Spanning 19 kilometres along Eglinton Avenue, the light-rail transit line includes a 10-kilometre underground stretch.
The tunnelling process depends on many factors, but contractors are aiming for 12 metres a day on average, according to Gary Kramer, resident engineer of Metrolinx.
The tunnelling should be completed by December 2016, with the majority done by summer of that year, Kramer said.
Meanwhile, machine performance and air quality are being monitored at an operator cab, where cameras show what’s going on inside the tunnel.
Also, the contractors are assembling about nine to 10 rings a day. Once completed, 13,000 rings will line the tunnel.
The Eglinton Crosstown project has been billed as Ontario’s largest public transit construction project in more than half a century. The province said the line will help to ease congestion and create thousands of jobs.
Expected to be in service by 2020, the line will include up to 25 stations and links to 54 local bus routes, three TTC interchange subway stations and GO Transit.