Shrinkage (ground)
During the drainage of a soil that was created by sedimentation in the water, a change in volume occurs, which is known as shrinkage . The shrinkage is particularly noticeable in clay soils , muddy soils and occasionally in silt soils through the formation of dry or shrinkage cracks.
The shrinkage of a soil particle , regardless of its material properties, is caused by the force of the surface tension of the water. At room temperature (20 ° C) this force is 72.75 mN / m and is therefore relatively high. When a soil dries out, there is a strong tendency to reduce the size of the interface between water and air, which leads to a pressure difference at the interface and thus to a capillary rise of water. There form menisci , the deflection is proportional to the pressure difference; the soil particles are pulled together.
The pressure difference at the meniscus, and thus the force to shrink, is greater the smaller the capillary diameter (→ soil water tension ). This is why the shrinkage processes are particularly pronounced in fine-grained soils, especially those with fine pores, and dry cracks occur.
literature
- Karl Heinrich Hartge: Introduction to Soil Physics, pp. 108–115, Stuttgart 1978, ISBN 3-432-89681-6
