Kelley digger shield takes the express route to Atlanta
In July, the Atkinson/Technique joint venture entered into a contract with Kelley Engineered Equipment (KEE) for the supply of a 90.25" (2.3 m) digger shield. Six weeks later, the machine was on site and ready to work.
Averaging about 5.3' (1.6 m) per day, the distance needed to install four rings of liner plate, the shield finished its drive on October 6th, 2020. The task at hand was tunneling 356' (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 154" (47 m) of the CSX railroad passing intermittently overhead with cover as low as 15' (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' (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 liner panels and thrust off smaller ID panels that were erected within the safety of the shield.