Theoretical semi-quantitative risk assessment methodology for tunnel design and construction processes

All engineering projects involve risk management applications. Sometimes, risks cannot be effectively managed, leading to catastrophic consequences. Engineers must consciously or unconsciously manage these risks. Regardless of how risks are handled, project risks need to be systematically evaluated. Therefore, risk management procedures must be implemented in every project, particularly in geo-engineering projects, to mitigate undesirable consequences and achieve project objectives. However, the use of risk management procedures in underground excavation projects is not common. Numerous commonly employed underground excavation techniques lack assessment of risks, notably geotechnical risks. Most of them only evaluate rock structures and excavation stability in accordance with the geological structure. This paper combines a universal risk management perspective with the underground engineering discipline. The tunnel engineering design and construction steps were evaluated for uncertainties using Scenario Structuring Modeling techniques to identify both technical and non-technical risks associated with underground excavation. Bayesian Network models were employed to identify connections that contribute to risk. To achieve this, objective and quantitative risk assessment tables have been devised using risk management philosophy, in accordance with tunnel design engineering principles and Turkish procurement laws. The primary objective of this study is to increase awareness of the use of risk management processes in tunnel construction projects and introduce a systematic approach to risk assessment in tunnel engineering projects. As a result, a semi-quantitative risk assessment method based on risk management philosophy is proposed for tunnel design and construction for the first time, evaluating not only geotechnical and engineering risks but also human, financial, and various other sources of risks.