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

土壤挖沟被广泛应用于岩土工程、采矿、隧道施工和地质环境基础设施活动中。由于挖土涉及到在有限的空间内进行挖掘工作，因此土沟的故障会直接导致人员伤亡。尽管加拿大的几个省份出版了指南，强调与沟渠故障相关的死亡事故相关的职业健康和安全问题，但每年仍有大量与土壤沟渠故障有关的工人死亡报告。安全高度、安全和竖立时间是土槽设计中需要考虑的两个关键因素。HSafe和Tstup的确定需要基于土体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下挖掘到土壤中的。由于这个原因，现有的估计HSafe和Tstup的方法可能是不合理的，因为它们没有考虑土壤的力学性质随着土壤水分(或基质吸力)的变化而变化。一些研究人员试图研究考虑基质吸力的非饱和土沟的稳定性，但他们的研究仅限于研究降雨入渗对HSafe和Taste的影响，目前还没有一种方法可以同时考虑各种实际情况，如降雨入渗、坡面夹角、土层表面不同类型的超载以及水通过土槽边坡的渗流等，来估计非饱和土沟的HSafe和TstUp。拟议的研究将集中在开发简单但严格的工具，以估计非饱和土沟的HSafe和Tstup，基于实验室试验和耦合的水-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钉的方法或协议。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，产生一份设计手册，以及一份加拿大基础工程手册。特别是在人口稠密的地区，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，工程支撑的设计对土、水及邻近建筑物的支撑至关重要。本文的研究成果可望有效地应用于各种实际情况下的工程支撑设计中，无论是否采用加固技术。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。

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.