Tunnelling in Soft Soil: Tunnel Boring Machine Operation and Soil Response

Constructing tunnels in soft soil with the use of Tunnel Boring Machines may induce settlements including soil movements ahead of the face, soil relaxation into the tail void, possible heave due to grouting, long lasting consolidation processes, and potentially several other mechanisms. A considerable amount of the total soil displacements seems correlated with the passage of the TBM-shield. Even so, the TBM-induced soil displacements have so far only been coarsely correlated to the total settlements. This paper attempts to relate the shield geometry and its operation through the soil with the observed soil displacements. The snake-like motion of the shield within the excavated soil profile is one of the key aspects as the erratic advance of the shield appears to induce unevenly distributed ground displacements at the interface with the soil. These displacements are expected to spread through the soil with a similar pattern. A numerical investigation on the TBM kinematics and the associated soil response has been performed based on the monitoring data from the construction of a tunnel in The Hague, The Netherlands, in order to quantify these aspects. Results confirmed that the geometry and the operation of the TBM-shield through the ground influence the amount and distribution of the induced soil displacements. The analysis also highlighted the essential role that the tail-void grouting has not only in filling-in the tail-void but also in compensating the kinematical effects of shield advanceGeoscience & EngineeringCivil Engineering and Geoscience