This paper presents case histories of TBM jamming accidents associated with weak rocks at Shanggongshan Tunnel, as one section of the water diversion and supply project of Zhangjiu River, Kunming, China. The weak rocks including faulted rocks, sandy and argillaceous slates. Structural geology with respect to folding and faulting located in the southeast side of Puduhe anticline resulted in complicated engineering geological conditions. During TBM excavation some engineering geological problems occurred in zones with fractured weak rocks and groundwater. It is apparent that the large deformation rate of weak rocks played a distinctive role causing TBM jamming accidents, where the space between shields and surrounding rocks were disappeared in a short time. Together with the analysis on accidents causes, this paper presents corresponding countermeasures adopted in detail. As a result, this paper presents significant experiences and lessons from TBM accidents, though TBM is not always feasible for unfavorable engineering geological conditions.
As a main feature of geological settings, weak rocks are worthy of paid much more attentions. The main considerations are that the weak rocks wi.th lower strength are usually emerged with certain kinds of geological structures, as faults, joints, even folds. And in many cases they are connected with groundwater flows. The distribution, area percent of the weak rocks and potential problems and resulted risks are key issues in decision making on selection of excavation methods as blast and cast, or as TBM. If the TBM method is chosen, then the excavation and support parameters will rock be determined without understanding the weak classification behaviors. Barton (2000) researched a rock mass value, classification based on an expanded version of the Q-value, termed QTBM. Einstein (2000) reviewed case Opalinus Clayshale. Alber (2000) evaluated advance rates of hard rock TBMs and their effects on project economics.
Detailed preliminary investigation and probe drilling are necessary in order for TBMs to meet the requirement of excavation in complex geological conditions (Pelizza et al., 2001; Barton, 2000). For example, in fault zones, the approaches should integrate field investigation, bore drilling, probe-drilling, geological radar, and daily logging (Zhang, 1999; Su et al., 2001; Xu, 2000; Liu and Cheng, 2000). Here it should be noted again that typical case examples with empirical or actual investigation results deserve complete re-evaluation and retrospective study (Bappler, 2001). Obviously, the case examples discussed in this paper are actual lessons for further TBM application and development.
Shanggongshan Tunnel, with a total length of l3.769km (Figure 1), a diameter of 3.00m, as the unique tunnel with TBM method, was started on April 2003. The final breakthrough to the TBM exit shaft is at the end of 2005. It is the longest one of the 16 tunnels in the Water Supply and Diversion Project of Zhangjiu River for water use in Kunming City. The designed water supply volume is 40 × 104t/d to 60× 104 t/d (Huang and Li, 2003).