Orientation of Planar Voids in Vertisols and Soils with Vertic Properties

Abstract

AbstractThe length, orientation, and area percentage of planar voids >75 µm in soil thin sections of several Vertisols from India and Ghana, and clayey soils with vertic properties from Saskatchewan were measured using an image analyzer. Cumulative lengths of planar voids for 10° intervals were expressed as a percentage of total length and plotted in polar coordinates to show the orientation of these voids. The orientation of planar voids was anisotropic in all the soils studied. The percentage of vosepic plasmic fabric (porostriated birefringence fabric) was determined by averaging counts from 40 fields of view under a petrographic microscope. The clay soils from Saskatchewan showed a predominance of vertically oriented planar voids; these probably developed as shrinkage cracks during drying. In the Vertisols from India, in accord with parallelepiped natural structural aggregates described for this soil order, the dominant orientation of planar voids was at an angle of 15° to 60° oblique to the horizontal, in either direction of the first or second quadrant. In those from Ghana, planar voids were oriented at various oblique angles as well as vertically. Together with plasmic fabric analysis, planar void orientation patterns were useful in determining whether soils have been subjected to stress‐strain forces.