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.
Theoretical Model of Shield Behavior During Excavation. I: Theory
Closed-type shield tunneling methods were developed together with computer-aided automatic control systems. However, automatic control systems are based on empirical relationships and do not have a precise theoretical background. In this paper, a model of the theoretical dynamic load acting on the shield during excavation is developed, taking into account shield tunnel engineering practices; i.e., the excavated area, the tail clearance, the rotation direction of the cutter face, sliding of the shield, ground loosening at the shield crown, and the dynamic equilibrium condition. To evaluate the validity of the model qualitatively, the simulation of shield behavior and the sensitivity analysis of the model parameters on the shield behavior are carried out in both straight and curve alignments for both sandy and clayey ground. The results for the shield behavior are examined, comparing them with the empirical and the theoretical one, and it is confirmed that the proposed model represents the shield behavior reasonably well.
FINITE ELEMENT MODELLING OF EXCAVATION AND ADVANCEMENT PROCESSES OF A SHIELD TUNNELLING MACHINE
During shield tunnelling operation, a shield machine is driven forward by applying mechanical jack forces behind the machine tail and excavating the soil in front of the machine with its cutting face. In this study, the advancement and excavation processes of the shield tunnelling operation are modelled using the finite element method in order to investigate the effect of these construction processes on the ground response. A new excavating finite element, which models the disturbed soil in front of the cutting face, is introduced. The operation of shield advancement and of soil excavation is simulated using the finite element remeshing technique at each time step of the analysis. The accuracy of the finite element remeshing technique is discussed by analysing one-dimensional consolidation of an isotropic elastic medium. The proposed modelling techniques of shield tunnelling construction are applied to simulate a tunnelling project in Tokyo and the numerical results are compared with the field measurements. The soil deformation mechanism associated with the shield tunnelling operation is examined in detail.