Abstract: Geotechnical soil parameters, and soil moisture content in particular, were found to have a significant effect on the total impulse inflicted on a structure by a buried explosive charge [1, 2, 3, 4]. Previous research conducted by Plasan [5] quantified the blast intensity of a buried explosive charge in graded gravel by two measuring routines: steel plate deformation and flying plate. The current study, which is an elaboration of the previous research, introduces additional soil types and soil parameters while utilizing improved measuring apparatus.
An experimental study was conducted on three different soils: sand, clayey sand and graded gravel with silt. Each of the experimental soils was mixed with water and compacted by layers in a steel- plate confined pit. A 2 kg TNT charge was buried below the soil surface and a mine impulse pendulum (MIP) was situated above the pit. Additional tests were conducted: (1) by setting the charge in a steel pot [6] and (2) by substituting the soil with water.
Soil types chosen for the research vary in their properties. Both standard laboratory tests and in situ measurements were performed in order to classify the soils and to determine their properties. Emphasis was given to the conducting of experiments with a diversity of soil moisture content levels. A complete covering of the soil moisture content spectrum was not achieved, however, sufficient data allow the outlining of the tendency of each soil, creating an overlay of total impulse with respect to geotechnical properties. Outlining results with respect to saturation ratio allows comparison of the different soil types on the same scale. Results obtained indicate that saturation ratio is the most dominant factor influencing buried- charge blast impulse magnitude. An explosive charge located in graded gravel may result in smaller impulse loading in comparison to sand or clayey sand when the two last have a sufficiently high degree of saturation.
Sequential to experiments, a numerical investigation was performed in order to characterize the blast and to relate its characteristics to soil type and properties. Finite element (FE) explicit simulation was conducted in Ls-Dyna. In the numeric model, impulse load was inflicted to the MIP by implementing both software embedded blast subroutines, i.e. *LOAD_BLAST_ENHANCED and *INITIAL_IMPULSE_MINE, and by Arbitrary Lagrangian Eulerian (ALE) formulation, modeling the soil test bed, air and TNT [7]. Results indicate that scaling explosive charge mass alone might be erroneous. In order to accurately simulate buried charge impulse load, it is required to use either ALE formulation or to scale reflected pressure pulse duration.
References
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[1]
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- Fiserova, "Numerical analyses of buried mine explosions with emphasis on effect of soil properties on loading," Cranfield university, 2006.
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[2]
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- L. Hlady, "Effect of soil parameters on land mine blast," MABS, 2004.
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[3]
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RTO-TR-HFM-089, "Annex C: Physics of mine explosions," NATO, 2004.
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[4]
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- D. e. a. Clarke, "The role of geotechnical parameters on the impulse generated by buried charges," MABS 22, 2012.
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[5]
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Katalan IK, Asaf Z, Ran E, Naroditsky D, Aizik F, "The Influence of Water Saturation in Soil," in International Symposium on Shock Waves, Manchester, UK, 2011.
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[6]
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AEP-55, Vol 2, " Procedures for evaluating the protection level of logistic and light armored vehicles," NATO, Allied engineering publication, 2006.
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[7]
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- Wang, "Simulation of landmine explosion using LS-DYNA3D software: benchmark work of simulation of explosion in soil and air. No. DSTO-TR-116," DEFENCE SCIENCE AND TECHNOLOGY ORGANISATION, CANBERRA (AUSTRALIA), 2001.
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