The influence of amorphous clay-size materials on geotechnical engineering properties is recognized only for soils developed from volcanic ash under extremely wet, alumina-rich soil environments (called Andisols). The objective of this study was to quantify the amorphous clay-size materials in less weathered volcanic soils that are rich in silica, and to determine the influence of the amorphous materials on plasticity and shrink-swell behavior of these soils. Soil and weathered rock samples were taken from a slow-moving landslide site in Honolulu. Quantification of amorphous and crystalline clay content was performed with x-ray diffraction and the Rietveld method. Atterberg limits and shrink-swell potential of the soil samples were determined. The results showed that clay-size fraction in both soil and weathered rock samples were predominantly amorphous (55–74% in soil and 48–63% in weathered rock). Smectite and halloysite were the primary crystalline clay minerals, constituting about 15–30% of the clay fraction in soils. Atterberg limits of the soil ranged from 65 to 135 for liquid limit, from 30 to 40 for plastic limit, and 9 to 25 for shrinkage limit. Volumetric free swell ranged from 2 to 21%. The plasticity and shrink-swell potential increased with increasing the content of amorphous clay-size materials in the soil. Air drying and oven drying did not significantly change the plasticity. The study concluded that silica-rich amorphous materials dominate the clay mineralogy of the soils studied, resulting in the plasticity and shrink-swell behavior similar to that of smectite-rich soils and distinct from that of Andisols.
A recently developed damping calculation method for undrained load-controlled cyclic tests was implemented on some 70 cyclic triaxial and direct simple shear tests conducted by various researchers on a range of different sands for a correct understanding of the high-strain (0.1%–4%) damping behavior of sands. The effect of various controlling parameters was investigated, including the shear strain, confining stress, number of cycles, void ratio, gradation, nonplastic fines content, and overconsolidation ratio. The data analysis shows that general trends at high strains are in good agreement with the damping behavior of sands at small strains. The results also indicate a direct correlation between the damping behavior of sands and cyclic strength. The recently proposed guideline on load-controlled damping ratio bounds for clean sands at high strains was also in good agreement with the damping behavior of sands with nonplastic fines content up to 25%.
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