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

土壤挖沟广泛用于岩土工程、采矿、隧道和地质环境基础设施活动。由于土槽开挖涉及有限空间内的挖掘工作，土槽故障可直接导致生命损失。尽管加拿大的几个省出版了指南，强调与沟渠故障相关的死亡相关的职业健康和安全问题，但每年仍有大量工人死亡与土壤沟渠故障有关。 安全高度Hsafe和直立时间Tstup是土槽设计中需要考虑的两个关键因素。确定Hsafe和Tstup需要基于土壤抗剪强度参数的主动土压力和土槽稳定性。土沟通常是在非饱和状态的土壤中开挖的。由于这个原因，现有的方法来估计Hsafe和Tstup可能是不合理的，因为他们没有考虑土壤的力学性质的变化相对于土壤水分（或基质吸力）的变化。一些研究人员试图调查的稳定性，考虑到基质吸力的非饱和土沟，但是，他们的研究仅限于调查降雨入渗的影响Hsafe和Tstup。 目前，没有方法来估计Hsafe和Tstup的非饱和土沟渠考虑各种实际情况下，同时考虑，如降雨入渗，边坡/土壤表面的角度，不同类型的土壤表面上的超载，和水渗透通过边坡的土壤沟渠。拟议的研究将侧重于开发简单而严格的工具，以估计Hsafe和Tstup的非饱和土沟的基础上，实验室测试和耦合的水力力学分析。此外，考虑到上述实际情况，还将研究在非饱和土沟中设计土壤NaClO的方法或协议。所提出的设计工具将通过现场大规模测试进行验证。 这项研究将通过与加拿大的各种建筑/设计机构、健康和安全协会合作，编写一本设计手册，并编写一本加拿大基础工程手册。特别是在人口密集的地区，由于工作空间有限，建造上层建筑或更换旧管道系统非常具有挑战性。在这种情况下，工程支护的设计就显得尤为重要，它不仅要对土、水及邻近建筑物起到支护作用。本研究将可有效地应用于工程支护设计中，并考虑不同的实际情况，包括有无土壤加固技术。 拟议的研究将涉及5名HQP（4名硕士和1名博士生），他们将通过实验室测试和数值模拟来研究非饱和土沟渠。

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.