Numerical Back Analyses of Time-Dependent Deformations of Tunnels in the Himalayas

Excavation of tunnels in squeezing ground conditions results in large deformation. Total deformation is a combination of instantaneous and time-dependent phenomena. To ensure the stability of the tunnel excavation, it is imperative to consider the deformation which manifests over time and design an adequate support system. In this study, finite element simulations are conducted to examine the time-dependent deformations around the tunnel across various geological settings. Specifically, three tunnel sections in the Himalayan region with overburden depths between 284 and 426 m are considered. The selected sections pass through Quartzitic Phyllite, Phyllitic Quartzite, and Biotite Mica Schist. The time-dependent phenomena is modelled using the Visco-Elastic Perfectly Plastic constitutive model. Moreover, the rheological parameters of the model are calibrated through back-analysis and the efficiency of the VEPP to simulate the time-dependent deformation is established.