Assessing ground interaction effects and potential damage on existing tunnels before and after new excavation works

隧道和地下铁路系统是一种流行的解决方案，以满足日益增长的城市环境中提供快速高效的运输系统的需求。因为在许多情况下，地面上既有密集的交通和服务隧道网络，也有很深的地基，所以新的隧道必须挖得更深才能从这些障碍物下面通过。新隧道的施工会引起地面应力变化和相应的变形，这些变化会传递并影响到其他现有结构。服务，特别是运营中的地铁隧道对这种移动非常敏感。铁路在狭窄的“运动包络”中运行，如果隧道变形从而限制了这个包络，火车的运行将受到严重限制，需要降低速度限制或关闭网络，在极端情况下，它们的稳定性可能会受到损害。在这些水平中的任何一个，都严重阻碍了列车网络的有效运行。如果有必要停止一条铁路线的运行，即使是很短的一段时间，每天都有天文数字的成本，因为机票收入的损失和通勤劳动力的时间损失。社会影响也是巨大的，给成千上万的人带来不便、沮丧和动荡。许多现有的隧道网络都是在一个多世纪以前建造的，当时传统的衬里主要由灰铸铁段制成。对于由这种材料制成的分段隧道衬砌的详细响应知之甚少，例如它们可以承受多大的变形以及何时以及如何破坏。灰口铸铁是一种非常脆的材料，它的响应取决于许多因素，如螺栓中的力，所使用的垫圈/密封圈的性质，以及“锅”是否填充了混凝土。横穿伦敦的新交通线路横贯铁路（Crossrail）今年获得皇家批准。工程将于2010年开工。横贯铁路的隧道比大多数现有的隧道更大、更深，它们将穿过40多个这样的隧道。其中许多是旧的，由铸铁段建造，每小时运送成千上万的通勤者。本研究项目旨在全面了解现有铸铁隧道在地下开挖（如隧道掘进）变形时的变形极限。由于这些衬里（连接等）的性质，有必要在适当的尺度上考虑它们的反应。采用三路径方法，对铸铁管片形成的大型环进行实验室测试，对横贯铁路隧道施工期间的现有隧道进行现场监测，并对实验室和现场条件进行数值分析。实验室研究将能够确定变形的极限，例如在不同条件下的屈服和破坏，例如螺栓力，垫圈类型。当环变形以模拟在原位观察和预测的典型形状时，将对环进行仪器监测，以监测应力、螺栓力等的变化。这与了解新隧道施工前后的情况有关。数值分析将用于模拟实验室的设置，并在对海德公园的现场情况进行预测之前进行完善。在海德公园，横贯铁路隧道将从中央线隧道下面穿过。我们会在该处的地面及现有隧道安装综合仪器，详细监测及了解新隧道开挖时的反应。然后，数值分析可以进一步完善，以实现对未来项目更准确的预测。把这三个研究组成部分结合起来，就可就预期和允许的隧道衬砌变形，以及涉及在现有隧道下挖掘隧道的未来项目的缓解措施的有效性，拟订准则，从而不会影响地下铁路网的安全和有效运作。

Tunnels and underground railway systems are a popular solution to the increasing need to provide fast efficient transport systems in urban environments. Because in many cases the ground contains dense networks of existing tunnels for transportation and services and also deep foundations, new tunnels have to be constructed deeper to pass beneath these obstacles. New tunnel construction results in stress changes and consequent deformations in the ground and these are transmitted to and affect other existing structures. Services and particularly operational metro tunnels are very sensitive to such movements. Railways operate within narrow 'kinematic envelopes' and if a tunnel deforms so as to restrict this envelope the running of trains is severely restricted, requiring reduced speed limits or shutdown of the network and, in the extreme case, their stability might be compromised. At any of these levels, efficient running of the train network is severely hindered. If it is necessary to halt operation of a train line, even for a short period, there are astronomical daily costs from loss of ticket revenue and from loss of time to the commuting workforce. The societal impact is also enormous with inconvenience to thousands of people, frustration and unrest.Many existing tunnel networks were constructed over a century ago when traditionally linings were made mostly from grey cast iron segments. Little is known about the detailed response of segmental tunnel linings made from this material, e.g. how much deformation they can sustain and when and how they will fail. Grey cast iron is a very brittle material and its response depends on a number of factors such as the force in the bolts, nature of the gaskets/grommets used, and whether the 'pan' is infilled with concrete.Royal Assent for Crossrail, a new transport link across London, was granted this year. Construction is due to start in 2010. The tunnels for Crossrail are larger and deeper than most existing tunnels and they will pass beneath more than forty such tunnels. Many of these are aged and constructed from cast iron segments and transport thousands of commuters hourly.This research project sets out to gain a full understanding of the limits of deformation of existing cast iron tunnels when deformed by underground excavation such as tunnelling. Because of the nature of these linings (connections etc) it is necessary to consider their response at an appropriate scale. A three-path approach is to be adopted with laboratory testing of large-scale rings formed from cast iron segments, field monitoring of existing tunnels during Crossrail tunnel construction and numerical analysis of both laboratory and field conditions. The laboratory study will enable limits of deformation to be established, e.g. yield and failure, under different conditions such as bolt forces, gaskets types. The rings will be instrumented to monitor changes in stresses, bolt force etc as the ring is deformed to simulate typical shapes observed and predicted in situ. This is relevant to understanding conditions both before and after new tunnel construction. Numerical analysis will be used to model the laboratory set-up and refined prior to making predictions of a field situation at Hyde Park where the Crossrail tunnels will pass beneath the Central line tunnels. Comprehensive instrumentation will be installed in the ground and existing tunnels at this location to monitor in detail and understand their response during new tunnelling. The numerical analysis can then be further refined to achieve more accurate predictions for future projects.Bringing together these three research components will allow guidelines to be drawn up on expected and allowable tunnel lining deformations and the effectiveness of mitigation measures for future projects involving tunnelling beneath existing tunnels, such that safe and efficient operation of underground railway networks is not compromised.