Article on Building of Cumberland Gap Tunnel
Scott M. Kozel
ASSOCIATED PRESS
Dateline: MIDDLESBORO, Ky.
Miami Herald, The (FL)
March 7, 1986
Engineers who have started digging a tunnel under the Cumberland Gap,
the only natural break in a mountain ridge extending from Georgia to
Maine, hope to improve travel while turning back time to the days when
Daniel Boone cleared the Wilderness Road for settlers.
Laborers working on the $156 million project are to use 300,000 cubic
yards of rock dug out of the mountain while making twin 36-foot-wide,
32-foot-high tunnels to cover the steep, twisting three miles of U.S. 23
through Cumberland Gap National Historical Park and recreate the rude
wagon trail of the 1700s.
Since the 1960s, studies have recommended a tunnel to improve the road
without further damage to the historic gap, where 300 years ago the
trail was a buffalo trace and later an Indian "Warrior's Path."
After years of on-again, off-again battles over the appropriation in
Congress and a five-month funding freeze by the Executive Branch last
year, the pilot bore finally started in December.
By December 1992, four lanes of traffic are to sweep through corridors
nearly a mile long and nearly 1,000 feet beneath the mountain separating
Middlesboro, Ky., and Cumberland Gap, Tenn.
The project promises to eliminate the last two-lane chokepoint in the
100 miles of U.S. 25E between Interstate 75 at Corbin, Ky., and I-81 at
Morristown, Tenn.
Some of the aura of the unknown from Boone's day remains.
The gap's potentially dangerous geology, for example, calls for unusual
precautions, including the use of spark-free equipment approved for
mining in explosive atmospheres.
The work began with immense earthmoving efforts at the tunnel approaches
and with a crew starting into the depths of the mountain, like scouts of
old, with a 10-foot-square pilot bore.
"No tunnels are easy," said project engineer Bob Campbell, a veteran of
27 years with the Federal Highway Administration.
On a recent tour of the site, Campbell's four-wheel-drive truck lurched
as he maneuvered to avoid heavy machinery swarming over mountains of
fill at the Kentucky and Tennessee ends of the projected tunnel,
clearing the future swath of the four-lane highway through the hills and
woods.
"This is ancient geology," he said. "It's not wise from an engineering
standpoint to start into the mountain with a 36-foot tunnel."
Campbell returned to the United States in 1983 after a two-year tour as
one of 16 engineers sent to develop roads in Saudi Arabia. The tunnel
was his next assignment. "I've studied and read everything I could
about the project," he said.
The gap cuts through a ridge, or overthrust, created when the Earth's
crust cracked and one edge rode up over the other. "This mountain runs
all the way to Maine and there's no other natural gap in it," Campbell
said.
The road, built in 1916 and reconstructed in the 1960s, averages 17,600
vehicles a day. Sixteen percent are trucks that crawl over the grade at
an average of 16 mph. Deaths, injuries and property damage in accidents
are six times the national average.
"The Claiborne (Tenn.) Progress calls it 'Blood Mountain.' The
Middlesboro Daily News calls it 'Massacre Mountain,'" he said.
The small pilot tunnel, which will take eight months to drill and blast,
will be enlarged to form one of the final corridors. Thirty-six feet
into the mountain it was in a sandstone layer, the first of about 15
sloping strata of sandstone, limestone, shale and dolomite Campbell
expects to encounter.
The rock is under 150,000 pounds of pressure from the mountain above, he
said. "If you make a hole, is it going to stay there or is it going to
move? We don't know that until we get there."
In the heavily instrumented pilot bore, some gadgets will measure almost
to the millimeter how thick a section moves in any shift of the rock.
Other indicators will tell the direction. Convergence points will
confirm whether it is the roof, walls or floor moving, and stress and
strain gauges will detect any potential "catastrophic failure," Campbell
said.
"I have a geologist in the tunnel at all times, and he's mapping the
type of rock, how it lays in the mountain, how it dips and how it
strikes," he said.
The added precaution of using equipment judged permissible for mining by
the U.S. Mine Safety and Health Administration is being taken because
surface tests indicate five or six coal seams in the mountain, as well
as underground watercourses. The seams are minor but pose the threat of
the deadly coal and water combination that produces explosive methane,
Campbell said.
That doesn't necessarily mean trouble.
"If we go through and do not encounter significant levels of methane
gas, we know it's not going to be a problem. If we do find it, we can
deal with it by including precautions when we go through with the main
tunnels," he said.
"There's certainly nothing impossible about building a tunnel through
the mountain," he said. "(But) this tunnel is through difficult
geology, so it requires more attention to detail."
[end of article]
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