Tuesday, December 6, 2011

Niagara Tunnel still clearing collapse zone

On July 2nd, a "fall of ground" took place at 6,050 meters, effectively cutting the tunnel into two sections: the outlet and the inlet.

Work has continued unabated to repair the area of the fall of ground. It has been taking place within each section of the tunnel simultaneously. By luck, a crew bus was stranded in the intake section of the tunnel behind the TBM, allowing crews to be shuttled the nearly 4 kilometers to the rock fall zone. Unfortunately, the crew bus on the intake side became totally disabled. This caused Strabag a major logistical problem. It needed a replacement bus however the remainder of the main-beam and cutterhead of the TBM at the mouth of the intake side of the tunnel precluded the ability to just lower another mini sized crew bus into the intake channel floor and be driving directly into the tunnel unobstructed.

Using perhaps modern engineering adaptation at its best, Strabag did what one could consider most unorthodox but quite unique and innovative. During the week of November 14th, they took a replacement crew bus and cut the roof off the bus. The bus was now in two pieces. The chassis portion of the bus was lowered to the bottom of the intake channel. Now with sufficient clearance the bus chassis was driven underneath the existing cutterhead and main-beam. Once inside the tunnel, the bus chassis and roof were again welded together. A crew bus is again in service on the intake side of the Niagara Tunnel.   

This is interesting.  I always wish we knew more about this collapse, but that would be 'airing your dirty laundry in public', and that sort of thing isn't done in Canada.  Last time they had a collapse, they used the phony excuse of a single ungrouted borehole.  They didn't bother 'excusing' this time, must have a lot of confidence.

Obviously, the rock continues it's massive squeezing pressure.  The longer they are delayed in placing the final massive lining, the more chance of added collapses.  Still, more convergence puts less pressure on the final lining.  How long will that liner last?  One only has to look at the old Toronto Power wheel-pit to see.

Despite this collapse, the budget remains rock-solid :)   Really????

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