Swan Lake to Lake Tyee Intertie
Geotechnical Construction | Micropile Foundations
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Project Description
The intertie project included construction of a 57-mile, 138 kV transmission line connecting the Swan Lake and Lake Tyee hydroelectric facilities, north of Ketchikan, Alaska. The new line provided for the interconnection of three major electric systems in the area, improving the overall utilization of available hydroelectric resources. Construction was completed exclusively by helicopter support, as the right-of-way was inaccessible by other means and precluded the feasibility of conventional transmission construction techniques. The line went into service in 2009 and was the first transmission project of this magnitude to be constructed using solely micropile foundations.
Team Members
Wilson Construction Company, Commonwealth Associates Inc., Dryden & Larue Inc., Tetra Tech EC Inc., Mountain Air Helicopters Inc, Temsco Helicopters Inc., and Crux Subsurface Inc.
Crux’s Role
Crux was contracted to provide foundation construction drilling services, and brought various cost benefits to the project. The line originally included 290 self supporting and guyed towers with 652 total foundations, but Value Engineering conducted in early 2004 reduced the number of tower locations to approximately 262 with 360 total tower foundations. Each tower location had between one and six foundations, supported exclusively by micropiles. The foundations were comprised of groups of three to nine vertical and battered micropiles, drilled and grouted at each site. Galvanized steel pile caps were installed using a bolted connection to the top of an all-thread reinforcing bar portion of the micropile. A total of 45,000 lineal feet of micropiles were installed, and an additional 9,000 lineal feet of guy anchors were installed at 500 anchor locations using similar methodology and equipment.
Further cost reductions were realized through Crux’s unique foundation design, which accommodates for various tower loads and geotechnical conditions by varying the number and depth of micropiles at each foundation. The foundation system was designed to identify and accommodate a range of geotechnical materials, from soft silts and clays to hard bedrock. The design also allows for efficiency and lower costs through the standardization of micropile materials. This permitted the use of uniform installation equipment. Light weight, highly capable, helicopter portable drill rigs were designed for efficient and environmentally sensitive setups at foundation locations, which varied from flat soft muskegs, to nearly vertical ridge-top locations. This highly flexible approach reduced project cost and minimized the potential of 'change condition' type change orders.
Flat deck barges and barge camps, including Crux’s “Alaska Solution”, were utilized as mobile living quarters, maintenance and machine shops, management and dispatch offices, helicopter landing zones, grout batch plants and materials storage yards.
In September 2005, The Swan Lake - Lake Tyee Intertie Project received a Special Recognition Award by the Outstanding Project Awards Program of the Deep Foundations Institute. Criterion for this award includes size, scope and challenges of the project, as well as the degree of innovation and ingenuity exercised and the uniqueness of the solution to the difficulties of the job.
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To request additional information, please use our Contact Page or call 866-CRUXSUB (866-278-9782).
