Numerical Investigation of Soil-Tunnel Interaction under Surface Blast Loads with Regression-Based Energy Correlations

The demand for sustainable development in cities has enhanced the utilization of underground urban space (UUS) by constructing underground structures. During war, this UUS may be utilized as protective structures (tunnels, bunkers, and strategic storage). Hence, their behavior in extreme events such as blasts, fires, earthquakes, etc., must be evaluated properly. This paper presents a numerical study on an underground metro tunnel constructed in sandy clay, subjected to a surface blast. The Mohr-Coulomb plasticity model was used to simulate soil behavior, while the concrete damaged plasticity (CDP) model captured the nonlinear response of concrete. Tunnel liner reinforcement was modeled using the Johnson-Cook plasticity model with a hardening law and rate dependence. Surface blast analysis was conducted using the CONWEP (Conventional Weapons Effects) tool, based on the US Department of Army technical manual (TM5-855-1) and Trinitrotoluene (TNT) explosive parameters. The simulations were carried out for 0.1 seconds. The validation of the model and process was performed with peak pressure calculations from the TM5-885-1 manual and empirical relationships established in published literature. However, a reassessment of these formulas has been done by regression analysis of simulation data. Further, relationships were established between energies (kinetic, plastic dissipation, and strain) generated in the soil and different TNT weights by regression analysis. Additionally, the stresses in the soil, deformation, and tensile damage in the tunnel liner due to different TNT weights have been examined for overburden depths of 15m, 12m, and 9m.