Responses of a Newly Built Metro Line Connected to Deep Excavations in Soft Clay

Abstract

Excavation-induced ground settlement causes adverse impact or damage on adjacent facilities. If a foundation pit is connected to the facilities, the responses of the facilities can be influenced by soil inside the pit. Through an extensive long-term monitoring program, this study investigates the responses of a newly built metro line to the excavations of foundation pits that shared structures with a metro station. The vertical displacement and the relative deflection of the rail tracks are analyzed in association with the excavation processes. The rotation of the metro station due to asymmetric soil unloading in each pit is studied. Moreover, a comparison of displacement development between the rail tracks and the supporting structures is carried out. Results indicated that (1) the rail tracks inside the metro station moved upward significantly, whereas the rail tracks in the tunnels settled slightly; (2) significant relative deflection of rail tracks was observed in the longitudinal direction and the maximum relative deflection was located at the connections between the metro station and shield tunnels; (3) the asymmetric soil unloading resulted in distortions of the metro station and the displacement of the rail track close to the pit was larger than the track located farther away from the pit; (4) the displacement developments of the rail tracks were concurrent with those of the interior steel columns and the common walls (the walls shared by the metro station and the foundation pits in this study) and the maximum displacements of the metro line were close to the vertical displacement of the common walls throughout each excavation; and (5) the superimposed effect caused by the deep excavations resulted in excessive movements of the rail tracks and noticeable dislocations were observed at the connection between the metro station and shield tunnels.