Tunneling posture of passive articulated EPB shield in soft soil: A multibody mechanical model-based investigation

Shield tunneling in soft soil is prone to lose control of attitude and seriously deviate from the designed tunnel axis, which causes large tunnel deviation and ground settlement. This paper presents an analytical model that describes the behavior and mechanical mechanism of a passive articulated shield tunneling in soft soil. The model formulates multibody mechanics equation that relate the shield movement to its body characteristics, loads acting on the shield, and shield-soil interaction. By using the proposed equation, the pose states of the front and rear parts of the articulated shield can be described. Then, based on the Suzhou Metro Tunnel-Line S1 project, the posture mode and mechanical mechanism of the passive articulated shield under different unit loads and load combinations is revealed by utilizing the proposed model. Furthermore, the validity of the model is confirmed by comparing the calculated results with the field observations. Finally, the sensitivity analysis of the parameters related to the soil, shield and the load acting on the shield has been conducted. The results show that the presence of articulation significantly affects the posture patterns of the front and rear parts of the shield. At the same time, soil characteristics, cutter head weight, segment force, and jack thrust intricately influence the shield posture and create challenges for attitude control in soft soil conditions. This model contributes to a better understanding of the shield behavior and the associated challenges in controlling its posture under such conditions.