In the modern world, the demand for bunkers has grown significantly as a vital means of protection against blast loads. This study investigates the structural response of underground bunkers subjected to surface blast loads using finite element (FE) analysis in ABAQUS/Explicit. The model uses the Mohr-Coulomb model for soil, Concrete Damage Plasticity (CDP) for the bunker liner, and Johnson-Cook for steel and aluminum. Five dome curvatures (flat, D/8, D/4, 3D/8, and D/2) were analyzed under a 1000 kg TNT explosion. Results show higher stress, deformation, and tension damage with increasing curvature, especially for D/2. Organic sandy clay caused maximum stress and deformation. Two mitigation strategies were proposed: upgrading concrete from M40 to M50 and adding an aluminum 2024-T3 liner. M50 concrete reduced stress by 19.23%, deformation by 5.09%, and damage by 2.63%, while the aluminum liner provided greater protection, reducing stress by 83.12%, deformation by 58.03%, and damage by 67.07%.
A non-linear simulation of a shallow buried cut-and-cover tunnel exposed to extreme surface blast conditions was performed utilizing finite element-based dynamic explicit analysis. The Mohr-Coulomb plasticity model was employed to simulate the soil, the concrete damaged plasticity model depicted the behavior of concrete, and the Johnson-Cook model was utilized for the steel reinforcement. The conventional weapons blast function simulated the trinitrotoluene charge weight. The parametric simulations encompassed four vehicular explosions, two soil types, the inclusion of sheet pile walls, and variable depth-to-height ratios (d/h) of the tunnel. The investigation focused on mitigation through the application of an energy-absorbing material, specifically steel-fiber-reinforced concrete. Results showed that the displacement of the upper slab escalates with an increase in charge weight. The existence of a sheet pile wall enhances the structure's stiffness, resulting in increased displacement and tensile damage, but the displacement of the top slab diminishes as the d/h ratio escalates. The extent of damage has been noted to decrease with an increase in the d/h ratio, or cover thickness. These findings underscore the significance of structural configuration and mitigation strategies in reducing the impact of surface blasts on cut-and-cover tunnels.
The present study investigates blast-induced deformations in the ground surface and lining of shallow tunnels. Using a 2D finite element method (FEM), numerical simulation of the interaction effect of factors such as depth, shape (circular and square), tunnel diameter, the modulus of elasticity of the soil, the size of the blast loading, and the distance from the explosion site to the center of the tunnel on maximum ground surface settlement, maximum deformation in tunnel crown, and maximum bending moment in tunnel lining are discussed. The results show that circular tunnels perform better than square tunnels under blast loadings. The tunnel's behavior is more suitable in soils with high elasticity. The improvement in the system's performance would be more significant for tunnels with smaller sections and deeper locations due to a larger distance from the center of the blast.
In order to evaluate the damage characteristics of buried natural gas pipelines with circular dent defects subjected to blast loading, based on pressure -impulse damage theory, explosion experiment and numerical simulations were implemented to evaluate the damage of a natural gas with circular dent defects buried in soil under blast loading in this research. The ALE method was used to develop a coupled pipeline-soil simulation model using LS-DYNA software, and the validity of the established model was verified correctly compared with experimental results and empirical theory equations calculations. Furthermore, according to regulations in the Assessment and Management of Pipeline Dents (American Petroleum Institute Recommended Practice 1183), the effect with different circular dent defect diameter on the mechanical properties of natural gas was also investigated and analysed. The results showed that, under the blast loading, plastic deformation happened on the surfaces of the pipeline facing the explosive, and the high-stress zone appeared in the circumferential direction with 32.27 degrees . The range of the high-stress zone firstly expanded along the axial direction of the pipelines and then along the circumferential direction. The larger diameter of the circular dent defects had, which resulted in a failure at the defects under the condition of the depth of the defects keeping constant. The effect of the size of defect diameter on the amount of pipeline deformation was further investigated, and the mathematical formula described the maximum plastic deformation with different defect diameter was established. Meanwhile, a finite element model of pipeline with a diameter of 457 mm was established for numerical analysis, which implied that the larger diameter of pipeline with the same defect had, the lower risk of pipeline in failure subjected to blast loading had. And through mathematical analysis and considering the feasibility of the actual situation, the curve described the maximum plastic deformation of the natural gas pipeline with three different defects varying in diameter were established respectively. In addition, a formula to express the relationship between pipeline defect diameter and maximum plastic deformation was established, which can effectively predict the critical plastic dent deformation of pipelines with different defect diameter subjected to blast loading. Besides, based on the pressure-pulse damage theory and with the damage assessment criterion of dent depth -dent length ratio of 0.072, the pressure -impulse diagrams of buried natural gas pipelines with defect diameters of 30 mm, 40 mm and 50 mm were defined, which can be used to predict the damage of pipelines with different defect diameters. Moreover, with the pressure -impulse damage evaluation curves, mathematical formula for the buried natural gas pipeline with the circular defects were established. Furthermore, the critical circular defect diameters with 30 mm was confirmed and the unique formula was also established, which could be effectively used to evaluate the safety of buried natural gas pipelines with the critical circular defects.