Santeetlah Dam, a concrete arch dam near Robbinsville, North Carolina, was constructed in 1928. Ten years later, two large buttresses were constructed on the downstream side of the dam. The owner, Alcoa Aluminum Company, was concerned that an alkaline-aggregate reaction might be occurring in the buttresses and that expansion of the buttresses caused by the reaction might be pushing the top of the concrete arch upstream.
In order to determine if the dam was experiencing bending due to the expansion of the buttresses, in situ stress measurements were conducted in the concrete arch. Three angled overcoring holes were drilled opposite each buttress from a barge located on the upstream side of the dam, just above the water level. A fourth hole was drilled inside the dam from a narrow inspection tunnel using DA Smith's (formerly Agapito Associates, Inc.) air-powered, man-portable CP-65 core drill. Measurements indicated that the dam was not experiencing significant bending stresses due to expansion of the buttresses.
In 2003, DA Smith (formerly Agapito Associates, Inc. Field Services)
was contracted to supply the specialized equipment and personnel required to conduct overcore stress measuremets at the U.S. Bureau of Reclamation (USBR) Seminoe Dam, located near Rawlins, Wyoming. The project consisted of two vertical holes drilled from the crest of the dam and two horizontal holes drilled from the downstream face of the dam. Eleven 2D stress measurements were completed using the U.S. Bureau of Mines borehole deformation gage method between 49 and 75 feet deep in the two vertical holes. Nine stress determinations were completed in the two horizontal holes from 10 to 30 feet deep.
In 2018-19, DA Smith (formerly Agapito Associates, Inc.) conventionally cored three 18-inch- diameter holes each to a depth of 35 feet on the crest of Shasta Dam for the United States Bureau of Reclamation (USBR). Large-diameter cores were required for concrete properties testing as part of the Shasta Dam Raise Project.
DA Smith subcontracted Groupe Fordia Inc., Northwest Machine, and other expert vendors to design and build the unique 18-inch-diameter coring bit and tools. Each 5-foot core run weighed approximately 1,000 pounds. The core was boxed in specially designed crates and shipped via temperature-controlled freight to the Denver Federal Center for materials properties testing. The 18-inch core holes and other 10-inch, 80-foot-deep holes were pump-grouted with non-shrink concrete.
In 2020, DA Smith cored a horizontal utility hole from the outside face of the Sutton concrete gravity dam through to a main access corridor inside the dam. The work was contracted with the the U.S. Army Corps of Engineers (USACE), operators of the dam. An extensive health and safety plan was prepared and security clearances obtained in accordance with USACE regulations. The project was completed safely and on schedule. [Contract No. W9123720P0078]
In 2017, DA Smith (formerly Agapito Associates, Inc.) completed narrow-access diamond core drilling, concrete sampling, and core structural logging, as part of an evaluation of the interior conditions at five locks and dams on the upper Mississippi River for the U.S. Army Corps of Engineers (USACE). Falling head tests were completed in the holes to measure permeability in the guide walls concrete. ESI Laboratory, LLC was subcontracted to perform concrete core petrographic and air void analyses. [Contract No. W912ES17P0091]
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.