NVF stipend 2014
Permafrost engineering applied for transportation infrastructure
Elena Kuznetsova, Postdoctoral fellow NTNU, BAT (Department of Civil and Transport engineering) 10.06.2014 [email protected] Permafrost engineering applied for transportation infrastructure 1
Executive Summary
NVF granted a stipend to Elena Kuznetsova to follow a one week course on permafrost engineering applied to transportation infrastructures at Yukon College in Whitehorse, Yukon, Canada. Besides the course, a visit was organized to the Yukon Innovation Center, and she also participated in a workshop on the project "ARQULUK: Preservation of Canada's northern transportation infrastructures."
Figure 1: Elena Kuznetsova, The stipend is linked up to her position as a postdoctoral fellow at the postdoctoral fellow at NTNU Road and Railway group at the Department of Civil and Transport Engineering, the Norwegian University of Science and Technology, where her research topic is frost heave on the Norwegian roads.
This report presents an overview of the course the trip and the workshop.
The course on permafrost engineering included a description of permafrost environments and dynamics, principles and methods for site investigations, design and management of roads, airstrips, railways and other linear structures built in permafrost environments. Finally, the course included two field visits on sites where interesting Figure 2: Guy Dore, professor at Laval permafrost and engineering features could be observed. University, Quebec
The course was taught by two internationally known professors from two Canadian universities:
Guy Doré, a professor of civil engineering at Laval University, Quebec, Canada.
Dr. Doré is specializing on pavement performance under the effects of frost and thaw. Before joining academia, he worked at the Quebec Ministry of Transportation for many years. He also leads the "ARQULUK" project. Figure 3: Chris Burn, professor at Carleton University, Ottawa Chris Burn, a professor of geography at Carleton University, Ottawa, Canada.
Dr. Burn’s main interest areas are permafrost and massive ices, and physical geography of Yukon and Northwest Territories. His research is focused mostly on the relations between climate and permafrost.
10.06.2014
Permafrost engineering applied for transportation infrastructure 2
Contents
Executive Summary ...... 1
Contents ...... 2
PART 1. Advanced seminar on permafrost engineering applied to transportation infrastructure ...... 3
Field trip 1: Takhini Permafrost Research Site ...... 5
Field trip 2: Visit of Alaska Highway ...... 7
Stop 1 (km 1446). Creep of the road embankment ...... 7
Stop 2 (km 1456): Takhini river retrogressive thaw slump 8
Stop 3 (km 1462): Thermal erosion and double culvert10
Stop 4 (km 1762): Ice wedge and drainage ...... 12
Stop 5 (km 1865): Beaver creek experimental road site15
Stop 6 (1845): Stability of cut slopes ...... 18
Stop 7 (km 1842): Massive ice and thermokarst ...... 19
Stop 8 (km 1801): Water ponding, longitudinal cracking and geogrids 20
Stop 9 (km 1762). Thermosyphon ...... 23
PART 2. Visiting the Yukon Innovation Center ...... 26
PART 3. Workshop on the project “ARQULUK: Preservation of Canada’s northern transportation infrastructures” ...... 27
10.06.2014
Permafrost engineering applied for transportation infrastructure 3
PART 1. Advanced seminar on permafrost engineering applied to transportation infrastructure
The seminar was held in Yukon College, in Whitehorse, on May 22 - 28, 2014.
Short seminar overview: This is advanced, graduate level course on permafrost engineering applied to transportation infrastructure. The course included a description of permafrost environment and dynamics. Principles and methods for site investigations, design and management of roads, airstrips, railways and other linear structures built in permafrost environments were also included in the course. Finally, the course included two field visits on sites where interesting permafrost and engineering features could be observed.
Plan of the seminar:
1st day / May 22 Lectures
Introduction: The context of northern Canada transportation infrastructure (economic and social role; condition, vulnerability, expected development)
Heat transfer: principles and calculation (heat transfer by conduction, convection and radiation; practical methods for calculation of thermal regime, heat transfer, heat balance)
The permafrost environment: Essential notions on permafrost environments for engineering considerations (permafrost characteristics and features, thermal regime, permafrost dynamics)
2nd day / May 23 Lectures
The permafrost environment (continuation)
Field trip on permafrost sites around Whitehorse
3rd day / May 24 Lectures
Basic considerations for embankment design in permafrost conditions: Thermal implications, mechanical implications, drainage considerations
Frozen/thawing soil mechanics: Frost action, mechanical properties of frozen and marginally frozen ground, thaw consolidation, mechanical properties of thawing permafrost and of the active layer. Site investigation: Key considerations for site investigation, description of geophysical methods, drilling and sampling, in-situ testing
10.06.2014
Permafrost engineering applied for transportation infrastructure 4
Embankment design: Key considerations, embankment materials, embankment geometry, thermal analysis, mechanical analysis, special protection techniques, consideration for frost heave
Practical exercise: 2-D embankment thermal design using Temp-W
4th day / May 25 Day off
5th day / May 26 Lectures
Slope stability: Stability of natural and cut slopes
Drainage: Implications of water concentration and channeling, control of surface water, erosion and thermal erosion, design of cross-drainage systems
Construction in permafrost regions: Logistic, environmental considerations, permafrost preservation, working with frozen or thawing materials
Management strategies: Risk analysis, preservation strategies, maintenance
Field trip Alaska Highway
6th day / May 27 Field trip Alaska Highway
7th day / May 28 Additional presentations; recapitulation of important points and discussion
Final examination
10.06.2014
Permafrost engineering applied for transportation infrastructure 5
Field trip 1: Takhini Permafrost Research Site
Southern Yukon is in the sporadic discontinuous permafrost zone. In Takhini River Valley there is less than 20% of the ground is perennially frozen. The study area contrasts 3 surface types, each associated with distinct ground thermal conditions. There is spruce forest, grassy meadow, and area burned by forest fire in 1958. Permafrost is found in the forest: the active layer is 1.4 m thick, and the thickness of permafrost is 17 m. The permafrost in the burned area is degrading, the top of the permafrost in now about 3.75 m below the surface. The meadow area has no permafrost (Burn, 1998).
Figure 4: Measuring the temperature in the borehole situated in the forest
10.06.2014
Permafrost engineering applied for transportation infrastructure 6
Figure 5: Crack on the asphalt pavement caused by thermokarst lake close to the road. Few years ago it was a forest covering the area all around the road, but it was removed for making the farming fields. Removing the forest leaded to changes in the temperature regime of underlying permafrost, active layer were getting deeper and in turn ice in the top of the permafrost started to melt
Figure 6: The borehole with thermistor cable situated in the forest which was burned in 1958. Now this area is covered by new spruce trees, moss and bushes
10.06.2014
Permafrost engineering applied for transportation infrastructure 7
Field trip 2: Visit of Alaska Highway
Stop 1 (km 1446). Creep of the road embankment
Creep is generally not taken into account in the design of an embankment because such movements are generally small. However, severe settlement can occur if: 1) ice contents are high, 2) the permafrost temperature is less than 2oC, 3) the salinity of the soil is high, 4) the embankment load is high (M-Lepage et al., 2014). Along the Alaska Highway corridor in the Takhini area, significant settlement related to creep has been observed in a few places where the embankments are unusually thick.
Figure 7: Creep of the Alaska highway in the Takhini Valley at km 1446 (side view)
10.06.2014
Permafrost engineering applied for transportation infrastructure 8
Figure 8: Creep of the Alaska highway in the Takhini Valley at km 1446 (front view)
Stop 2 (km 1456): Takhini river retrogressive thaw slump
The Takhini River retrogressive thaw slump, located adjacent to the Alaska Highway 30 km west of Whitehorse, is a good example of a thaw slump process which is capable of inducing subsidence of the road. This thaw slump was trigged by Takhini River bank erosion. Since 2004, the thaw slump stabilized a few meters short of the highway, but it requires constant monitoring (M-Lepage et al., 2014).
10.06.2014
Permafrost engineering applied for transportation infrastructure 9
Figure 9: Retrogressive thaw slump adjacent to Alaska Highway. View from the road to the river
Figure 10: Erosion terrace down of the hill. The straight position of the bushes and spruces show that there were no movement of the soils during last several years
10.06.2014
Permafrost engineering applied for transportation infrastructure 10
Figure 11: River bank with silty clays
Stop 3 (km 1462): Thermal erosion and double culvert
Flowing water in the form of permanent and intermittent steams or sheet flow has a warming impact on the underlying permafrost and results in accelerated thawing of surrounding frozen soils (TAC, 2010). Particles of the thawed soils are detached by the moving water, transported, and deposited downstream. This is a dynamic process of thermal erosion which has both hydraulic (mechanical) and thermal (melting of ground ice) components (M-Lepage et al., 2014). The finer-grained the soil and the higher the ice content, the faster and more destructive the process of thermal erosion is (figure 13).
10.06.2014
Permafrost engineering applied for transportation infrastructure 11
Figure 12: Thermal erosion along the embankment
In areas underlying by permafrost, culverts often act as heat sources and cause deeper thawing. The excessive settlement of culverts leads to frequent pipe breakage, sediment blockage, internal water ponding and subsequent freeze-up, which can completely block the drainage system.
In the north, culverts should be designed with large safety factors (two to three times the size that would be used in non-permafrost areas) to compensate for design uncertainties, ice, snow and sediment blockage, and subsequent settlement (TAC, 2010). In this case, the use of a small culvert above the main culvert (figure 13) has been considered in the design to provide a backup in case of obstruction of the main culvert.
10.06.2014
Permafrost engineering applied for transportation infrastructure 12
Figure 13: Double culvert system
Stop 4 (km 1762): Ice wedge and drainage
Severe erosion of a road embankment can also be caused by concentrated flow in a side ditch located very close to the embankment toe. If interceptor ditches are used they need to be set back by a minimum of 10 m from the toe of the embankment (TAC, 2010). However, ditches can still be subjected to active erosion if the soil is ice-rich., which can increase both their depth and width. Solar radiation and snow accumulation in ditches can also have a warming impact on frozen soils. Even if interceptor ditches tend to slump in initially, if they are built with sufficient capacity they still function as intended (TAC, 2010). Ditches usually stabilize within a few years as vegetation regrowth occurs (M-Lepage et al., 2014).
10.06.2014
Permafrost engineering applied for transportation infrastructure 13
Figure 14: The interceptor ditch was constructed in the fall 2013
Thermal/construction/crack polygons, also referred to ice/wedge polygons are the most widespread, most visible, and most typical features of permafrost terrain. After pore and segregation ice, ice/wedge ice constitutes the third most important ground-ice type in terms of volume (French, 2007). Ice wedges are wedge-shaped bodies of ice, composed of foliated or vertically-banded ice (Figure 15). Favorable environments for their formation are poorly-drained tundra lowlands underlain by continuous permafrost.
10.06.2014
Permafrost engineering applied for transportation infrastructure 14
Figure 15: Ice wedge observed along the ditch at the test site
One of the research projects of the Arquluk program conducted at Laval University aims at the identification of key factors for an optimal drainage design. As part of this project, thermal regime around culverts as function of water flow and air temperature is documented. This culvert has been instrumented with several thermistors in September 2013 during the reconstruction of the Alaska Highway (Figure 16).
10.06.2014
Permafrost engineering applied for transportation infrastructure 15
Figure 16: The culvert was instrumented in September 2013 by the Arquluk research team from University of Laval
Stop 5 (km 1865): Beaver creek experimental road site
In order to better understand permafrost degradation on transport infrastructure, an experimental road site has been constructed on the Alaska Highway near Beaver Creek. The test site was constructed along a 600 m length of highway in April-June 2008 approximately 8 km south of Beaver Creek and 30 kilometers south of the Canada-United States border. There were several sections to test one or several combined methods of thermal stabilization, such as convection air embankment, heat drains, snow/sunshed, grass-covered embankment, reflecting surface and snow clearing on embankment slopes. These sections were built to prevent permafrost from thawing by extracting heat present in the ground under the highways or by reducing solar radiation adsorbed by the surface. These methods should allow for the reduction of the active layer thickness and limit the development of differential settlements. Figures 17-21 show these techniques.
10.06.2014
Permafrost engineering applied for transportation infrastructure 16
Figure 17: ACE (Air Convection embankment): constructed using 150 mm to 300 mm, crushed, rock to form interconnected, convective cells in the embankment. During the winter air cooled in the upper voids travels down into the embankment displacing warm air which rises and exists from the embankment
Figure 18: Inlet and outlet pipes which are attached to the geocomposite layer (dimple board or drain board) used to transport air through the embankment, parallel to the road embankment at regular intervals
10.06.2014
Permafrost engineering applied for transportation infrastructure 17
Figure 19: Longitudinal culverts for heat extraction by natural convection (in the winter, cold air is drawn into the embankment at the inlet and warmed air exits at the outlet; in the summer, inlet and outlet are blocked to minimize warm air input)
Figure 20: Snow/sun sheds to protect embankment slopes during winter and summer (in the winter - promote air circulation and protect embankment slopes from snow insulation; in the summer - reduce solar radiation on the embankment slopes)
10.06.2014
Permafrost engineering applied for transportation infrastructure 18
Figure 21: Standard BST placement procedure with light aggregate. Light-coloured aggregate reflects more sunlight, less heat absorption into the embankment
Stop 6 (1845): Stability of cut slopes
Cut slopes in high or medium sensitive permafrost can be expected to be unstable. If they cannot be avoided, the area should be selectively sub excavated and blanketed using gravel or crushed stone protection layer over a geotextile. The protective layer applies a weight load that accelerates consolidation of the thawing soil and water drainage in areas where permafrost thaws underneath the protection blanket (M-Lepage et al., 2014). Backslope protection blankets have been successfully used as backslope protection for ice-rich cut slopes on many highway projects in the Yukon (figure 22).
10.06.2014
Permafrost engineering applied for transportation infrastructure 19
Figure 22: Backslope protection using rock
Stop 7 (km 1842): Massive ice and thermokarst
During reconstruction of the Alaska Highway in the Dry Creek area in the mid-1990s, a thick deposit of outwash granular material surrounding the road alignment at that location was used as construction material for the highway embankment. The excavation was limited by the presence of a poorly characterized silty, ice-rich soil deposit underlying the gravel deposit (TAC, 2010).linier settlements began to be observed just after overlying vegetation and gravel was removed from the site (2003). The ground subsided catastrophically on the east side of the highway resulting in a 10 m-high bowl-shape opening (figure 23). This phenomena seems to be associated with the melting of buried massive ice (M-Lepage et al., 2014).
10.06.2014
Permafrost engineering applied for transportation infrastructure 20
Figure 23: A thermokarst depression adjacent to the Alaska Highway
Stop 8 (km 1801): Water ponding, longitudinal cracking and geogrids
Issue: Poor embankment performance due to malfunctioning drainage system.
Groundwater flow along and under the road is not always taken into account in road design, which can lead to water ponding along the embankment toe and subsequent permafrost degradation by heat transfer. Permanently flowing water, or intermittent streams or sheet flow, have a warming impact on underlying permafrost and can result in accelerated thawing of surrounding frozen soils (TAC, 2010). Embankment degradation at that site seems to be related to water infiltration underneath the embankment.
Cracks along embankment shoulder surfaces are a common phenomenon observed along the Alaska Highway (figure 24 and 25). The lateral berms, used to present longitudinal cracking on the road surface, worked to some extend initially but now that road is approximately 15 years old, distresses are prevalent on the road surface as well as the berms (TAC, 2010).
In the summer, more heat is introduced to the system by water penetration through the cracks and by ponding along the embankment toe. The culvert which was built to let the water flow
10.06.2014
Permafrost engineering applied for transportation infrastructure 21 and not to be accumulated on another side of the road, stopped to perform properly from 2014 (figure 26). Few meters away from the embankment massive ice was observed (figure 27).
Yukon HPW maintenance treatments for longitudinal cracking mainly involve filling cracks with gravel, followed by periodic embankment remonstration. Since 2011, Yukon HPW is installing geotextiles and geogrids to reinforce the road embankment and to prevent the opening of such cracks.
Figure 24: Longitudinal cracking along the embankment shoulder
10.06.2014
Permafrost engineering applied for transportation infrastructure 22
Figure 25: Longitudinal cracking along the embankment shoulder and the culvert system. In some places geogrid comes out to the surface
Figure 26: The culvert doesn't perform as it should be
10.06.2014
Permafrost engineering applied for transportation infrastructure 23
Figure 27: Massive ice observed aside of the road
Stop 9 (km 1762). Thermosyphon
Thermosyphons make full use of heat transfer principles, including construction, condensation, evaporation, and convection. The purpose of the device is to extract heat beneath embankments in order to keep the soil frozen. A thermosyphon is composed of a pipe which includes a refrigeration gas, such as ammonia, carbon dioxide, or propane in a liquid and gas states. When the air is colder than the ground, heat from the ground causes the liquid to vaporize. When air temperature is warmer than the saturation temperature of the liquid, the thermosyphon is dormant. The main problem with thermosyphons is their relatively high cost. For this reason, thermosyphons are typically used only in severe permafrost degradation areas.
10.06.2014
Permafrost engineering applied for transportation infrastructure 24
Figure 28: Thermosyphons under the Donjek Bridge
References Burn, C.R. (1998). The response (1958-1997) of permafrost and near-surface ground temperatures to forest/fire, Takhini River valley, southern Yukon Territory, Canadian Journal of Earth Sciences, vol. 35, no. 2, p. 184-199.
French, H.M. (2007) The Periglacial Environment, 3rd ed., Chichester, England, John Wiley & Sons publication, 458 p.
M-Lepage, J., Dore G., Burn C. (2014) Advanced Seminar on Permafrost Engineering Applied to Transportation Infrastructure. Field Guide – Alaska Highway.
TAC: McGregor, R., Hayley, D., Wiklkins, D., Hoeve, E., Grozic, E., Roujanski, V., Jansen, A. & Dore, G. (2010) Guidelines for Development and Management of transportation Infrastructure in Permafrost Regions, Transportation Association of Canada, 177p.
10.06.2014
Permafrost engineering applied for transportation infrastructure 25
GROUP PHOTO
Figure 29: Our group included teaching professors, master and PhD students from Laval University, permafrost researchers from Yukon College and industry and myself from NTNU
10.06.2014
Permafrost engineering applied for transportation infrastructure 26
PART 2. Visiting the Yukon Innovation Center
Place: Yukon College, Innovation Centre.
Cold Climate Innovation (CCI) is focused on the development, commercialization and export of sustainable cold climate technologies and related solutions for subarctic regions around the world. CCI supports the partnership between applied scientific researchers, industry and government dedicated to addressing cold climate issues affecting northerners. CCI project areas include alternative energy, building construction, climate-related research, environmental remediation, food security and mechanical innovation.
During staying in Whitehorse, I had a short visit to cold laboratory, where several experiments are going on; there are different equipment and collection of frozen core samples in the lab.
Figure 30: Core permafrost samples from the boreholes
Figure 31: Machine for cutting rocks and frozen soil samples
10.06.2014
Permafrost engineering applied for transportation infrastructure 27
PART 3. Workshop on the project “ARQULUK: Preservation of Canada’s northern transportation infrastructures”
Place: Yukon College.
Arquluk is a cooperation research and development program financed by NSERC and 12 partners from public and private sectors (among them are Laval university and Yukon College).
The project goal: improve current adaptive methods beneath transportation infrastructure, by developing expertise for mitigating permafrost instability.
In order to achieve this goal, the following objectives are proposed:
1) Improve knowledge of factors affecting the performance of pavements built on sensitive permafrost,
2) improve techniques for detection and characterization of instable soils and embankments,
3) develop guidelines for the application of different construction and maintenance strategies to mitigate permafrost degradation problems resulting from pavement construction and climate change based on the cost, the feasibility and the effectiveness of applicable solutions
4) develop a practical framework as well as support tools for the management of transportation infrastructure on permafrost
During the workshop several presentations were given, which were focusing on 3 main themes:
Theme 1. Improvement of the current knowledge on permafrost degradation and its effect on transportation infrastructures.
- Monitoring of experimental test sites in Beaver Creek (Yukon) and Tasiujaq (Nunavik) (Master thesis) - Development of engineering parameters (PhD thesis)
Theme 2. Improving capacity to identify and characterize thaw sensible permafrost
a) Geophysical and thermal analysis methods (Master thesis) b) Analysis of longitudinal profiles of existing pavements (Master thesis) c) In-situ oedometric tests (Master thesis) d) Mechanical behavior of marginally frozen soils (Master thesis)
Theme 3. Development of adaptation techniques for transportation infrastructure built on unstable permafrost for design and maintenance
a) Laboratory and numerical modelling (Master thesis) b) Development of maintenance materials and techniques for embankments affected by permafrost degradation (Master thesis)
10.06.2014
Permafrost engineering applied for transportation infrastructure 28 c) Development of guidelines and strategies for the risk management of transportation infrastructure built on degradation permafrost (PhD thesis)
10.06.2014