Influence of lagging distance on ground surface settlement due to mechanized twin tunneling - 3D numerical simulation

Abstract

The predictions of ground surface settlement due to mechanized twin tunneling is necessary for establishing the suitable countermeasure during excavation. The predictions are often done by superposition of settlement curves (commonly in form of Gaussian distribution) from excavation of each individual tunnel. However, only the distance between two tunnels in parallel is considered in the current method. The lagging distance, which has also the effect on ground surface settlement, has not been taken into account. Thus, this research investigates the influence of lagging distance on ground surface behavior to get insight into this behavior and provide a basic understanding for further improvement of prediction. Series of parametric study by 3D Finite Element Method (FEM) on the validated prototype case is conducted. The parameters of the Metropolitan Rapid Transit Chaloem Ratchamongkhon Line (MRT Blue Line) projects, e.g. soil profile, tunnel characteristic, are used to model in this study. In the analyses, the lagging distance (longitudinal direction) and distance between the two tunnels (transverse direction) are varied.