Friday, November 20, 2009
Geofish Caused the Niagara Tunnel Collapse
"The crown fall happened in a area surrounding a 20-year old bore hole," said Ernst Gschnitzer, Project Manager for Strabag. "The hole had a long time to deteriorate and eventually the ground gave way."
I didn't exactly drill that borehole, but it was drilled shortly after I helped define the St. Davids Gorge with geophysics. That was just after the old Geotechnical Engineering Department broke up, and I was shuffled to nuclear. Before that, we always grouted up an exploration borehole, in fact it was the law because of possible natural gas in the region. My old colleagues have a lot to answer for!
So, the TunnelTalk article is out. I'm glad they could pin the 100 ton collapse to a single old borehole, because without that extraordinary cause, the whole tunnel would be suspect. The Queenston Shale is totally impermeable, so that was one heck of a hole to have caused water damage! I'm glad all the other holes didn't do this.
The sandstone has proven to be abrasive, and I think there are more sandstone layers ahead for them. I'm glad they talked to the reporter, since I wasn't expecting much. Oh well, it's good be wrong, since I was way too gloomy on this. If my mechanism is correct, we shall have some more major collapses, but for now, let's regard this happy article as a Christmas present! :)