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May 21, 2021
Lower Granite Dam Spillway Pit Tag Design-Build
Location: Clarkston, Asotin County
General contractor: Northbank Civil and Marine
This project’s design constraints required tight control on materials and standards. Coupled with the design assumptions made during project development, this meant that all of the components were custom made. This requirement not only increased lead time but made vendor selection difficult because every company was starting from scratch. Each supplier was brought into the project only after a partnering meeting to explain the requirements and expectations, resulting in every component fitting as designed, with no rework required. The work area of this project was confined to the dam’s spillway deck (45 by 75 feet). During planning, it was quickly identified that this small area would not accommodate the large amount of permanent materials and construction tooling required. Northbank outfitted a 10-by-50-foot crane barge to both store material and provide lifting capacity. Only items that were earmarked as critical were allowed onto the barge or into the work area; all other items were stored off-site and brought in when needed using the just-in-time delivery method. Due to the limited cell phone and internet coverage within the Snake River canyon, communication occurred with each delivery company’s shipping departments during specific times of the day, allowing managers to prevent overcrowding and delivery delays. The area surrounding the antennas couldn’t have any metallic items within their scanning zone. This included concrete, rebar, anchors and any other item that could be potentially be cast into the concrete. A foreign-object sign in/out sheet was used to ensure that no item was misplaced in the antenna zone. Though concrete mix designs are not new, the fact that it had to be non-metallic and exceed 5,000 psi strength after 90 days, had to be placed on a 1:1 slope and be batched one hour and 25 minutes away completely changed the normal understanding of concrete. With input from local experts, Northbank’s concrete finishing team proved that this innovative mix design would work.