Thirty-Ninth Canadian Geotechnical Colloquium: Unsaturated soil mechanics — bridging the gap between research and practice

The majority of geoengineering applications occur in the unsaturated (vadose) zone, which is the near-surface region forming the connection between meteorological phenomena above and saturated ground below. The key characteristic of the unsaturated zone is that water is in tension or, put another way, pore-water pressure is negative. Moisture content, as well as most material properties, vary spatially and temporally in the unsaturated zone and coupled processes are common. In geoengineering applications in the vadose zone, unsaturated soils may be present during part or all of their design lives. The question is how or when to consider the unsaturated soils’ principles in an analysis or design. Although most geoengineering applications have an unsaturated component, use of unsaturated soil mechanics in practice lingers behind the prolific number of publications due the uncertain benefit of accounting for unsaturated effects, complexity, and conservativeness among other reasons. The focus of this colloquium is to continue bridging the gap by illustrating unsaturated soils’ principles using application-driven examples in the areas of capillarity as well as flow, strength, and deformation phenomena. As principles of unsaturated soils become more understood and demand increases for incorporating climate change effects in design, use of unsaturated soils’ principles in practice will continue to increase.