Replacing a WWII-Era Dock
December 12, 2018
The dock facility serving the Biorka Island NEXRAD installation is at the end of its service life. The Federal Aviation Administration (FAA) is replacing the dock to allow continued use of this facility, as well as other activities on the island. R&M provided civil and geotechnical engineering, surveying and environmental services under contract to Parsons Technical Services, Inc. (Program Manager) for this dock replacement.
A WWII-Era Facility in Need of Upgrades
Biorka Island is located on the western perimeter of Sitka Sound in Southeast Alaska. The western or offshore side, of the island is exposed to the open North Pacific Ocean. The dock site is located in Symonds Bay on the Northeastern side of the remote island.
It is believed the dock dates back to WWII when facilities were constructed on the island by the U.S. Army. The Coast Guard, FAA and National Weather Service have used this pier since 1955. Other stakeholders include the U.S. Forest Service, State of Alaska and Southeast Alaska Regional Health Consortium (who has a camp facility on the island).
The dock was repaired and extended in 1955, 1971 and 1998. Wave protection, as well as a floating dock and ramp, were added in 1998. These facilities had reached the end of their intended service life and in recent years, load restrictions were placed on the structures. The facility is used by FAA personnel for moving people on and off the island, delivering heavy equipment to shore and supplying the sites with fuel. The dock replacement provides a new pier, pedestal crane, barge landing ramp and small craft float facilities, along with enhanced wave protection. This will allow the FAA to continue maintenance and upgrades of the existing upland structures/equipment and support environmental cleanup activities on the island.
Key Design Decisions A key decision that needed to be made in the concept and alternative analysis phase was to identify what type of dock was advanced for design and construction – an earth filled sheet pile wharf or a pipe pile supported platform dock. A comparison of the technical functionality and economic feasibility of construction of these alternatives was provided. To assist with the decision-making, R&M conducted analyses to better understand the environmental conditions at the site. R&M conducted a geotechnical field exploration, upland and offshore surveying, a coastal analysis to identify design winds/waves, and a site visit by the engineering and permitting team. The information gathered in these investigations was used to develop a comparative analysis of various alternatives, including concept level designs and cost estimates.
Ultimately, it was decided, based on the shallow bedrock conditions and the lack of suitable fill (which would have had to be imported to the site), that a steel pile-supported dock would be best suited for this site. In addition to the dock, R&M examined and developed designs for a small craft float and gangway, with provisions for lifting the gangway out of the water in inclement weather; a pedestal crane for the dock; berthing and moorage features, such as fenders and bollards; a barge landing ramp; and enhancements to the wave protection, lighting, electrical and fuel headers.
R&M also led the environmental permitting effort to support the project. This involved coordinating and obtaining an Incidental Harassment Authorization to allow construction in the environmentally sensitive Sitka Sound without unauthorized take of protected marine species.
R&M is currently supporting the project by providing engineering support during construction. Construction is scheduled to be complete by spring 2019.
Unique Challenges – Shallow Bedrock, Location and Wave Climate A unique aspect of this project is the shallow bedrock and remote location and associated logistical and construction means/methods challenges that need to be considered and planned for, as well as being addressed quickly as issues arise during construction. For this reason, the project was put out to bid using two alternate designs based on two primary construction approaches. Turnagain Marine Construction was awarded the construction contract. After award, R&M assisted in value engineering, which allowed the contractor to put forward value-added means/methods approach. The value engineering centered on providing larger precast concrete decking and a revised structural framing system, which allowed the contractor to maximize the efficiency of their large floating crane barge.
Another unique aspect, also related to the location of the site, is the wave climate. Waves are reported to have washed over the top of the existing small craft float at the site. Also the gravel barge landing site was routinely washed away by large storm events. There is an approximate 20-mile fetch across Sitka Sound to the north and an 11-mile fetch to the north-northwest. These fetches have the potential to produce large locally-generated waves at the site. Since Biorka Island is located at the outer fringe of Sitka Sound, it is also susceptible to open ocean swells from the North Pacific. This can result in large horizontal oscillations and large wave forces on fixed structures. To deal with this adverse wave climate several unique features were designed, including:
- A sheet pile wave barrier and rubble mound breakwater extension to protect the new small craft float.
- Energy absorbing pile collars on the small craft float.
- A new barge ramp with sheet piling around the perimeter and a reinforced interlocking concrete deck system.
R&M Staff Involved
John Daley, PE; Kim Nielsen, PE; Duane Anderson, PE; Josh Zellmer, PE; Josh Crowe, PE; Jean Cumlat, EIT; Kristi McLean, LEED AP BD+C, CESCL; Bob Pintner, PE; Brian Mullen, PE; Mike Adams; Bill Preston, PLS, GISP; Jim Robar, PLS; Jake Austin, PLS; Brian Meyers, PLS, CFedS; John Bennett, PLS, SR/WA; Luke Boggess, GISP; Jessica Koloski
Owner: Federal Aviation Administration
Civil Design Engineer: R&M Consultants, Inc.
Fuel Systems: Great Northern Engineering
Electrical Engineer: Morris Engineering Group, Inc.
Noise Studies: JASCO
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