Difficult Access Core Drilling
The San Vicente Dam Raise Project, located approximately 25 miles outside San Diego, was an emergency water storage project designed to increase the capacity of the existing reservoir by 152,000 acre-feet. The existing 220-foot concrete dam was raised 117 feet to 337 feet using the roller-compacted concrete technique (RCC). During the final stages of completion and certification of the dam raise, the California Department of Water Resources, Division of Safety of Dams, required coring and testing of the RCC to verify that design standards were met.
San Diego County Water Authority
Crux provided geotechnical drilling and sampling services prior to the dam raise, and was selected to return to participate in the post-construction coring program. The scope included 6-inch diameter wireline coring, core extraction, development of a customized core transport system, and design and installation of specialty platform setups.
10 borings were completed on the right abutment, which allowed for conventional access. Three borings were completed, two vertical and one angled, from the downstream face of the dam. Crux employed a customized drill platform designed and installed by Crux using crane support. Three borings were also completed on the left side of the spillway, which required helicopter support and helicopter-portable mini cranes to transport equipment and assist in core handling. Overall, Crux completed 16 borings, ranging between 56 and 167 feet, for a total of 1,586 feet of drilling.
Challenges included extracting and transporting unfractured 10-foot core samples, which was essential to the RCC program. Crux worked directly with the tooling manufacturer to develop custom sized inner tubes with tighter tolerances, which remedied the mechanical fractures being caused the industry standard core barrel system. Once obtained, the 300-pound core samples were transported across the crest of the dam by a specialty pulley system designed and implemented by Crux.