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Hard rock breakthrough achieved on Atlanta water tunnel

Breakthrough on a new 8km tunnel in Atlanta, US will help bolster the city’s water supply as key part of the Atlanta Water Supply Programme which is scheduled to become operational in September 2019.

The project will turn a disused quarry into a 9.1bn litre reservoir and connect it to water treatment facilities around the city.

“Our schedule for the project was very aggressive but the project team stayed together to overcome issues related to the mining of the tunnel,” said Bob Huie, who is project director for the project construction risk manager PC Russell JV.

The project used a 3.8m diameter Robbins Main Beam tunnel boring machine – named Driller Mike after local rapper and activist Killer Mike, to drive the curved tunnel through hard granite ground conditions.

The designer for the construction works including tunnel and shafts JP2, formed by Stantec, Prad Group and River 2 Tap, specified the use of a hard rock TBM for the scheme to meet the construction schedule. Operation and assembly of the TBM was then sub-contracted to a joint venture of Atkinson and Technique.

The TBM was launched in 2016 and ground conditions meant that advancement rates were as low as 1.5m in eight hours in the early stages. “The granite has a UCS of between 117 and 310MPa UCS. The beginning of the job was tough,” said PC Russell JV tunnel superintendent Larry Weslowski. However, the project team later improved advance rates to as much as 38.4 in one day.

The scheme also encountered contaminated groundwater which required remediation before it could progress.

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