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  • Wanapum Monolith Stabilization - survey


Project Highlights:

  • Engineering News-Record Northwest’s Energy/Industrial Project of the Year in 2015
  • Quick response survey and inspection work for a spillway crack
  • Established survey control on the dam for use in measurements and drill hole layout
  • Provided 24/7 inspection as needed for repairs
Wanapum Monolith Stabilization - spillway
Wanapum Monolith - steel tendons
Wanapum Monolith - surveying

Project Summary

Client: Grant County Public Utility District
Location: Grant County, WA
Services Provided:
  • Land Surveying
  • Construction Inspection
In February 2014, Grant County PUD discovered a 65-foot long, 2-inch wide horizontal crack across one of the spillway monoliths at the Wanapum Dam. Drawdown of the reservoir began immediately to reduce pressure on the dam, stabilize the crack, and allow for detailed inspections.
Grant County PUD quickly began working with experts and regulators to assess the damage and begin repairs. MacKay Sposito was called upon to provide survey and construction inspection, and we quickly mobilized a survey crew to establish control on the structure to allow for measurements and drill hole layout.
Following assessment, the design and construction team began working night and day on the repairs, which consisted of drilling vertical tendon holes through the dam into bedrock, inserting post-tensioned stranded steel tendons, and adding grout to affix them to the bedrock. Grouting work was also completed to fill voids and fissures and prevent water leakage through the underlying bedrock. Repairs were completed in March 2015.
During repairs, MacKay Sposito provided onsite construction inspection and materials testing 24 hours per day to help ensure the work was properly documented and completed in accordance with the construction documents.
Successful completion of this emergency project can be attributed to the teamwork and collaboration between Grant County PUD, regulators, contractors and consultants. In September 2015 this project was awarded Engineering News-Record Northwest’s Best Project of the Year in the Energy/Industrial category and was a recipient of the 2015 American Council of Engineering Companies Project Award.