Estimating the critical height of unsupported trenches in unsaturated soil

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University of New Brunswick
Trenching (or excavating) is integral to construction activities in the practice of geotechnical, mining, tunnelling, and geo-environmental engineering. Many projects are initiated by excavating trenches for infrastructure to be installed. Workers are often required to enter trenches during the construction process, which may present serious risks. Trench failures can result in death and/or damage to adjacent properties, therefore trenches should be excavated with extreme precaution. The critical height (i.e. maximum depth that can be excavated without failure) is the most important design consideration for ensuring the stability of unsupported trenches. Excavation work is often done in unsaturated soils, in which case the critical height of unsupported trenches can be more reliably estimated by considering the influence of matric suction. The purpose of this study is to investigate the influence of soil type, the matric suction distribution, and surcharge pressure in assessing the critical height of unsupported trenches. Extended Rankine earth pressure theory, the limit equilibrium method, and finite element analyses were used to estimate the critical height of unsupported trenches in two unsaturated soils.