The Reliability of a Tunnel Boring Machine

Greater levels of complexity in tunnelling with Tunnel Boring Machine (TBM) allow higher chances of failures that may increase the potential hazardous risks. This paper presents the results of a study on TBM reliability using risk analysis. Machinery Failure Mode and effect analysis was applied to analyze the risks of a TBM using QS9000 and SAE J1739 recommendations. For this purpose, 48 failure modes were postulated for the TBM main systems and all subsystems. Afterwards, the effects of every failure were listed. Safeguards or controls that might prevent or mitigate the effects of each failure were also listed. In the final step, essential remedial actions to prevent or mitigate the failure were recommended. Risk Matrix was developed for each possible failure to be used for risk ranking. For this, the Risk Priority Number (RPN) was estimated for each failure mode for pro and post application of control measures to identify the most critical failures. The results revealed that 7 failure modes had risk priority numbers higher than 80 therefore, they were categorized unacceptable. Cutter head stop due to bad rock condition with RPN=240 was the significant critical failure. The results also showed that 3 failure modes in TBM required modification due to high severity rate. The findings from this study were applied to a long tunnel under construction and significantly reduced the accidents during the next two years tunnelling period. It can be concluded that, MFMEA is a superb tool for TBM reliability evaluation and promotion.