REPAIRS OF SPILLWAY GATE WELD DEFICIENCIES AND UPSTREAM FACE OF DAM PIER CRACKS AND WALL WEATHERING AND EROSION,HARTWELL DAM

摘要

Hartwell Dam is located on the Savannah River, about 89.3 miles upstream from Augusta, Georgia. The project consists of a gravity type concrete structure constructed across the Savannah River channel on a bedrock foundation flanked by earth embankments on the Georgia and South Carolina sides. The dam has a controlled ogee spillway with flip bucket consisting of 12 tainter gates (40 feet long by 35.5 feet high each). The concrete section is 1,900 feet long with a maximum height of 204 feet and a controlled spillway of 568 feet long. With the rolled-earth embankments, the total length of the dam is 17,852 feet. The powerhouse contains 5 conventional generating units with a total capacity of 422,000 kw. The project provides hydropower, flood control, water supply and recreation. During tainter gate inspections in 2002, numerous weld deficiencies such as undersized welds, excessive undercut, lack of fusion, arc strikes, unacceptable profile, rust, missing welds, plate delaminations and plate cracks were observed. The gates were fabricated in the late 1950's when it appears that there was lack of quality control and a lack of qualified welders. Partial annual funding has resulted in the repair of 9 of 12 gates. The project is under an operational restriction in using the gates for flood control conditions. Significant economic and environmental impacts would result from the failure of a gate. Erosion and leaching of the surface of the piers and walls of the upstream face of the Hartwell Dam have been occurring for many years. This on-going process has been periodically inspected and monitored since 1977. A Phase I Reconnaissance Report has been prepared to address causes, evaluation of conditions, and recommendations for further investigations and remediation. The deterioration and weathering of the concrete is confined to an area on the piers and walls limited to an estimated 8 feet in height. The weathering of the concrete is suspected to be caused by the rise and fall of pool levels and the impact of wave action. Poor concrete quality may be contributing to the accelerated process. The concrete in the affected zone is becoming increasingly porous and a proliferation in the number of cracks and craters is being observed. It is suspected that this condition also exists below the water surface. Complicating factors promote deeper water infiltration into the wall likely reacting with the concrete causing further deterioration through this on-going cycle.