As 2025 kicks off, the Ontario Line project is making major strides downtown, and this year marks a key phase of construction: the year of digging. Across the southern portion of the line, excavation work is intensifying, with a variety of different methods being used to carve out the underground path for the city’s newest subway line.  

From open cut excavation at Queen, Moss Park, Corktown and the tunnel portal near Exhibition, to the use of roadheader machines to create caverns at Queen-Spadina, Osgoode and King-Bathurst stations, to the arrival of the first tunnel boring machines (TBMs) for deep tunnelling, 2025 will be a year of significant progress below ground.  

Cut-and-cover excavation at key sites  

The cut-and-cover method was used to build the initial stretches of Toronto’s first subway lines, and its long history dates back to the early days of subway building, such as London’s Underground and New York’s subway, both of which relied heavily on this technique. As most people would guess given its relative simplicity, this is an ancient construction technique that has been in practice for thousands of years. 

Cut-and-cover excavation is continuing this year at Moss Park and Corktown, where crews are digging deep into the earth, up to 40 metres below the surface.

At Queen, construction needs to take place in the roadway because of the heavily built-up infrastructure both above and below ground in the area – particularly the TTC’s existing Line 1 Queen subway station. Excavation is starting here soon, to carve out space for a station below the existing TTC station.  

Roadheaders creating pathways to caverns  

At the King-Bathurst, Queen-Spadina and Osgoode station sites, roadheaders are being deployed this year to help build underground spaces. Roadheaders, machines traditionally used in mining, use the sequential excavation method to cut through hard rock and create small spaces. In 2025, our roadheaders will continue to carve the pathways that will connect the main Ontario Line subway tunnels to future underground caverns that will eventually house underground stations.   

Crews will also begin digging these caverns this year, which will accommodate station platforms, elevators, escalators and other necessary infrastructure. The cavern at King-Bathurst will be approximately 135 metres long, 23 metres wide and 17 metres high. For comparison, the length of a football field is about 100 metres. Its width is roughly equivalent to the length of a tennis court, and its height is nearly as tall as a five-story building!

Two Ontario Line tunnel boring machines will join the Metrolinx family  

This year, twin TBMs will embark on a journey from Germany to Toronto, where they will play a crucial role in shaping the Ontario Line. These machines are set to dig the twin tunnels that will stretch from Exhibition to the Don Yard, just east of the Don River, carving through rock and soil as deep as 40 metres below ground. Once they arrive in Toronto, the TBMs will be carefully assembled and prepared for their monumental task.

From cut-and-cover excavation to the use of roadheaders to the arrival of new TBMS, digging will bring the Ontario Line several steps closer to reality in the year ahead. Once complete, this brand new, 15.6-kilometre subway line will bring 15 new stations to the city and ease congestion on the existing transit network, thanks to connections to more than 40 other travel options along the way.