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UNSATURATED SOIL MECHANICS: BRIDGING THE GAP BETWEEN RESEARCH AND PRACTICE Session: Keynote / Conférence Greg Siemens, Department of Civil Engineering, Royal Military College of Canada (Canada) Most geo-engineering applications occur within the unsaturated zone or include an unsaturated component. For example all compacted construction materials are unsaturated following placement. In nature, the unsaturated zone (also known as the vadose zone) is the near-surface ground area, which is the linkage between weather systems above and the saturated groundwater system below. Unsaturated soil mechanics describes the principles of soil behaviour for the conditions ranging from completely dry (Sr=0) to saturated (Sr=1,0). Canada has a long and productive legacy of unsaturated soils research focusing on advancing the theory and practical use of unsaturated soil mechanics. The Canadian Geotechnical Journal is widely recognized for its repository of unsaturated soils publications in theoretical, laboratory, and case studies from Canadian and international authors. New advancements in laboratory testing, constitutive modeling, and field studies have provided breakthroughs in fundamental understanding and provide for the practical use of unsaturated soil principles in some cases. However, use of unsaturated soil mechanics in practice continues to lag significantly behind the state-of-the-art. In design, unsaturated effects are often viewed as providing additional safety factor rather than an opportunity for greater efficiency. For example, design of a shallow foundation will often consider the saturated friction angle of a granular material and ignore the depth of the foundation relative to the water table. This colloquium will examine the principles of unsaturated soil mechanics principles through illustrative examples. The illustrations will provide motivation for examining the tension between research and practical use of unsaturated soil mechanics. The ‘lessons learned’ from the cases are beneficial to the geo-engineering community and to generate new interest and wider use of unsaturated soil principles.
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