Impact of the Pressure Differences Between Road Galeries On Tunnels Generated by the Smoke Control System

Long motorway tunnels equipped with two independent unidirectional galleries are usually provided with longitudinal ventilation. This ventilation scheme, when applied to smoke control, can generate significant pressure differences between both roadway galleries, which may have an impact on the use of transverse galleries (escape routes). This paper present two-case studies where the results of measurements of these pressure differences taken in Marão and Gardunha tunnels allowed the assessment of relevant flow parameters, as the pressure loss coefficient of the entrance portal, the friction factor in the tunnel and the coefficient of installation of the jet fans. The assessed parameters were used in the steady-flow energy equation for a streamtube to predict the impact of pressure differences on the protection of transverse galleries (emergency exits) in the case of fire. The results show that the predicted pressure in the fire road gallery increases upstream the location of the fire and decreases downstream that location, when taking the pressure profile of the flow without fire as a reference. The models show that predicted pressure differences between the two road galleries in case of fire may be within the interval [200 Pa; − 100 Pa] in Marão tunnel and [12 Pa; − 48 Pa] in Gardunha Tunnel, while the measurements in the no fire case show that they lay within the interval [29 Pa; − 50 Pa] in Marão tunnel and [− 13 Pa; − 35 Pa] in Gardunha Tunnel.