Numerical analysis of underground tunnels in various soil types under surface blast loading: a parametric study on damage, settlement, and safe depth

The increasing demand for underground transportation necessitates robust tunnel designs capable of withstanding extreme loading conditions, including surface blast events. This study numerically investigates the blast response of underground tunnels in sandy clay and silty clay soils using the finite element method in Abaqus/Explicit. The Concrete Damage Plasticity (CDP) and Mohr–Coulomb models are employed to simulate tunnel and soil behavior under surface blasts ranging from 100 to 1000 kg TNT. The charge (TNT) has been assumed at the middle of the top surface of the soil model, and the simulation is carried out for 0.35 s. A comprehensive parametric study has been done to determine the effects of TNT weight; the safe tunnel depth in each soil type has been evaluated. Results indicate that silty clay provides better blast resistance due to its higher modulus of elasticity, leading to lower tunnel deformation compared to sandy clay. A minimum burial depth of 15 m is recommended for ensuring tunnel integrity under a 500 kg TNT blast. Beyond this limit, tensile cracking initiates in the liner, progressively leading to structural failure. The study also confirms that damage severity increases nonlinearly with charge weight and is significantly influenced by soil type. These findings provide practical insights for blast-resistant tunnel design, improving safety assessments for underground structures subjected to extreme loads. © The Author(s), under exclusive licence to Springer Nature Switzerland AG 2025.