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Using blinding as struts in cut and cover excavations

在明挖和覆盖开挖中使用盲法作为支柱

基本信息

批准号：
EP/D505488/1
负责人：
Robert Vollum
金额：
$ 30.43万
依托单位：
Imperial College London
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2006
资助国家：
英国
起止时间：
2006 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=EP%2FD505488%2F1
关键词：
Using blinding struts cut cover

项目摘要

The term blinding is used to describe the thin layer of unreinforced over-site concrete which is used to protect the base of excavations. Blinding is not generally seen or exploited as a beneficial structural element even though it clearly provides some temporary lateral support to the walls of cut and cover works until the base slab is constructed. This proposal stems from Powderham's pioneering work at Mott MacDonald, which shows that blinding struts can eliminate the need for temporary steel propping in cut and cover excavations. Mott MacDonald has used blinding struts in the construction of the Channel Tunnel cut and cover works, the Limehouse Link and the Heathrow Express cofferdam. The hallmark of these projects was the elimination of temporary steel propping from a series of deep excavations which paved the way for further time and cost saving schemes. It is important to note that in all these applications, the actual capacity of the blinding struts and the loads they were carrying were unknown. Therefore, a very conservative approach was adopted for the blinding struts which resulted in the struts being thicker than necessary with consequent cost and environmental implications. Research is required since many clients are unwilling to sanction the use of blinding struts because their performance has not been definitively established.The research will develop a numerical method for predicting the response of blinding struts in cut and cover excavations that is calibrated with data from laboratory tests and field data where possible. Predicting the failure loads of blinding struts is complex since the buckling load depends on factors including cracking, creep, shrinkage and the rates at which the lateral and transverse loadings are introduced into the slab relative to the development of concrete strength. This problem will be solved by carrying out a coupled analysis using both geotechnical and structural finite element programs. A simplified model for the structural response of the blinding strut will be used in the geotechnical analysis. This will enable strut loadings to be determined which will then be used in a refined structural analysis of the strut itself. The overall process will involve iteration, with the structural analysis refining the simplified strut model used in the geotechnical analysis, which in turn will provide improved estimates of the strut loading. This process, combined with the results from the laboratory testing, will lead to a proposed model for the non-linear behaviour of the blinding strut that can be adopted by others in their geotechnical analyses accounting for the specific site and construction conditions.The numerical analysis of the blinding strut will be carried out using the nonlinear structural analysis program ADAPTIC, developed by Izzuddin, which already provides all the necessary elements and material models for assessing the timedependent response of the blinding strut. The geotechnical analysis will be performed using the finite element program ICFEP developed by Potts. This program has been written specifically for geotechnical engineering and has been applied to a wide variety of soil-structure interaction problems. The geotechnical analysis will investigate the behaviour of an embedded cantilever wall with and without a single prop near its top. In both cases, a temporary blinding strut will be modelled at final excavation level. The construction sequence will be based on the procedures adopted at the Limehouse Link, Heathrow Express Cofferdam and Airside Road Tunnel constructions. Soil conditions will also be based on these sites with analyses conducted for excavations in predominantly London Clay and in the Lambeth Group. A series of 20 laboratory tests will be carried out on scale models of blinding slabs with variations in material properties, end conditions and lateral imperfections. The test results will be used to validate and refine the numerical analysis.

盲道一词用于描述用于保护基坑底部的无筋现场混凝土薄层。尽管在底板建成之前，盲板显然为明挖和覆盖工程的墙壁提供了一些临时的侧向支撑，但它通常不被视为或利用为有益的结构元素。该提案源于 Powderham 在莫特麦克唐纳 (Mott MacDonald) 的开创性工作，该工作表明盲撑可以消除明挖和覆盖开挖中对临时钢支撑的需要。莫特·麦克唐纳 (Mott MacDonald) 在英吉利海峡隧道明挖回填工程、莱姆豪斯连线和希思罗机场快线围堰的建设中使用了致盲支柱。这些项目的特点是消除了一系列深坑开挖中的临时钢支撑，为进一步节省时间和成本的计划铺平了道路。值得注意的是，在所有这些应用中，致盲支柱的实际容量及其承载的负载都是未知的。因此，对于盲撑杆采用了非常保守的方法，导致撑杆比必要的更厚，从而产生了成本和环境影响。需要进行研究，因为许多客户不愿意批准使用盲撑，因为盲撑的性能尚未确定。该研究将开发一种数值方法，用于预测明挖和覆盖开挖中盲撑的响应，并尽可能使用实验室测试数据和现场数据进行校准。预测盲杆的失效载荷是复杂的，因为屈曲载荷取决于开裂、蠕变、收缩以及相对于混凝土强度发展的横向和横向载荷引入板的速率等因素。该问题将通过使用岩土工程和结构有限元程序进行耦合分析来解决。盲杆结构响应的简化模型将用于岩土工程分析。这将能够确定支柱载荷，然后将其用于支柱本身的精细结构分析。整个过程将涉及迭代，结构分析将改进岩土分析中使用的简化支柱模型，从而提供改进的支柱载荷估计。这一过程与实验室测试的结果相结合，将得出盲杆非线性行为的拟议模型，其他人可以在考虑到特定场地和施工条件的岩土工程分析中采用该模型。盲杆的数值分析将使用 Izzuddin 开发的非线性结构分析程序 ADAPTIC 进行，该程序已经提供了用于评估随时间变化的所有必要元素和材料模型。致盲支柱的响应。岩土工程分析将使用 Potts 开发的有限元程序 ICFEP 进行。该程序是专门为岩土工程编写的，并已应用于各种土壤-结构相互作用问题。岩土工程分析将研究顶部附近有或没有单个支柱的嵌入式悬臂墙的行为。在这两种情况下，将在最终开挖高度上对临时盲杆进行建模。施工顺序将基于莱姆豪斯连线、希思罗机场快线围堰和空侧公路隧道施工所采用的程序。土壤条件也将基于这些地点，并对主要在伦敦粘土和兰贝斯群进行的挖掘进行分析。将对盲板的比例模型进行一系列 20 项实验室测试，这些盲板模型的材料特性、最终条件和横向缺陷各不相同。测试结果将用于验证和完善数值分析。