Monday, February 22, 2010

Niagara Tunnel - Asymmetric Overbreak in Cap Rock

February 21st 2010
The tunnel is 17.7 meters from reaching the 6,000 meters mark.
There is 1-2 meter over-break to the left side of the TBM cutter-head crown.
Daily mining average is 9 meters

Since January 1st 2010 the TBM has mined 501.6 meters

February 19th 2010
The tunnel is 5,958.3 meters long at an elevation below the surface of 88 meters.
There is 1-1.5 meter over-break. TBM averaging 18.5 meters per day

The Concrete Invert Bridge is at 4,100 meters

The Restoration Carrier is at 1,100 meters

Well, they finally reported! They were scared of my upcoming made-up story! I had such a good one! I'm quite amazed at this latest overbreak. The usual folly is to zoom through this rock at high speed, put in a stiff lining, and then watch everything fall apart. I can't conceive of the implications of overbreak in this rock, but it is slowing them down again.

As well, this overbreak is once again strongly to the left. I don't how they are getting such strong polarization of the principle horizontal stress in these upper rocks. It has never been measured as such. If you could measure it, the stress here would be gold medal material!

They have stopped publishing those nice pictures. Obviously their fear only extends to text! I should start making up pictures!

Their rig for extra shotcrete is trundling along at a decent rate. I doubt they have entered the really bad overbreak zone, since that would require multiple layers of shotcrete. As I've said before, hanging tons of concrete on this roof will be interesting....

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