Prediction of Single and Twin-Tunneling-Induced Ground Settlements: A Comprehensive Review of Methodologies

Estimation of tunneling-induced ground settlements is vital for the stakeholders of the underground projects to take necessary precautions for the safety of surface structures. The estimation of these settlements become more important in case of shallow tunneling in urban areas. However, complex geological conditions, construction sequence, tunneling methods, and twin tunnel arrangements lend complexity to the estimation process. Therefore, it is important to understand the influence of these factors on the ground response during the tunneling excavation, and correspondingly assess their effect on the settlement estimation methodologies. The present study comprehensively reviews the reported studies on estimation of ground settlements due to underground tunneling excavations. The paper first addresses the reported prediction methodologies for single tunnel excavations. It discusses the effect of tunneling methodology, ground conditions, and behavior of soil around the excavated section on the ground response parameters, namely, greenfield settlement and heave. The paper then discusses the change in these ground response parameters when another tunnel is constructed next to an already existing tunnel. Summarily, the paper condenses the available knowledge on estimating the values of maximum surface settlement, ground loss, and width of settlement trough for different cases of single and twin tunneling arrangements.