The World Tunnel Congress (WTC) was hosted this year by the very active Norwegian Tunneling Society in the beautiful and picturesque city of Bergen. The congress had many interesting sessions with stimulating oral and poster presentations. Of particular interest was the risk management session, with contributions dealing with both construction and commercial case studies and considerations, but also construction insurance. This risk management session reconfirmed the importance of risk engineering management and the significant added value of the early active engagement of highly qualified and experienced engineering professionals in the whole spectrum of a project, from its conceptual and feasibility study up to its construction and operation-and-maintenance (O&M) phases.In a particular contribution, which is widely based on a paper co-authored by Ruler’s directors and presented in the previous WTC 2016 in San Francisco, the root causes of publicly available failures in tunnels and underground projects and their statistical elaboration was presented. It was of no surprise that the primary cause of failure is to be attributed to design errors and engineering misjudgment. In the majority of the cases under assessment, the project was disrupted due to face collapse or support failure, which disruption had led to sometimes significant and even un-insurable financial loss and project schedule overruns.

As we have already mentioned through this forum in previous blogs, post a failure event, the same questions are raised in the construction insurance industry. Was it foreseeable or unforeseen? Was there a proper risk assessment carried out and could the failure and its consequences have been avoided? Was there an active instrumentation and monitoring campaign carried out?

Fortunately, it is becoming a common approach and realisation that investing in early risk engineering involvement and hazard identification and mitigation can yield significant results with decisive positive impact on project decision making, execution and overall budgetary and schedule success.

Coming back to the abovementioned WTC 2017 paper contribution and the design failure of tunnel faces and excavation supports, the industry has developed and established many, commonly accepted and used, analysis and design methods which theoretically should have captured the failure mechanisms. But given the inherent unknowns of the underground, the risk of failure and the design uncertainties can – to a certain extent – be reduced and mitigated by moving from the deterministic approach (single prediction) to the probabilistic and statistical methods (multi-parametric). Among a number of available methods, Ruler directors have developed the CULT-I approach (Capacity Utilisation of Linings in Tunnels- Index) for the design optimisation of tunnel support systems and have contributed to the establishment of the TSF (Tunnel Stability Factor) for the probabilistic assessment of tunnel face stability.

We will discuss how can these methods can be applied in a risk engineering framework and contribute positively to construction insurance by reducing and/or minimising the total ‘Cost of Risk’ in an upcoming contribution. Stand by!