Braced excavations: what about the corners?

当一个新的地铁站或一个深地下室要在城市建设，一个大洞在地面上是必要的。该洞需要安全的工作，并允许进入，通常选择的解决方案是支持与支撑嵌入式挡土墙的大孔的侧面。这些都是大量的临时工程，成本相当高。最近的例子是在伦敦的帕丁顿新的Crossrail车站进行的230米长× 24米宽× 23米深的开挖。这种建筑形式的一个重要特征是跨越墙壁之间的大型支柱，以支撑它们。对于那些负责设计道具大小、位置、数量和墙壁的人来说，关键问题是预测挖掘附近的地面运动（这可能会对建筑物产生负面影响）和支撑力（以便使用正确的支撑物，虽然英国建筑信息组织CIRIA最近出版的一些出版物中存在设计师指南，关于这两个设计问题的挖掘拐角处的行为的覆盖范围很差。关于支撑开挖的计算建模，有大量已发表的研究，但仅在二维（即，通过长墙的切片）中，其中一些研究针对现场数据进行了验证，但考虑到拐角分析所需的3D效果，这是罕见的，也是不可靠的。提高我们对这些角落的行为以及它如何受到土壤行为、系统刚度和支柱载荷的影响的理解，将导致（a）支撑方案的更大经济性和（B）角落附近地面运动预测的更大确定性，可能减少防止损坏相邻结构所需的调节工程。这里提出的研究方案包括复杂的计算模拟支撑开挖施工，考虑到几何形状，材料和顺序的差异。这个问题只能使用3D模型来解决（与岩土工程中的许多其他问题不同），然而即使在今天，当我们尝试在3D中建模时，我们使用的计算工具也很难快速提供结果。因此，在本提案中，我们将使用一种聪明的方法，其中“降阶模型”（ROM）将使用相对较小的复杂3D模型集的结果。ROM更容易使用，并且通过操纵有限数量的高保真3D模拟来生成。从这些ROM中，我们将得出的结果，并准备指导工程师设计支撑开挖，这将使更便宜，更简单的方案被使用。该项目的研究人员来自达勒姆和邓迪大学，并得到了一个项目监督小组的支持，包括来自英国行业的关键人物。

When a new metro station or a deep basement are to be constructed in a city, a large hole in the ground is needed. The hole needs to be safe to work in and to allow access and very often the chosen solution is to support the sides of the large hole with a braced embedded retaining wall. These are substantial pieces of temporary works of considerable cost. Recent examples are the 230 long by 24 m wide by 23m deep excavation for the new Crossrail station at Paddington in London. An important feature of this form of construction is large props that span between the walls, to hold them up. For those tasked with designing the prop size, location, number and the walls the key issues are prediction of ground movements adjacent to the excavation (which could negatively affect buildings) and propping forces (so that the right props can be used and while guidance exists for designers in some recent publications produced by the UK construction information organisation, CIRIA, coverage of the behaviour at excavation corners as regards both design issues is poor. There is substantial published research on the computational modelling of braced excavations but only in two-dimensions (i.e. s slice through a long wall), some of it validated against field data, however accounting for 3D effects as required for the analysis of corners is rare and insubstantial. Improving our understanding of the behaviour of these corners and how it is affected by soil behaviour, system stiffness, and prop loading will lead to (a) greater economy in propping schemes and (b) more certainty in the prediction of ground movements adjacent to corners, potentially reducing the accommodation works required to prevent damage to adjacent structures. The programme of research proposed here comprises complex computational simulations of the construction of a braced excavation, taking into account differences in geometry, materials and sequences. The problem can only be properly tackled using a 3D model (unlike many other problems in geotechnical engineering) however even today, the computational tools we use struggle to deliver results quickly when we try to model in 3D. So, in this proposal we will be using a clever method where "reduced order models", (ROMs) will be made, using results from a relatively small set of the complex 3D models. A ROM is much easier to use and is generated by manipulation of a limited number of the high fidelity 3D simulations. From these ROMs we will derive results and prepare guidance for engineers designing braced excavations which will enable cheaper and simpler schemes to be used.The researchers on the project come from Durham and Dundee Universities and are supported by a Project Oversight Group comprising key figures from the UK industry.