Pressure-induced dipole theory and pressure pulsation in shallow urban road tunnels with top vents

Abstract Shallow urban road tunnels with top vents represent environmentally friendly and energy-saving technology. To date, four such tunnels are operational in Nanjing, and their intra-tunnel air quality has been widely acclaimed. However, no prescriptive design methods have been developed for this technology. Natural ventilation at the top of the tunnels is caused by the pressure difference inside and outside the top vents. Thus, a prerequisite to the development of scientific design methods for such tunnels is a complete understanding and representation of the pressure wave distribution pattern in the tunnels. Based on an analogy with an electric dipole, we propose a pressure-induced dipole theory and construct an intra-tunnel pressure distribution model. An experimental platform is developed to evaluate the pressure distribution inside tunnels under 6 operational conditions. The results suggest the following. (1) The proposed pressure-induced dipole theory can well describe and explain the pressure wave distribution rules in road tunnels. (2) With a uniform and continuous traffic flow, the real-time pressure on each point in the tunnels demonstrates periodical asymmetrical quasi-sinusoidal pulsation, where the cycle is given as T = (S + L)/v. (3) Periodical pressure pulsation with decaying amplitude exists around the top vents. With large top vents, the pressure exchange between the inside and outside of the tunnels is significant.