Abstract: Large continuous broken rock mass in the fault area is one of the adverse geological conditions in the tunnel construction. Geohazards such as large scale collapse, groundwater intrusion, are prone to occur under this condition. This paper presents a case history of the groundwater intrusion mitigation in the construction of left tunnel of Longtan Tunnel.  The construction techniques that were used in this mitigation are summarized in the paper. Further, the groundwater movement is simulated with numerical analysis. The evacuation route is also optimized through the numerical analysis.

Key words: Broken Rock Mass, Tunnel Construction, Groundwater and Mud Intrusion, Numerical Simulations