A Case Study for Escape Route Optimization after Water Inrush in a Backward Excavated Karst Tunnel

With the development and utilization of underground space in karst area, water-inrush is becoming a major geological disaster in tunnel engineering. The investigation for escape routes optimization after water inrush in process of karst tunnel excavation is particularly important. In the present study, a case of water inrush from the working face is investigated in a backward excavated karst tunnel. Numerical simulation is carried out by using the FLUENT software, the variation laws of velocity and pressure along with distance are analyzed and discussed by selecting a series of probing lines in a plane. Then flow characteristics of water after inrushing during double-line tunnel excavation are summarized. Finally, the optimized escape routes are made. The results show that: (1) the water velocity nearby the tunnel side wall is the minimum, while it is the maximum in the middle position. So people in tunnels should first move to the tunnel side wall and then escape quickly when water inrush happens. (2) The water pressure at the intersection area of the cross passage and tunnels is large. So people must not stay at the intersection area of the cross passage and tunnels when water inrush happens. (3) When water inrush happens in the left tunnel, if people meet the cross passage during escaping, they should pass through it rapidly, turn to the right tunnel and run to the entrance. (4) If there is not enough time to escape, people can run to the trolley and other equipment in the vicinity of the right tunnel working face. In addition, some rescuing equipment can be set up at the high location of the cross passage. (5) Even if large flow water inrush occurs in the tunnel, people can escape safely as long as the disaster is observed in time and the escape routes are optimized scientifically and rationally. The results are of important practical significance and engineering value to ensure the safety of tunnel construction.