Tuesday, June 12, 2012

A Road Header Rendezvous

9:46 AM June 12, 2012

Inside of a 13-foot diameter hole carved into the Alameda foothills, crews waited yesterday morning staring at an imposing rock wall.  A moment later, as if it came from within the mountain, a spinning titanium studded knuckle broke through. It moved back and forth and up and down until the wall disappeared.  What happened next was a long time coming: two crews, dressed in identical hard hats, headlamps and goggles stepped through the new hole, shook hands and then shared a laugh.

Video Captured with Permissible Camera

After 13 months of digging the New Irvington Tunnel from four separate tunnel headings, miners from two of the headings met up with each other underground today. Called a ‘hole-through’ in tunneling terminology, the road header teams from the Irvington Portal in Fremont and the Vargas Shaft 4,500 feet away shook hands somewhere under the mountainside and formally completed this section of tunnel excavation.

The road header holes-through the rock face

Miners at the Irvington Portal watch the road header hole-through from the Vargas Heading 

Miners celebrate their achievement
Photographs by R. Scheswohl ©2012 SFPUC, All Rights Reserved

The tunnel is excavated using conventional mining methods including a road header (a tracked tunneling machine) and, in sections of hard rock, controlled detonations.  In May 2011, a 55-ton road header was lowered down the 115-foot Vargas Shaft and began to grind its way west.  A month later, miners at the Irvington Portal in Fremont began tunneling east and set the two crews on a collision course.  

Following today’s hole-through, miners will prepare the tunnel for the installation of 102-inch diameter steel pipe.  The pipe, manufactured in California, is installed in 50-foot sections and welded together inside of the tunnel.   The much longer 14,400-foot Alameda West-Vargas tunnel segment is currently being excavated and is expected to hole through in fall 2013.  Construction of the entire project is scheduled for completion in fall 2014.

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