The Hydraulic Stability Assessment of Jointed Rock Mass by Analysis of Stress Path due to Underground Excavation

In this study the effects of the stress path on the hydraulic conductivity characteristics during excavation are analyzed using a 2-D discrete element method. The variation of the stress path of the joints at specific locations (the bottom and wall) and around the periphery of an underground opening have been analyzed. The hydraulic stability of the opening is evaluated using the new concept of the trend distance ratio and trend orientation angle. The results from the analysis of the stress path at the bottom and wall of the opening are as follows: Firstly, most of the stress paths of the joints normal to the excavation surface are within the stable zone, and the hydraulic conductivity of the joints is decreased by 21% in average. Secondly, all of the stress paths of the joints parallel to the excavation surface are within the unstable zone, and the hydraulic conductivity is increased to 2.2 times in average. And the variation of the stress path and hydraulic conductivity is further analyzed for those joints having various distances from the opening. The joints parallel to the excavation surface showed the normal stress decreased by 38% and the hydraulic conductivity increased up to 1.9 times in average. This study makes it possible to determine the hydraulic stability of the underground opening excavated in a jointed rock mass.