Monitoring Study: Yellowknife Highway #3 Construction Test Sections

In 2011 the Government of Northwest Territories Department of Transportation secured $157,500 in funding from the Northern Transportation Adaptation Initiative (NTAI) aiming to assess the vulnerability of Yellowknife’s Highway 3 and prepare it for the challenges anticipated from climate change. Highway 3 is located between Rae and Yellowknife in Canada’s Northwest Territories (NWT) and it is the only all-weather road connecting the city to Southern Canada. Between 1999 and 2006, the final 100 kilometres of Highway 3, from Behchoko to Yellowknife, were re-aligned, straightened and paved to meet design standards allowing posted driving speeds of 100 km/hr. The project was a collaboration between the Government of Northwestern Territories’ Department of Transportation (GNWT-DOT), Engineers Canada and BGC Engineering Inc who acted as consultants. Located in in discontinuous permafrost, the combined increase in both snowmelt and rainfall during the last decade has led to numerous issues such as; significant sagging in soil-covered areas, cracking and undulations in the road surface, shoulder rotation, ruts, potholes, and visible camber in culvert crown. Following the PIEVC protocol, more than 1100 highway infrastructure element – climate event combinations were assessed. Site investigations found the most acute areas of road instability resulted from melting of ice-rich permafrost in areas of sub-surface transition (i.e., soil-rock, unfrozen-frozen, warm-cold permafrost), where the road was constructed adjacent to a water body and where the road crossed over the old alignment. BGC designed and constructed four test sections to address these problems. The test sections involved varying levels of embankment reconstruction as well as thermistor cables were installed within the embankment to measure and monitor changes in temperature.

Read the Summary Link to Full Case Study

Identifying Actions

The Public Infrastructure Engineering Vulnerability Committee (PIEVC) protocol was followed to assess impacts of climate change on the infrastructure and incorporate adaption into the design, development, asset management and decision-making. This assessment was led by BGC Engineering, with input from the Senior Transportation Planner at GNWT-DOT and the Manager of Professional Practice at Engineers Canada. The PIEVC has developed a generalized step-by-step protocol for the vulnerability assessment of infrastructure to climate change. This protocol provides a general framework and can be used for any infrastructure and has the following steps:

  • Step 1: Project Definition
  • Step 2: Data Gathering and Sufficiency
  • Step 3: Risk Assessment
  • Step 4: Engineering Analysis
  • Step 5: Recommendations

The limitations of the assessment where concerned with the uncertainty in projecting future ground and water temperatures. Unlike air temperatures, ground and water temperatures are more difficult to predict because they depend on other factors such as precipitation, ground water levels, snow cover or vegetation cover. A 1.5 day Vulnerability Assessment Workshop was also conducted in which 15 participants from Operations and Maintenance, Planners, Engineers, Scientists were brought to the table. This workshop included a ½ day highway drive with stops and was very helpful in identifying new elements. The mixing of the groups during different break-out sessions worked well however time was an issue and no pre-selection of crucial combination was carried out.

Implementation

The field investigation activities carried out in 2010, included jet wash drilling, auger drilling, cone penetration testing, electrical resistivity tomography profiling, test pit excavations and active layer probing. Ground surface temperature data loggers were installed at some locations to collect ground temperature data. After the investigation and assessment process, four test sections ranging from 10 to 60 m were constructed by replacing parts or all of the existing highway embankment In the fall of 2012. To assess the thermal conditions of the test sections, thermistor cables were installed within the road embankment during construction. Construction at Test Section 1 involved relocating and replacing the culvert with an open-arch culvert and geosynthetic-reinforced fill. At Test Section 2, the upper 1.5 m of the road embankment was excavated and replaced with three layers of geogrid-reinforced fill, to stabilize the road over the rock to permafrost soil transition. At the east end of the test section, the shoulder of the embankment was replaced as a ventilated shoulder with clean, coarse cobbles and boulders to promote air circulation and convective cooling of the embankment shoulder and permafrost foundation. Remediation strategies at Test Section 3 focused on stabilizing the road embankment as it transitions from frozen to unfrozen clay and from frozen clay to bedrock. The upper portion of the road embankment was partially-excavated and a 0.4 m thick layer of cellular concrete was installed directly beneath the base. Adjacent to this section, another 40 m section was partially excavated and replaced with two, 0.5 m layers of geogrid-reinforced rock fill. Both sections are intended to provide structural rigidity to the embankment and limit abrupt differential settlements. At Test Section 4, the existing road surface had an abrupt dip beneath the west bound lane, therefore remedial work at this site involved replacing the rock drain with a small open-arch culvert and geotextile-reinforced fill.

Outcomes and Monitoring Progress

Performance assessment of the test sections has been done through semi-annual site visits (one in the spring and one in the fall), that include visual inspection of the road surfaces and embankments. The large open-arch culvert is effective in cooling the embankment and passing the flow. Measured air temperatures at the culvert floor and wall were approximately 6°C and 2°C colder, respectively, than Yellowknife Airport air temperatures during the summer. The small open-arch culvert is not successful in passing water; stagnant water forms, connecting ponds on both side of the road. The small open-arch culvert causes warming of the embankment fill. The ventilated shoulder cools the embankment shoulder on average by approximately 4˚C compared to the reference section. Mean embankment temperatures immediately beneath the cellular concrete are warmer than the reference section, indicating that the insulating layer reduces the net heat extraction of the embankment base as it insulates the embankment from cold winter temperatures more so than from warm summer temperatures. Five years of monitoring of the test sections along Highway 3 have demonstrated that the construction and maintenance of highway infrastructure on warm, ice-rich permafrost is extremely challenging and a paradigm shift in road design is required.

Next Steps

The monitoring and rehabilitation process of Highway 3 has continued over the years since the initial PIEVC assessment. Below is a summary of recently ongoing and upcoming projects:

  • Km24.4: Deh Cho Bridge cleaning and erosion control (summer 2020)
  • Km 201: Production and stockpile of construction material (spring/summer 2020)
  • Km 244.1 to 256.3: Highway rehabilitation, including clearing of trees and bushes in the right-of-way, levelling and compacting the road surface material, and culvert replacements (summer 2020)
  • Km 256 to 332: Surface repairs (summer 2020)
  • Km 272: Production and stockpile of construction material (spring/summer 2020)

Resources

Link to Full Case Study

Additional Resources: