Numerical study on the smoke control using point extraction strategy in a large cross-section tunnel in fire

The Point Extraction System (PES) is effective for smoke control and popular for long and large cross-section shield TBM (Tunnel Boring Machine) tunnels. To clearly comprehend the fire characteristics on the cross-section and correctly apply the smoke control strategy, a series of 3D numerical Computation Fluid Dynamics (CFD) simulations are conducted. Smoke temperature, minimum visibility and carbon monoxide (CO) concentration are analyzed to evaluate the efficiency and effect of the PES on the evacuation environment according to the standard safety criteria. Three fire scenarios i.e. 5 MW, 20 MW, and 50 MW are employed in the simulations. Fire characteristics and smoke control in different transverse fire locations, dimensions of smoke exhaust openings and smoke exhaust rate are simulated, respectively. The results indicate that transverse fire location slightly affects the evacuation environment due to the nature of large cross section. With the same area, the slender exhaust opening perpendicular to the longitudinal direction of the tunnel can control the smoke better than the short one, especially in the areas far away from the fire source. The smoke extraction efficiency of PES is determined by the smoke exhaust rate. Higher smoke exhaust rate improves the smoke control efficiency to a large extent.