Risk analysis and risk ranking in tunneling: A case study

Constructing tunnels underground is generally described as a high-risk activity owing to the fact that conditions in the surrounding area tend to be unpredictable. This would create unique dangers in every situation. It is important to gain a deep understanding of the risks associated with tunneling, in order to reduce the likelihood of their occurrence and severity of their consequences, should they occur. For this to be achieved, different risks should first be evaluated and ranked according to their relative importance and criticality. Amir Kabir tunnel is considered to be one of the most dangerous tunnels in Tehran, Iran in terms of the risks involved in its excavation and their potential consequences. In particular, part T4 of the tunnel passes through a zone of different strata and a compound of various soils. This paper studies part T4 of Amir Kabir tunnel from a risk analysis and risk management point of view. In doing so, factors increasing total cost of the project, causing delay in the project completion time, decreasing the operation rate and downgrading project quality were identified and ranked according to their importance, using the aggregate primary index risk method. For this purpose, a comprehensive questionnaire was designed and completed by experts within the field of tunneling. By responding to the questionnaires, the experts determined the relative likelihood of occurrence of the studied factors and their potential consequences. As a result, the experts suggested several alternatives to reduce the risks involved in this particular study. Moreover, the experts completed new questionnaires whilst taking into account different alternatives. In the next step, the risks before and after applying the alternatives were compared. As a result of performing the said analyses, it was concluded that firstly, the aggregate primary index risk is an effective tool in identifying the risks involved in such projects. Secondly, it was concluded that by taking into account different alternatives when analyzing and ranking the risks, severity of the said risks can potentially be reduced. By taking into account such matters when analyzing the risks of tunneling, the efficiency of tunneling projects can greatly increase as a result of reducing the risks that threaten all financial and human resources involved in tunneling project execution. The approach introduced in this paper, together with the methodology described, can be adopted by the mining design engineer in all similar situations. They will be of particular advantage in such methods as room and pillar where the number of similar tunnels required is high