The assessment of the hydro-jacking risk of the pressurized water tunnel by theoretical and numerical method

摘要

Different from the common tunnel such as road/railroad tunnel, a pressurizedwater tunnel is known to be exposed to water pressure applying on an inside of tunnel. The internal water pressure acts on the concrete liner of tunnel, and it causes damage in the liner as well as leakage into the surrounding rock mass. Apart from damages in the liner, the surrounding rock mass also can be damaged from crack initiation and propagation by water leakage. Therefore, a careful analysis on the hydraulic damage should be carried out when the stability of internal water tunnel is needed to be concerned against “hydro-jacking”. In this study, hydro-jacking related analysis has been performed on the stability of old drainage tunnel at dam site with theoretical and numerical methods. Itwas predicted from the stability analysis that hydro-jacking can be occurred at the existing pressurized tunnel when new drainage tunnel is constructed nearby. On close examination it was found that the safety factor of the old drainage tunnel was higher than a permissible range. Consequently, old drainage tunnel was expected to be stable against the hydro-jacking not only at the current state but after new drainage tunnel construction.