In Atlanta, a severe drought in 2009 made the city realize that it needed a longer-term source of water, so planning began for a tunnel solution to provide an alternative water source for the metro area of 4 million people. The $300-million project, including a five-mile-long tunnel, is being built to connect the 400-ft-deep quarry with two water treatment facilities and the Chattahoochee River. When complete, the Bellwood quarry will become a 2.4-billion-gallon raw water storage facility that can provide emergency drinking water for up to 90 days for the city.
This project is the first of its kind in the U.S. where a tunnel-boring machine (TBM) was assembled on site. The 400-ft-long, 12.5-ft-dia TBM, dubbed Driller Mike, has completed about three of five miles of the project. Approximately 40% of the bored tunnel will receive 10-ft-dia cast-in-place lining, adds Gevan McCoy, vice president with Guy F. Atkinson Construction. Atkinson and Technique Concrete Construction are the joint venture tunneling subcontractor.
Like transportation tunnels, improving technology is making construction of tunnels easier, safer and cheaper, and advances in TBMs are a big part of those improvements. TBMs can be refurbished and moved to a new job. The TBMs and computer systems monitor and measure everything, allowing work to be completed uniformly.