Quantification of risks to bridges from erosion and blockage: An elicitation of expert views

该项目的目的是量化桥梁和涵洞易受堵塞或冲刷影响的不确定性，以便为基础设施管理者及其合作伙伴（如铁路网和环境署）提供更好的指导和风险模型。该方法将是一个正式的“专家启发”，以量化面临冲刷或堵塞风险的桥梁和涵洞的脆弱性。对于跨越河流或较小水道的主要基础设施网络来说，侵蚀和堵塞是两大危险。在英国，自19世纪40年代以来，估计有15人因结构的洪水/冲刷失败而死亡（RSSB, 2004）。近年来，一些著名的事故包括1989年威尔士的格兰莱德铁路桥，该桥由于桥墩冲刷而倒塌，导致一列火车试图通过倒塌的桥梁并落入河中，造成四人死亡。2002年6月，兰开夏郡的Lower Ashenbottom高架桥倒塌，部分原因是洪水期间的冲刷，但碎片的存在加剧了情况。在2009年坎布里亚郡的洪水中，七座道路和人行桥梁由于冲刷和水动力载荷的共同作用而倒塌。沃金顿北部公路桥的倒塌造成一人死亡和大规模破坏。虽然灾难性的桥梁故障很少发生，但涵洞和桥梁的堵塞，即使是在相对较小的河流上，也会导致洪水和对安全至关重要的土方工程的侵蚀。即使是小事故也会给基础设施运营商带来额外的运营成本和风险，包括与碎片清理和紧急结构检查相关的成本和风险。对于广大市民来说，这些事故可能会由于速度限制、延误、时间表更改或改道等操作措施而造成干扰。仅铁路网上的水道上就有近1万座桥梁，资产存量的规模是巨大的。尽管行业多年来一直在努力，但这些资产的个体弹性仍然存在很多不确定性，而且对这种不确定性的定量认识有限。关于冲刷和堵塞概率的信息的不确定性和不同性质表明，正式引出专家判断对于寻求得出当前知识的综合是有用的。在这种情况下，不确定性不可避免地对风险评估和任何相关决策产生重大影响；需要有一个结构化的程序，从一系列意见中得出专家判断，以便在评估促成因素时使用的不确定性量化的适当水平上取得合理的共识。为决策支持征求专家意见并不是什么新鲜事。但是，一般来说，这是在非正式的基础上进行的。然而，非结构化的方法很少（如果有的话）能让各方都完全满意。它也不可能免受来自一方或另一方的合法批评或审计。为了解决这些缺点，结构化的专家判断使得将整个过程与明确和透明的方法规则联系起来成为可能，其目标是在正式的决策过程中以与“正常”科学数据相同的方式对待专家判断。文献中描述了评估和结合专家不确定性的各种方法。直到最近，最熟悉的方法是提倡一个小组决策会议框架来征求意见，但现在存在其他方法来更客观地执行这一过程。其中最突出的是被称为经典模型的专家加权程序，由Cooke（1991）提出。利用英国和国际专家的知识和专业知识，该项目将使用库克的经典模型来量化桥梁和涵洞易受堵塞或冲刷的不确定性，为基础设施管理者提供更好的指导和风险模型。

The aim of the project is to quantify uncertainties in the vulnerability of bridges and culverts to blockage or scour, in order to support better guidance and risk models for infrastructure managers and their partners, such as Network Rail and the Environment Agency. The approach will be a formal 'expert elicitation' to quantify the fragility of bridges and culverts at risk of scour or blockage.Erosion and blockage are two significant hazards for major infrastructure networks where they cross rivers or smaller watercourses. In the UK there are estimated to have been 15 fatalities due to flood/scour failure of a structure since the 1840s (RSSB, 2004). In recent years notable incidents include the Glanrhyd railway bridge in Wales, which collapsed in 1989 due to scour of a pier, resulting in four fatalities when a train attempted to cross the collapsed bridge and fell into the river. The Lower Ashenbottom viaduct in Lancashire failed in June 2002 as its central pier collapsed, partially due to scour during a flood event but exacerbated by the presence of debris. In the 2009 Cumbria floods, seven road and foot bridges failed due to the combination of scour and hydrodynamic loading. The collapse of the Northside road bridge in Workington caused one fatality and massive disruption. Whilst catastrophic bridge failures are rare, blockages of culverts and bridges, even over relatively small rivers, can cause flooding and erosion of safety-critical earthworks. Even minor incidents can lead to additional operational costs and risks for infrastructure operators, including those associated with debris clearance and emergency structural inspections. For the wider public, these incidents can cause disruption because of operational measures such as speed restrictions, delays, time-table changes or diversions. With nearly 10,000 bridges over watercourses on the rail network alone, the scale of the asset stock is significant. Despite industry efforts over the years, there remains much uncertainty about the individual resilience of these assets, and there is limited quantitative knowledge of this uncertainty.The uncertain and disparate nature of information about scour and blockage probabilities indicates that a formal elicitation of expert judgements will be useful in seeking to draw out a synthesis of current knowledge. Inevitably, uncertainty has a major influence on a risk assessment and on any associated decisions in circumstances such as this; a structured procedure for eliciting expert judgements from a range of opinions is needed to obtain a rational consensus on the appropriate level of uncertainty quantification to use in the appraisal of contributory factors. Soliciting expert advice for decision support is not new. Generally, however, it has been pursued on an informal basis. However, an unstructured approach is rarely, if ever, entirely satisfactory to all parties. Neither is it likely to be immune to legitimate criticism or auditing from one side or another. To address these shortcomings, structured expert judgement makes it possible to tie the whole process to stated and transparent methodological rules, with the goal of treating expert judgements in the same way as 'normal' scientific data, in a formal decision process.Various methods for assessing and combining expert uncertainty are described in the literature. Until recently, the most familiar approach has been one that advocates a group decision-conferencing framework for eliciting opinions, but other approaches now exist for carrying out this process more objectively. Prominent amongst these is the expert weighting procedure known as the Classical Model, formulated by Cooke (1991). Drawing on the knowledge and expertise of UK and international experts, this project will use Cooke's Classical Model to quantify uncertainties in the vulnerability of bridges and culverts to blockage or scour - to support better guidance and risk models for infrastructure managers.