Reclamation Information Sharing Environment (RISE)

Hydraulic jacking is a serious threat to concrete spillway chutes, illustrated by the catastrophic chute failure that occurred in 2017 at Oroville Dam, a California Department of Water Resources facility. To support Reclamation’s efforts to mitigate against hydraulic jacking failures, experimental data from the existing literature were reanalyzed and new experiments were conducted. Analysis of previous work produced new relations between uplift pressure and the dimensionless aspect ratio of offset height and gap width at an open spillway joint. New laboratory testing led to further improvement, with new equations for estimating uplift pressure, flow rate through joints and cracks, and the effects of various methods of remediating existing offsets. The new laboratory tests included measurement of boundary layer velocity profiles approaching a modeled spillway joint. Uplift pressures were normalized to the velocity head near the boundary rather than the mean channel velocity head used by previous investigators. This normalized uplift varies with the joint aspect ratio and the flow depth to offset height ratio. This reduces the uncertainty of predicted uplift pressures by a factor of about 3 compared to previous methods that ignored the boundary layer. The new tests of flow through joints showed that extremely large flow rates are possible. Testing of joints and cracks with irregular geometries led to useful relations for estimating uplift at joints that are chamfered, rounded, skewed, beveled, or otherwise relieved to reduce uplift. Finally, the new relationships developed in this research were incorporated into spillway analysis software tools used at Reclamation.