大断面/中断面、长距离隧道施工通风特性及风险分析

Study of construction ventilation characteristics and risk assessment for the large and middle cross-section long-distance tunnels

针对上海崇明越江遂道(大断面)及青草沙原水工程越江(中断面)超长距离隧道,基于通风的有关理论建立物理数学模型,利用有限体积方法和SIMPLE算法,研究隧道施工中盾构机掘进面附近流场的湍流特性。参照隧道内作业环境标准,讨论大断面隧道掘进而环境温度较高的情况与中断面隧道发生有害气体意外泄漏的事故,分析相应的通风方案对盾构机工作区域热量释放及对有害气体扩散的控制。

The physical and mathematical models of construction ventilation were conducted based on ventilation theory for the cross-river tunnels of Shanghai Yangtze （large section）, and Qing-cao-sha water tunnel （middle section） with long distances. Based on RNG k-s model and two-layer zonal model, the complicated turbulent flow characteristics inside tunnel were simulated numerically through Reynolds-averaged Navier-Stokes equations differentiated by the finite volume and SIMPLE scheme. In order to control the atmosphere temperature around shield-working-field for large cross-section tunnel, the jet fan is utilized. The computed results show that with the increase of the quantity of longitudinal ventilation and exhaust, the heat of tunneling areas is drawn out, and the concentrations of harmful gases are decreased. For the limit of Qing-cao-sha water tunnel＇s diameter, there is large resistance of wind system. Therefore, correspond measures are adopted. As wind-leak ratio of 100 meters is below 1.16%, the ventilating requirement is satisfied for the tunnel. When the instantaneous release of harmful gases inside middle cross-section tunnel happens, the mea- sures of forced ventilation and exhaust are adopted for the Qing-cao-sha water tunnel. For the leakage accident of combustible and highly-toxic gas H2S, the computed results show that the period of harmful gases concentration of tunneling areas reaching allowable level is shortest, and ventilation effect is optimum under 380.00 m^3/min of ventilation and 200 Pa of exhaust pressure. When the continuous release of harmful gases inside middle cross-section tunnel takes place, the variations and distributions of harmful gas concentration were simulated numerically. The computed results show that H2S concentration is less than the standard for tunnel under ventilation condition. Therefore, with the increase of ventilation quantity, the ventilation effect is better. The study on construction ventilation characteristics and risk assessment provides a theoretical basis for ensuring the safety construction of large and middle cross-section long-distance tunnels.