Chamber Pressure Optimization for Shield Tunneling

Stability of soil in front of tunnel excavation face should be guaranteed during shield excavation. Therefore, the corresponding equilibrium principle and appropriate pressure of shield chamber are important for practical purpose. In conventional methods, soil water pressure at the central axis of tunnel cross-section is used as standard value. However, according to investigation in this paper, it can only maintain the resultant force in an equilibrium state while making resultant moment non-zero due to the fact that unit weight of residual soil in shield chamber differs from that of in-situ soil. A new method using earth pressure at rest at the position of 2/3 times the tunnel’s diameter to the vault as reference value is formulated in this paper, in which resultant moment is ideally zero; meanwhile, the related resultant force occurs with a small value which is beneficial to control ground settlement deformation.