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Influence of fines on the monotonic and cyclic shear behaviour of volcanic soil “Shirasu”
Abstract Drained and undrained monotonic and undrained cyclic triaxial tests have been carried out on reconstituted samples of Shirasu originally deposited from pyroclastic flows in the Kagoshima area, Japan. This material contains 20%–30% fines derived from the same minerals as the coarse grains. Well-graded fines can form a weakly interlocked structure in loose Shirasu separating the coarse grains and resulting in a weak liquefiable soil. In order to clarify the mechanical characteristics of Shirasu, a series of triaxial tests were carried out on the original Shirasu and a material whose fines had been washed out. The “fines” Shirasu was weak with its properties highly dependent on the confining stress while the “no-fines” Shirasu had a high strength which decreased with increasing confining stress due to breakage of asperities. The presence of fines between coarse grains altered the location of critical state line of Shirasu. Under undrained cyclic loading and low confining pressures, the weakly interlocked structure of medium-dense “fines” Shirasu collapsed resulting in contractive behaviour and liquefaction. As the confining pressure was increased, this weak fine structure was compressed and the soil structure became stiffer under cyclic loading. In practical terms, this means that Shirasu which is placed as a loose hydraulic fill will be prone to liquefaction. The undrained cyclic response of medium-dense “no-fines” Shirasu was similar to that of dense “fines” Shirasu. Thus, the removal of fines was equivalent to compacting the material to a relatively high density.
Highlights Shirasu with and without fines exhibit different stress-strain response. The presence of fines in Shirasu matrix leads to a downward shift of critical state line. Particle crushing occurs for Shirasu during monotonic and cyclic loadings. The removal of fines from Shirasu produces a much liquefaction resistant material.
Influence of fines on the monotonic and cyclic shear behaviour of volcanic soil “Shirasu”
Abstract Drained and undrained monotonic and undrained cyclic triaxial tests have been carried out on reconstituted samples of Shirasu originally deposited from pyroclastic flows in the Kagoshima area, Japan. This material contains 20%–30% fines derived from the same minerals as the coarse grains. Well-graded fines can form a weakly interlocked structure in loose Shirasu separating the coarse grains and resulting in a weak liquefiable soil. In order to clarify the mechanical characteristics of Shirasu, a series of triaxial tests were carried out on the original Shirasu and a material whose fines had been washed out. The “fines” Shirasu was weak with its properties highly dependent on the confining stress while the “no-fines” Shirasu had a high strength which decreased with increasing confining stress due to breakage of asperities. The presence of fines between coarse grains altered the location of critical state line of Shirasu. Under undrained cyclic loading and low confining pressures, the weakly interlocked structure of medium-dense “fines” Shirasu collapsed resulting in contractive behaviour and liquefaction. As the confining pressure was increased, this weak fine structure was compressed and the soil structure became stiffer under cyclic loading. In practical terms, this means that Shirasu which is placed as a loose hydraulic fill will be prone to liquefaction. The undrained cyclic response of medium-dense “no-fines” Shirasu was similar to that of dense “fines” Shirasu. Thus, the removal of fines was equivalent to compacting the material to a relatively high density.
Highlights Shirasu with and without fines exhibit different stress-strain response. The presence of fines in Shirasu matrix leads to a downward shift of critical state line. Particle crushing occurs for Shirasu during monotonic and cyclic loadings. The removal of fines from Shirasu produces a much liquefaction resistant material.
Influence of fines on the monotonic and cyclic shear behaviour of volcanic soil “Shirasu”
Hyodo, Taichi (author) / Wu, Yang (author) / Hyodo, Masayuki (author)
Engineering Geology ; 301
2022-03-01
Article (Journal)
Electronic Resource
English
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