Consultant Ramboll, contractor Bam and sub-consultant Sweco are building the new British Antarctic Survey wharf at Rothera, to the south of the Cape Horn to accomodate research ship the RRS Sir David Attenborough.
Designers have kept the wharf structure simple, but contractors still face major challenges building it in one of the remotest parts of the planet.
The site is in a remote location 14,500km from the UK. As a result, transporting construction equipment and people has been worked out in minute detail.
The same goes for working out craneage, working times, construction methods, and wharf designs so that project can be completed safely, on time and on budget.
The new wharf is being built because the RRS Sir David Attenborough is too big for the old wharf.
Original designs involved keeping the existing wharf operational for as long as possible and incorporating the existing structure within the new one.
But it was decided that it was too risky to complete the complex work in the time available, and so the strategy changed.
Under the new plan, the research station at Rothera will be without a wharf for around 18 months while the old one is dismantled and the new one built.
The station is located on a spit of land in the north west of Antarctica where temperatures range from 0°C to 5°C in the summer and -5°C to -20°C in the winter.
Conditions in the winter are too harsh for construction workers to live and work on the wharf so all work must be carried out in the summer season – from mid-November to early May.
The new structure was designed in modules and constructed off site in the UK during the Antarctic winter, to minimise work required on site.
To create the new 84.5m long and 36m wide wharf, the team has designed a series of 10 steel frames which are fixed back to a rock protruding into the water.
Sheet pile walls enclose the frames and the area will be backfilled to create the new berth. Installation of the frames is being carried out in two stages with the 36m long frames divided into two 18m long modules.
New wharf design
In season one, which runs from mid December in 2018 until the end this month, the existing wharf has been removed and the first halves of 10, 18m long back frames, have been installed. These have been backfilled to create a working platform for the work being carried out in the second season.
In the second season, which runs from December 2019, 18m long front frames will be connected to the back frames via pinned connections. The sheet pile walls around their perimeter will also be installed, the longest of which will be about 16.5m long. They will then be backfilled.
To connect the new structure to the rock, a 63mm diameter vertical rod on the front of each half frame is inserted into a 150mm diameter hole in the hard granodiorite igneous rock and then grouted in place.
This type of connection minimises the need for divers to carry out work in the water.
“This proposal greatly reduces the amount of diver times which greatly reduces the down time for us as they can’t dive if there are any marine mammals in the water or if there’s brash (loose) ice as their lines can get trapped,” said BAS senior infrastructure programme manager David Seaton.
Rock to infill the new wharf had to be blasted from an adjacent cliff. But because of the severe environmental constraints of working in Antarctica, these had to be limited in size and timing, with monitoring to ensure the underwater noise does not affect marine life.
The structures were modelled in 3D and the sequence tested in virtual reality, to reduce risks to safety and to the programme. The nearest hospital to the site is a five hour flight away and bad weather can sometimes prevent aircraft from landing.
“The effort that went into this was phenomenal,” said Seaton. “First of all the dismantling method statement was about 600 pages long, [setting out] what happens if you do this or that. The amount of planning was huge and it’s now paying dividends as it’s come down safely.
“We had to make sure we weren’t working out our problems at site and that the number of surprises were limited.”
Excavators with 30m long booms also had to be used and were shipped out in pieces and reassembled on site.
Even the mix for the grout has been specially designed to minimise work on site and any problems with the pumping operations.
“We’ve devised a mix that is prebagged and premixed and we’ve done it so we don’t need any aggregate,” said Sweco design team leader for the Rothera Wharf project Stewart Craigie. “We did investigate some clever grouts which were designed for off-shore wind turbines, but they couldn’t give us the certainty we were looking for.
“We did 32 trial mixes. Number two would have given us the physical characteristics we needed, but we went with number 29 to give us the right performance.”
Construction workers also had to be carefully vetted to ensure they could cope with living in such a remote location for the near five-month season.
Getting the workers out to the station is also challenge.
After reaching Punta Arenas on the southern tip of Chile or Stanley in the Falkland Islands (a 24 to 36-hour journey from the UK) personnel are flown out to the station from on a small turbo-prop Dash 7, taking around five hours.
Boats carrying the engineering equipment needed for the construction take around 38 days to sail from the UK to the research station.
The demolition and construction programme is half complete as the project reaches the end of its first season. But before the team leaves for the winter, it must pack up and “winterise” equipment that can be left on site.
“Anything left outside will be buried in snow and so part of the plan is to store it in such a way that it can be easily dug out/retrieved at the start of the summer,” said Ramboll technical advisor to BAS Jenny Symons.
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