Anisotropic shrinkage and swelling of some organic and inorganic soils

Abstract

SummaryShrinkage and swelling affect hysteretic changes of soil volume as a function of water content. The processes complicate the precise description of changes to soil structure during cycles of wetting and drying, particularly the interpretation for pore structure from water retention characteristics. We investigated soil shrinkage and swelling curves and the hysteresis of void ratio as a function of moisture ratio of four soils (Eutric Histosol, Histic Gleysol, Calcic Gleysol and Dystric Gleysol), and illustrated the anisotropy of soil shrinkage and swelling in two dimensions. We used a model we had developed previously to fit and to define the endpoints of different shrinkage or swelling ranges. The two organic‐rich soils showed only structural and proportional shrinkages, whereas the two inorganic Gleysols covered all four shrinkage ranges. Of all the shrinkage ranges, proportional shrinkage contributed to 60.2–96.8% of total decrease in volume. A typical soil swelling curve was composed of two distinct parts, which were defined as virgin swelling and residual swelling with separation of the wet‐side maximum curvature. The virgin swelling accounted for 81.2–91.9% of the total increase in soil volume. We found pronounced hysteresis during shrinkage and swelling. A single cycle of wetting and drying lost 10–78% of the soil volume. Shrinkage of the organic‐rich soils was significantly greater than that of inorganic Gleysols. The geometry factor, depicting the relationship between the vertical and horizontal deformation, increased from 1.0 to 3.2–4.0 during drying but decreased from 4.6–21.7 to 3.5–5.6 during wetting. The dependence of water content on the geometry indicates anisotropic shrinkage and swelling of the soils. Our results improve the understanding of the alteration of soil structure during shrinkage and swelling and can be also applied to predict hydraulic properties more accurately.