Centrifuge modeling of tunneling-induced ground surface settlement in sand

Stress changes in the soil induced by tunnel excavation may cause excessive ground settlement. However, high-quality experimental data on ground settlement due to tunnel excavation are limited. In this study, centrifuge tests are conducted to investigate the three-dimensional ground surface settlement, considering different intersection angles and cover-to-tunnel diameter ratios. The results indicate that the major influence zone along the longitudinal direction on the ground surface settlement is ± 1.25D, where D is the tunnel diameter. When the monitoring section is perpendicular to the tunneling direction, the transverse ground settlement due to the tunnel excavation is symmetrical with respect to the tunnel centerline. In contrast, an asymmetric ground settlement profile is observed when the monitoring section intersects the tunneling direction at an angle of 60 degrees. Applying a Gaussian curve to fit the ground surface settlement curve, the width parameter, K (i.e., the distance between the tunnel centerline and the inflection point of the settlement trough to the tunnel burial depth), varies from 0.33 to 0.39. The ground surface settlement induced by twin tunnel excavation can be captured reasonably by superimposing two identical Gaussian curves. When the cover to tunnel diameter ratios (C/D) are 1.5 and 2.7, the maximum ground surface settlements are 0.67% of D and 0.35% of D, respectively. It is clear that the maximum ground surface settlement decreases with an increase in the C/D ratio.