Evaluation of surface settlements in the Istanbul metro in terms of analytical, numerical and direct measurements

In urban areas, the use of pre-support in shallow tunnels is increasing in order to improve the excavation stability and reduce ground settlements induced by the tunneling. This paper describes the effects of pipe roofing on surface settlements and evaluates the settlements associated with the twin tunnels in the Istanbul metro in terms of numerical, semi-empirical and measured values. FLAC3D was used for the numerical modeling and the method suggested by Herzog for the semi-empirical solution. The numerical results indicate that the tunnel roof formed by the pipe roofing provides a restraining effect, reducing deformation and ground surface settlement by up to 65?%. Herzog’s model yields higher maximum surface settlements than those observed. When modified to include the effect of pipe roofing and the distance between the pipes however, there is good agreement between the direct measurements and the values predicted by the numerical and modified Herzog models.