As permafrost thaws, experts learn to build on shifting ground

Best practices are emerging for building on frozen – and thawing – ground, filling a longstanding gap in construction guidance.  

From his home office in Yellowknife, Ed Hoeve has periodically kept an eye on the foundation of a bridge more than a thousand kilometres away.

The bridge, which crosses the Hans Creek floodplain in the Beaufort Delta, is roughly halfway along the Inuvik-Tuktoyaktuk Highway (ITH). As a geotechnical engineer, Hoeve was involved in designing the bridge’s foundation in 2013 and reviewing ground temperatures at the foundation a few years later, before the bridge was finalized. Earlier this year, he again analyzed temperature readings – this time, out of his own interest.

“I’ve been doing it just because I think it’s important,” he told Cabin Radio after last month’s Yellowknife Geoscience Forum. (The territorial government also regularly monitors and inspects the bridge, Sonia Idir, a spokesperson for the NWT’s Department of Infrastructure, said by email.)

Hoeve has good reason to be paying attention.

The bridge is built on piles – steel pipes embedded in holes drilled into the ground. Piles usually sit on bedrock where it is accessible, Hoeve said, but along the ITH, they depend on the strength of the permafrost.

“Cold permafrost is stronger than warm permafrost,” he said. Knowing the temperature of the ground is therefore crucial for estimating how quickly it will deform over time, and how soon the bridge risks being damaged.

In 2016, Hoeve found that the ground was about one degree warmer than the assumption he and his colleagues made in their design.

“Honestly, we were a little bit surprised,” he said.

Since then, ground temperatures have largely held steady at the bridge’s piers and cooled slightly at the supports on each end, according to his analysis of data up until 2021.

The findings suggest that the ground may need to be cooled to slow the bridge’s settlement sooner rather than later, Hoeve said. Although this was always in the plans, he said the experience highlights the importance of monitoring.

In Canada, engineers can often build something and walk away, Hoeve said. But that’s not the case in the North, especially as the ground warms.

“We’re pushing this whole idea of supporting things in frozen ground to the limit,” he said.

Climate change is bringing its fair share of challenges to northern infrastructure, but experts have been finding ways to adapt and manage common problems. They’ve also made strides toward establishing best practices for building on frozen ground.

In the past decade, standards and guidelines have been published for installing thermosyphons (passive cooling systems that help preserve permafrost), conducting site investigations, managing permafrost degradation and incorporating climate change considerations into infrastructure planning. More permafrost-related guidance is on the way.

“There’s been quite a bit of advances,” said Guy Doré, a retired professor in the Department of Civil and Water Engineering at Laval University, who has studied the effects of permafrost thaw on infrastructure.

Yet Doré said as our warming climate reshapes the North, experts still have a lot to learn.

A standards gap

For years, experts and policy advisors have recognized the lack of northern building standards.

In a 2009 report, the National Round Table on the Environment and the Economy – an external advisory body to the federal government at the time – acknowledged that the North is “an afterthought” when it comes to infrastructure.

“Codes and standards for buildings reflect little of what it takes to design, build, and maintain infrastructure in the North, let alone a North facing climate change challenges,” the authors wrote.

By default, many engineers and builders working in the North have therefore used standards better suited to other parts of the country, according to Doré. “That was creating lots of problems,” he said.

Many buildings sit on top of a concrete slab, for example. To adapt this typical building technique to the North, Doré said some people have added insulation under the concrete. But the design transfers heat from the building to the ground. If the permafrost is ice-rich, the structure will sink.

“In most cases, these buildings have failed in a few years,” Doré said. In Salluit, Nunavik, for instance, the community’s fire station sank into the ground a year after it opened, as CTV reported.

The increased need for maintenance and repairs as a result of climate change is one of the driving forces behind the flurry of building standards and guidelines, according to Doré. At the same time, northern development is on the rise, he said.

“People are realizing that we need better guidance and better standards to work in the North.”

A timely addition

One of the organizations working to fill the gap is the Standards Council of Canada. Since 2011, the SCC has been working to support the development of standards for the North through the Northern Infrastructure Standardization Initiative, known as NISI (pronounced NEE-see).

So far, the initiative has resulted in more than a dozen standards with more in development, said Kala Pendakur, the SCC’s manager of infrastructure and climate change. Among standards covering a range of climate-related issues, a handful focus on designing, building and maintaining infrastructure in permafrost regions.

Northerners may have already had this know-how, Pendakur said, “but we’re helping to make sure that it’s written down and it’s viewed by people.”

Similarly, the Canadian Geotechnical Society is planning to include a chapter on permafrost in a 2023 edition of a foundation engineering manual used by consultants in Canada and abroad.

“It’s about time,” said Jim Oswell, a geotechnical engineer and permafrost expert who is leading the chapter’s development. There hasn’t been a significant addition to the literature on permafrost foundations for more than 20 years, he said. “We’ve managed without it, but I think it’s a good addition.”

Oswell points out that documenting best practices for building on permafrost is timely. Many engineers with permafrost expertise are retired or approaching retirement, he said, with few early-career professionals set to take their place.

As the pool of permafrost engineering expertise declines, it’s a good time to document knowledge, he said.

Are best practices helping?

So far, best practices for building on permafrost have largely taken the form of guides or standards.

“By default, standards are voluntary unless they are put into a regulation or a code,” Pendakur said.

Some best practices are slowly making their way into regulations. Provisions for building in permafrost regions were introduced in the 2019 edition of the Canadian Highway Bridge Design Code, according to Dwayne Torrey, director of construction and infrastructure standards for the CSA Group, a standards organization. The code lays out design requirements for bridges in most of Canada.

The code’s next iteration, to be released in 2025, will include more permafrost-specific provisions, including some related to site investigations, thermal modelling, foundation design and climate change considerations, Torrey said in an emailed statement.

The aim is to “support the design of resilient bridges in the North,” he wrote.

Permafrost-related building standards are already making a difference according to Stephen Wolfe, a research scientist with the Geological Survey of Canada. New infrastructure being built is better suited to conditions in the North, he said.

Some structures built in the past would be unlikely to be built today, Wolfe said. As an example, he points to Yellowknife’s Northern Frontier Visitors Centre, which was demolished in 2020. Partially built on stilts over a pond, the building had structural issues related to frost heave and had to be abandoned.

Wolfe also thinks guidance on climate change adaptation is being used more widely.

In the past, he said, few buildings in Yellowknife were constructed on bedrock. “You basically had the Explorer Hotel and that was it.” But in the past 20 years, he said, there has been a move toward building on rock because it provides a more solid foundation.

According to Pendakur, the goal is to make infrastructure that is safer, more reliable and that requires fewer repairs. But it may take a while to see the full effects of the emerging guidance. The NISI standards are still in the process of being implemented, she said, and permafrost thaw doesn’t happen overnight.

Oswell thinks monitoring infrastructure to see how it performs will now be especially important. Keeping an eye on infrastructure can help owners catch potential problems before it’s too late – or much more expensive – to intervene, he said.

As temperatures continue to rise, experts may also have to come up with new methods for building on permafrost, according to Doré. Approaches for managing permafrost degradation typically rely on cooling the ground, he said, which may become increasingly challenging. Engineers may have to consider pre-thawing permafrost prior to construction or designing structures that can withstand shifting ground, he said.

At Hans Creek bridge, there are still no signs of settlement or movement, according to the GNWT’s Idir.

Looking back, Hoeve said he and his colleagues should have known the permafrost underlying the bridge might be warmer than they assumed. “The clues were there,” he said.

The information wouldn’t have changed the bridge’s design or the need for intervention, he said, but it serves as an important reminder. “We can learn lessons from what we do.”

This article is produced under a Creative Commons CC BY-ND 4.0 licence through the Wilfrid Laurier University Climate Change Journalism Fellowship.