Work is anything but boring when you are boring a tunnel 165 ft. beneath an urban residential neighborhood.

A 7.1-mile, 20-ft.-diameter tunnel is under construction on Milwaukee's Northwest Side and intended to add 88 million gallons, or 22 percent of current capacity, to the city's 405-million-gallon deep-tunnel system.

The $117 million Northwest Side Sewer Relief project began in May 2002 and is slated for completion in 2006.

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Martin Vliegenthart, project manager/general superintendent for Bethesda, Md.-based J.F. Shea Inc. of the Shea Kenny Joint Venture contracting team, said the project employed both traditional drill and blast methods of tunneling and a tunnel-boring machine. Wheeling, Ill.-based Kenny Construction Co. is the other member of the contracting team.

He said of the 11 shafts required on the project, which include drop shafts, access shafts and diversion structures, seven were bored and four were created with drill and blast. A TBM was used for the length of the tunnel itself.

Having a Blast

Blasting the various shafts in densely populated neighborhoods required communication with residents nearest the blasting operation and proactive steps to ensure that no damage was caused on the surface.

"We had complaints when we first started blasting," said Roger Maurer, conveyance section manager for the Milwaukee Metropolitan Sewerage District. "But that's pretty normal."

He added that there were only two blasts per day, one in the morning and one in the afternoon. At that pace, the shafts descended at a rate of about 8 ft. per day.

Maurer said although the blasts sound like the rumble of thunder, it took a significant effort to assure neighborhood residents that no harm was being done to their homes.

In addition to setting up six seismographs at various points on the surface during blasting, the MMSD visited homes within a radius of about 500 ft. of the blast beforehand to establish the condition of the properties.

"We went through and recorded cracks in the walls and foundation on videotape beforehand," Maurer said.

A local TV station aired a segment on the blasting and its effect on homes, which also helped allay fears. During the segment, a seismograph was set up in the living room of a home to monitor a blast. The test demonstrated that someone walking through the room created more vibrations in the house than the blasting.

"They control blasts now so that not all the charges go off at once," Maurer said. "There are millisecond delays in the fuses - you can't really hear that - but it helps control surface vibrations."

Bill Graffin, public information manager for the MMSD, said, "We had some calls when the tunnel-boring machine was right under people's homes. Most would call and say they heard a rumbling, not loud, more like the fan on the furnace kicking on."

Vliegenthart called the operation a success, saying, "Nobody sued us."

Using a TBM

The boring machine, a 22-ft. Robbins TBM that was 800 ft. long with its trailing gear, was shipped to Milwaukee in pieces. It had to be assembled and given a test run above ground before it could be disassembled, lowered into the ground and reassembled to begin work on the tunnel.

The test was performed in a vacant Allis Chalmers shop in nearby West Allis.

Once underground, the machine relied on a computerized global positioning system unit to guide it, and several geologists to predict what was ahead. Both water and uneven limestone lay in the machine's path.

Maurer said crews removed water from the tunnel at a rate of about 2,500 gallons per minute, but, "It's always hard to predict how much water you are going to hit."

He said that it is always preferable to err on the conservative side. The prediction was closer to 5,500 GPM.

"If we hit more water than we expect, we simply don't have the facilities to deal with it," he said.

Water pumped from the tunnel was treated at a temporary treatment facility and then funneled into a nearby river. Tunneling on a slight upgrade, about 0.05 percent, kept water flowing away from the operation.

"But the big unknown is what the rock is going to be like down there," Maurer said. "We did borings every 1,000 ft., in 2.5-in. bore holes. But usually when you hit bad areas, they are right between bore holes."

In the case of this tunnel, the problems were a long crack that made the area generally weak and crumbly. Although the weak rock and the additional water inflow it created were concerns, proceeding slowly and carefully got the machine through it. The job is set to come in under bid price.

Maurer said the problems were nothing compared to what some tunneling operations have hit in other parts of the country.

"The industry is awash in horror stories of tunneling jobs gone bad," he said, citing projects in which levels of corrosive hydrogen sulfide in the tunnels have presented significant hazards to workers and have crippled TBMs. In extreme cases, the hydrogen sulfide levels can require abandonment of the tunnel with the boring machine still in it.

Muck Trains from Abroad

Although the tunneling itself went relatively smoothly on this project, with the machine coming to within a quarter of an inch of its mapped goal, "Planning was a nightmare," Maurer said.

He added that the tunnel and some of the drop shafts had to be located close to a Moss-Superfund site and some on privately owned land. A lengthy process of letter writing eventually got the project moving forward, but in some areas the top 5 ft. of top soil had to be removed to waste management before shaft work could begin.

Finding an above-ground site for the operation in an urban location also presented a problem. The solution was found on vacant land that is part of the Milwaukee County Institution.

Although the site offered sufficient open land for the project, it also presented some vibration concerns. Maurer said a nearby building, in which eye surgery is performed, necessitated testing and also presentations to hospital staff.

Removing the muck created by the immense boring machine is always an issue in large tunnel projects. Unlike Chicago's Deep Tunnel project, which employed a conveyor to move muck from the tunnels, the Milwaukee project used an underground train system.

"We used five muck trains with five locomotives," Vliegenthart said. "These are the same muck cars that were used to do the Chunnel between England and France. We bought all of them."

The muck was hauled to a shaft where it was transferred to the surface by a vertical belt and then trucked to designated dump areas.

The tunneling operation, which took a little under one year, is now complete. In mid-June, crews were preparing to pour the concrete lining of the tunnel.

"We will hopefully pour between 205 and 245 ft., or 660 cu. yds., per day," Vliegenthart said. "We have a concrete pump that can pump 120 yds. per hour."

He said concrete is pumped down from the surface into steel forms in 3,000-ft. increments. Then the pump is moved 6,000 ft. down the tunnel to the next drop hole and the process begins again.

Once the concrete is in place grout will be applied to stop any seepage.