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North Buckhead Newsletter

October 2004

Harold Cunliffe is the NPU-B rep on the Nancy Creek Tunnel Technical Advisory Committee (NCTAC). 
Previous reports are at www.nbca.org/tunnel.htm. 
I am reporting events to the best of my recollection and I will try to differentiate when I am offering an opinion.  This Report may not be the position of the NCTAC nor the City of Atlanta. 
To date, the Tunnel Boring Machine (TBM) that was launched from the R.  M.  Clayton Shaft is just 826 feet short of the Roswell Shaft.  That means it is sitting under Post Chastain and is a week or two from its final destination.  The TBM that began its journey at the Roswell Shaft arrived at the Johnson Ferry Shaft in early June.  Work is well underway on the Intake Tunnels that connect the existing trunk sewer main to the Tunnel.  Although this involves blasting, there have been no reports of disconcerting rumbling or shaking. 
The Tunnel walls will be lined with concrete throughout its entire length.  This operation has begun at the Johnson Ferry Shaft and has proceeded 2,370 feet downstream towards the Roswell Shaft.  In April, a significant fissure in the rock resulted in a leak and several streams in the vicinity of Windsor Parkway dried up.  An irrigation system was installed to protect trees from drought conditions.  The Tunnel lining operation will reach the Windsor leak in 6 - 8 weeks and then 4 weeks after lining, grout will be injected behind the new Tunnel wall.  It is anticipated that this will plug the leak.  The recovery of the ground water table will then begin but it could take another year before flow is restored to the creeks. 

A small creek in the vicinity of Pineland has also dried up.  The City arborist is monitoring the trees and soil moisture monitors (tensiometers) are being installed.  Should the trees show stress or should the tensionmeters indicate drying, an irrigation system will be similarly installed and operated until the stream flow is restored. 
The completion of the Tunneling will mark a significant risk milestone.  The biggest variable in terms of cost and schedule was the condition of the subsurface rock.  With this nearly out of the way, the City can now make projections with much greater confidence.  Based on these continuing reports, it is my belief that the City will meet the Consent Decree Date of December 31, 2005 and that the Tunnel will open prior to January 24, 2006 under budget. 
Please e-mail questions that are of general interest and they will be answered next Report.  Here are a few that have been posed:
Q: Why can't the grouting begin immediately after the Tunnel liner is installed at Windsor?

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