INTERACTION OF SOIL DEFORMATIONS, STRUCTURE AND PERMEABILITY

Soil deformations, structure and permeability are linked in consistent and qualitatively Predictable ways. The critical state concept of soil mechanics provides a useful framework for the description of deformations and the changes in structure and permeability in agricultural operations. Changes in structure are limited until yield (the onset of permanent deformation) occurs either in uniaxial compression or shear. Following yield, changes are more pronounced and may be expansive or compressive. Expansion during shear is accompanied by localised zones of aligned fabric, while compression during shear results in more general rearrangement of structure. Uniaxial compression and compression during shear both result in decreases to permeability. Expansion during shear leads to increases or decreases in permeability, depending on the initial structure. In all cases, shearing appears to cause a change in permeability towards a unique set of relationships among the stresses, void ratio and permeability. Quantitative predictions of changes in structure and permeability resulting from soil deformation cannot be made using current information. Systematic studies of the interaction between soil deformations and structure are required, together with further systematic studies of the interaction between soil deformations and permeability. The critical state concept suggests useful directions in which to explore these interactions.