A Numerical Parametric Study on the Effects of Surface Structure on Tunneling-Induced Settlements

The need for development of an urban underground transport network is increasing in modern cities. Nowadays, to excavate metro tunnels in urban areas, earth pressure balanced-tunnel boring machine (TBM-EPB) is widely employed. Nevertheless, inevitable ground movements in the surroundings of the tunnel could still be dangerous for surface structures and urban infrastructures. In this study, the effect of surface structure on tunneling-induced surface settlements was investigated. This study consisted of some sections of Madrid metro project and three hypothetical monolayer sections, and the three assumed variables were soil type, number of surface structure stories, and surface loading to tunnel diameter ratio (C/D). Three types of soil (calcareous sand, brown clay and blue plastic clay), three number of stories for surface structure (3, 5 and 10) and three C/D ratios (1, 1.5 and 2) were chosen for the parametric study. The volume loss control method and Mohr-Columb model for soil were used in the two-dimensional modeling of TBM tunneling. Results indicated that the existence of surface structures and their stiffness effect have always decreased tunneling-induced settlements. However, the intensity of this settlement reduction varied with soil type, number of surface structure stories and C/D ratio, and by changing the soil type, the effectiveness of the other two parameters varied sensibly.