Wanapum Dam repaired using post-tensioning anchors

Abstract

In central Washington, the flow of the Columbia River is harnessed by the Wanapum Dam which is part of the Priest Rapids Hydroelectric Project owned and operated by Grant County Public Utility District (GCPUD). The dam extends approximately 8300 feet from bank to bank and includes earth embankments, concrete gravity sections and a 10 unit powerhouse. Adjacent to the right embankment is a concrete gravity spillway featuring radial gates measuring 50-feet wide and nearly 70-feet high. In the early 1960s, when built, these seven-story spillway gates were the highest in the world. In February 2014, during a routine maintenance inspection, observant workers noticed a slight misalignment in the roadway deck curbs and handrails on top of the spillway. Further investigation uncovered a 65-foot long by 2-inch wide crack that spanned the full length of Monolith 4. Due to the potential risks of a catastrophic failure, GCPUD immediately drew down the reservoir and began work on developing an emergency remedial procedure to repair the crack in the dam. Sixty-one-strand post-tensioned anchors, underwater Ogee Spillway bar anchors and a grouting program to seal the crack were among the main techniques performed to repair the Dam. This case study will address in detail the successful use of these techniques.