Massive void forming below a major Toronto intersection and it looks like a cave

A vast cavern is taking shape beneath a major Toronto intersection as part of the push to build the new $27 billion Ontario Line.

The new transit line will relieve existing subway interchanges with a 15-station, 15.6-kilometre route between Exhibition Place and the shuttered Ontario Science Centre.

With tunnelling soon to begin for the six-kilometre underground section of the line between Exhibition Place in the southwest and the Don River to the east, work is in full swing to ready the sites of the future underground stations, including the formation of impressive subterranean caverns.

At the future King-Bathurst station, crews recently began working to excavate a sizeable void below the intersection.

Metrolinx informed the public in the final weeks of last year that "the next phase of excavation will begin this December 2024 and continue into late 2025."

During this excavation stage, workers will dig out a large underground space that Metrolinx refers to as a "cavern," extending southwest from the newly excavated shaft at the northeast corner of King Street and Bathurst Street. 

According to Metrolinx, "this cavern also creates space for the future tunnel boring machines to pass through as they create the Ontario Line subway tunnels through downtown Toronto."

Massive Ontario Line 'cavern' about to be dug below major Toronto intersectionhttps://t.co/yTpIsMJzD2

— blogTO (@blogTO) December 6, 2024

Work has since begun on this cavern, and is making swift progress below the busy intersection, unbeknownst to many of the thousands of commuters who cross above it daily.

An update was shared by Ontario Transit Group (OTG), a consortium responsible for building the Ontario Line's southern civil components, including stations and tunnels.

In OTG's recent LinkedIn post on the project, the company announced that "Cavern work at the future King-Bathurst station is officially underway" and offered up a technical explanation of the work at hand.

According to OTG, "the construction team is using the sequential excavation method, taking advantage of the natural strength of the surrounding earth to efficiently dig underground."

"The roadheader featured in this photo has rotating cutter head and pivoting arm to provide flexibility in shaping the tunnels and caverns that are needed during this phase of excavation."

The excavated material, known as rock spoils, is being removed from the station's shaft and trucked off-site.

Of course, you probably won't be able to see or hear any of the construction activity for yourself, thanks to some careful efforts by Metrolinx. Excavation work is being carried out within the confines of a large temporary structure that Metrolinx refers to as an "acoustic shelter." 

The Ontario Line is expected to open by 2031.