Foundation pressure reduction and monitoring at Skelton Embankment Dam

Skelton Dam is a hydroelectric project located on the Saco River in southern Maine. The project is owned and operated by FPL Energy Maine Hydro LLC (FPLE), who purchased the project in 1999 from Central Maine Power Company. Skelton Dam was constructed in the late 1940’s, and was put into service in 1949. It is classified as a high hazard structure that is about 1,695 feet in overall length, and 75 feet high. The dam consists of a 495-foot-long concrete gravity spillway and non-overflow section on the left (referenced looking downstream), and a 1,200-foot-long earth embankment section on the right. This paper focuses on the embankment section of the dam. The embankment was constructed on a natural ridge consisting of stiff to soft marine clayey silt. The lower, softer portion of the clayey silt is interbedded with alluvial sand layers, and underlain by bedrock. During design of the dam, the subsurface conditions at the proposed location of the embankment section were the subject of significant subsurface investigation, laboratory testing and engineering evaluation. This work is summarized in two reports, which indicated that the potential for artesian pressure in the confined alluvial sand layers underlying the dam via a hydraulic connection to the reservoir was a major concern with regard to the long term stability. 16 pp., 7 references, 7 figures.