Failure of Sella Zerbino Secondary Dam in Molare, Italy

摘要

Supplementing the Bric Zerbino main dam, the Sella Zerbino secondary dam was a concrete gravity dam about 46' high and 360' long, located in Molare, Italy and completed circa 1925. In 1935, the secondary dam failed catastrophically, resulting in at least 111 fatalities. Starting with the planning of the project four decades prior to the failure, a series of human and physical factors interacted and compounded, until a 1000-year storm (more than 15" of rainfall in less than 8 hours) was the final physical trigger for the failure. Additional physical factors included lack of a spillway for the secondary dam, instability and erodibility of the foundation rock at the secondary dam, and grossly inadequate discharge capacity for the reservoir, which was exacerbated by clogging of spillways and outlets. The human factors contributing to the failure included hasty design and construction of the secondary dam after a late decision to raise the height of the main dam, inadequate geologic investigation and missed warning signs related to the foundation of the secondary dam, and lack of rainfall data to adequately design spillways and outlets. This paper describes these and other factors, viewed in the context of a general framework for assessing human and physical factors contributing to dam failures.