Shrinkage properties of differently managed clay soils in Finland
Rasa, K. | Horn, R. | Räty, M. | Yli-Halla, M. | Pietola, L.
Soil cracking is a well-known phenomenon, also seen in clay soils in the boreal climatic zone. This study was carried out to quantify soil shrinkage properties in six differently managed clay soils in Finland (Vertic Cambisols, 51% clay). Cylinder samples (100 cm³) were taken in spring from two depths (0-5 and 5-10 cm), then saturated with water and dried as a function of applied suction. The heights of the sample were measured after each drying step and the volume of soil was calculated assuming isotropic shrinkage. The volume loss by shrinkage at a suction of -50 kPa was 1.6-3.8% and the total shrinkage was 5.2-10.5% of the total soil volume, respectively. All shrinkage curves showed structural shrinkage which occurred in the matric potential range from saturation to around -6 kPa. The shrinkage curves were characterized by minor proportional and wide residual shrinkage zones. Eight of twelve sites showed a steeper shrinkage in the proportional shrinkage zone than the theoretical 1:1 line. Large slope values, up to 3.0, reflect the collapse of inter-aggregate pore space due to shrinkage pressure. The results indicate significant particle rearrangement and structural changes, e.g. structural collapse and changes in inter-aggregate pore space due to shrinkage pressure. Continuous water saturation and variable periods of freezing between spring and autumn are mostly responsible for soil weakness against increasing effective stress as soil dries. It is presumed that shrinkage behaviour will change substantially with increases in drying and wetting cycles.
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