عنوان مقاله [English]
In recent decades, due to increased military and terrorist attacks in the world, attention has been paid to the construction of underground security structures. Since most of the vital, sensitive and important structures of the country, like other structures, are based on soil or in soil, the study of the effect of the explosion on the performance of these structures is essential for their safe design. Secure underground structures are structures that are constructed at a certain depth of the ground, generally made by reinforced concrete, then the embankment is applied as overhead cover. Overhead embankment plays an important role in removing the tensions caused by the explosion. Consideration of this aspect of the design of underground structures requires the expertise and knowledge of geotechnical engineering that combines civil engineering with passive defense, a step forward in the design of secure structures underground. In the present study, modeling of the soil mass and the geofoam layer in ABAQUS finite element software examined the efficiency of geofoam as an obstacle to the explosive separator. For modeling soil behavior, modified Dracke-Prager model with a cap and for modeling the behavior of geofoam, stress strain graphs under a high strain rate have been used, also, in order to analyze the effect of using geofoam in reducing the pressure caused by explosive charge, a reduction percentage was used to compare the results. Investigations have shown that the use of geofoam layer in underground structures overhead, the maximum pressure due to explosion significantly reduced (up to 61%). The change in the specific mass of the geofoam layer from 110 to 80 Kg per cubic meter, the reduction percentage has changed +10%. By changing the thickness of the geofoam layer in the range of 0.25 m to 1 m, the percentage of reduction +14.7% has improved and by changing the length of the geofoam layer in the range of 2 to 8 m, the reduction percentage has changed +15.8%. By increasing the thickness of the overhead embankment above the geofoam layer, the reduction percentage has changed +9%. With considering the specific circumstances of each project, including the cost-benefit graph, can be obtained an optimal and appropriate amount for each of the variables declared. At the end of this research, a relationship has been found to calculate the reduction coefficient that will be effective in designing intelligent defense embankments.