Tools for estimation of the stability of unsupported trenches extending the mechanics of unsaturated soils

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Soil trenching is extensively used in geotechnical, mining, tunneling and geo-environmental infrastructure activities. Since soil trenching involves excavation work in limited spaces, soil trench failures can directly result in loss of lives. Although several provinces in Canada published guidebooks to emphasize occupational health and safety concerns related to fatalities associated with trench failures, a large number of worker deaths are still reported each year associated with soil trench failure. ******Safe height, Hsafe and stand-up time, Tstup are two key factors required in the design of soil trenches. Determination of Hsafe and Tstup requires active earth pressure and stability of soil trenches based on shear strength parameters of soils. Soil trenches are typically excavated into the soils in a state of unsaturated condition. Due to this reason, the existing approaches to estimate Hsafe and Tstup may not be reasonable since they do not consider the variation of mechanical properties of soils with respect to the change in soil moisture (or matric suction). Several researchers attempted to investigate the stability of unsaturated soil trenches taking into account matric suction; however, their research was limited to an investigation of the influence of rainfall infiltration on the Hsafe and Tstup.******Currently, no approach is available to estimate Hsafe and Tstup of unsaturated soil trenches considering various practical scenarios simultaneously, such as rainfall infiltration, angles of side-slope/soil surface, different types of surcharge on the soil surface, and seepage of water through the side-slope of soil trenches. The proposed research will focus on developing simple yet rigorous tools to estimate Hsafe and Tstup of unsaturated soil trenches based on laboratory tests and coupled hydro-mechanical analyses. In addition, methodology or protocols to design soil nailings in unsaturated soil trenches will also be investigated, taking account of the aforementioned practical scenarios. The proposed design tools will be validated through large-scale tests in the field. ******This research will result in a design manual by working with various construction/design agencies, health and safety associations in Canada, and a Canadian Foundation Engineering Manual. Especially, in highly populated areas, construction of superstructures or replacements of old pipeline systems are very challenging due to limited work spaces. In this case, the design of engineering shoring is vital to support earth, water and adjacent structures. This proposed research is expected to be effectively used to design the engineering shoring considering various practical scenarios with and without soil reinforcement techniques. ******The proposed research will involve 5 HQPs (4 Master's and 1 PhD students) who will study unsaturated soil trenches through both laboratory tests and numerical modeling.**