Estimating the probability of failure due to scour
Despite the undesirable consequences associated with structural failures at river crossings, it is rare that sufficient funds are made available to undertake all necessary improvement activities. It is in the face of limited budgets that difficult decisions must be taken in order to decide how and where limited resources should be invested and, conversely, where intervention is not financially justified. Understanding risks along transport networks is fundamental to their operation and provides an evidence base to define management actions and strategies.
HR Wallingford has developed a new framework and method to develop a probabilistic scour risk assessment. This will contribute to assessing the risks of scour failure at bridges. As a result decision makers will be able to have greater confidence in the risk assessments on which they are basing their infrastructure investment decisions.
The work has been developed under the FUTURENET project funded by EPSRC and part of the Adaptation and Resilience to Climate Change. The research project addresses the issue of identifying vulnerabilities in transport infrastructure to climate change. The London-Glasgow transport corridor including highways and railways is used as the focus of the project.
Climate change is putting a renewed focus on assessing the likelihood of failure of key structures such as bridges. Examples of recent bridge failures in Europe are:
The new methodology uses fragility curves to account for uncertainty as well as taking into account the protection around bridges. The presence of protection works aims to change the relation between scour and the probability of failure of the infrastructure, as protection “delays” the possible exposure of bridge foundations by controlling the channel position and increasing the hydraulic load needed to fail the protection.
The methodology developed to estimate the probability of bridge failure due to scour at river crossings aims to be repeatable, as much as possible, independent of the user, and easy to update as more information or better knowledge becomes available. It does not aim to estimate the risk associated with a particular event but, instead, to estimate all possible events in order to obtain an annual probability at each bridge site. The annual probabilities calculated for different climate change scenarios can then be compared to chosen thresholds of safety levels to establish the necessary management strategies.
The work was developed under the FUTURENET project funded by EPSRC, and part of the Adaptation and Resilience to Climate Change