Risk models are not often used in tunnelling, despite the fact that these models can be deployed to identify critical factors associated with critical failure events. For a PhD research performed by Ibsen Chivatá Cárdenas at the University of Twente it was gathered evidence that shows that causal risk models can make an important contribution to managing risks in tunnelling. Experts involved in the Sluiskiltunnel in the Netherlands (a tunnel under the channel between Ghent and Terneuzen) participated in the research. They saw the added value of using models that integrate existing risk-related knowledge.
Tunnel construction entails many risks. Typically, the underground conditions can affect the stability of a tunnel. Other risky issues are the undesirable interactions between the tunnelling process and the ground being excavated, unexpected features in the soil and on-going construction activities and infrastructure on the surface. Overlooking these risk factors interactions can lead to serious consequences. To prevent this happening, the use of procedures and tools that systematically manage risk-related knowledge (prior knowledge) is highly desirable and will decrease the likelihood that those interactions are overlooked. A risk model that integrates risk-related knowledge is one of these tools.
Risk management
‘Such risk models are a good alternative to databases or repositories that are currently used in the construction industry. The risk models developed and used in this research allow professionals to share their expertise, ensuring that the relevant information available supports risk management decisions. This kind of risk models are rarely used in tunnel construction projects. Moreover, models that comprehensively make the interrelationships between risk factors and failure events explicit are absent from the literature on tunnel works’ This was the reason for Cárdenas to focus his PhD research on this subject.
Critical risks in tunnels construction
"My risk models yield information on the relevant risk factors for a construction project by means of sensitivity analysis. The power of the developed models in this research lies in that they can be customized and updated using project specific information according to conditions of the project under scrutiny. A set of models were developed for some major risks in tunnelling, as follows: face instability in soft soils when using Slurry Shields, face instability in soft soils when using an Earth Pressure Balance Shield, collapse and large deformations in shaft excavations, collapse and large deformations of excavations for cross passages in soft soils, excessive volume loss leading to surface settlements in tunnels bored in soft soils, excessive deformation, damage, and leakage of concrete lining.
Expert help
The input information used by Cárdenas for developing the risk models was obtained from risk databases, reports on geotechnical failure and specialized literature on tunnel construction. He augmented this information with probability estimates provided by experts. Thirty-one experts contributed to the research, all of them involved in on-going or completed Dutch tunnelling projects. This research project has also benefited enormously from the professionals involved in the Sluiskil tunnel project in the Netherlands, as well as, Witteveen+Bos’ specialists who took part in the case study for this research.
More information
Ibsen Chivatá Cárdenas completed his PhD research at the Faculty of Engineering Technology (CTW) of the University of Twente. He was supervised by Prof. J.I.M. Halman, Prof. A.F. van Tol and Dr S.H.S. Al-Jibouri. The thesis is available on request. The PhD ceremony will take place on 16 November at 12.45 in the Waaier building, Prof. dr. G. Berkhoff-zaal, University of Twente, Enschede.
