Metrolinx has officially broken ground on the Scarborough Subway Extension today (June 23), though work is already well underway.

The importance of the day is to mark a moment when the signs of progress on the project start becoming very real – the shovels in the ground excitement of something big happening. In this case, an extension that will be part of a much larger connected system of transit routes and options and opportunities.

The new extension will bring 7.8 kilometres of subway service further into Scarborough and provide one reliable, smooth ride to and from downtown Toronto and within the city’s growing east end.

Since the release of the preliminary design business case in February 2020, teams at Metrolinx and Infrastructure Ontario have moved rapidly to advance planning and procurement so that tunnelling can begin on the project. Just a few weeks ago, Strabag was awarded the tunnelling contract for the project and even before then, crews have been hard at work at the launch shaft site, where the tunnel boring machine will eventually be lowered into the ground.

“This project is about delivering the reliable and modern rapid transit the people of Scarborough need,” said Phil Verster, Metrolinx CEO and President. “We’re so glad that shovels are now in the ground and people are hard at work to turn long-discussed plans into reality.”

Fencing is up

For those who live or work in the area, they would have noticed new fencing and signage being installed around the site in the past few weeks. The signs and messages on the fencing are a reminder that this is really happening and work is underway to deliver the long-awaited subway extension. It also serves as a safety reminder for pedestrians and workers to be vigilant and use caution when they’re moving around the area.

The drill rigs have arrived

Area residents may have also noticed some very large drill rigs on the site, like the ones pictured below. These drill rigs, which are over 33 metres tall, are used to create a watertight, foundational wall around the launch shaft before excavation can begin.

And this is no casual digging exercise – it’s a massive hole that will be about 28 metres wide, 80 metres long and 30 metres deep. To give a sense of how big that is, the hole will be about as deep as a 10-storey building is tall.

To keep such a massive excavation open and safe for the duration of construction and tunnelling, some special excavation supports need to be drilled into the ground with the drill rigs. Strabag crews have started installing these supports, commonly referred to in the construction industry as a shoring system. The type of shoring system being used for the Scarborough Subway Extension launch shaft is called a secant pile shoring system.

A secant pile shoring system uses a series of concrete columns with steel reinforcements, called piles, to create a strong, water-tight barrier that holds soil and water in place and out of the excavated area.

Breaking ground by drilling deep

The installation of this secant pile shoring system marks the beginning of the excavation process at the launch shaft site and also the official start of construction on this important project for Scarborough.

To begin installing this shoring system, crews dig up a path around the perimeter of the launch shaft where the piles need to be installed. Circular forms are placed along this path to identify where the piles need to be inserted into the ground.

The drill rigs have augers, a giant drill bit, that drills into each circular formation and inserts piles deep into the ground, around the perimeter of the future excavation.

Although the launch shaft only needs to be excavated about 30 metres deep, the piles go much deeper than the base of the launch shaft. This is a critical requirement to extend support below the base of the launch shaft so that water doesn’t get into the shaft.

Strabag will be drilling over 300 of these secant piles into the ground over the next few weeks to create a water-tight wall around this excavation.

After the secant piles are drilled and the shoring system is fully installed, crews will begin excavating the area to prepare for the arrival of the tunnel boring machine in early 2022.

Stay tuned for a community contest later this year to crowdsource names for the new tunnel boring machine.

As work officially begins, Metrolinx will continue to keep the community informed about progress and what to expect during every phase.

Stay up to date on all the progress being made by signing up for the Scarborough Subway Extension newsletter and following the project on Twitter @ScarbSubwayExt.