Bridges

The RTA Bridge Engineering Branch and Asset management Section routinely assess proposals by external developers that involve deep excavations for new infrastructure construction located adjacent to its bridge structures. These excavations have the potential risk of pier, abutment and bearing displacements and rotations, causing twisting and cracking of bridge superstructures. In order to mitigate these risks, the RTA developed technical criteria and other requirements the developers were required to satisfactorily address in a submission including the following:

• Identify and quantify the effect of the excavation on the existing bridges.
• Determine the need for lateral supports to minimise displacements and rotations of existing substructure and superstructure to acceptable limits.
• Methodology for restricting/preventing any adverse effect of rock mass movement.
• Staging of excavation to minimise movement of rock mass.
• Strengthening of the existing bridge to resist effects from the movement of the rock mass.
• Provision of monitoring regime, trigger limits and contingency plan.

This paper discusses some case studies of risk mitigation on some projects.