Stability of the excavation face on a shield tunnel crossing beneath an existing tunnel

When a shield tunnel crosses the route of an existing tunnel, the new tunnel will have great influence on the inner structure and the upper surface of the existing tunnel. The support force of the excavation face is an important factor in controlling the ground surface deformation. In the construction of shield tunnelling, the damage caused by insufficient supporting force at the excavation face is much greater than the damage caused by excessive supporting force. In this paper, Abaqus software is used to simulate the instability of the excavation face caused by the small support pressure of the excavation face when the tunnelling machine crosses the route of the existing tunnel at close range. The variation of the ultimate supporting force of the excavation face and the influence of the support force of the excavation face on the existing tunnel and the ground surface settlement are analysed for different horizontal distances between the excavation face and the existing tunnel. The results show that the existence of the existing tunnel has a significant impact on the ground settlement caused by the excavation of the new tunnel. Moreover, when the shield is pushed to the same position, different supporting pressures will produce different vertical deformation increments for the new tunnel segments.