Characterization and mineralogical interpretation of shrink-swell behavior of Hawaiian kaolinitic Vertisols
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1990
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Abstract
It is questionable that kaolinite is causing the high shrink-swell of Hawaii kaolinitic Vertisols. In the taxonomic terms, these soils do not meet the requirement to be classified as kaolinitic. As identified by electron microscopy, the dominant phyllosilicate mineral in the Waihuna soils is dehydrated halloysite not kaolinite. The mechanism of shrink-swell in the so-called kaolinitic Vertisols is of interest. The majority of these soils contain zero to trace amounts of X-ray diffraction (XRD) detectable smectite. In this study these kaolinitic vertisols are characterized in terms of their physicochemical and mineralogical properties to gain an understanding of the mechanism that promote their shrink-swell behavior. The cation exchange capacity (CEC) of the Waihuna and Honouliuli soils is 20 to 36 cmol kg^-1 and 30 to 42 cmol kg^-1 , respectively, a difference that was not reflected by XRD. Swelling pressure and percent volume change are both higher for the Waihuna series than for Honouliuli series. Ionic strength and exchangeable sodium percentage (ESP) are not correlated with swelling potential, but specific surface area data indicates the presence of expandable mineral phases in the soils under study. Evidence from electron microscopy, oedometer test, specific surface area data, chemical data and calculated XRD patterns indicate that smectite is present as tactiods with range of order so short that distinct XRD peaks are not produced. Interparticle diffraction, however, can account for many of the XRD observations. Mica, deposited as tropospheric dust, is believed to be unstable and to have transformed to smectite. There is also evidence that the Waihuna series contains a significant amount of randomly interstratified illite/smectite and possibly interstratified kaolinite or halloysite/smectite. Presence of smectite as tactiods, not detected by XRD, and as an interstratified mineral is believed to be responsible for the physico-chemical behavior of the kaolinitic Vertisols of Hawaii. Based on this study, it is recommended that the mineralogy class of these series be changed from kaolinitic to mixed; the rest of the taxonomic name (Soil Taxonomy) stays the same.
Description
Typescript.
Thesis (Ph. D.)--University of Hawaii at Manoa, 1990.
Includes bibliographical references (leaves 137-150)
Microfiche.
xiii, 150 leaves, bound ill. 29 cm
Thesis (Ph. D.)--University of Hawaii at Manoa, 1990.
Includes bibliographical references (leaves 137-150)
Microfiche.
xiii, 150 leaves, bound ill. 29 cm
Keywords
Vertisols -- Hawaii, Soil dynamics -- Hawaii, Kaolinite
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Theses for the degree of Doctor of Philosophy (University of Hawaii at Manoa). Agronomy and Soil Science; no. 2517
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