| Severe water inrush occurred in 180 (28%) of 644 cases of geological risk events related to mountain tunnel construction. For the purpose of reducing the risk of water inrush、we analyzed cases in which drainage operations were minimally effective despite the use of advance boreholes. Analysis results revealed two disadvantages to advance borehole operation. First、geological or hydrological interpretation from core observation was uncertain due to insufficient observable core. Second、the amount of drainage from advance boreholes was not an accurate reflection of the existing water due to the complexity or heterogeneity of permeability distribution. |
