Centrifugal model tests on characteristics of deep foundation pits in starting well of shield tunneling machine

In order to explore the stress, deformation and soil pressure distribution of the surrounding soils during the excavation process of deep foundation pits in starting well of the shield tunneling machine, two sets of centrifugal model tests are conducted using the simulation method of shutdown excavation support under typical soil conditions, including square foundation pit and circular foundation pit, by generalizing the engineering prototype. The bending moment of the diaphragm wall and the horizontal displacement of the subsequent soil are analyzed A comparative analysis is conducted on the engineering characteristics of two types of shield tunneling machines during the excavation process of the deep foundation pits, including the distribution of soil pressure on the outer side of the foundation pit and surface settlement. The results show that the ground settlement gradually increases with the increase of the excavation depth of the foundation pit, forming a settlement trough shape. The variation of soil pressure on the diaphragm wall is non-linear. As the excavation of the foundation pit deepens, the soil pressure near the surface gradually increases, while the soil pressure at the deeper depth gradually decreases. In the fifth step of excavation, the horizontal displacements of the underground continuous walls in both models reach their maximum values. The circular foundation pit is 1.4 times that of the square foundation pit, and the bending moment of the underground continuous wall also reaches its maximum value. The circular foundation pit is 320 kN·m smaller than the square foundation pit. The research results can provide guidance for the optimization design and excavation of deeply buried tunnels and deep foundation pits.