Shallow tunnels in stratified clay: stability and induced ground movements

软基隧道开挖区域对加拿大特别重要。在过去的十年里，加拿大政府在基础设施项目上投资了超过120亿美元，其中20亿美元用于对国家和地区具有重大意义的大型项目，包括交通、供水和废水等。隧道是这些基础设施的重要组成部分，也是项目支出的主要部分。控制软土地基浅埋暗挖隧道的地表沉降量是隧道工程师面临的一大挑战。地表下沉可由多种因素引起，如隧道工作面、盾构尾部和隧道衬砌后的地面损失。隧道施工除了引起地表沉降外，还会引起隧道工作面前方地表的横向变形和纵向移动。已有多项研究致力于解决软土地基中隧道施工引起的变形问题。这些方法大多是经验性的，主要是基于对英国隧道的实地观察。伦敦粘土(一种坚硬的海洋沉积物)中的沉降预测所需的土壤硬度和破坏模型并不代表在加拿大不同地区发现的层状粘土沉积物中开挖隧道的地面响应。这种模糊性导致隧道设计者使用一种有着良好记录的技术，而不是一种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会导致不经济或不安全的方法。采用块状粘土土样的离心机模型试验和重力模型试验来模拟隧道施工过程。还将开展理论研究，以建立层状粘土卸荷特性的本构模型。这项研究的结果将有助于解释在加拿大和世界各地建造几条隧道期间进行的现场测量。这项研究计划将直接为培养三名研究生和一批暑期学生做出贡献。

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.