Numerical investigation of tunneling induced surface movement: A case study of MRT line 1, Dhaka

The proposed underground tunnel for Mass Rapid Transit Line 1, Dhaka brings immense attention to the engineers and experts not only because of its construction challenges through a densely-built city, but also for the potential tunneling-induced ground settlements. This very preliminary study investigates the ground surface movement due to the progression of the tunnel boring machine (TBM) using numerical analysis. A series of finite element (FE) models have been developed using PLAXIS 3D, in which Mohr–Coulomb (MC), modified Cam-Clay (MCC), and hardening soil (HS) have been considered. The in-field data of Mashhad Metro Line-2 have been compared to verify PLAXIS 3D's efficacy in tunnel modeling. Subsequently, the outcomes of the FE analyses are compared with the existing empirical formulas. The PLAXIS 3D analysis considering the MCC soil model exhibits strong agreement with the real monitored data, with a variance of only 3.85%. After simulating different stages of the tunnel construction, results are reported in terms of the distance of the inflexion point from the center, the settlement trough pattern, the maximum transverse settlements, and the vertical settlements. They are also compared with the established empirical formula. In order to comprehend the surface settlement with various tunnel depths and diameters, a parameter dependency study has been carried out. The analysis findings showed that increasing the TBM’s depth and radius causes the inflexion point’s distance from the center of the tunnel to increase by 4% and decrease by 5%, respectively. It is also observed that as tunnel depth increases, the overall settlement of the tunnel lowers by 11% for every additional 5 meters of depth. The MCC model, out of the three, exhibits the most accurate value of the settlement compared to that obtained from the empirical solutions, and also the best-fit form to the Gaussian curve.