A numerical model for the tunnel boring machine interaction with soil
Mechanized shield tunnelling is a reliable way of constructing tunnels in soft soil, particularly in urban areas. However, a lack of understanding of the physical interaction between the TBM-shield, the soil, and the process fluids contributes to the long learning curves often experienced and hinders improvement of the machine’s driving rationality. A numerical shield-soil interaction model is proposed that bases the extent and spatial distribution of the displacements induced by the advancing shield on TBM monitoring data. The model includes the unloading-reloading condition of the surrounding soil and the possible infiltration of process fluids around the shield periphery. This infiltration influences the equilibrium of the TBM. A set of novel soil reaction curves is also introduced specifically to model a TBM interaction with the surrounding soil. The study offers an innovative outlook on the tunnelling related soil displacements. Results indicate that a more rational approach to mechanized shield tunnelling in soft soil is possible.
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 advance
Shield Tunnel Construction in Centrifuge
A large number of centrifuge model tests for simulating the shield construction process in dry sand was carried out by using a newly developed 100 mm diameter miniature shield tunnel. Different construction processes were modeled by three series of tests. A buried tube test was conducted to measure the lining stress under a centrifugal acceleration, a “tail void test” simulated the process of tail void formation only, and a “shield test” dealt with the complete process of shield construction. Lining stresses, transverse and longitudinal surface settlements, and earth pressures around the tunnel were simultaneously measured during advancement of the shield at a centrifugal acceleration of 25\ig. The lining stress at the crown elevation was well predicted by Terzaghi’s loosening earth pressure. From the comparison with the recent field measurements and the comparative results of three series of tests, it was confirmed that the shield construction process was successfully simulated in a centrifuge. An experimental formula for estimating the surface settlement above the shield was deduced by a function of tail void thickness and cover-to-diameter ratio.