By Lynda Myer
Commencing work process on the Scarborough Subway Extension, has been done by Metrolinx on 23 June 2021. While the northeast corner of Sheppard and McCowan, is determined for launching the shaft for the TBM by crews, fences are up, drill rigs are on site and crews are working hard to retain the momentum Metrolinx has set over the past year.
The advantages of this new advancement, will be a 7.8 km long subway service further into Scarborough and providing a reliable, smooth ride to and from downtown Toronto and within the city’s growing east end. In order to progressing the planning and procurement, Metrolinx and Infrastructure Ontario teams have acted quickly since revealing the preliminary design business case in February 2020, so that tunnelling can start on the project. While crews have been commenced working at the launch shaft site, where the tunnel boring machine will finally be lowered into the ground, just a few weeks ago, Strabag was granted the tunnelling contract for the project.
Large drill rigs – over 33 m tall – will be used to create a watertight, foundational wall around the 28 m wide, 80 m long and 30 m deep launch shaft, before excavation can begin.
Implementing a strong, water-tight dam, which keeps soil and water in place and out of the dug area, will be possible by installation of a secant pile shoring system, using a series of concrete columns with steel reinforcements, called piles.
Hence for beginning the installation process of this shoring system, crews excavate a path circa the perimeter of the launch shaft where the piles are due to be installed. Circular forms along this path are the indication points of 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.
Due to creating expanded support below the base of the launch shaft so that water doesn’t get into the shaft, the piles go much deeper than the base of the launch shaft, although the launch shaft only requires to be dug almost 30 meters deep.
Strabag aims to drill more than 300 of these secant piles into the ground during the future few weeks to create a water-tight wall around this excavation and the next step will be providing the proper space by completing the shoring system and excavating the area by crews for the arrival of the TBM in early 2022.
A public competition is due to be hold in later this year to select source names for the new TBM.
