Surface settlement caused by twin stacked tunnels excavated beneath buildings

Abstract

Underground construction plays a crucial role in the development of megacities by addressing key urban transportation challenges such as traffic congestion and limited parking. One of the most effective solutions to the growing global demand for efficient transportation systems is the development of underground public transit networks, particularly subways. To support the rapid expansion of such infrastructure, this study investigates the impact of twin stacked tunnel excavation on ground surface settlement through three-dimensional (3D) numerical modeling. The models were developed under various excavation scenarios, considering factors such as groundwater level, soil conditions, face pressure, and grouting pressure applied by the Tunnel Boring Machine (TBM). The Ben Thanh - Suoi Tien metro line in Ho Chi Minh City was used as a reference case study, with settlement data from the tunnel site employed to validate the numerical model. The results show that all investigated parameters significantly influence ground settlement above twin stacked tunnels. In particular, variations in water level, soil conditions, face pressure, and grouting pressure have significantly influenced the surface settlement when the upper tunnel is excavated. This indicates their critical role in ensuring ground stability and must be carefully considered during the construction process