Experimental and Numerical Investigation of Fundamental Mechanism of Tunnelling and Influence on Nearby Flat Foundation

To investigate interaction problems between tunnel and existing shallow foundation, 2D model tests and the corresponding numerical simulations were carried out. For the model tests, a new tunnel apparatus to simulate tunnel excavation was developed, where the vertical and horizontal movement of the tunnel itself is allowed with satisfying the equilibrium between tunnel and the surrounding ground. The corresponding finite element analyses were conducted using FEMtij-2D software where elastoplastic model named the Subloading t(ij) model is used as a constitutive model of soil. It is shown from model tests and numerical simulations that real movement of tunnel during excavation process is in between the conditions of fixed centre and fixed invert, though it is close to the condition of fixed invert in shallow tunnelling. The earth pressure distribution around the tunnel depends on the movement of tunnel itself as well as the inner displacement of the tunnel. The surface settlement trough is also very much influenced by the tunnel movement even if the inner displacement of tunnel is the same. In the influence of tunnelling on existing shallow foundation, the shear band in the ground develops toward the both edges of foundation. It follows that the maximum surface settlement occurs not above the tunnel but at the position of foundation, when the foundation exists near the tunnel. Unsymmetrical earth pressure distribution is seen around the tunnel near the existing foundation.