Reclamation Information Sharing Environment (RISE)

Hydraulic jacking has caused catastrophic spillway chute failures in recent years, including at Oroville Dam in 2017 and on the fifth drop structure of the St. Mary Canal on Reclamation’s Milk River Project (Montana) in 2020. Void development beneath spillways is a frequent issue on Reclamation projects and hydraulic jacking failure modes are commonly considered in Reclamation risk analysis studies. This project reanalyzed laboratory tests performed ca. 1976 and 2007 to develop improved predictive relationships for uplift pressure at sealed joints (no foundation drainage) with varying geometries. Uplift pressures were related to mean channel velocity, estimated boundary layer velocities, and the dimensionless ratio of gap width to joint offset height. New laboratory testing performed in 2021 led to a better understanding of the role of boundary layer velocity profiles in the generation of uplift pressure and developed the first experimentally validated relationships for predicting flow rates through open joints. These findings will aid spillway designers and risk assessment teams considering spillway slab anchors and foundation drainage systems. Also see https://data.usbr.gov/catalog/8049.