Design and Construction Criteria of Twin Tunnel: Taking an Adverse Wind Condition Effects on Air Pollution Short Circuit at Tunnel Portals as a case

Hadj Miloua

doi:10.34118/jbms.v7i1.73

Abstract

This paper aims to study the influence of the tunnel portal designs, wind conditions and ventilation rate on the amount of air pollution short circuit from one tunnel tube to the other. These effects are investigated by Computational Fluid Dynamics (CFD) code used a Large Eddy Simulation (LES) method to control air quality inside the tunnel and reduced as far as possible a short circuited (flow Recirculation) flow level. A validation of CFD code to experimental data in 1:100 scale model of the road traffic tunnel tested in wind-tunnel showed that the CFD gave satisfactory prediction of the air pollution short circuit in the vicinity of tunnel portal. The predicted concentration of the gas tracer (CO2) used as the safety criterion provide the useful information about a short circuit amount resulted for each structural variant of tunnel portals, such as a central dividing wall built as extensions from the end of road tunnel and offset tunnel portal entrance exit tested under different speed ratio of wind and ventilation. A detailed look at results is beyond the scope of analysis to determine optimal air pollution short circuit percentages. Finally, the perfect tunnel portals geometry can be suggested.

Highlights

Ventilation and fire safety design in road tunnels under external wind effect are one of the most complexes issues that need to be carefully considered and analyzed in the designing stage of any tunnel project
The data given from the experiments are compared with the predicted results of the Computational Fluid Dynamics (CFD) model based to the values of efficiency in different sizes of central dividing wall and offset tunnel portal entrance exit
Computational Fluid Dynamics (CFD) models validated, for the simulation of the behavior of contaminant originating from short-circuiting flow between tube of road tunnel for both structure of tunnel portal designs such as “Central Dividing Wall” and “Offset Tunnel Portal Entrance Exit” designs

Summary

Introduction

Ventilation and fire safety design in road tunnels under external wind effect are one of the most complexes issues that need to be carefully considered and analyzed in the designing stage of any tunnel project. Most of the road tunnels were designed as a twin tube equipped with longitudinal ventilation system in each traffic direction. The disadvantage of this system of ventilation reported by Kashef et al (2003) is that adverse wind conditions maybe short-circuit the flow from the exhaust tube to the nearby tube, causing the contamination of fresh in supply tube. Muhič and Mazej (2014) clearly indicated the negative effect of external wind in the case of a longitudinally ventilated road tunnel. A testing ventilation system of close tunnel model was established by Tan et al (2015) is intended to provide drivers

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Conclusion