Successful construction of an Olympic Park access beneath an old sewer bridge in north London revealed that cast iron can be much stronger than assumed from design codes. Intensive monitoring and assessment of the 150-yearold sewer barrels demonstrated the conservatism in allowable stress limits that are generally used for cast iron. By making positive adjustments to the bridge and refining construction methodology, safe construction of the access underpass was ensured without impairing the bridge's stability and strength. London Olympic Park underpass leads to better understanding of cast iron Proceedings of the Institution of Civil Engineers Civil Engineering 166 August 2013 Issue CE3 Pages 129-136 http://dx.