Surface Settlement Induced by Slurry Shield Tunnelling in Sandy Cobble Strata—A Case Study

The construction of shallow tunnels induces a settlement trough on both the transverse and longitudinal profile, which could cause severe damages to nearby tunnels and buildings. In the design stage, predictions of the resulted soil subsidence are important, especially if the tunnel is located in densely populated zones. Several authors proposed different methods for this task. However, the accuracy of the methods depends on the geotechnical features and the tunnel layout, and the prediction methods vary a lot. This study reports the result of an analysis carried out to predict the surface settlement induced by slurry shield in sandy cobbles through using different predicting methods (analytical, empirical and 3D numerical method). Before the prediction, a series of large-scale triaxial compression tests were performed to carefully calibrate the constitutive parameters of sandy cobbles. Different predictions were then compared with the measured data from Lanzhou Metro line 1, the result of which indicates the validity and the limitation of the applied methods. Conclusions about the applicability of the methods were drawn to provide insight in future projects with similar ground conditions.