There are some things that are hard to really
capture in a photo. Take the gargantuan cliffs of Yosemite, the Great Pyramid of
Giza or a sunrise on the Manhattan skyline. A selfie at these spots generally
fails to convey their true grandeur and magnitude.
Soon, a new location can be added to this list: the
caverns for the Deep Underground
Neutrino Experiment (DUNE) being built under the Black Hills of South Dakota
at the Sanford Underground Research Facility (SURF).
“The DUNE caverns are mind-bogglingly big. There is
no question about it,” says Joshua Willhite, one of the engineers leading the
DUNE excavation and a South Dakota
Mines mechanical engineering graduate. “It’s impossible to wrap your mind
around it without being there. I can show you all the pictures and diagrams,
but without actually seeing it, you can’t truly fathom an opening that big
underground."
Two of DUNE’s main caverns are seven stories tall, a
football field and a half long and 64 feet wide. A third utility cavern is
three stories high, two football fields long and 64 feet wide. This video helps explain the size
of the DUNE caverns. “They are enormous,” says Willhite.
Willhite is an engineer at the U.S. Department of
Energy’s Fermi National Accelerator Laboratory, which leads
the DUNE project. He is the project manager for the infrastructure being
installed for DUNE located in the former Homestake Mine. He notes there are
other caverns of similar or larger size on the planet that are closer to the
surface. But he says nothing the size of DUNE has ever been done at this depth
(4,850 feet below ground).
The engineering challenges of construction this far
below the surface are formidable. In a normal construction project, you’d have
air to breathe, you’d have enough water and you’d have room to move heavy
equipment and building materials in and excavated rock out. But none of this is
a given in the DUNE construction project.
Clean air to breathe underground is essential.
“Every bit of air that is underground has to come down through one shaft and go
back out another shaft, and this requires management of air movement,” says
Willhite. At the 4,850 level of SURF, the natural temperature of the
surrounding rock walls is 95 degrees, so ventilation for air conditioning is
key. “We don’t do anything to generate excess heat underground,” he adds.
Water cannot be taken for granted in the DUNE
construction. Take something as simple as installing a bathroom. Pumping water
between the surface and the construction site would require almost 2,200 psi of
pressure. Engineers like Willhite have broken down the plumbing that supplies
water to DUNE into a series of stepped segments to reduce the pressure needed
by individual pumps. “It still requires a lot of power to pump water back out.
Because of these challenges, we try to limit water use wherever possible,” says
Willhite.
Heavy equipment like excavators and front-end
loaders and construction materials like long steel beams that are normally a
part of any construction operation are not so easy to come by at DUNE. “These
massive caverns take huge equipment. But we are supplied by mine shafts that
are not that much bigger than a normal elevator, and there is no piece of
excavation equipment that will fit in an elevator, so we have to disassemble
the equipment at the surface and reassemble it at depth,” says Willhite. On top
of this, the rock being excavated from these large caverns must be placed back
on conveyances and moved to the surface.
The size and complexity of the DUNE construction are
not the only mind-blowing details about the project. The facility, funded by
the US Department of Energy, which is being built inside this giant underground
expanse, is arguably more impressive. DUNE is a true international project that
includes 1,000 scientists and engineers from more than 30 countries around the
world. DUNE will become the world’s largest physics experiment in the study of
neutrinos. The tiny subatomic particles, sometimes called ghost particles, could
be a key that helps us understand the origins of the universe. (Learn more
about the study of
neutrinos in this video.) The large caverns of DUNE will hold massive tanks
of liquid argon that will detect the neutrinos coming in from a beam generated
at Fermilab in Illinois. Argon liquifies at about 300º below zero Fahrenheit.
Willhite will help with the construction of two tanks the size of five-story
buildings that will each hold 17,000 tons of -300ºF liquid argon.
“To maintain that temperature, we use a large
nitrogen generator and refrigeration system to create liquid nitrogen at -320°F,”
says Willhite. The liquid nitrogen will be used to help cool the argon, he
says. “Aside from the ridiculously cold temperature, when these liquids boil,
they expand over 700 times their volume. There is nothing inherently hazardous
about argon gas except it displaces any oxygen. We have to ensure that this
expansion is minimized, controlled and ventilated properly for worker safety.”
For Willhite, the engineering challenges at DUNE are
part of what make it a fulfilling project. “We’re working with world-renowned
engineering firms in the design and construction of this project,” he says.
Willhite grew up in the Black Hills of South Dakota
and was drawn to engineering as a kid working on cars. He attended South Dakota
Mines to study mechanical engineering. “I was good at math, and I liked to work
with my hands as a mechanic,” he says. Willhite remembers one professor at
Mines in particular, Dr. Dan Dolan, who is now an emeritus faculty member at
the university. “The thing with Dr. Dolan is that he wanted you to get into the
lab and look at how things are put together. He let you make mistakes and then
he helped you understand how to fix them. His excitement for engineering showed
in everything he did.”
Willhite left the Black Hills after graduating. “At the
time, there were not many engineering jobs in the area,” he says. In 2010, he
was invited to work at the site that would become SURF. “I was not looking for
a job at this time, but this was not an opportunity I could pass up,” he says.
Today, he is more excited about the future of the area than ever. “When I came
back here in 2010, the area around Lead was still suffering from the loss of
the former Homestake Mine back in 2001. You go through Lead now, and the town
is booming,” says Willhite. “I think the Black Hills has always been known for
natural beauty and tourism and not so much for professional job opportunities.
I think this project at SURF and other developments are changing
that.”
Photos thanks to Joshua Willhite at Fermilab along
with Adam Gomez and Matt Kapust at SURF.
This article first appeared in
The Hardrock
the South Dakota Mines alumni magazine.