What’s 22 metres long, weighs 115 tonnes and can work its way through 1,000 tonnes of material every day? It’s not a Brachiosaurus – it’s a roadheader. These powerful rock-cutting machines are used around the world in road and rail tunnel projects, and we’re using them to build the Ontario Line.

Roadheaders can accurately operate in a wide range of rock formations. With careful planning and their advanced computer systems helping guide them, these machines use a rotating cutter head (the pineapple-shaped part on the front) with tungsten carbide teeth that can chew through incredibly hard rock.  

The cutting head is attached to an arm, which can freely swing side to side or up and down. But what about all the material it excavates? Roadheaders are also equipped with gathering arms that move the excavated rock in front of the machine to a conveyor belt system on its tail where it simultaneously loads a truck. The roadheader is also equipped with a crawler track, allowing it to move forward during excavation.  

Compared to a tunnel boring machine (TBM), which is limited to excavating a space that is roughly equal to its own size, the pivoting arm of a roadheader allows for flexibility in the shape of the tunnels or caverns it excavates. Roadheaders work in what’s known as the sequential excavation method, which takes advantage of the natural strength of the surrounding rock or soil when digging underground. As segments of tunnel are excavated, temporary support systems are implemented such as concrete and rock bolts, holding the tunnel’s shape as work continues. The flexibility and maneuverability allow it to work in smaller, more restricted areas to create underground space for the Ontario Line’s future stations.  

We’re deploying four roadheaders to help build underground spaces at the King-Bathurst, Queen-Spadina, Osgoode and Queen station sites. Before we can excavate those caverns, we need to get the roadheaders underground by way of an excavated shaft. Each machine arrives on site separated into six main components, each weighing no more than 45 tonnes – the weight capacity of the crane that will be used to lower the disassembled roadheader pieces.  

The Ontario Line will completely change the way we travel across the city of Toronto with stops from Exhibition Station to the Eglinton Crosstown LRT at Don Mills Road, allowing riders to get from one end to the other in under 30 minutes.  

Once complete, the Ontario Line will accommodate nearly 400,000 trips every day, bringing nearly 50,000 jobs within distance of a short transit trip and reducing daily car trips by 28,000.  

Its 15 stops will offer over 40 connections to other modes of transit, including GO trains, streetcars and bus lines.