Abstract:

To perform the ventilation and gas reduction during the construction of largesection highway gas tunnels effectively, based on the Daliangzi tunnel of GulinJinsha highway, the computational model of the twobench excavation method with an inverted arch is developed by SCDM software, and numerical simulation is conducted based on Fluent software. The features of the ventilation flow and gas migration laws in the tunnel face and the neighboring areas under the different lengths of the bench, distance of the air duct outlet from the tunnel face, and the layout of the double air ducts on opposite sides and on the same side are disclosed and then validated using field monitoring data. Results reveal the following: (1) The flow field stabilizes after 20 min of ventilation, although vortices arise in the upper bench and the inverted arch, which hinders gas transport, diffusion, and dilution. With an asymmetric air duct placement, gas accumulates opposite the air duct at the tunnel face. (2) The ventilation sensitivity in the tunnel is influenced by the following: the double air duct and the layout form > adjusting the distance of wind pipe outlet from the tunnel face > adjusting the length of the bench. Prioritizing the use of the sameside layout for the air supply by the double air ducts, followed by adjusting the distance of the air duct outlet from the tunnel face by 20–25 m and the length of the bench by 15–20 m are recommended. (3) Ventilating the tunnel with double ducts on the same side increases the wind speed at the tunnel face and immediate areas, remarkably lowering the gas concentration. The results of the field air supply experiments agree with those of the numerical calculations, verifying the reliability of sameside double ducts for air supply.

Key words: threelane highway tunnel, gas tunnel, large crosssection tunnel, ventilation method, arrangement form of double ducts, gas migration laws