Libby Dam Hemispherical Bulkhead, Gates and Spillway Inspections
Since 2009, HDR has inspected the spillway radial gates and regulating outlet tainter gates at the Seattle Districts Libby Dam. The inspection included rope access structural inspection, hoist system mechanical inspection, and non-destructive testing of fracture critical welds. HDR also performed a crack and joint survey of the Libby Dam spillway documenting the existing condition including cavitation and environmental deterioration.
Additionally, in a two-phase inspection effort between 2008 and 2011, HDR inspected both the downstream (dry) and upstream (wet) sides of the Libby Dam hemispherical bulkheads. The 20-foot diameter bulkheads were installed during the original construction of the dam as "temporary" penstock plugs where generating units were not installed. No ready access to either side of the bulkheads existed and they had not been inspected since installation. HDR's inspection was performed via rope access, under permit-required confined space guidelines. It included the design, fabrication, installation and operation of a lightweight drain system capable of being installed on-rope yet withstanding over 250 feet of head. Inspection access required the use of industrial magnetic anchors for accessing the downstream side of the bulkheads and a 200-foot decent through an emergency stoplog slot to access the upstream side of the bulkhead. The inspection included visual structural inspection and NDT of the bulkhead welds.