Abstract:Tunneling by tunnel boring machine(TBM) in unfavorable engineering geological conditions often incurs accidents from engineering geological problems when the lectotype and collocation of TBM are ignored. These problems reflect the inherently poor flexibility of TBM to complicated geological conditions. Three cases of TBM accidents occurred respectively in Kashmir of India,Yunnan Province and Taiwan of China,deserve retrospective analysis. They are unique examples where TBM encountered huge amounts of accidents and resulted in disasters,which were replaced by the drilling and blasting method(DBM) in the end. The occurrence of these problems implies the unreasonable decision-makings,which are based on scare considerations of the risks but on blind believes of the TBM advantages to a certain extent. As a result,the disadvantages of TBM are obviously exposed,which bucks its advantage as fast advancement rate. Therefore,the construction time is delayed for 1–8 years. From the three cases,it is known that,in regions with active tectonic movements,intensively fractured rock mass and enriched groundwater flows,the selection of tunneling method must face the problems of uncertainty and unpredictability of complicated geological conditions. Approaches purely based on technical innovation and engineering experiences cannot solve all of these problems very well. Therefore,risk analyses should be carefully made,instead of the wishes to obtain one mixed TBM with multiple functions and feasible to various complicated geological conditions. In a word,the selection of TBM should be based on argumentation and demonstration of multi-disciplinary experts to support scientific decision-makings.