Numerical simulation of ventilation in the Jiaoxihe tunnel of the Hanjiang-to-Weihe River Water Transfer Project
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Abstract:
Hanjiang-to-Weihe River Water Transfer Project is a large water conservancy project to ease the water shortage in Guanzhong Plain in Shaanxi province. The Jiaoxihe tunnel crosses a river and faces complicated geographical and geological conditions. We simulated the ventilation in the tunnel with a branch tunnel using CFD numerical simulation, studied the variation of the flow and concentration fields in the tunnel during the construction period under several typical conditions, and analyzed the influence of the vortex on airflow and harmful gas distribution near the working face and in the branch tunnel. When the exhaust passage was hindered, the size and position of vortexes would change periodically near the working face, and their influence range would gradually decline with the ventilation time. In addition, the harmful gas and smoke produced from tunnel blasting would move and diffuse gradually out of the tunnel. After studying the airflow and dissipation of harmful gas in the main tunnel and branch tunnel, we had the following findings: A vortex zone would form after tunnel blasting due to ventilation near the working face and the intersection of the main tunnel and branch tunnel. The production and variation of vortexes would continuously consume the mechanical energy of ventilation, reduce ventilation efficiency, and hinder the dissipation of harmful gas. The dissipation process of the harmful gas in the tunnel included movement and diffusion. The movement process drove the CO out of the tunnel. The diffusion process continuously reduced the peak CO value in the tunnel. We calculated the time needed to reach safety concentration in the tunnel under different conditions and gave relevant suggestions on the construction progress.
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