Self-healing in fractured fine-grained soils

Fine-grained soils, when exposed to cyclic freezing and thawing, generally, but not always, experience considerable increases in hydraulic conductivities, due to the formation of a system of fissures and cracks. Some soils, such as nonplastic or very low-plastic soils on the one hand, or very highly swelling soils on the other hand, do not experience such changes in permeability, even though after the freezing stages ice-filled separation zones can be commonly observed in the soil matrix. Self-healing of these cracks occurs during subsequent thawing and permeation. To identify possible self-healing mechanisms and to understand when they can be expected, data from freeze&thaw tests on fine-grained soils (as found in the literature and supplemented by a series of additional tests) were analyzed and discussed. Three main causes for closure of fractures in fine-grained soils could be identified: (i) an increase of effective stress above the level of the undrained shear strength of the intact soil; (ii) clogging of fractures by particles eroded from the fracture surfaces during permeation for non- or low-plastic soils; and (iii) swelling of the clay particles near the fracture surfaces in highly swelling clay. The boundaries between soils that were affected and those that were not affected by self-healing are quantified on the basis of standard classification tests, such as plasticity index and activity, for an initial assessment of their suitability as mineral soil liners.