Fermi National Laboratory

Volume 25  |  Friday, May 24, 2002  |  Number 9
In This Issue  |  FermiNews Main Page

Diggin In

by Kurt Riesselmann

April 2000S.A. Healy starts excavation
May 2000First blast to remove rock
July 2000First access shaft complete
Jan. 2001Excavation of target hall complete
March 2001Tunnel boring machine begins operation
June 2001MINOS access shaft complete
Dec. 2001TMB completes 3,000-foot-long tunnel
March 2002MINOS hall complete
May 2002Blasting of sump hole will complete excavation

It’s dark, it’s wet and—most of all—it’s huge. Miners of the S.A. Healy company are carrying out the final excavation work for a new underground facility at Fermilab that could easily store thousands of cars, neatly lined up and stacked on top of each other. Since April 2000, construction crews have worked in three shifts, six days a week, to create an intricate system of tunnels and halls.

But this new space isn’t tagged as a parking garage. Physicists will use the new caverns to build a research laboratory called Neutrinos at the Main Injector (NuMI). Two large underground halls and 4,000 feet of tunnels will host scientific equipment to create and analyze neutrinos, the most evasive particles of the universe.

Scientists will crash protons from Fermilab’s Main Injector accelerator into a graphite target in the first NuMI underground hall, at a depth of 150 feet. The resulting neutrinos will then traverse a second underground hall, 350 feet deep, where a particle detector will record the neutrinos’ properties. From there the neutrinos will continue their journey through 450 miles of rock to hit a second detector in a former iron mine in Soudan, Minnesota. While traveling through the rock—no tunnel is needed—the neutrinos may “change flavors,” transforming from one type into another. Because of its relevance to the evolution of the universe, this process is of great interest to physicists.

The assembly of the tunnel boring machine in February 2001 represented an important milestone for the NuMI project The only tunnels required for the NuMI project are a tunnel connecting the existing Main Injector accelerator to the new target hall, and a half-mile-long tunnel connecting the target hall to the near detector hall. Miners completed these tunnels in December.

But unlike conventional transportation tunnels, NuMI’s will never have traffic jams.

“The NuMI underground construction is different from—and probably a bit more difficult than—a transportation-tunnel project,” said John Sollo, NuMI construction coordinator. “Access to the NuMI main tunnels is only through vertical shafts rather than a drive-in portal from either end.”

In the absence of elevators (to be installed this fall), workers enter the construction site via a metal cage that is lifted and lowered into the tunnels by a crane. Every piece of equipment, from shovels to front-end loaders, has come through the access shafts. And every piece of rock has gone out through one of the shafts. Millions of pieces. Or more precisely: one hundred thousand cubic yards of rock, more than 2,000 truckloads.

Excavating tunnels is nothing for the faint at heart. The environment underground is cold and wet. Temperatures of 55 degrees Fahrenheit are the norm, and fog is not unusual. During the construction, a couple of hundred gallons of water have entered the NuMI tunnels—per minute! Even after the facility is complete, engineers expect a continued inflow of approximately 150 gallons per minute, which will be removed by powerful sump pumps.

Taking no risk
Maintaining the safety of workers is an important task. In June 2001 an accident severely injured a man drilling an air vent hole at the surface and led to increased attention to safety procedures and reinforced the training of crew members.

“The only way to improve safety culture is through communication,” said Mike Andrews, who joined the NuMI project after the accident to become the coordinator for environment, safety and health. “We really beefed up the daily hazard analysis program. We have safety meetings, toolbox meetings and daily planning meetings to help the crew members understand what the issues are. The foremen are now very clear on what they mean and how they present it. And the miners know that we don’t just talk about safety, but that we really mean it.”

Miners completed the excavation of the NuMI target hall in January 2001. With a height of 60 feet and walls of rock, the hall's interior is reminiscent of a cathedral. The new approach has had the desired effect. Since the accident the number of safety incidents per worked man-hour has dropped by almost 50 percent compared to the first sixteen months of the project. For Fermilab’s project managers, however, this is not yet enough.

“Safety constantly needs attention,” said construction manager Dixon Bogert. “It’s fair to say that safety has improved, but it’s not an area in which we can relax.”

Having a blast
Mining is labor-intensive work and requires the right tools. To break the limestone and shale, the construction crews have relied on three different excavation methods: drilling and blasting, mechanical removal with a hoe-ram, and use of a tunnel boring machine.

“The various NuMI tunnels and halls have different dimensions and cross sections,” said project engineer Chris Laughton. “Healy chose the excavation methods that they considered the best for the different parts of the project. Using a variety of excavation techniques is not a technical challenge but a logistical one.”

Miners used the tunnel boring machine to excavate the 21-foot-diameter tunnel between the two underground halls. At its best, the TBM advanced by more than 70 feet a day, but more typically mined at less than half that rate. To excavate the access shafts and underground halls, miners carried out more than 400 blasts, removing up to ten feet of rock in one blast.

To limit the impact of blasts on both Fermilab’s scientific facilities and the surrounding neighborhood, miners had to follow strict specifications.

“The noise and vibration restrictions [specified in the contract with S.A. Healy] were a main issue during drill and blasting,” explained Sollo. “Those restrictions are common in urban areas, but unusual for most underground work.”

Fermilab closely monitored the noise and vibration created by each blast. Although the blasts never exceeded vibration levels, some blasts were much louder than expected. Unfavorable northeast winds and dense cloud coverage sometimes intensified and projected the noise into the adjacent neighborhood, startling neighbors by rattling windows.

“We’ve greatly appreciated the patience and cooperation of our neighbors,” said NuMI project manager Greg Bock. “Their observations and feedback were as valuable to us as the data we obtained from scientific monitoring equipment.”

The NuMI excavation, with only a few blasts still to come, has lasted twenty-six months, so far some six months longer than originally anticipated. According to a revised schedule, accepted by a Department of Energy review committee in September 2001 (see FERMINEWS, Sept. 28, 2001, vol. 24, no. 16), the NuMI facility will be operational in 2005.

“This work has taken much longer than we expected,” Bock said. “But since March, when Healy significantly increased their work force, progress has been good and we’re looking forward to starting the follow-on contract toward the end of the year.”

Precise aim
Miners, here wiring explosives inserted into the rock, set off more than 400 blasts to create three shafts and two huge underground halls. In April, S.A. Healy began the installation of a 2,000-foot-long decay pipe. The work is part of Healy’s 30.5-million-dollar contract with the Department of Energy. It presents the first important step in outfitting the tunnels with infrastructure and scientific equipment.

The manufacturer of the steel pipe will deliver fifty-six sections, each forty feet long and seven feet in diameter. Welders have already put together more than a third of the total decay pipe inside the NuMI tunnel.

“There is a bunch of things involved to make sure that the beam goes to the right point in Minnesota,” said Wesley Smart, the physicist in charge of NuMI’s alignment. “The contractor is responsible for putting things in the right place, and Fermilab surveyors do the quality assurance.”

Physicists expect the center of the neutrino beam to hit the far detector in Soudan to within forty feet. To achieve this goal, the alignment of the tunnels at Fermilab must be exact within a few inches. The most critical part will be the installation of all beamline components. Since neutrinos have no electric charge, it is impossible to manipulate the direction of the neutrino beam after it has been created.

So far, Smart is pleased with what he has seen.

“Healy’s picked a good surveyor,” he said. “The first part of the decay pipe is within three quarters of an inch of the ideal location. That’s what the contract allows.”

New buildings to come
At the end of the year, a new contractor will begin the second phase of the NuMI project. Physicists Rob Plunkett and Catherine James will supervise the work.

“When Healy is done with its contract,” said Plunkett, “the next step is to change the empty hole in the ground to an underground laboratory, from a hostile environment into a friendly one.”

A few weeks ago, Plunkett and his colleagues sent out requests for bidding proposals for the new contract, which includes the construction of service buildings on top of two access shafts. The work is expected to take one year and cost more than ten million dollars. It includes a service building that will stand near Fermilab’s main entrance (see graphic below).

“It will be an industrial-type building with a big hole —350 feet deep—in the floor,” said Rob Plunkett. “The building is mostly used for staging. Eventually, the MINOS detector, one plane at a time, will come through this space.”

The Main Injector Neutrino Oscillation Search detector at Fermilab will consist of 280 planes of steel and scintillator. Technicians are currently assembling the planes at Fermilab. It is a smaller version of the detector at Soudan, which is already under construction and almost half complete.

“So much work has to come together,” said Plunkett. “It has to grow like an organism.”

Three years from now, NuMI will be all grown up and ready to run.

“The next step is to change the empty hole in the ground to an underground laboratory.”


On the Web:
The NuMI-MINOS homepage
For our neighbors


last modified 5/24/2002   email Fermilab