Palmer Station Small Boat Ramp Design

Location: Anvers Island, Antarctica

Michael Baker provided structural, geotechnical, and civil engineering design for an Antarctica boat launch ramp, gangway, and floating dock.

The station is located on the south end of Anvers Island, facing Hero Inlet in Antarctica. The inlet is characterized by a steep rocky shoreline and seasonal sea ice. Researchers use 10- and 15-foot inflatable boats in their work; in the future, 24-foot rigid inflatable boats will be used. The station also has a search and rescue vessel, and the research vessel (R/V) Laurence M. Gould, an icebreaker, ties up to the sheet pile pier. The station required a new small boat launching facility and floating dock for the inflatables. Safety was a key challenge because of the steepness of the shore and difficulty launching boats or loading people and gear in the sometimes harsh Antarctic conditions.

Michael Baker analyzed the tides, waves, and ice conditions in the harbor; assessed the geology of the site; and considered the remoteness of the location in the design. Michael Baker also evaluated custom dock systems in saltwater small boat harbors throughout Alaska.

The sea ice in Hero Inlet is not a continuous ice cover. There are tidal cracks along the shoreline and pancake and brash ice with bergy bits (small icebergs) in the inlet. These normal ice conditions are regularly affected by strong winds that alternately push ice into the area or clear the area, depending on wind direction. Michael Baker analyzed the actual force exerted directly by the wave, wind, or ice, and the loads from vessels affected by these forces. No engineering or geology reports were available to characterize the subsurface soil or rock. Site conditions were interpreted based primarily on photographs with confirmation by communication with Palmer Station staff.

The new boat launch ramp consists of reinforced concrete planks placed on ground-supported, rolled, structural steel support beams. The planks are reinforced with longitudinal and transverse deformed steel reinforcing bars, which are epoxy-coated for corrosion protection. The concrete mix design specifications included air entrainment to improve freeze-thaw performance and corrosion resistance. A design challenge was to provide the graded, even surface for plank installation. Michael Baker considered concrete walls, bulk fill, and steel column supports and the construction methods likely available at this remote site. A steel support system attached directly to the rock was the most viable alternative. This method had the advantage of prefabrication with conventional steel erection on site.
The shoreside and nearshore topography/bathymetry was problematic. Normal practice is to limit a boat ramp slope to approximately 15 percent. Because the grade of the Palmer Station slope is about 20 percent, significant changes in slope would have required expensive rock excavation or a lengthy projection into deeper water. Safety was an issue because of reduced traction from snow and ice on the ramp surface. The design incorporated a winch for the tow vehicle while on the ramp. The 20 percent ramp slope was used, which reduced the length of the ramp extending into the cove and the risk of damage from ice.

The natural slope of the seafloor from the tidal zone seaward is about 34 percent; the seafloor "drops away" from the boat ramp. The intact, unweathered rock made it difficult to mechanically alter the surface slope to conform to the boat ramp slope. To minimize rock removal, the bottom of the ramp is supported above the existing seafloor on rolled structural steel beam supports.

The floating dock is a pre-manufactured modular system adapted to the site with custom built elements. The dock can moor two 10- or 15-foot inflatables and two 24-foot rigid inflatables. It is connected to shore via struts pinned to anchors bolted into rock. The dock is accessed via a pre-manufactured 5-foot-wide by 24-foot-long aluminum gangway with handrails and an expanded metal grating for a walking surface.

The greatest threat to the dock is ice driven by onshore wind. The dock is designed to be removed from the harbor if threatened by adverse ice or storm conditions. The connecting struts and the gangway are designed to remain in place throughout the year.
 

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