Little Calumet Leg
$171
Million Job Ends 'Deep Tunnel' 1st Phase
by
Craig Barner
The $171.2 million Little Calumet Leg Tunnel is expected
to be complete in March, and it will mark the end of the first phase of the Chicago
area's $3.1 billion Deep Tunnel project.
|
The Deep Tunnel's first phase is made up of 109.4 mi. of tunnels
under Cook County, and tunneling began in 1975, said Joe Sobanski, chief engineer
of the Metropolitan Water Reclamation District of Greater Chicago, the city agency
overseeing the project. The construction of the prototypes goes back to 1967.
Greg
Hauser, project manager with the South Holland-based Jay Dee Contractors Inc./Affholder
Inc. Joint Venture, the general contractor on the 7.9-mi.-long Little Calumet
Leg, said, "We could do our testing and start-up before the end of the year."
Other tunnels completed in the first phase are already in service.
The
second phase of the Deep Tunnel, which is formally known as the Tunnel and Reservoir
Plan, will focus on the construction of three reservoirs, the Thornton and McCook
basins under way, and the already complete O'Hare reservoir.
All three
reservoirs are expected to be done in 2019 when the TARP project as a whole will
be finished. The TARP system will offer pollution and flood-control benefits for
Chicago and 51 Cook County suburbs.
Part of Calumet System The Little Calumet Leg is part of the Calumet System,
one of four systems that make up TARP.
It is composed of the reservoir
in Thornton; four main tunnels including the Little Calumet Leg and auxiliaries
that collect overflows from combined sewers that carry storm water and raw sewage
in the same pipe; and a treatment plant at 130th Street in Chicago.
The
tunnel, which runs from Lansing near the Indiana state line northwest to Dixmoor
near Interstate 57, will provide pollution control and overflow abatement for
all or parts of eight south suburban communities.
The Little Calumet Leg
will offer relief for the Little Calumet River, which was inundated with overflows
from combined sanitary and storm sewers during heavy rains. The project will prevent
2 billion gallons of combined raw sewage and 1.5 billion lbs. of polluting organic
material from being discharged into the waterway each year, according to projections
from the water reclamation district.
Several structures make up the Little
Calumet Leg:
The system of combined sewers constructed generations ago
will flush effluent to "hundreds" of vertical connecting structures,
Hauser said. They will channel the sewage to soft-ground horizontal exit tunnels
ranging between 36 in. and 120 in. diameter. A regulating structure with a sluice
gate controls the system via radio signals or hard wiring.
When the sluice
gates are up, the exit tunnels empty into the Little Calumet Leg's 10 concrete-lined
drop shafts that range between 7 ft., 2 in. and 30 ft. in diameter. The sewage
will plunge more than 100 ft. into a chamber - often referred to as a "boot"
- that marks the starting points of the tunnel journey.
The 16-ft.-diameter,
concrete-lined main tunnel is sloped so gravity can be used to flush the sewage.
The tunnel ends are 160 ft. deep, and the middle is 210 ft. deep.
A connection
to be built will link the Little Calumet Leg to the previously constructed Indiana
Avenue Tunnel, a passageway that is about 300 ft. below ground. The 30-ft.-diameter
tunnel leads to a pumping station that channels sewage to the 130th Street treatment
plant. Making the Connection
Making the connection between the Little Calumet Leg and the existing Indiana
Avenue tunnels is the last major element to be done, and a plan is being reviewed.
A
potential problem is that the Indiana tunnel, which is in service, could fill
with effluent after the connection between it and the Little Calumet tunnel above
it is opened, Hauser said. The flood could then back up into the Little Calumet
tunnel.
As a result, the plan calls for diverting flow and installing a
bulkhead in the Indiana Avenue tunnel that will take about 30 ft. out of service
and prevent flows from pushing into the Little Calumet Leg.
"It (the
bulkhead) would prevent us being flooded out every time the Deep Tunnel fills,"
Hauser said. "It then prevents work stoppages and prevents us from having
to clean up and get back in there."
An existing drop shaft with access
to the Indiana tunnel would allow equipment to be brought in. The work would include
saw cutting the existing concrete lining, socketing the 10-ft.-thick concrete
bulkhead to the limestone and exploding the remaining 30 ft. between the Indiana
Avenue and Little Calumet Leg tunnels.
"The rock is very hard at that
location," Hauser added. "The microtunnel machine won't break it up." Major
Work Several major elements have gone into the Little Calumet Leg project,
and they included the following:
The shafts were opened with explosive
emulsion, the main tunnel was mined with a tunnel-boring machine and the near-surface
tunnels were created with soft-ground TBMs.
The shafts and tunnel
were lined with concrete, usually reinforced with rebar, and about 140,000 cu.
yds. of concrete was required. In addition to the 10 drop shafts, one access shaft
was made, Hauser said.
Concrete with strength of 10,000 to 12,000
psi was installed at the bottom of the drop shafts to resist the impact of water
dropped from about 100 ft. By comparison, the other concrete used on the project
for lining was usually about 4,000 psi.
Ninety-eight surface structures
were opened with backhoes, and these allowed the connecting structures to be formed
between existing sewers and the soft-ground tunnels that feed the drop shafts.
The surface structures were also needed to install the regulating structures.
Some sewer segments were taken out and replaced with about 6 mi. of new sewer.
Rock cut for the main tunnel was brought to a shaft with a continuous conveyor
and removed from the ground with a vertical conveyor. Mud for the tunnels and
shafts in the soft ground was removed with a train on rails, brought to a surface
structure and lifted out with a crane.
Coordination was required on the
project because the partnership was a line-item joint venture, Hauser said. For
example, Chesterfield, Mo.-based Affholder Inc. was responsible for the mining,
and Livonia, Mich.-based Jay Dee Contractors oversaw the soft-ground work.
"Once
we started making connections, the issues of ventilation, access and power supply
came up," he added. "We had to sort that out just to keep the dollars
straight so both of us could do our work."
|
print this page
e-mail this page
