Ensuring adequate ventilation during tunnel construction is a critical issue that directly affects construction efficiency. A good ventilation environment can effectively guarantee the construction progress. In this paper, by repeatedly selecting the flow field simulation parameters and continuously summarizing the calculation methods, a reasonable model is selected to simulate the tunnel engineering. Specifically, the eddy current zone near the working face is obtained by analysing the flow field of forced ventilation tunnels. Furthermore, we analyse the dispersion and accumulation of harmful gases in the tunnel. The CO concentration at typical locations in the tunnel is also examined in order to determine areas with the lowest likelihood of harmful gas discharge. We then propose adding a jet fan to the tunnel to create an extraction plus ventilation tunnel. Simulation results reveal that the addition of a jet fan causes eddy currents that improve the extraction of harmful gases, thereby greatly reducing ventilation time and increasing efficiency. The results of the model can effectively guide the actual project, and help them save the construction time.
Toxic and harmful gases generated during tunnel construction endanger the life and health of construction personnel. Reasonable design and solution of ventilation problems become the key to ensure the safety of engineering construction. By repeatedly selecting model parameters and calculation methods, this paper establishes a reasonable model to simulate tunnel ventilation engineering. By simulating the distribution of the flow field in the tunnel under various ventilation modes, the mechanism of the turbulent air flow generated by the restriction of jet and wall is proved. The retarding effect of vortex region on pollutant transport is analyzed. The results showed that the retarding effect of vortex and pollutant transport diffusion mechanism resulted in two peak distributions of pollutants. The mechanism of fan accelerating pollutant transport in stagnation zone was also revealed. The time cost law of ventilation saving under different modes is found through comparison. According to the distribution characteristics of flow field and the migration rules of pollutants under various ventilation modes, a new annular ventilation mode is proposed, which provides a reference for the optimization of engineering ventilation time. By comparing different ventilation modes, optimization measures are proposed for specific projects.
Ventilation problems are critical in tunnel engineering, and the loss of air volume in ventilation ducts is generally estimated using empirical methods. The air volume calculation is difficult to meet the accuracy requirements, resulting in resource waste or insufficient air supply. In this study, the forced ventilation system of the tunnel under construction was investigated based on the computational fluid dynamics method. The mechanism of air leakage on air flow distribution and pollutant transport in the tunnel is determined. Air leakage reduces the distribution peak of pollutants and effectively accelerates the emission of harmful gases. However, this effect decreases with distance from the air duct inlet. Through the calculation results of nearly one hundred models, it is found that the air leakage of duct can be fitted by logarithmic function and verified by empirical equation. The matching degree between the fitting function of the model and the empirical equation depends on the length of the tunnel. On the basis, the calculation formula of effective air volume near the working face is derived. This study can be applied to the ventilation engineering of the tunnel under construction, and provide a theoretical basis for the calculation of the effective air supply.
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