Risk analysis for tunnelling ground movement assessments

Ground movements arising from tunnelling projects in urban areas have the potential to cause damage to overlying structures. Clients of tunnelling projects are therefore required to consult with owners of structures to demonstrate that the construction techniques proposed for the works will limit damage to an acceptable level. Displacements arising from tunnelled excavations are often calculated using a semi-empirical approach by considering the ground movement profile to be modelled by a Gaussian or normal distribution. A staged approach is then conventionally used for appraising the level of damage that structures will be subjected to as a consequence of these ground movements. This paper describes a quantitative risk analysis processes that can be used alongside a staged approach to damage assessment. The approach described in the paper allows project participants to make informed decisions for selecting cost-effective mitigation measures that may be required for tunnelling in urban areas. The process outlined demonstrates benefits for insurers, clients, and consulting and contracting engineers in understanding the level of risk of damage to structures. The process can also be integrated into an appropriate risk management strategy.