Shallow tunnels in stratified clay: stability and induced ground movements

软土隧道施工对加拿大来说特别重要。在过去十年，加拿大政府在基础设施项目上投资超过120亿加元，其中20亿加元用于具有重大国家和区域意义的大型项目，包括交通、供水和污水处理等。控制软土浅埋隧道施工引起的地表沉降是隧道工程师面临的一个重大挑战。地表沉降可能由几个因素引起，例如隧道掌子面、盾构尾部后面和隧道衬砌的地层损失。隧道开挖除引起地表沉降外，还会引起掌子面前方地层的侧向变形和纵向移动。几项研究致力于开发解决方案，在软土地基中隧道施工引起的变形。这些方法大多是经验性的，主要是基于英国隧道的现场观察。在伦敦粘土（一种坚硬的海洋存款）中进行沉降预测所需的土壤刚度和破坏模型并不能代表在加拿大不同地区发现的分层粘土沉积物中对隧道开挖的地面响应。这种模糊性导致隧道设计者使用一种具有良好记录的技术，而不是代表实际地面条件的技术。在层状粘土中使用这些方法可能导致不经济或不安全的方法。采用离心模型和重力模型对块体粘土样品进行试验，以模拟隧道施工过程。理论研究也将进行开发成层粘土卸载行为的本构模型。这项研究的结果将有助于解释在加拿大和世界各地的几个隧道施工过程中采取的现场测量。这项研究计划将直接有助于三名研究生和一些暑期学生的培训。

The area of soft ground tunnelling is of particular importance to Canada. Over the past ten years, the government of Canada has invested over $12 billion on infrastructure projects with $2 billion towards large-scale projects of major national and regional significance including transportation, water and wastewater, etc. Tunnels are essential components of this infrastructure and constitute a major portion of project expenditure. Limiting the surface settlement produced by shallow tunnels in soft ground is a major challenge for tunnel engineers. Surface subsidence can be caused by several factors such as ground loss at the tunnel face, behind the tail of the shield, and through the tunnel lining. Besides surface settlement, tunneling also produces lateral deformation and longitudinal movement of the ground ahead of the tunnel face. Several studies have been devoted to develop solutions for the deformations caused by tunneling in soft ground. Most of these methods are empirical in nature and based on field observations of mainly UK tunnels. Soil stiffness and failure models required for settlement prediction in London clay (a stiff marine deposit) does not represent the ground response to tunneling in stratified clay deposits found in different parts of Canada. This ambiguity leads tunnel designers to use a technique that has a good track record rather than one that represents the actual ground conditions. Using these methods in stratified clays may result in either uneconomic or unsafe approaches. Both centrifuge and gravity scale model tests on block clay samples will be used to simulate the tunnel construction process. Theoretical investigations will also be carried out to develop a constitutive model for the unloading behavior of stratified clays. Results of this study will facilitate the interpretation of field measurements taken during the construction of several tunnels in Canada and worldwide. This research program will directly contribute to the training of three graduate students and a number of summer students.