Prediction of air losses in compressed air tunneling using numerical models

A numerical model based on the theory of water-air two-phase flow model is proposed to simulate the process of the transient air flows from the compressed air tunnel into the surrounding ground induced by excess air pressure inside the tunnel.The transition between water phase and gas phase in seepage process is taken into account.In order to allow an accurate prediction of the amount of air losses in the design process and to provide pore pressure distributions,the air loss rates through the tunnel face and shotcrete lining and the distribution of seepage field in different advance rates for subway tunneling are calculated through a numerical example.The analytical results show that for the homogeneous formation the magnitude of air loss rate through the tunnel face is constant along the advance of the tunnel,however,the air loss rate through the shotcrete lining increases linearly with increasing length.Finally,two suggestions for improving the accuracy of numerical simulation of prediction of air losses in compressed air tunneling using water-air two-phase flow model are presented.