Friday, December 7, 2012

Filling the Void

Last week, crews digging the New Irvington Tunnel excavated an astounding 92 feet in just 3 days. This feat was all the more surprising given that the tunnel was passing through a fault zone where miners excavating the original Irvington Tunnel encountered an enormous amount of groundwater pouring into the tunnel. So much so that it was dangerous for the workers. What was different this time around? Grout.

Crews knew they had entered this zone when they probed 100 feet ahead of their tunnel face and found large amounts of groundwater. Before crews could do any mining forward, they had to inject 66,000 pounds of grout (think liquid cement) into the rock ahead of them to fill cracks and voids in the earth. That’s enough to fill up the water tank pictured below! Grouting fills these voids and keeps groundwater out of the tunnel. It keeps our miners safe and allows tunneling to continue.

Grout is taken by rail to tunnel heading and mixed inside of the tunnel. In November alone, approximately 423,000 lbs. of cement was injected into rock fractures, filling cracks ranging up to 1.5 inches in width.

As of December 4, 2012, over 13,100 feet has been mined. With 5,500 feet to go we expect tunnel expect tunnel excavation to be complete by mid-2014. For those that remember our Road Header Rendezvous Challenge we’ll have another one next year to celebrate NIT’s final hole-through!

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