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，以满足城市环境中日益增长的快速高效交通系统的需求。由于在许多情况下，地面包含密集的现有交通和服务隧道网络以及深基础，因此必须在更深的地方建造新隧道才能从这些障碍物下面通过。新的隧道建设会导致地面应力变化和随之而来的变形，这些都会传递到其他现有结构中并对其产生影响。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“运动范围”内运行，如果隧道变形以限制这一范围，列车的运行将受到严格限制，需要降低速度限制或关闭网络，在极端情况下，其稳定性可能会受到影响。在这些级别中的任何一个，列车网络的有效运行都受到严重阻碍。如果有必要停止一条铁路线的运营，即使是很短的一段时间，每天都会因为门票收入的损失和通勤劳动力的时间损失而付出天文数字的代价。对社会的影响也是巨大的，给成千上万的人带来不便、沮丧和不安。许多现有的隧道网络是一个多世纪前建造的，当时传统的衬砌大多是由灰色铸铁管片制成的。人们对这种材料制成的节段式隧道衬砌的详细反应知之甚少，例如它们能承受多大的变形，以及它们何时和如何失效。灰口铸铁是一种非常易碎的材料，它的反应取决于许多因素，比如螺栓上的力，所用垫圈/垫圈的性质，以及锅子里是否填满了混凝土。今年，皇家批准了横跨伦敦的新交通线路Crossail。工程将于2010年开工建设。横贯铁路的隧道比大多数现有隧道更大、更深，它们将从40多条这样的隧道下面通过。这项研究计划的目的是全面了解现有铸铁隧道在地下开挖(如挖掘隧道)变形时的变形极限。由于这些衬里(连接等)的性质，有必要在适当的范围内考虑它们的响应。将采用三路径方法，通过实验室测试由铸铁管片形成的大型环，在横轨隧道施工期间对既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不同条件下的变形极限，例如屈服和失效，如螺栓受力、垫圈类型。当环变形时，环将被测量以监测应力、螺栓力等的变化，以模拟现场观察和预测的典型形状。这与了解新隧道施工前后的情况有关。在对海德公园的现场情况进行预测之前，将使用数值分析来模拟实验室的设置和改进，在那里交叉铁路隧道将从中线隧道下方通过。将在该位置的地面和现有隧道安装综合仪器，以详细监测和了解他们在新隧道施工期间的反应。把这三个研究部分结合起来，便可就隧道衬砌的预期和容许变形，以及未来涉及在现有隧道下挖掘隧道的工程的缓解措施的成效，制订指引，使地下铁路网络的安全和有效率运作不会受到影响。

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.