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SOIL PHYSICS

The Reference Shrinkage Curve at Higher than Critical Soil Clay Content

Agricultural Engineering Division, Faculty of Civil and Environmental Engineering, Technion, Haifa 32000, Israel

^* Corresponding author (agvictor{at}tx.technion.ac.il).

The objective of this work was to construct and validate a model that shows how the clay shrinkage curve, under the influence of a silt–sand admixture as well as an inter- and intraaggregate structure, is transformed to the soil shrinkage curve. To meet this objective, we investigated (i) the reference shrinkage curve, that is, one without cracks, because cracks lead to a multivalued shrinkage curve; (ii) the rigid superficial (interface) layer of aggregates, with changed pore-size range and distribution, compared with the intraaggregate matrix; and (iii) soils with sufficiently high clay content when large pores inside the intraaggregate clay (so-called lacunar pores) are nonexistent. The methodology is based on detail accounting for contributions of the interface aggregate layer and intraaggregate matrix to the soil volume and water content during shrinkage. The reference shrinkage curve is determined by six physical soil parameters: oven-dried specific volume; maximum swelling water content; mean solid density; soil clay content; oven-dried structural porosity; and the ratio of aggregate solid mass to solid mass of the intraaggregate matrix. Only the last parameter was fitted for lack of data and compared with an unfitted estimate. The model was validated using data for eight soils. The important new conclusion is that the mere existence of the rigid superficial aggregate layer leads to a soil reference shrinkage curve that is convex upward in the structural shrinkage area, unlike the shrinkage curve of the clay contributing to the soil. The model can have numerous applications.