In 2016–17, DA Smith (formerly Agapito Associates, Inc. Field Services) completed drilling, instrumentation, and overcore in situ stress measurements for HDR at Duke Energy’s Walters concrete arch dam located on the Pigeon River in western North Carolina. The investigation was conducted under the oversight of the Federal Energy Regulatory Commission and an Independent Board of Consultants.
Tasks completed included:
Drilling was conducted on the non-overflow sections of the dam and on the dam spillway 180 feet below the crest. Difficult-access conditions required placing drilling equipment with a high-lift crane and use of a barge to access remote sections of the dam.
Drilling was completed using DA Smith's Ingetrol 75E electric-hydraulic drill mounted on a specially-modified narrow track frame to allow access to constricted areas of the dam.
Drilling into the face of the dam was conducted through a special, valved stuffing box as a precaution to shut in water flow in the event of a dam breach.
All drilling was conducted using redundant environmental containment systems to prevent contamination of water sources. Biodegradable food-grade oil was used in all drilling equipment. Excellent intact core samples suitable for testing were achieved through the concrete-bedrock interface at the base of the dam.
Stress measurements were conducted using three different overcoring techniques. Excellent agreement was achieved between the methods. The Sigra method, which utilizes an onboard data logger instead of a cable to store strain relief measurements during overcoring, allowed measurements to reach to the deepest parts of the dam, thereby producing a unique and complete vertical stress profile though the dam. Resulting stress measurements provided HDR with key baseline input for 3D finite-element structural modeling of the dam.
Read technical paper on project: “In Situ Stress Measurements and Instrumentation Installation—Duke Energy Walters Dam, Waynesville, North Carolina,” Association of State Dam Safety Officials, Dam Safety 2018 Conference, Seattle, WA, September 9–13, 2018.