What exactly are they doing there?
What on the planet are you talking about?While Eglinton Crosstown LRT line will intersect north of Eglinton Subway Station on Yonge line,.... here south of Eglinton Station it looks like they’re extending the tunnel south,.... just a bit,.... providing more of a protective covered buffer area to reduce the amount of wind and snow blowing into Eglinton subway station platform,..... but also to provide more protection for the crossover track & mechanism that are just south of the platform.
To protect St.Clair subway station, something similar was done between St.Clair and Summerhill station about 25 years ago; there, they actually covered the entire track with an upper deck - basically making it into a tunnel
What on the planet are you talking about?
The reason the trench section between St.Clair and Summerhill was covered up had nothing to do with protecting St.Clair from the elements, much in the same way this current project has nothing to do with protecting Eglinton from the elements as evidenced above..