It took plenty of coordination among multiple entities to get work started on the $168.7 million Little Calumet Leg, the last passageway in Cook County's 109.4-mi.-long Deep Tunnel system.

Utility firms moved gas and water lines because of the potential for service disruption during the sinking of more than 50 shafts for the 7.9-mi.-long project, said Greg Hauser, project manager for the Jay Dee/Affholder Joint Venture, the South Holland, Ill.-based general contractor.

ComEd, a local utility, routed electrical service to the construction shaft because energy was required for below-ground lighting and other systems.

Union Pacific Railroad Co. allowed 2,000 ft. of its utility road for a nearby rail line to be used to transport workers and materials to the main construction shaft, thereby saving cost and labor.

Multiple government agencies - the U.S. Army Corps of Engineers, the village of South Holland, the Illinois Department of Transportation - helped ensure proper access and siting for the Little Calumet Leg project, the last passageway of the $3.1 billion Deep Tunnel system that will ultimately provide pollution and flood-control benefits for Chicago and 51 Cook County suburbs.

The Calumet project's original site configuration was a mile long and 300 ft. wide due in part to adjacent wetlands, Hauser said. A wider space was preferable so equipment could be staged near the construction shaft and the substantial amount of rock removed from tunneling could be easily piled.

"Now, we got a wider [site]" that's not as long but easier to work in, Hauser added.

Several nearby towns, such as South Holland, Calumet City and Dolton, organized community meetings so the blasting and mining process could be explained and residents' concerns allayed, Hanson said.

Explosive emulsion, rather than dynamite, was used to open the drop shafts. The emulsion, which is less sensitive than dynamite, is safer.

"The nitroglycerin fumes from dynamite are not toxic, but they give you a heck of a headache," Hauser said. "We don't have those fumes here."

Fathoming the Tunnel

The tunnel will provide pollution control and overflow abatement for all or parts of eight south suburban communities. It runs in a southeast-to-northwest direction between the Indiana line and Interstate 57.

The tunnel will provide relief for the Little Calumet River, which was previously inundated with overflows from combined sanitary and storm sewers during heavy rains. The project will prevent 2 billion gal. of combined raw sewage and 1.5 million lbs. of polluting organic material from being discharged into the waterway each year, according to projections from the Metropolitan Water Reclamation District of Greater Chicago.

The project started in February 2002 and is expected to be complete by March 2006.

Soil, Rock Tunnels in Design

A large number of tunnels and shafts in the soft ground near the surface and deep in the limestone rock comprise the design of the Little Calumet Leg tunnel.

Connecting shafts in the soft ground intersect the combined sewer system at many points to channel effluent into exit tunnels, said Jim Foley, project engineer with the Jay Dee/Affholder Joint Venture. About half of the more than 47 soft-ground shafts are already complete.

Sensors will monitor water levels in the exit tunnels, and regulating structures will open sluice gates when levels are high. About 5 mi. of exit tunnels between 42 in. and 120 in. in diameter and 15 regulating chambers will channel runoff into drop shafts, which range between 7 ft., 2 in. and 30 ft. in diameter.

"At each of the 10 drop shafts, we're picking up at least one and in most cases, [two to six] system sewers," Hauser added.

Effluent is dropped more than 100 ft. into a chamber, which was formed by drilling and explosives.

Air pressure due to the onrush of water was accounted for in the design, Hauser said. Three drop shafts are next to sister shafts that allow air to rush out.

The others have a divided wall of precast concrete, Foley said. Water spills into one side, and air shoots up the other.

Notches were put in the shaft walls when they were formed, and precast panels were inserted, Foley added.

Each shaft is equipped with a louver that allows air to be vented during rain while preventing noxious vapors in the tunnel from escaping during dry weather, he said.

The main tunnel has a slope so gravity can be used to channel effluent, Foley said. It runs down-hill from the tunnel ends, which are 160 ft. deep, to the middle, which is 210 ft. deep.

A connecting passageway will link the Calumet tunnel with the previously constructed, 30-ft.-diameter Indiana Avenue tunnel, which is 313 ft. below ground, Hauser said. It channels sewage to a treatment plant at 130th Street.

"If the whole tunnel system is full, then it will still have to overflow into the Little Calumet River, but that will be after the initial flows have gone into the Deep Tunnel," Hauser said. "That will be much cleaner."

Tricky Tunnel Logistics

Project logistics are complex.
Because it is 300 ft. long, the tunnel-boring machine for the limestone tunnel came in components and needed careful assembly, Foley said. The pieces were staged above ground, and a crane lowered them into the passageway. Once down, each piece was moved slightly forward so room was available for the succeeding piece immediately after.

The assembled machine consists of several components, such as the cutting wheel and trailing gear, said Jim Davis, engineer with the Jay Dee/Affholder Joint Venture.
Teeth form the leading edge, and the cutting wheel turns to slice rock.

TBMs for soft-ground use created the tunnels for the near-surface areas.

Another logistical issue involved removing the debris cut away during mining, Hauser said. A continuous conveyor in the limestone tunnel removes debris as it is cut, and additional conveyor bracket is installed as the TBM moves along.

The conveyor terminates at the main shaft, where a vertical conveyor takes over. A system of buckets brings the debris to the surface, where it is piled.

In the soft-ground tunnels, trains on rails removed the debris.

Moving formwork and concrete was important because each structure is to be lined with concrete. Platforms were used to suspend workers from cranes, the formwork and rebar were installed and the concrete was pumped in.

Because of the depth and length of the Calumet tunnel, a different method of installation was used to line it. The concrete is pumped into the tunnel in large quantities and put into cars with agitators. They are rolled, the forms are installed and the concrete is pumped.

Unlike the shafts, the tunnels are not reinforced with rebar.

"The lining is not structural," Hauser said. "It's for infiltration and exfiltration, to keep the sewage in and the groundwater out."

Approximately 7,000 to 8,000 cu. yds. of concrete is presently being pumped a month, and the peak is expected next summer at 15,000 cu. yds. a month, Hauser said.

"Right not we've only finished nine structures in concrete," he added.