6 minute read
Overcoming the challenge of piling in a changing north
Setting the first pile for the foundation of a 900kW wind turbine. (B.Walsh, STG Inc.)
STG Technician preparing and setting foundation piles. (B.Walsh, STG Inc.)
Climate change is altering the permafrost foundation of the Arctic, and challenging the resilience and innovation of piling companies operating in the far north like never before
By Paul Adair
Building in the Arctic has always presented a set of unique challenges for construction companies, from isolated communities with limited access to skilled workers and equipment, from working through harsh winters and navigating rough geographic terrain to gaining project acceptance from local communities. Overcoming these kinds of challenges can prove difficult and tend to add to a project’s overall complexity and costs.
“If you go into those remote locations where they rely on winter roads or have fly-in access only, things like Internet interconnectivity, sourcing and moving materials, housing costs, energy costs, and food costs can be substantial, particularly in those months when the winter roads are unavailable,” says Paul Gruner, President and CEO at Det’on Cho Management LP in Yellowknife, NT. “Farther north, in places with even less access, you will have to plan your projects a season in advance, at a minimum.”
PERMAFROST’S FOUNDATIONAL PROBLEMS
For piling, the logistical hurdles to overcome are compounded by the onset of climate change that’s causing the permafrost underfoot to become somewhat less permanent. Permafrost is defined as any ground that remains completely frozen for at least two years in a row – essentially, a frozen solid mass of earth or frozen water with small amounts of soil particles.
Even under ideal conditions, piling in permafrost conditions can prove to be difficult. Taking into account long-term and rapidly accelerating climate warming, however, there’s an increased risk to northern structure foundations. Because some permafrost is essentially just water, it has nearly zero compressive strength when thawed, as evidenced by the growing number of sagging buildings across the north.
“Where the permafrost underlying buildings is ice-rich, any degradation of the permafrost could lead to thaw settlement and building distress,” says Canadian Construction Association President Mary Van Buren. “As such, managing erosion and sedimentation for northern community infrastructure will be a specific challenge for the piling industry going forward.”
PILING IN THE NORTH
There are generally two kinds of piles commonly being used for foundations
“Managing erosion and sedimentation for northern community infrastructure will be a specific challenge for the piling industry going forward.” – Mary Van Buren, CCA
installed into permafrost: drilled and slurried piles or driven piles. A third type − helical (rotated-in) pile systems − has also seen some increased interest as a potential piling solution.
Drilled and slurried piles are installed in a drilled hole approximately 150 millimetres larger than the pile diameter to a specified depth. The annulus between the pile and the in situ material is filled with a sand (or sandy-gravel) and water slurry that’s mixed to about a 100 millimetre to 150 millimetre slump, which is placed like concrete and vibrated to reduce voids.
Driven piles are placed similarly to driven piles in conventional thawed material, with the exception that the permafrost can be very hard to penetrate and there’s the possibility of structural damage to the pile from overdriving when using an impact hammer. Both impact and vibratory hammers are used and, occasionally, pre-drilling and temporary ground-warming systems are used to increase production.
Whatever piling method is used, however, it will require contractors to invest in either reliable equipment that works in a northern climate without breaking down, or additional measures to protect piling equipment from the frigid cold.
“Much of the equipment and construction techniques designed for construction down south are simply not well-suited the arctic cold,” says Edward Yarmak, President at Alaska-based Arctic Foundations Inc. “Much of this can be solved by using engineered controls such as temporary structures or enclosed equipment, which – while effective - all add to the cost to the project.”
Foundation piles with thermal-coils, set in place, waiting to be slurried. (B.Walsh, STG Inc.) A crane moving a Thermo Helixpile. (B.Walsh, STG Inc.)
THE CHALLENGES ARE HEATING UP
As climate change becomes more evident in the north, the once-permanent permafrost is thawing and a greater rate than in years past. And because permafrost is a viscoelastic material with strength that is temperature dependent, it grows weaker as the active layer (the top layer of soil that undergoes freeze thaw action seasonally) increases in thickness.
“Basically, what’s stable today may not be stable tomorrow,” says Yarmak. “Overall, the designers are calling for deeper − and sometimes larger-diameter − piles when climate change is considered. So, larger and more robust equipment is becoming necessary for installation. Some existing foundations are moving when they shouldn’t, and repairs increasingly need to be considered.”
To help counter the challenges to piling created by the thawing permafrost, Arctic Foundations manufactures Thermopiles and Thermo Helix-piles, which are both installed through the drill and slurry technique.
The Thermopile is a passive groundcooling device that removes heat from the soil whenever the air is colder than the soil, helping to ward off the effects of climate change locally. The Thermo Helix-pile, on the other hand, is a thermo-
– Edward Yarmak, Arctic Foundations Inc.
pile with a continuous flight of helix attached in the bearing zone. The Thermo Helix-pile uses frozen soil shear along the helix perimeter and/or the edge of the drilled hole to resist axial load and is probably the highest-capacity pile that can be installed in permafrost.
The durability of this product is impressive; the very first thermopiles were installed back in 1960 at a site with marginal permafrost, and they’re still in service today!
Where there are issues that preclude drilling open holes for drill and slurry installations, Arctic Foundations manufactures thermosyphons, which are non-structural thermopiles that can be installed in, or adjacent to, driven pile systems to remove heat from the ground and maintain the thermal regime.
“We have supplied hundreds of thermosyphons that were installed by drilling next to existing piling in order to cool the bearing zone and reduce pile movement so that existing structures can continue to be used,” says Yarmak. “Generally speaking, because our passively refrigerated systems remove heat all winter, the piles never see the freefield ground temperatures.”
THE PATH AHEAD
Without changes to existing practices that do not prioritize climate resiliency in infrastructure, climate change costs for Canada could escalate, particularly in places like the Arctic, where the impact of warming will be felt more acutely. Research has shown that the benefits of investing in community adaptation, innovation, and resilience at the frontend, will outweigh the cost of such investments by a ratio of six to one.
“We will certainly need to take advantage of new technologies to overcome the challenges presented by climate change,” says Gruner. “Not piling-specific, but when you look at a project like the Inuvik to Tuktoyaktuk Highway, where they’re able to contain permafrost and somewhat control melting, we can really see how technology and science are able to be brought in to help us weather climate change for the better.” l
