In this paper, the potential risk of undesirable events occurring during tunneling with application of a
shield tunnel boring machine (TBM) method is discussed along with the risk analysis which can systematically
assess overall risk levels. Potential risks and typical scenarios pertaining to shield TBM tunnels
have been investigated based on previous case histories and correspondence with experts. The relevant
risks from undesirable events were categorized into four groups: cutter-related malfunction, machine
blockage or hold-up, mucking problems that hinder transporting excavated materials, and segment
defects. A fault-tree set was constructed by grouping risk factors (or causes) into geological, design
and construction/management factors. Risk analysis was performed by adopting fault-tree analysis
(FTA) and an analytic hierarchy process (AHP) with consideration of the probability and impact of the
risks. In addition, the proposed method was reliably validated by comparison with field observation,
and thus indicates its applicability to risk management for shield TBM tunneling