Here’s how a massive subway station is being dug below a Toronto park

Toronto’s forthcoming $27 billion Ontario Line subway has breezed through several early construction milestones on its way to linking Exhibition Place with the shuttered Ontario Science Centre along 15.6 kilometres of new rapid transit infrastructure.

The project recently celebrated the start of excavation for the tunnel’s launch shaft at the future Exhibition Station ahead of a roughly six-kilometre journey for a pair of large tunnel boring machines that will soon be lowered into the ground.

Among the six downtown stations along the Ontario Line’s tunneled run through the city centre, work is racing along for the future Moss Park station under construction within the public park of the same name at Queen and Sherbourne.

The site along the south edge of the park fronting Queen Street East is now in the midst of a sizeable excavation to form a large void where the new station will be constructed. 

Metrolinx shared new photos of the sprawling dig site on Friday via the Ontario Line account on X.

📍 Moss Park, where excavation work is underway to build a brand new underground Ontario Line station. Once complete, this station will ease congestion on popular surface routes including the 75 Sherbourne bus and 501 Queen streetcar. pic.twitter.com/wvpUzm1sUz

— Ontario Line (@OntarioLine) December 13, 2024

Here’s how Metrolinx is going about excavating an enormous subway station from a public park.

Work began in mid-2024 with the start of piling work around the perimeter of the future station. This critical stage saw piles inserted into the ground to stabilize the surrounding soil, allowing for safe excavation conditions.

Next, starting this summer, work began on the actual excavation of soil and rock to form shafts to the station’s level, a process scheduled to stretch into summer 2025. 

During this process, crews have been removing surface layers of soil using a combination of excavators and bulldozers.

Excavation is being carried out in sequential layers, with every strip of material removed from the pit revealing another portion of the pile wall formed earlier in construction.

As layers are removed, lateral struts are installed to support the pile walls in a process known as braced excavation.

The pit will eventually extend 30 metres below street level.

The final phase of the excavation process, lasting through fall and winter 2025, will see the station box reinforced with concrete ahead of the arrival of tunnel boring machines that will soon begin chewing their way below downtown Toronto.

A June update from Metrolinx stated that construction would advance with the arrival of a tower crane at the site in September, though this milestone has since been delayed to January 2025.

This tower crane will allow the actual construction of the new station infrastructure, and later, the surface-level buildings that will connect commuters to the Ontario Line trains below.

Once all is said and done, the area currently being excavated will be restored to park conditions.