Safety Inspection and Design Review of Spillway Radial Gates

Failure of the Folsom Dam Spillway radial gate no.3 on July 17, 1995, resulted in an uncontrolled release of water from the reservoir and prompted the dam safety community to rethink the safety of radial gates. In response to a request from the California Division of Safety of Dams, the authors performed safety inspections, design reviews and analyses on radial gates of sixteen Pacific Gas and Electric Company dams in California. This paper summarizes some lessons learnt during the authors' inspection of the gates. General considerations on the performance and safety of existing spillway radial gates, exposed to normal operational load, have been developed from the results of the investigation. Of particular interest are the design of the gate leaf, arm column system, and the trunnions and their anchorage, with respect to strength and operating or induced loads and vibration. Major areas to look for weaknesses in the existing gates include the bracing system and the moment capacity of the arm columns, as well as corrosive loss of metal and adequacy of connections. Induced loads include trunnion friction-induced moment in the arm columns and flow-induced vibration of partially submerged gates. 10 pp.