Scarborough’s three-stop subway extension continues to take shape with crews starting work on the project’s headwalls.

Headwalls are underground support structures made up of a series of concrete columns, called piles, that create a watertight wall around the area of future subway stations and emergency exit buildings.

https://blog.metrolinx.com/2022/04/12/headwall-construction-begins-for-scarborough-subway-extension/