In total, the machines bored 6.4 kilometres (about 4 miles) of twin tunnels and placed 8,493 rings or liners to build the tunnels.

Two pairs of tunnel boring machines (TBMs) built the tunnels for the project: “Holey” and “Moley” are one pair, “Yorkie” and “Torkie” are the second. Holey and Moley bored the tunnels south of Finch West Station, or “the Southern Tunnels”. Yorkie and Torkie built all of the tunnels north of Finch West Station, or “the Northern Tunnels. The TBMs build the tunnels, using pre-cast reinforced concrete rings.

Southern Tunnels

In the summer 2011, Holey began tunneling from a launch shaft at the future Downsview Park Station site. Holey completed its first drive — 1.6 kilometres (or about 1 mile) May 1, 2012 after placing 1,041 rings. On December 7, 2012 Holey broke through the headwall at the extraction shaft on the east side of W.R. Allen Road, just north of Sheppard West Station (which were currently calling Downsview Station). In total, Holey drilled 1.2 kilometres (about ¾ mile) and placed 785 rings for the second drive. You can watch a video showing how a subway tunnel is constructed and see the breakthrough of Holey here.

In late fall 2011, Moley started boring in the tunnel beside Holey toward Finch West station and arrived at the extraction site on Keele Street June 4, 2012, after placing 1,025 rings. On March 5, 2013, Moley broke through the headwall at the extraction shaft just north of Sheppard West Station after placing 800 rings and completing 1.2 kilometres (about ¾ mile) of subway tunnel.

Holey and Moley finished the 2.8 kilometer (1.7 mile) Southern Tunnels portion of the project by placing 3,651 rings.

Northern Tunnels

In November 2011, Yorkie began the first northern tunnel drive from a launch shaft near the future Pioneer Village Station and broke through at the extraction shaft on Keele Street at Murray Ross Parkway — north of Finch West Station — on November 29, 2012, after placing 1,110 rings. Torkie began tunnelling in February 2012 and also broke through at the extraction shaft on November 29, after placing 1,119 rings. This made project history as the first double-TBM breakthrough, a rare occurrence in North America. Yorkie and Torkie completed 1.7 kilometres (1.05 miles) of twin tunnels on these two drives. (You can view a video of the double breakthrough here.)

On March 19, 2013, Torkie began tunneling south from the Highway 407 Station site and arrived on June 13, 2013 at the Pioneer Village Station extraction shaft, north of Steeles Avenue West and east of Jane Street. On April 2, 2013, Yorkie launched from the Highway 407 Station site, boring southbound in the adjacent tunnel to Yorkie, and broke through at the Pioneer Village Station extraction site on June 14, 2013. During this drive Yorkie and Torkie, bored 1 kilometre of twin tunnels and placed a total of 1,365 rings. The contractors then dismantled both TBMs and moved them to the Highway 407 Station northern launch shaft.

On August 15, 2013, Yorkie began the second-last tunnel drive from the Highway 407 Station, boring north toward the Vaughan Metropolitan Centre Station. On October 7, 2013, Yorkie broke through the headwall at the extraction shaft. Yorkie completed 935 metres of tunnel and placed 623 tunnel rings in the tunnel.

Torkie is created the tunnel beside Yorkie, and began boring the final drive for the project on September 13, 2013. Torkie tunneled 938 meters (3,068 feet) of tunnel and placed 625 tunnel liners. On November 8, 2013, Torkie completed the final drive for the project.

Now that the tunnels are built, contractors can begin the next phases of tunnel work, installing:

• invert slabs (providing a flat bottom for the track), safety walkways and conduits;
• tracks;
• the traction power system;
• the signalling system;
• the communications systems.