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Projects > Skokie, IL South Leg Tunnel

This project involved a 75 year old sewer tunnel 8,800 feet (268m) long located in Skokie, Illinois. The 78" diameter horsehoe-shaped tunnel was in need of rehabilitation. Initial planning involved relining the tunnel with six inches of rebar-reinforced concrete with an epoxy coating. To meet deadlines, the selected contractor (Kiewit/Powers joint venture) had begun fabricating steel arch forms to be used in relining the tunnel.

Because the tunnel was in use and carrying a 2/3 capacity normal flow, it could not be inspected prior to the initial planning stages. Prior to the start of the project, a videotape of the tunnel was made by floating a video camera and flood lights through the tunnel on a pontoon raft. Upon inspection, it was realized that only a short segment of the aging tunnel was straight enough to reline using the methods originally planned.

It was determined that the relining would require a wet mix shotcrete application with rebar reinforcement (using a remotely operated arm and nozzle assembly) followed by a hand-trowel finish that would act as a base for the final epoxy coating. The wet mix shotcrete specification called for 6,000 psi concrete. The first layer would be 5 to 6 inches thick, with alkali-free accelerator added at the nozzle for better adhesion and faster set. The second coat would be applied without accelerator and finished with hand trowels so that the epoxy could be applied later.

Shotcrete Technologies' Shot-Tech Robotic Arm and Shot-Tech Nozzle assembly were selected because of their demonstrated ability to apply high-quality, high-production consistent shotcrete. The safe operation of the robot in the small tunnel was also of great importance to the Kiewit/Powers personnel.

The South Leg Tunnel project confirmed a number of Shotcrete Technologies' capabilities that solve tough shotcreting problems:

Using the Shot-Tech Robotic Arm, wet mix shotcrete can be accurately and consistently placed in a small, confined tunnel or other similar enclosed space.

Wet mixed shotcrete can also be used to finish large areas. Kiewit/Powers realized daily production progress of 120 to 150 linear feet per day.

Wet mix shotcrete can be easily pumped through a small diameter line from a source hundreds of feet from the robot.