Weak rock behaviors contributing to TBM block accidents in the Shanggongshan Tunnel of Kunming

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.