Ground settlement induced by NATM tunneling and surface loads in Shiraz metro station

Abstract

Urban tunneling, especially in the construction of shallow metro stations, can lead to significant ground movements that may affect the safety and integrity of nearby surface structures. This research explores how surface settlements develop during NATM-based tunnel excavation, focusing particularly on the role of ground surface loads from traffic and buildings. The study centers on a real-world subway station in Shiraz, Iran, and employs the FLAC3D v9 software to simulate ground responses during excavation using the finite volume method. Initial modeling, carried out in the absence of surface loading, showed a maximum ground settlement of 62.3 mm. Subsequently, variable surface loads, including traffic and building weights, were applied to the ground surface above the metro station. The results demonstrated a linear increase in surface settlement with increasing surface loads. For instance, the load of a 3-storey building elevated the settlement to 73.3 mm, while that of a 9-storey building further increased it to 93.4 mm (21.5% increase). Similarly, traffic loads exhibited proportional effects on settlement. In a final analysis mimicking the conditions at Esteghlal Station, a combined surface load consisting of 20 kPa traffic load and a 3-storey building load was applied. The findings revealed that the lateral stress imposed by side buildings mitigated vertical stresses on the station, thereby reducing surface settlement. The lateral load from buildings above the metro station decreased maximum surface settlement by approximately 5 to 10 mm (6.5–14.8% reduction). These results suggest that moderate lateral loads from side surface structures can positively influence settlement behavior during urban tunneling projects.