Evaluating safety of concrete gravity dam on weak rock: Scott Dam

Scott Dam is owned and operated by Pacific Gas & Electric Co. (PG&E) as par t of the Potter Valley Project. Although it is an unimpressive concrete gra vity dam [233 m (765 ft) long with maximum water surface 33.4 m (110 ft) ab ove tailwater], the dam has unusually complex and weak foundation rocks; th is condition caused design changes during construction, numerous subsequent special investigations, and several corrections and additions. A main stum bling block to clarification of the dam safety issue for Scott Dam has alwa ys been difficulty in characterizing the foundation material. This paper di scusses an approach to this problem as well as how the safety of the dam wa s subsequently confirmed, following a comprehensive program of research, in vestigations, and analysis from 1991 to 1997.