Alteration of soil behaviour after cyclic freezing and thawing

The purpose of this research is to determine the effects of cyclic freezethaw on the mechanical properties of a high moisture content, sensitive natural clay soil not previously subjected to freezing. Testing involved two systems of freeze-thaw: closed and open freeze-thaw systems, the former without and the latter with drainage facility provided. Initial properties and composition of an unfrozen sample were established as a reference. Artificial soil samples were prepared to assess the influences of composition on cyclic freezethaw effects. The samples were subjected to 1, 2, 4, 8, 16 and 32 freeze-thaw cycles to examine the extent of changes effected at each stage. Results obtained indicate significant changes in liquid limit and the undrained shear strength of the samples after only one freeze-thaw cycle. Such pronounced changes are not apparent in prolonged freezing and thawing. Decreases in specific surface area, reduced ability for moisture retention and changes in grain size curves after cyclic freeze-thaw provide an idea of the significance of ice-crystals in the alteration of soil structure and the promotion of particle aggregation. The significance of mineralogical factors is demonstrated by using two different ’pure’ soils, kaolinites and Avonlea bentonite. Correlations between changes in surface area and the undrained shear strength indicate the role of aggregation and its effect on soil strength and thixotropy. This study also indicates the enduring effect that desiccation in the open system of freezethaw can have on mechanical properties of the soil.