An anti-rotation shelf to mitigate the rotation of shield tunnels subjected to normal faulting

Normal fault deformation can cause large movement and severe damage to shield tunnels. However, there is a lack of effective measures for protecting shield tunnels from rotating when they parallel a normal fault rupture. In this study, an anti-rotation shelf is proposed to mitigate the rotation of shield tunnels subjected to normal faulting. Validated numerical modelling is performed to investigate the interaction mechanisms of soil and shield tunnels with and without a shelf during normal faulting. In addition, the function of the shelf and influencing factors are discussed. The results show that the responses of the shield tunnel depend on the tunnel location, burial depth, dip angle, etc. There are three possible interaction mechanisms between the soil and the tunnel during normal faulting: the hanging wall mechanism, shear mechanism, and footwall mechanism. The shelf is effective in protecting the shield tunnel from normal faulting. Its function is to induce an additional anti-rotation moment to conquer that caused by normal faulting. The protective effects of the shelf are related to shelf position, shelf length, tunnel location, and fault magnitude.