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BY DON W. HAYLEY, P.ENG.
(click on images to view)
 Canada’s
scientific community continues to preach the climate change
message, constantly reinforcing the
belief that observed climatic warming trends are greatest
in the
north. Design engineers who provide services on northern
projects may find the array of published predictions from
global circulation models confusing, but anyone who assesses
the historical records from communities in the north, particularly
the Mackenzie Valley, will find the evidence for a climatic
warming trend rather compelling.
The air temperature in the valley has, in fact, warmed about
1.7 C° over the past century, according to Environment
Canada.
The Canadian Council of Professional
Engineers held a workshop last February to examine the role
of Canada’s engineers
in adapting to climate change. This article is a brief summary
of a presentation I made at the workshop. It describes our
success at EBA Engineering Consultants Ltd. implementing
a procedure into our practice that explicitly recognizes
climate change as one more variable to be considered for
design of structures on permafrost foundations.
The Intergovernmental Panel on Climate Change concluded
in the early 1990s that arctic regions are particularly vulnerable
to climate change, partially because of a perceived concern
about widespread thinning or disappearance of permafrost.
Environment Canada formed a project group with funding from
the Panel on Energy Research and Development to establish
guidelines for permafrost engineering design. The objective
was to provide a strategy for incorporating climate change
into long-term planning in Canada’s North.
The results were presented in an Environment Canada report,
Climate Change Impacts on Permafrost Engineering Design (1998).
The study team comprised government scientists, academics
and practitioners prominent in northern climate and permafrost.
Early skepticism about the outcome turned into acceptance
and support for a project screening tool that has been in
common use at EBA for the past five years. Implementation
and application of the risk-based principles from that process
to many projects have proven to be both rational, and to
pass the test of peer and regulatory reviews.
Project Screening
For Climate Change Risks
A project is screened to determine its sensitivity to climate
change, identified as a probability that climate change will
adversely affect permafrost soils or rock that must remain
frozen to ensure stability of any structure it supports.
Secondly, the consequences of any change, should it actually
occur, are examined.
The screening process schematic is shown here. The relationship
between sensitivity and consequence define the risk that
climate change imposes on the project. A criterium is provided
in the study report that establishes the level of analysis
that is appropriate for project design, based on the risk
of failure.
The analysis complexity can range from no action required
or simple qualitative assessment based on judgment to complete
quantitative analyses supported by complex ground thermal
modeling tools.
These quantitative analyses require cautious attention and
documentation of the input parameters that describe the climatic
effects over the life of the structure and their annual variability.
Specific guidance is provided in the study report on how
to assess the sensitivity and the consequence level for any
project.
Three projects from EBA files were used in the February
workshop to demonstrate how the system has been adopted into
our engineering practice. They included a water dam with
a permafrost core at Ekati Diamond Mine, a complex building
foundation in Inuvik, and upgrading of the primary highway
leading to Yellowknife. That highway lies over particularly
sensitive, discontinuous permafrost.
The relative positions of these projects on the risk chart
are shown in the attached figure.
For this discussion, I will describe only the building in
Inuvik as it embodies all of the facets of the project screening
system.
Inuvik Regional Health Centre
The new regional health centre, constructed in Inuvik in
2001/02, required an innovative approach to foundation design
for permafrost soils prone to substantial settlement if allowed
to thaw.
Most previous foundations for large buildings in Inuvik have
been elevated and supported on timber or steel piles frozen
into the underlying permafrost. Over the years, this type
of foundation system has fallen out of favour for architectural,
functional, esthetic and cost reasons.
An alternative and somewhat high-tech foundation solution
is to intercept heat transferred from the structure to the
underlying permafrost with two-phase heat pipes or thermosyphons.
These passive cooling devices extract heat from below the
structure and dissipate it to the atmosphere during the cold
winter months.
The mechanical components are designed, manufactured and
installed by Arctic Foundations of Canada Inc. The geotechnical
design requires two-dimensional heat flow analyses in order
to configure the piping system required to confirm long-term
thermal stability of the underlying permafrost.
The principal variable in such analyses is the anticipated
variability of outside air temperatures and any climatic
trends that could affect future long-term performance.
Application of the screening principles to this project
identified that the permafrost sensitivity was high because
of the presence of abundant shallow ground ice within the
Town of Inuvik. The failure consequence was rated as major
or medium to high because the structural design has a low
tolerance for differential movements and the economic or
social impact of hospital closure could be significant.
This placed the project into a high-risk category, requiring
a complete quantitative analysis of climate change effects.
Comprehensive geothermal modeling of the foundation system
was required, adding considerably to the complexity and cost
of the foundation system design.
The foundation design included a probabilistic evaluation
of Inuvik air temperature records in order to anticipate
long-term trends for a design service length of 30 years
starting in 2000. The results were interesting because they
show that all five years preceding 2000 were well above the
mean, and the 43 years of record and one warm year (1998)
had a 1/100 annual exceedance probability For this project
the design was tested for all of the following scenarios:
• Five consecutive 1/5 annual exceedance probablity
warm years followed by a 1/100 AEP year,
•
Ten consecutive 1/5 AEP years,
•
Warming trend of 0.47 C° per decade.
The design was judged appropriate for any one of the above
climate variability scenarios.
Climate change can be considered one more variable to be
considered within a probabilistic framework for the design
of northern structures. This is particularly true where stability
of underlying permafrost soil or rock is essential to long-term
performance.
Application of climate change principles to design still
requires considerable judgment because regional climatic
trends are poorly defined and the literature contains conflicting
information that, if taken at face value, could stifle rational
northern development.
Reference: Etkin, D., 1998, Climate Change Impacts on Permafrost
Engineering Design. Internal report by Environmental Adaptation
Research Group, Environment Canada.
Don Hayley, P.Eng., is principal engineer at EBA Engineering
Consultants Ltd. He has been active in northern engineering
worldwide for more than 30 years.
Editor’s Note: This article
is the second in a series presented by APEGGA's Environment
Committee regarding the
role of professional members in sustainability, climate change
impact and adaptation. These articles will address industry
specific initiatives, international initiatives, and regulatory
considerations - meant to raise the level of awareness and
generate discussion. The opinions expressed by the author
are his own and not necessarily those of APEGGA.
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