NZ Geomechanics News

Winter drilling in Antarctica

The Australian Antarctic Division (AAD) is in the process of investigating the feasibility of providing year-round aviation access to the continent through the construction of a paved runway near Davis Station, East Antarctica. Currently access to Davis is limited to icebreaker ships throughout the summer season, approximately 2 weeks travel time from Hobart, Tasmania; or by air via the summer-only link from Hobart through the Wilkins aerodrome ice runway, located approximately 70km inland from Casey station. Travel between the stations can result in significant delays due to weather, and the requirement for good ice conditions at Wilkins means this route is only open for a few weeks at the start and end of summer, as midsummer temperatures soften the ice surface. Additionally, early season access to Davis is achieved by the construction of a skyway on the sea ice near station, the condition of which varies year to year.

Davis Station is located on a rocky outcrop on the coast of the Vestfold Hills, a predominantly ice-free area covering approximately 410 square kilometres. The station is located 20km from the edge of the ice plateau, and conditions are somewhat mild for an Antarctic station, with temperatures around zero degrees through the height of summer, and reaching as low as -40C in the winter. 

With its location in the Vestfold hills, one of the only ice-free areas of East Antarctica, Davis Station presents an opportunity to develop a more reliable air-link to Australia, which can be functional throughout the winter months, as well as being less reliant on stable ice conditions to allow travel in summer. 

Along with the AAD, AECOM have been undertaking investigations into potential runway sites for a number of years and, having identified a potential candidate, a ground investigation program was developed to sample the permafrost sediments and bedrock across the site to assist with the detailed engineering design, delivery and construction methodology process, pending project approval. In order to limit environmental impacts from drilling and reduce disturbance to native fauna typically present during the summer months, the program was planned to be carried out in winter. A team consisting of specialist drillers from Northern Canada and a Geotechnical Engineer from AECOM New Zealand were engaged to carry out this field investigation. They would be joined by 22 other expeditioners at Davis for the winter season.

After jumping through COVID hoops to get as far as Hobart, the team departed by ship in late February. After two and a half weeks crossing the Southern Ocean, the group arrived at Davis, and began the task of unloading the ship and resupplying station before the previous wintering group departed. Over the next few weeks the drill rig was put together from the numerous shipping containers of equipment sent down from Canada, temperatures fell and winter began to set in.

Due to the fact that contact with the outside world is limited to a satellite internet link over winter, and getting people in or out is almost impossible, medical emergencies have to be handled on station with limited support. Medical facilities are relatively limited, so health and safety practices, and accident/injury prevention are of key importance. With plans to drill off-station throughout winter, with cold temperatures, limited weather forecasting ability, and with no sunlight for a significant portion of the winter, the next few weeks were spent working to develop robust safety documents and plans for all aspects of the drilling program, as well as preparing emergency management plans and conducting exercises with the station Search and Rescue team. 

Once the documentation for drilling practices had been finalised and signed off, the initial part of the drilling program began within station limits, while work carried on to ensure the appropriate controls, training and support were in place for drilling off-station. A number of shallow boreholes were drilled across the wider station area, intended to support the design of future station infrastructure, for temporary support of the Davis Aerodrome construction, and for the future development of Davis station. Throughout the next few weeks of drilling the field team worked to come up with processes to deal with drilling in the worsening winter conditions, including travelling onto the now formed sea ice to drill holes and pump seawater to use as drilling fluids, combating rapidly freezing water hoses and aggressive permafrost threatening to grind progress to a halt and lock drill rods into the ground, and coercing machinery to start in the sub-zero temperatures. 

One of the biggest challenges was dealing with the weather, which is very difficult to predict due to the lack of monitoring locations across the continent. Throughout the winter the weather typically fell into one of two broad patterns: stable high pressure systems, with relatively low winds, clear skies and cold temperatures; or low pressure systems which brought comparatively warmer weather, but high winds and snow. High winds and low visibility during the low pressure systems made work unsafe, with blizzards routinely exceeding 50 knot sustained winds (90km/h) and entombing buildings and the drill rig in large snow drifts. The highest winds experienced during the winter reached over 94 knots (175km/h) and required multiple days to dig the buildings and roads around station free. Drilling was focused around the calmer days where work could be carried out more safely, however these days were typically much colder, which brought its own challenges, such as keeping drilling fluids liquid, getting equipment started and keeping it running, and avoiding cold injuries from exposure to wind chill temperatures, which reached -46C on our coldest day. 

Throughout this period the wintering team settled into their new home on station, complete with lots of comforts and distractions to keep everyone happy throughout their stay. The station spent time working on hobbies in the workshop, keeping fit in the gym, as well as many nights playing pool or watching movies from the extensive DVD collection in the cinema, and more than a few hours spent in the station bar or making more supplies in the (now defunct) station brewery. An inter-station darts competition was held between the four Australian Antarctic and Subantarctic stations, with Davis topping the table, took an award in the 48 hour Antarctic Winter Film Festival and the on-station chef ensured the winterers maintained their first layer of protection against the cold throughout the season. 

Those willing to brave the temperatures outside got to see auroras overhead throughout the winter, occasionally on their way back to the mess hall for lunch during the darkest months. After everyone had completed their field travel and survival training (including spending a freezing night out in a plastic bivvy bag in -30C overnight temps), groups were able to travel on the sea ice to reach the four field huts spread across the area for recreational overnight trips, and to see the sights of the Vestfold hills. To mark the midwinter solstice, a huge feast and celebration was prepared, and a large hole was cut in the sea ice to prepare for the traditional midwinter swim. Air temperature on the day was -23C, with a water temperature of -1.8C keeping the swims short and sweet. 

Eventually all of the paperwork, training and planning came together to allow the drilling program to progress off-station. Under strict environmental controls and permits, the rig was moved from drill site to drill site, along the route of the proposed access link and aerodrome site, drilling boreholes ranging from 4 to 40m in depth. The sites covered varied terrain, with core samples recovered from hard metamorphic bedrock, to sediment filled valleys with permafrost and extensive subsurface ice lenses. The frozen ground surface acted to limit water infiltration from drilling, and the utmost care was taken not to impact the fragile environment of the investigation sites. Temporary access tracks were formed to allow the drill rig to reach the investigation sites, with extensive documentation of the existing conditions to allow reinstatement after the work is complete. 

Progress along the site alignment carried on throughout the rest of the winter, interspersed with frequent blizzards which required clearing snow from the station and access roads before the drill rig itself could be reached to be dug/melted out of the snow. The use of tracked vehicles, Hagglunds, to access site sped this process up a bit, however between the weather and the challenges of drilling and moving the rig around the site throughout winter, progress was still limited to 1-2 boreholes a week. 

By early September, the strong polar sun made the days considerably warmer, and while this made drilling progress easier, it posed additional challenges in maintaining the integrity of the recovered permafrost samples, and core boxes had to be quickly ferried back from site into refrigerated shipping containers to avoid losing the ice from the cores. 

By early November, the team reached the far end of the site alignment, and completed all of the main priority boreholes. After this the rig was brought back to station in order to be dismantled, washed down and packed away for transport back to Canada, while the team got ready to hand the station over to the next group of expeditioners coming in for the summer season. The warmer weather brought wildlife back to station for the first time since March, and the last few recreational trips were made to see the nearby penguin colonies and newborn Weddell seal pups on the ice. The first plane landed on the sea ice outside station in mid-November, and the winterers of the 74th ANARE gradually departed station to fly to Casey station on their way back to Tasmania, with the team having successfully completed their winter drilling season in Antarctica.

Tags : #Antarctica#drilling#Winter

NZ Geomechanics News
Tiarnán Colgan
NZ Geomechanics News>Issue 102 - December 2021

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