Experimental study of soil microfabrics induced by anisotropic stresses of confined swelling and shrinking

Abstract

This experimental study examines the micromorphological changes resulting from confined swelling and shrinking of aggregated samples. Two factors, namely bulk density (two levels) and sample composition (five levels) were considered. Thin sections were cut and the microfabrics studied in detail both qualitatively and quantitatively. A broad range of significant and systematic microfabric changes were observed. With an increase in the activity and content of the clay fraction, the void volume (especially those >30 μm) decreased drastically whereas the shape changed from compound packing voids to occluded planar voids and vughs. Aggregates were flattened at contacts, became more angular and showed evidence of fusion into compound units. Related distribution patterns were altered from dominantly matrigranic to matrigranoidic, fragmoidic and porphyric with scattered vughs. There was a gradual closing of voids and a concomitant coalescence of aggregates. Plasmic fabrics showed mainly an increase in long (> 10 μm) and narrow (<5 μm) but sharply defined plasma separations. High bulk density resulted in a more vigorous and conspicuous expression of fabric unit deformation and movement. The pedological implications are discussed in relation to the dynamic properties of clay-water interactions, stress-strain regime of swelling soils, and the concept of plastic deformation of soils according to the Mohr-Coulomb theory of failure. © 1986.