ABSTRACT
Economical tunnel design and efficient construction strategies are critical to reduce the environmental impact of underground construction works for transportation infrastructure. A clear understanding of the ground response to underground construction is crucial to inform the application of innovative solutions which seek to reduce the carbon footprint of the project. On TBM tunnel projects, the ground response during the tunnel launch process presents is a key project and programme risk, and thereby further inform the viability of innovative solutions.
To better understand the effects of launching a TBM on the surface settlements, this paper focuses on the back-analysis of tunnelling-induced ground deformations at the launch sites through an evaluation of monitoring data from previous tunnelling projects in Copenhagen, Denmark. The monitoring data has been gathered from the construction of the Copenhagen metro extensions into Nordhavn and Sydhavn.
This study considers and compares nine surface monitoring arrays above the twin tunnel alignment within mixed-face ground conditions and limestone conditions at two different locations. This study includes a commentary on the geological features in Copenhagen and a description of the EPB-TBM used.
The analysis of the monitoring results indicates that larger settlements, and therefrom volume losses, are generated in mixed-face tunnelling conditions in comparison to limestone tunnelling conditions, with the ground displacements closest to the TBM breakout observed to be most significant. A gradual decrease of the induced settlements is observed between the TBM launch up to a distance of 40-100m from the launch site. A decreasing trend of ground settlements for an increasing embedment depth of the tunnels in the Copenhagen limestone is shown.
