AAI drilled at the Roanoke Rapids concrete buttress dam in 2007, 2009, and again in 2014–15 as part of an ongoing investigation of the dam’s structural stability. Tasks included core drill, in-situ stress measurements using the United States Bureau of Mines (USBM) Borehole Deformation Gage (BDG) method, borehole imaging, core logging, permeability testing, and geotechnical instrument installation.
In 2007, AAI completed the following:
- Drilled two 6-inch-diameter core holes vertically through the dam and into the foundation.
- Drilled four HQ3 core holes through the dam for observation and instrumentation.
- Completed two stress determination holes using the USBM BDG overcore method. A total of 18 stress measurements were made at depths ranging from 6.5 to 63.5 feet deep.
- Installed vibrating wire piezometers, lightning-protected proving rings, and data loggers.
- Performed high-resolution borehole imaging of all holes.
- Core drilled through the emergency spillway from the narrow crest of the dam.
Two of the drill sites were on the emergency overflow section of the dam that is less than 6 feet wide. The drill rig was disassembled down to five parts at the toe of the dam, and then lifted to the crest of the dam with a high-reach crane and reassembled. A work deck was built on-site to provide a safe work location on the narrow crest.
Core was structurally logged, depth marked, striped, photographed, and boxed. A high-resolution borehole image was made of each borehole. Holes were grouted with cementitious grout.
Vibrating wire piezometers and proving rings were installed with lightning protection and connected to a data logger system. Signal cables were run through conduit. A summary report of all field activities, stress determinations, core logs, borehole images, and instrumentation installation details was generated.
In 2009, the following tasks were completed:
- Installed two inclinometer casings in HQ core holes drilled through the dam and 50 feet into bedrock.
- Installed three Geokon Soft Inclusion Stress Cells (SISCs) in Block 26 of the emergency spillway.
- Video surveyed holes using a WC1750 Slimline Dual View Camera.
- Conducted permeability testing of the foundation bedrock.
- Completed unconfined compressive strength (UCS) tests on selected samples of concrete and bedrock.
- Prepared a final report.
In 2014–15, AAI completed core drilling and 74 USBM BDG overcoring runs in seven vertical holes up to 62 feet deep to measure in-situ stress. Measurements were conducted according to specifications prepared by HDR Engineering, Inc. of the Carolinas, and were ultimately used for thermomechanical modeling of the dam.