Raw Water Intake Tunnel, Southland Contracting
This project for the Monroe County Water Authority includes one 45-ft diameter shaft 170 –ft. deep; 6000 lf of 114-in tunnel under Lake Ontario with a 4” thick 4,000psi shotcrete liner; six 60-in. drilled pump shafts 100-ft deep; 220 lf 12-ft main pump adit tunnel; and two marine intakes (114-in and 36-in diameter, 120-ft deep in 60-ft of water) on Lake Ontario.
The 45-ft diameter 170-ft deep Riser shaft was excavated by drill-shoot. Liner plate, rock bolts and fiber reinforced shotcrete were used to support the excavation. During the shaft excavation, the 220 lf main pump adit tunnel was excavated by drill-shoot. Rock bolts and fiber reinforced shotcrete were used to support the adit tunnel. The 114” Diameter - 6000 lf tunnel under Lake Ontario was lined with a 4” thick layer of 4,000psi fiber reinforced shotcrete the entire length of the tunnel. The shotcrete was applied with a custom built electric powered Shot-Tech Robotic Arm supplied by Shotcrete Technologies (see photo of Robotic Arm and carrier especially designed to travel in a circular tunnel). Material delivery was accomplished by dropping the shotcrete down a drop pipe to the bottom of the 170’ deep shaft into a remix box. Shotcrete would then flow out of the remix box into a six cubic yard moran car. Then the mix was transported down the tunnel via the electric moran cars which then fed the shotcrete to the custom electric shotcrete pump also supplied by Shotcrete Technologies.
Challenges: Transporting the shotcrete mix down the tunnel 6000 LF. It took some trial and error to adjust the chemicals to get the mix just right—ShotSet 250 liquid Accelerator was used throughout. Kristian Loevlie of STI played a big part in fine-tuning the final mix design. Applying shotcrete in a 114” diameter tunnel isn’t an easy task. The custom built robot/electric pump allowed Southland to be efficient when applying the shotcrete. A total of approximately 3000 CY of shotcrete was applied during the project which lasted 2 ½- 3 years.
