Impact of Tunnel Excavation Geometry on Surface Subsidence in Cohesionless Soils

Indian cities like Mumbai and Delhi are rapidly developing, and the demand for infrastructure is increasing due to the rising population. The growing population also leads to a higher need for transportation, which requires extensive infrastructure development. Underground projects such as subways, rail, and metro tunnels are necessary to address this demand. However, surface subsidence can occur during the construction of underground projects, potentially affecting existing infrastructure. Therefore, a study should be conducted to address this issue. In this study, an analysis was carried out using the Delhi Metro tunnel project, considering a 42 m x 42 m area of cohesionless soil. The entire analysis was performed using RS 2D. FEM (Finite Element Modelling) software. Different tunnel excavation geometries, such as Circular, Arch, Horseshoe, and Square, were analyzed. The study included three conditions: one where the entire area was unsaturated cohesionless soil, and two others considering the effects of the water table, i.e., saturated and unsaturated soil conditions. The results show that circular tunnel excavation results in the least surface subsidence, while square tunnel excavation causes the maximum surface subsidence. Excavation shapes such as Arch and Horseshoe produce a moderate amount of subsidence. These findings indicate that load distribution is more uniform in circular tunnel excavation compared to square tunnel excavation, where the load distribution is less uniform, for both saturated and unsaturated surrounding soil conditions.