Flow Characteristics and Escape-Route Optimization after Water Inrush in a Backward-Excavated Karst Tunnel

Abstract

In this study, using the background of Qiyueshan high-risk karst tunnels, flow characteristics and escape-route optimization after water inrush in a backward-excavated karst tunnel are researched. First, five case studies are simulated and investigated under different velocities of water inrush. One special probing line is selected, respectively, in the left tunnel, cross passage, right tunnel, and along the height direction of the tunnel centerline. For each probing line, the corresponding velocity and pressure curves are obtained based on the numerical simulation results. The change rules of velocity and pressure under the five water-inrush velocities are analyzed and concluded. Then, focusing on one velocity of water inrush, the variation laws of velocity and pressure in a plane are analyzed and discussed by selecting a series of probing lines. Flow characteristics of water after inrushing in a backward-excavated tunnel are summarized. Finally, for such cases, the optimized escape routes are made in the tunnels. The results show that (1) as the water-inrush velocity increases, the flow velocity in the tunnels also increases proportionately; (2) as the water-inrush velocity increases, the pressure in the tunnels also increases, but there exists no direct linear relationship between them; (3) there is little flow velocity close to the tunnel side wall as well as at the working face without water inrush and at the high location of the cross passage; and (4) the pressure at the intersection area of the cross passage and the tunnels changes greatly. Research results provide a theoretical basis for making scientific and rational escape routes.