The Mechanical Response of Wet Volcanic Sand to Impact Loading, Effects of Water Content and Initial Compaction
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RESEARCH PAPER
The Mechanical Response of Wet Volcanic Sand to Impact Loading, Effects of Water Content and Initial Compaction L. Varley1 · M. E. Rutherford1 · L. Zhang1 · A. Pellegrino1 Received: 16 November 2019 / Accepted: 11 July 2020 © The Author(s) 2020
Abstract The effects of water content and initial compaction on the dynamic response of volcanic sand from Mount Etna were investigated by a series of experiments on a long Split Hopkinson Pressure Bar apparatus capable of generating stress pulses of duration exceeding one millisecond. The dynamic stress–strain characteristics were determined until large final compressive strains were achieved. An experimental protocol for the preparation of samples characterised by different initial porosity and moisture content was defined in order to reproduce, in a laboratory environment, granular volcanic aggregates representative of naturally occurring soils in different initial density and water content states. It was found that, for limited amounts of water content, the dynamic response of the investigated volcanic wet sand is more compliant than in dry conditions. Conversely, highly saturated samples exhibit a steep increase in stiffness occurring at strains when the dynamic compressive behaviour becomes dominated by the response of the nearly incompressible water. The presence of water has negligible effect on the mechanical behaviour when the samples are loaded at quasi static strain rates. The grain size distribution and morphology of samples tested in different conditions were evaluated and compared by means of edge detection analysis techniques applied to high contrast images. Keywords Granular materials · Hopkinson bar · Impact · High strain rate · Volcanic · Etna · Sand
Introduction Granular materials like sand and soils are widely used in several engineering applications, ranging from construction techniques such as pile driving to water treatment systems, and are of great interest in civil, geotechnical, petroleum and mechanical engineering. Particulate media exhibit remarkable stress wave attenuation and kinetic energy dissipation properties when subjected to highly dynamic events such as blast loading [1, 2], earthquakes [3] and projectile penetration [4, 5] and are, consequently, of particular relevance also to defense and mining industry. A comprehensive conspectus on the experimental and numerical techniques relevant to the study of rapid projectile penetration into granular media was presented in [6].
* A. Pellegrino [email protected] 1
Department of Engineering Science, University of Oxford, Oxford OX1 3PJ, UK
The extensively increasing adoption of granular materials in impulsive loading applications requires the characterisation of their mechanical response at high strain rate. The dynamic behaviour of granular materials is dependent on their particle morphology, initial density, confinement, water content, and strain rate [7–10] and is commonly measured by means of experiments conducted on the Split Hopkinson Pressure bar app
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