Methods And Approaches For Mitigating The Risk Of Ground Movement Impacts From Tunnelling

Ground movements from excavation works can present project risks with stakeholder engagement, construction approvals, 3rd party claims for damage, time delays and additional cost for mitigation works. The theory of the prediction of ground movements and phased assessment of impacts on structures and infrastructure using simplified approaches has been documented in papers by Rankin (1988), [1] Burland (1995) [2] and several others.

In reality there are numerous complexities which come into the assessment including historical movements, modelling assumptions, quality of asset data, existing condition and individual structural layouts and sensitivities. Many of these variables cannot be modelled, or it is not practical to model. To manage these risks, sets of acceptance criteria have been developed, and where the assessment is within the criteria, the risk of more onerous cracking, deformation or loss of service is considered reasonably low. Similarly, where an assessed impact is higher than a given damage category or acceptance criteria, it indicates the risk is unacceptably high, but the event/failure may not actually occur. On this basis ground movement impact assessments need to be considered as a risk assessment as opposed to an absolute prediction. Often it is the ability to repair any damage which is more important than the magnitude of any cracking itself.

This paper discusses some of the challenges, considerations and approaches that the author has used on major infrastructure projects, along with some of the opportunities and new technologies available for assessment, instrumentation and monitoring and mitigation of the risk of ground movement impacts.