Assessment of the impact of impulse loading caused by explosion and impact on under-ground protective structures and soil
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Abstract
The calculation of protective structures embedded in soil media under the action of impulse loading caused by an explosion or impact is a complex problem that requires knowledge of modern physical and mathematical tools for describing transient deformation processes in materials with varying strength and stiffness. To solve such problems, numerical modeling is most commonly used today. The accuracy of the results depends on the correctness of the computational model, the choice of mesh generation method and finite element mesh operation, as well as the selection of material behavior models and their parameters for soil, concrete, and steel reinforcement. These models must accurately describe the behavior of the structure and surrounding soil under transient and large deformations and account for the changes in material properties under impulse (short-term) loading compared to static (long-term) loads.
This study presents the results of an assessment of the effects of explosion and impact on a buried protective structure using the Ansys/LS-Dyna software suite. The analyzed structure is a modular construction consisting of two large-sized reinforced concrete elements, embedded in a soil environment modeled as sandy soil.
In the creation of the computational model, the buried structure was modeled using a Lagrangian mesh, while the soil, air, space around the structure, and the explosion zone were modeled using an Eulerian mesh. This hybrid approach allows for the benefits of both methods to be utilized.
The simulations of explosive impact caused by a 50 kg TNT-equivalent charge were conducted for three burial depth scenarios: soil backfill of 0.5 m; burial depths of 1.0 m and 1.5 m. It was found that increasing the burial depth from 0.5 m to 1.0 m reduces the pressure on the structure's surface by a factor of 20, reduces displacements by a factor of 4, decreases reinforcement stress by 68%, and significantly reduces the size of the plastic deformation zone.
In the study of impact effects from a 200 kg projectile traveling at 50 m/s at a 60° angle to the soil surface, the structure was buried at depths of 0.1 m and 0.5 m. It was determined that increasing the burial depth significantly reduces the extent of damage to the buried structure: the number of damaged zones decreased by 80% when the burial depth increased from 0.1 m to 0.5 m. This indicates that a 0.5 m thick soil layer effectively performs a damping function
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