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对堵塞或冲刷的脆弱性的不确定性，以便为基础设施管理人员及其合作伙伴（如铁路网和环境局）提供更好的指导和风险模型。该方法将是一种正式的"专家启发"，以量化桥梁和涵洞在冲刷或堵塞风险下的脆弱性。冲刷和堵塞是跨越河流或较小水道的主要基础设施网络的两大危害。在英国，自19世纪40年代以来，估计有15人因结构物的洪水/冲刷破坏而死亡（RSSB，2004）。1989年，威尔士的Glanrhyd铁路桥因桥墩冲刷而倒塌，导致一列火车试图穿过倒塌的桥梁并坠入河中，造成四人死亡。2002年6月，兰开夏郡的下阿什伯顿高架桥因其中央桥墩倒塌而失败，部分原因是洪水事件中的冲刷，但由于碎片的存在而加剧。在2009年坎布里亚郡的洪水中，由于冲刷和水动力荷载的共同作用，七座公路和人行桥失败了。沃金顿的诺斯赛德公路桥倒塌造成一人死亡和大规模破坏。虽然灾难性的桥梁故障是罕见的，涵洞和桥梁的堵塞，即使在相对较小的河流，可能会导致洪水和侵蚀的安全关键土方工程。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，包括与碎片清除和紧急结构检查有关的成本和风险。对于更广泛的公众来说，这些事件可能会因为速度限制、延误、时间表更改或改道等运营措施而造成中断。仅在铁路网络上就有近10，000座桥梁跨越水道，资产存量规模巨大。尽管行业多年来一直在努力，但这些资产的个别弹性仍然存在很大的不确定性，并且对这种不确定性的定量知识有限。有关冲刷和堵塞概率的信息的不确定性和不同性质表明，正式的专家判断将有助于寻求得出当前知识的综合。不可避免的是，不确定性对风险评估和在这种情况下的任何相关决定都有重大影响;需要一个结构化的程序，从一系列意见中引出专家判断，以便就评估促成因素时使用的不确定性量化的适当水平达成合理的共识。为决策支持征求专家意见并不新鲜。然而，一般来说，这是在非正式的基础上进行的。然而，一个非结构化的方法很少，如果有的话，完全令人满意的所有各方。它也不可能不受来自一方或另一方的合理批评或审计。为了解决这些缺点，结构化的专家判断使得有可能将整个过程与规定的和透明的方法规则联系起来，其目标是以与“正常”科学数据相同的方式对待专家判断，在正式的决策过程中，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，最熟悉的方法一直是提倡一个群体决策会议框架来征求意见，但现在有其他方法可以更客观地执行这个过程。其中最突出的是专家加权程序，称为经典模型，由Cooke（1991）制定。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对堵塞或冲刷的脆弱性的不确定性-为基础设施管理人员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.