No description available.

No description available.

Clay coatings from a variety of soils were studied using the petrological microscope, the scanning electron microscope, the transmission electron microscope and various X-ray techniques in order to ascertain their morphology and composition. It was hoped that their mode of formation could also be determined.Thin section results showed that the morphology of the clay can be divided into seven types, according to the extinction patterns seen in crossed polarized light. These patterns indicate that the clay does not usually lie in flat parallel sheets, but that the sheets have a wavy form, with variations in wavelength and amplitude. Within the coatings there are frequently areas of clay which have no obvious orientation relationship to the main clay particle orientation.The scanning electron microscope work confirmed the optical results and also showed that in several cases, at low magnification, the surface of coatings have pseudohexagonal ridges and high magnification sharp ridges and overfolds are present i.e., the surfaces are not smooth. The most significant result from this part of the study was that clay coatings are not composed of tightly packed sheets of clay, but that these features have a very open packing. arrangement, with eliptical pores seen in cross-section.Elemental and mineralogical analysis indicated that the type of clay in the coatings is very dependant on the intensity of the weathering environment and that it is similar to the clay in the matrix.The results imply that clay illuviation is the dominant process responsible for clay coating formation.

This study aimed to investigate soil structural changes in two clay soils under different forms of cultivation and different crops, and to identify the main processes responsible. The range of definitions, classifications, methods of determination of structure and the factors and processes which affect soil structure are reviewed. At Cruden Bay, Aberdeenshire, three sites were chosen at different stages in a seven year rotation and sampled throughout two growing seasons. At Compton Beauchamp, Oxfordshire, the effects of direct drilling, ploughing and permanent grazing on the soil structure were compared over one growing season.Rainfall and soil water content were recorded at both locations. Infiltration rates were recorded at Cruden Bay but variability in soil properties (texture, horizon thickness, structure) and climatic conditions at the three sites affected infiltration results so that its true value was difficult to assess. Plaster of Paris was used to preserve the seedbed for sampling, and to help identify field cracking and earthworm channels. Impregnated blocks were used to study structure. Macroporosity (pores >350 Jim) was measured by image analysis. Thin sections were prepared where necessary.At both locations differences in cropping and water extraction led to different field cracking patterns. At Compton Beauchamp pore continuity and earthworm activity were greater in the direct drilled and grass sites than in the ploughed site.The surface structure formed after seedbed preparation was composite subangular blocky/granular. The effects of shrinking was to create macropores, and the effects of swelling was to close macropores. Earthworm activity led to the development of channels, crescentic pores and vermicular structure. Since many of these processes are cyclic, the resulting structural states showed a cyclic recurrence.The results indicate the need for the concepts of incomplete and complete structure, composite structure and cyclical structural change.

The erosion behaviour of clay soils has been investigated through a comprehensive program of laboratory testing. Three different erosion test methods have been employed including the rotating cylinder test (RCT), the hole erosion test (HET), and the slaking test (SLT). A new rotating cylinder test device is designed and manufactured capable of testing disturbed and undisturbed soil samples in saturated and unsaturated states. Details of the equipment along with its calibration, testing and sampling procedures are provided. The HET has been reviewed and modified to provide consistent test results. In addition, the slaking test has been customised to accept samples identical to those used in the RCT. A total 111 RCT, 139 HET, and 108 slaking tests have been conducted and analysed. Typical shapes of the erosion curves are identified, based on a wide range of shear stresses and erosion rates analysed. Correlations are presented between the RCT and HET, and between the RCT and SLT to allow characterisation of clay soil erosion in a consistent and unified manner. The erosion modes of clay soils are investigated and categorised into three main groups: ???dispersive erosion???, ???saturated non-dispersive erosion???, and ???unsaturated non-dispersive erosion???. It is shown that soils falling in the same category exhibit near identical erosion characteristics. Factors affecting clay soil erodibility are investigated and displayed for each erosion mode. All findings are presented in a unified framework. A suggested procedure is provided for the evaluation erosion potential in clay soils for practical applications.

Thesis (Ph. D.)--University of Hong Kong, 2009. / Includes bibliographical references (p. 240-254) Also available in print.

Thesis (M.S.)--West Virginia University, 2009. / Title from document title page. Document formatted into pages; contains viii, 114 p. : ill. (some col.), col. map. Includes abstract. Includes bibliographical references (p. 55-61).

Thesis (Ph. D.)--University of Wisconsin--Madison, 1938. / Typescript. Includes abstract and vita. eContent provider-neutral record in process. Description based on print version record. Bibliography: leaves 47-49.

Thesis (M. Phil.)--University of Hong Kong, 1996. / Includes bibliographical references (leaf 84-88).

Thesis (M.S.)--University of Wisconsin--Madison, 1982. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 98-100).