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Chattahoochee Raw Water Transmission Main

The Chattahoochee Raw Water Transmission Main project was constructed by the DeKalb County Department of Watershed Management as part of an effort to replace aging and failing infrastructure, and to meet water demand requirements for a newly expanded water treatment plant.  The new 96-in transmission main is approximately 2.5 mi long and includes several significant tunnel crossings.  The 10 ft diameter horseshoe-shaped Run 7 crossing is roughly 800 ft long and was excavated using drill and blast methods.  The complex geology along the alignment consisted of inter-layered metagraywacke, mica schist, and biotite gneiss of the Piedmont province.

Lachel provided tunnel engineering services to the contractor on the project including review of available geotechnical and historical information, development of a geotechnical investigation and laboratory testing program, rock mass characterization and analysis, and design of initial ground support for the tunnels and shafts.

During construction, Lachel worked with the contractor in the field to address variable ground conditions and modify the ground support as necessary.