Structural stability of highway embankments in the Arctic corridor

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De Guzman, Earl Marvin
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There are uncertainties related to the mechanical behaviour of highway embankments where frozen soil is used as fill material and experience natural thawing and settlements during the first thawing season following construction. Side slope sloughing, fill cracking, and development of localized thaw settlements underneath the embankment shoulders and side slopes typically occur due to thawing of the frozen soil and permafrost foundation. Test sections were constructed and instrumented with temperature and displacement sensors along the Inuvik-Tuktoyaktuk Highway in the Northwest Territories, Canada to assess the thermal and mechanical performance of frozen fill embankments. One of the test sections was reinforced with layers of wicking woven geotextiles at its side slopes to provide reinforcement against lateral movements and instabilities during the thawing season. This is the first research where woven geotextiles were used for slope reinforcement of initially frozen fill in Arctic regions. Significant lateral displacements occurred in the summer following end-of-construction for the control (unreinforced) and reinforced test sections, with the reinforced section showing reduced lateral movements. Temperatures in the embankment and permafrost foundation have also been increasing due to warming air temperatures, leading to additional displacements as the previously compacted frozen fill thaws. Large-scale direct shear and pullout tests were conducted on the soil and woven geotextiles, respectively, under different moisture contents and environmental conditions to quantify their influence on embankment performance. The most critical condition, based on the tests conducted, occurs during the onset of the first thawing when the ice bonding in the soil matrix melts. The interface properties obtained from the pullout tests showed that the wicking geotextile has higher interface friction properties compared to a non-wicking geotextile at comparable strain levels. Thermal modelling and coupled thermal-mechanical modelling were carried out using commercially-available finite element software TEMP/W and ABAQUS, respectively, and were calibrated with recorded field data. Climate modelling scenarios were also used to evaluate performance under near-term and long-term conditions. The coupled models confirmed the benefit of using woven geotextiles in reducing displacements when used as reinforcement in thawing slopes. With confidence on model results for the test sections, parametric studies were conducted to investigate the influence of embankment thickness, slope inclination, reinforcement length, and reinforcement spacing on the thermal and mechanical performance of these embankments. The monitored field performance, use of woven geotextiles as slope reinforcement, and numerical modelling considering the effects of climate change presented in this thesis will help improve the existing design guidelines for highway embankments in Arctic regions.
Highway embankments, Winter construction, Permafrost, Frozen fill compaction, Reinforced slopes, Wicking geotextiles, Interface resistance, Shear strength, Large-scale direct shear test, Pullout test, Numerical modelling, Climate change