[nfitz]

... On a side note, they have been constructing an intervention headwall on the southside of McCowan and 401. Does that mean the TBM ran into problems under the 401?

I'm not familiar with the term "intervention headwall" - but it doesn't sound good. What does it mean in this context?

 

[Space Gary]

I'm not familiar with the term "intervention headwall" - but it doesn't sound good. What does it mean in this context?

The intervention headwall is basically a thick, low-strength concrete wall of secant piles that the TBM can drive into and depressurize the cutter head and allow maintenance work / tool changes to be performed safely. Not sure if this is what they're doing in this context or if they're merely adding another Emergency Exit Building south of the 401.

 

[crs1026]

Sounds like a dozen or so headwalls are needed at various points along this tunnelling drive. This one may or may not have been planned all along.

Headwall construction begins for Metrolinx’s Scarborough Subway Extension

It will take crews roughly four to six months to build each headwall, and work will also involve utility relocations.

www.masstransitmag.com

- Paul