London Underground: unravelling 150 years of structural secrets

The London Underground railway system has a massive civil engineering asset portfolio, with around 8000 bridges and 12 000 structures. Built since the mid-1860s by various private operating companies, less than 40% of record drawings were kept, let alone material specifications, design calculations or loading information. This made asset management and upgrades increasingly difficult, so it was decided in the mid-1980s to embark on a major project to determine the extent, condition and load-carrying capacity of all bridges and structures. This paper describes how the project has progressed over the past 30 years, including the development of ground-breaking inspection and assessment standards, innovative surveying and investigation methods, and a unique risk-assessment system. The results have enabled maintenance and improvement works to be cost-effectively prioritised, resulting in dramatic improvements in both safety and operation.