ABSTRACT
To reduce machine loads during Earth Pressure Balance (EPB) shield tunneling, the auxiliary air pressure balance mode is gradually applied. However, the improper control of auxiliary air balance mode may cause inadequate support pressure, leading to higher risk of tunnel face instability. This study employs a two-phase flow model of muck and air using Computational Fluid Dynamics (CFD) method to simulate the pressure distribution inside shield chamber during tunneling with auxiliary air balance mode. The pressure unbalance is observed between the left and right sides of the chamber resulting from the muck rotating flow. Furthermore, the disturbance of moving shield components leads to an obvious pressure fluctuation in the muck zones near components. The growing supporting pressure is accompanied by growing fluctuation and unbalance with increasing auxiliary air pressure. In addition, the supporting pressure has little change but the pressure fluctuation and unbalance decrease with increasing foam injection ratio. The results indicate that face stability and chamber pressure control require a combined adjustment of auxiliary air pressure and foam injection ratio.
