 billion in value added to the Canadian economy and $1.9 billion in revenues to the three orders of government.
The project will also provide critical flood protection by creating a naturalized mouth for the Don River, which will be surrounded by new parks, green spaces and public amenities, in addition to new wetlands to support native species better.
“Toronto’s waterfront is the gateway to the city and its Port Lands area has bountiful potential, but it has been underutilized for decades,” said Richard Males, field technician at Keller North America. “The new Don River channel will allow flood waters to flow safely into Lake Ontario, concurrently providing habitats for wildlife, residential development and a new community oasis close to the heart of the city.”
The local branch of Keller North America operating out of Acton, Ont., along with support from Keller’s specialty services division, came onto PLFPEI in December 2020, and recently completed Phase 1 of the project using its diaphragm wall technology. Diaphragm walls are installed as a series of panels (or trenches) excavated to specified depths and widths while being supported by an engineered bentonite slurry. A rebar cage is installed and the excavation is filled with concrete to form a reinforced panel.
Diaphragm walls were selected over secant piles because of the significant advantages the technology brings, including fewer construction joints, a stiffer wall with less overall deflection and substantial schedule and financial benefits for the client.
“The diaphragm wall was designed to act as a temporary bulkhead and support of [the] excavation system to allow for the excavation of the new west mouth of the Don River into Lake Ontario,” said Males. “It is also acting as a permanent water cut-off for the new river channel to prevent contamination migration from existing soils. This innovative solution offered a reduction in the overall construction schedule and exceptional cost savings for Waterfront Toronto.”
Using its Bauer BC 40 Hydromill hydraulic cutter, Keller installed the elements of the diaphragm wall with a 25- to 30-centimetre overlap to meet excavation verticality tolerances, as well as to ensure high quality joints between the panels and to comply with the project’s water tightness requirements.
“The BC 40 Hydromill has hydraulic cutter wheels, which can excavate through an array of soil conditions – including hard rock – and is supported by a large crane (Liebherr HS885 HD hydraulic crawler crane), which handles the weight and supply of hydraulic power to the Hydromill,” said Males. “The BC 40 Hydromill was the workhorse of our operations and performed phenomenally through the sand, silts, soft clay and shale bedrock where the machine’s output is among the best in the industry.”
The diaphragm wall at Port Lands was constructed using two different panel designs: primary and closure panels. The Keller team first excavated ‘Primary Panels’ in a process requiring three ‘bites’ to complete. The first bite on one side of the trench, the second on the opposing side and a third completing the excavation in the middle; repeating until the desired depth was reached. The length of the primary panel is typically three times the width of the Hydromill, approximately 7.3 metres long.
Once the Primary Panels were excavated and poured, Keller was able to commence ‘Closure Panels’ installation, a single-bite panel that overcut 25 to 30 centimetres of concrete to create the watertight panel joint. As part of the project, Keller also incorporated a special ‘TShape-Panel’ (both Primary and Closure) in the design along the West Plug Wall, which increased the stiffness of the wall structure to act as the temporary bulkhead.
At Port Lands, bentonite powder (a specialized clay used in several geotechnical applications to support the excavation process) was mixed with water in a colloidal mixer to a specific engineer-design specification, left to hydrate for 12 hours and then pumped to the panel as bentonite slurry. The slurry supports the excavation walls to allow Keller to excavate to depths up to 44 metres with less than 0.5 per cent vertical deviation at the tip of the panel on this project.
A large-scale desanding and treatment process was at the heart of Keller’s Port Lands operations, producing, recycling and redistributing the bentonite slurry to the excavation site. It was also critical in maintaining a slurry head within the guide wall – and specifically above the known water table – to avoid panel collapse during excavation.
“The BC 40 Hydromill was the workhorse of our operations and performed phenomenally through the sand, silts, soft clay and shale bedrock.”
– Richard Males, Keller North America
“Our desander separates sand from the bentonite slurry by pumping the slurry over a series of shaker screens, separating larger particles through a hydrocyclone to remove finer sands and silts,” said Males. “Slurry is pumped tangentially into the system to create a vortex. The heavier sand particles are separated from the mud by centrifugal force and exit the bottom of the cone, and the mud with finer particles exits out the top.”
Prior to installing the rebar cage, the Hydromill completes a final cleaning. The process uses the Hydromill wheels and suction pump to remove any sand or silts that have settled to the bottom, as well as cleaning the sides of the excavation. This process is critical to avoid cement contamination during the pouring process.
Large prefabricated reinforced rebar cages of varying sizes and configurations were lowered into the panel in one length using a 200T Liebherr 895 Crawler Crane, due to the immense length and weight of cages, which each weighed up to 50,000 pounds. Once the cages were lowered into the panel, the Keller team began installing up to four tremie tubes through the reinforced cage to near the bottom of the excavation.
“This tremie system allows concrete to be placed from the bottom of the excavation, displacing the bentonite slurry in the panel – which is then pumped back to the desander for recycling,” said Males. “As sections of tremie tubes were removed between rounds of concrete, it was vital to maintain a minimum distance of tremie tube embedment to ensure the quality of the concrete in the panel. When the concrete elevations were achieved to the design requirement, all the sections of tremie tubes were removed and the panel was complete. The process was then repeated for the next panel.”
“This project will act as a steppingstone to see the continued growth of the diaphragm wall technology in Canada.”
– Richard Males, Keller North America
There were several challenges encountered at the Port Lands project, which included unforgiving winter weather along Lake Ontario, contaminated soil conditions at the site, large volumes of concrete required to complete the primary panels and – of course – working through the Covid-19 pandemic. The overall success of this project has helped to showcase Keller’s status as a premier geotechnical contractor and their ability to execute a major project with global strength and local focus.
“Keller continuously seeks to provide the highest levels of safety, quality and innovative – yet cost effective – solutions for our clients and this project demonstrated just that,” said Males. “This project will act as a steppingstone to see the continued growth of the diaphragm wall technology in Canada.”
The next phase of PLFPEI will see the relocation of Cherry Street and help mitigate any construction impacts on the surrounding community as much as possible.
Phase 2 is scheduled to commence in early 2022, and once complete, other contractors will continue the excavation of the Don River towards Lake Ontario. The entire project is expected to wrap up in late 2023/early 2024. 