Numerical simulation of TBM construction ventilation in a long diversion tunnel

A three-dimensional Renormalization-group (RNG) k-ε model has been performed for forced ventilation to the working face of a long diversion tunnel, taking into account the effects of air leakage and the frictional resistance along the tunnel. The case study involves the working face during TBM construction of the Xinjiang 81 Daban long diversion tunnel, China. Analysis of the flow-field distribution and the pressure distribution near the working face and tunnel outlet revealed the relationships among the air leakage rate per 100 m, pressure difference at the air leakage port, and quantity of air in the air duct. The simulation results show that the air flux, velocity, and leakage rate gradually decrease along the tunnel. The air leakage rate per 100 m increases logarithmically along with pressure growth when the latter is limited within a certain pressure difference range. A low-pressure area can be found on the duct wall near the air leakage port, and the pressure inside the tunnel gradually decreases from the working face to the tunnel outlet; the velocity is relatively high near the leakage port, and is low in the tunnel. The simulated results were in good agreement with the experimental work by Cigdem Aydin and Hui-min Wang, and the simulated axial velocities of the tunnel were validated with the empirical value.