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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