Metrolinx Tunneling Under Two Highways for GO Transit Project

Urbantoronto.ca
December 24, 2019

A major infrastructure upgrade is quietly progressing below 21 lanes of active traffic at the busy interchange of Highways 401 and 409 in northwestern Toronto. A recent Metrolinx blog post details work to construct a new rail tunnel just east of Etobicoke North GO station that will allow the upcoming upgrade to two-way, all-day train service on the GO Transit Kitchener line.

We last looked at the project in July shortly after work commenced, and in the busy months since, crews first prepared the site of the new tunnel through the berm below the highways, and adjacent to the existing GO underpass that remains in service. Most recently, heavy equipment arrived to begin boring the 176-metre tunnel using technology called Sequential Excavation Method (SEM). SEM allows excavated material to be removed safely and consistently by dividing the tunnel into upper and lower sections, which are excavated separately in one-metre increments. This method is best suited to shallow mined tunnels through dry soil, as is the situation here.

Preparations for the current boring phase included the installation of canopy tubes in the spring. These were put in place using the auger boring method, where a series of 12-metre-long pipes were driven hydraulically with a 0.795 metre diameter drill bit to create a solid structure for the tunnel excavation.

Since then, additional specialized pieces of equipment have arrived to assist the excavation. Among them, a front end loader known as a ‘scooptram’ carries away roughly five tonnes of material at a time.

As the tunnel is excavated, crews line the tunnel walls with a thin layer of shotcrete fed through pressurized hoses. This lining holds the tunnel in place, and is followed by the installation of a reinforced temporary lining known as welded wire fabric.

Metrolinx, GO Transit, Toronto, Etobicoke, Highway 401, 409
A "shotcrete robot" spraying pressurized concrete to the excavated top of the tunnel, image via blog.metrolinx.com

The application of the shotcrete is shown in a brief video included in the Metrolinx blog post.

Before the project is completed in 2021, crews will excavate 31,000 cubic metres of material from the work site, and line the new tunnel with over 8,000 cubic metres of shotcrete.