On July 1, 2020, the Atkinson/Technique joint venture entered into a contract with Kelley Engineered Equipment (KEE) for the supply of a 90.25-in. (2.3-m) digger shield. On Aug. 15, just six weeks later, the machine was on site and ready to work. Averaging about 5.3 ft (1.6 m) per day, the distance needed to install 4 rings of liner plate, the shield finished its drive on Oct. 6, 2020.
The task at hand was tunneling 356 ft (109 m) of varying stiff clays, saprolite and mylonite for the City of Atlanta’s Water Supply Project Phase II. This undertaking connects a new 3.4 billion gallon (12.9 million m³) emergency drinking water reservoir to a new treatment plant. However, the shield’s most important job was to provide the required Cooper E-80 loading support under CSX railroad passing intermittently overhead with cover as low as 15 ft (4.6 m).
In addition to thrust and steering systems, the unit was designed with special features to expedite assembly and disassembly in the heading. After the collapsed shield was lowered down a 30-ft (9.1-m) diameter shaft, it was transported through an existing pre-lined tunnel and assembled at the mining site. The shield was assembled within these liner panels and thrust off smaller ID panels that were erected within the safety of the shield.
Fabrication, workshop assembly and factory acceptance testing were performed at KEE’s longtime partner, Wolf Hills Fabricators, LLC in Abingdon, Virginia. Wolf Hills supplied exceptional quality and was instrumental in achieving the very quick delivery.
Atkinson Construction’s Konner Horton was quoted as thanking KEE for “a machine that worked great and getting it done for us so quickly.”