Walter F. George Lock and Dam Major Rehabilitation Evaluation Report, Prevention of Potential Structural Failure

The Walter F. George Lock, Dam and Powerhouse is situated on the Chattachoochee River near Ft. Gaines, Georgia within the Apalachicola, Chattahoochee and Flint River System. The Walter F. George Project has been in service for 35 years (1963 - 1998) providing major benefits of navigation, flood control, power generation and recreation to the surrounding community and the nation. In addition to normal maintenance costs, the project has had to fund major repair efforts over those years totaling $20,930,000 including $11.5 million spent from 1981-1985 for the embankment cutoff walls. These repairs have not been the result of infrequent storms or structural design deficiencies. It is because the limestone foundation material is deteriorating from erosion and solutioning under normal operating conditions. Because this phenomenon can not be accurately predicted and distress in the structure does not become evident until the condition borders on eminent failure, this condition is considered a very serious safety issue.

A Board of Expert Consultants was convened in May 1996 to review the current situation and offer solutions. The Board listed the main causes of seepage as: (1) Inherent discontinuities in the Earthy Limestone formation from joints, natural weakness, sinkholes, etc.; (2) Manmade penetrations, such as core borings, monitoring and dewatering wells, sheetpile penetrations, and excavations for foundations; (3) Erosion and solutioning of the formation due to seepage velocities and the chemical determination of the water. The Board listed 5 possible courses of action that the District could undertake for the future of Walter F. George. (1) Do Nothing; (2) Continue current activities with grouting; (3) Install an impervious blanket upstream of the dam; (4) Perform innovative grouting; (5) Install a concrete cutoff wall with a concrete apron immediately upstream of the dam structures. The District has deemed that the innovative grouting and the impervious blanket options are not viable techniques at this site. The current grouting program has had some success but can not solve a worsening problem. The Board strongly recommended against the "Do Nothing" alternative. Therefore, risk assessment alternatives, having in common the placement of a continuous concrete cutoff wall with a minimum thickness of two feet extending horizontally some 2040 linear feet along the entire length of the spillway, powerhouse, non-overflow wall, and lock monoliths and 400 feet east of the lock approach, was the optimum solution. The work includes a 5 foot thick concrete cap immediately upstream of the monoliths to beyond the cutoff wall to seal the lake waters from entering the formation between the wall and the structures. The concrete wall would be placed by overlapping 34 inch diameter concrete piles spaced such to provide a minimum 24 inch thickness of wall. 12 pp.