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Elevated Station Design for the South Pole Redevelopment Project
at Amundsen-Scott South Pole Station
7. Amundsen-Scott Station Design Features
If there was an advantage for the development of an elevated station at the south pole site of Amundsen-Scott, (compared to the Halley and Filchner sites), it is the comparatively milder conditions of winter winds and annual snow deposition, and the absence of significant horizontal movement of the ice sheet. Whereas Halley’s Brunt Ice Shelf site had to overcome gale force winds and annual snow accumulation of 1.5 meters, the Amundsen-Scott site must only deal with 200 mm of annual snow deposition, and moderate winter winds (the strongest recorded wind at the South Pole was 87 kph and the average winter wind which causes drifting is on the order is 24-32 kph). Compared to the annual horizontal movement of the Filchner site of approximately 850 meters, the site at Amundsen-Scott moves only 10 meters. These comparatively milder conditions allowed the design team to approach the development of the elevated station from a different point of view. Instead of being faced with the disruptions and expenses of raising the building every year, they could, through effective snowdrift control, develop schemes that would postpone the need for jacking for more than a decade.
Ultimately, the adopted objective at Amundsen-Scott was to limit the number of times the facility would need to be raised during its design life of 25 years to a maximum of twice. With this premise in mind, a series of predictive studies at the Canadian based research facility of Rowan Williams Davies & Irwin (RWDI), including wind tunnel testing, Computational Fluid Dynamics, and Finite Area Element computer modeling techniques were initiated. The studies indicated that the linear complex of C-shaped building forms elevated approximately 3 meters above the surface with the long axis oriented perpendicular to the prevailing winter winds and a tapered windward face would perform well. The tapered leading edge smoothly channels the wind beneath the station complex. Forced to accelerate, the wind carries the snow well past the buildings where it is deposited in long leeward drifts. A windward drift also forms just in front of the station. Over time, the leeward and windward deposits will tend to connect around the ends of the station and gradually build into a rough crater shape. Eventually, the windward drift will build to a point where it will prevent the wind from channeling beneath the station, and as a result, drifting will begin to fill in beneath the structures. At that point, the station will be raised approximately 4 meters (one floor level), and the cycle will begin again. The duration of the initial cycle has been effectively increased by NSF’s decision to initially erect the station on a compacted snow berm which is itself 2 meters higher than the surrounding grade. Subsequent studies indicate that when all factors are considered, the station’s ability to control drifting could continue until the windward drift approaches the height of the station’s mid section. This prediction indicates that it may not be necessary to raise the building for 15 years or longer. The actual time period will ultimately be determined by the growth rate of the windward drift.
It was a recognized early on that no matter how well snow drifting could be controlled, at some point the station would need to be raised. While snow drifting control issues were being studied and tested, therefore, an equal amount of attention was being given to the jacking and structural systems relationships.
Because of the large size of the station (6,040 square meters is roughly 5 times the floor area of Halley V), the duration of the jacking process and the size of the crew which would be needed to do the work were important concerns. Maintaining full operations during the jacking process was also an objective, which implied the need to develop a way to maintain flexible connections with utilities and plumbing while the station was being lifted to its new height.
The final structural/jacking design involves an integral main building floor “platform”, supported by double trusses that straddle primary 914 mm diameter steel pipe columns located outboard of the building envelope. The primary columns transfer building loads to welded steel box beams on timber raft footings. Jacking involves adding a 4 meter column extension to the top of each column, placing hydraulic jacks under spreader beams at the top of each extended column, connecting the spreader beam to the trusses with steel rods, disengaging the trusses from the columns, hoisting the station up a full floor’s height (3m), and then securing the trusses again at the top of the column extension.
It was also determined that the most practical solution would be to lift one C-shaped Pod at a time, in an alternating series of 250 mm lifts until the full 3 meter lift was accomplished. The process requires one 100-ton hydraulic jack and operator at each column during the process. With 18 columns per C-shaped Pod, a minimum crew of 18 operators and 36 jacks is required (the crew will alternate between Pods for each lift). The entire process is estimated to take approximately 30 days.
Proceed to next section: 8. Conclusion
Table of Contents
1. Abstract
2. Background
3. Old Casey Station
4. Filchner Station
5. Halley V
6. A New Vision for Amundsen-Scott Station
7. Amundsen-Scott Station Design Features
8. Conclusion
9. References
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