On the importance of risk assessments in tunnel crossings

Urban tunnelling poses some specific challenges, often the biggest being asset protection. Tunnelling inevitably causes ground movements and assessing the impact of those movements, controlling them and mitigating them can be a major part of any urban tunnelling project.

For major asset owners, especially those with tunnelling or similar experience, they often have extensive documentation in place describing the critical elements of an assessment for their assets. But may asset owners do not. They may not have the experience or the scale for such documentation to be produced. In that case we often have to advise the asset owner what documentation they should expect to ensure that a piece of tunnelling does not damage their asset.

In that case, what documentation should we be requesting, what is the most critical document that those planning and undertaking the tunnelling can produce?

My view is the by far the most important document is the risk assessment. It is from this document that almost all other documentation is produced. Those undertaking the tunnelling must undertake a site specific, construction method specific, asset specific and comprehensive risk assessment highlighting where the risks associated with their chosen approach are.

The risk assessment should highlight by what mechanism the asset is at risk. From this should flow the analytical assessments of the asset covering the mechanisms highlighted by the risk assessment. These mechanisms and the enumerated values will direct the control methods and monitoring that needs to be used. The risk assessment will highlight unknown information that is critical, directing any further ground investigation or surveys that must be undertaken.

Of course, all the documentation needs to be produced correctly and be representative of the situation being assessed. But for me, the document that should always guide the whole assessment is the risk assessment.