The design of tunnel ventilation system for a long vehicular tunnel

Abstract

Longitudinal, semi-transverse and transverse ventilation systems are the traditional approaches employed in the design of vehicular tunnel ventilation system. The Memorial Tunnel Fire Ventilation Test Program which carried out full-scale tests on fire heat release rate up to 100 MW for various ventilation schemes had demonstrated that longitudinal tunnel ventilation system is an effective means of controlling smoke during fire emergency. Consequently, many of the short vehicular tunnels have been designed with longitudinal tunnel ventilation system using a series of jet fans to bring pollutants out of the portal and to create an air velocity greater than critical velocity to prevent the backlayering of smoke during fire. However, the major constraints of longitudinal ventilation system are the excessive air volume and air velocity, and that it cannot ventilate long uni-directional vehicular tunnel due to the building up of pollutant concentration levels in the direction of travel unless air exchange points are provided. Long vehicular tunnel coupled with long slip roads presents special challenges in tunnel ventilation system design. During normal traffic operation, the vehicular emissions have to be removed to ensure that the air quality in the tunnel is kept within acceptable limits. The pollutants discharged from the ventilation buildings to the atmosphere have an air quality impact on surrounding development which has to be carefully assessed. The ventilation system also has to be designed to prevent the building up of temperature beyond tolerable limit during traffic congestion where vehicles may pile up bumper to bumper for several kilometres. When there is a fire emergency, smoke control to enable safe evacuation has to be addressed for the main tunnel, long in-ramps and long out-ramps. This paper describes the design of the ventilation system for the Kallang/Paya Lebar Expressway which is a major expressway in Singapore linking the East Coast Parkway in the south and the Tampines Expressway in the north. It is a complex project made up of tunnels, slip roads, viaducts, open expressways and ventilation buildings. It has a total length of 12 km of which approximately 8.7 km is in tunnel. The Expressway tunnel is linked to 8 entry and 9 exit slip roads and will be one of the longest dual three-lane road tunnels in Southeast Asia when completed in 2007. This paper addresses the major elements in the design of the tunnel ventilation system for the Expressway tunnel including: (a) Evaluation of different types of ventilation systems. (b) Air quality impact on the environment. (c) Ventilation system design for normal and congested traffic operation. (d) Ventilation system design for fire emergency operation. (e) Special considerations for long in-ramps and long out-ramps. Subway Environmental Simulation program has been used in the analysis of the ventilation system. As some the concepts employed in the design are unique, Computational Fluid Dynamics (CFD) techniques have been employed to validate the design. The results of the CFD analysis are presented in this paper. (A). Reprinted with permission from Elsevier. For the covering abstract see ITRD E124500.