Post-Tensioned Anchor Load Distribution for Gated-Spillway Lift Joint Stabilization

While constructing a spillway overlay in 2014 at the six-bay gated-spillway at the Boney Falls Hydroelectric Development, horizontal lift joints in the mass concrete making up the ogee section were observed. Observed leakage indicated possible debonding of the lift joints. Field coring indicated possible increased uplift pressures within the joints. With uplift assumptions based on the field data, the ogee sections at the lift joints did not satisfy Federal Energy Regulatory Commission (FERC) stability criteria. To improve stability of the ogee sections, post-tensioned anchors were considered. Since the anchors were to be installed with tainter gates in the down position, only one anchor per bay could be installed, avoiding the gate structure with the drill while engaging and improving the stability of lift joints. To improve load distribution at the uppermost joint across the bay, a spreader beam, pocketed into the ogee, was installed. The anchors were proof tested in a two-stage tensioning process.