Difficult Access Horizontal Coring
The Gorge Dam is one of three generating facilities operated by Seattle City Light on the Skagit River in Washington State. The dam’s original power tunnel is still in service, and has been providing power to the city of Seattle since 1924. In order to improve the efficiency of the Gorge Powerhouse, a second power tunnel was commissioned and entailed boring through rock between the Gorge Dam and Gorge Powerhouse. Once complete, the second tunnel was expected to help Seattle City Light realize its goal of 15% power from renewable resources.
Seattle City Light
Crux was contracted to provide exploratory drilling along the proposed tunnel alignment. This challenging project entailed drilling deep vertical, angle and horizontal borings in highly fractured bedrock. Optical Televiewer (OPTV) data acquisition for feature orientation, packer testing, and the installation of vibrating wire piezometers were also completed in select borings. Six boreholes were drilled in total, to depths between 360 and 800 feet, using an HQ wireline coring system. Crux drilled two of these boreholes from within an existing 1000-foot adit, requiring specialized illumination, air ventilation and safety training. All crew members entering the adit were required to complete a confined space drilling course.
Access constraints were also a key component of the project, as helicopter transport was required to access the two borings completed inside the Devil’s Elbow Adit. Equipment was flown in and placed on a wheeled platform at the adit portal. The platform was then winched inside the adit to the required location.