In this study, the problem of frost penetration in high-clay content soils is examined with the view to assessment of cyclic freeze-thaw effects on initial virgin unfrozen natural clays. The requirements for control of the frost-heave problem in many construction projects in the northern regions of Eastern Canada demand that proper prediction be made for both frost-heave pressures and magnitudes of frost heaving in the high-clay content soils. Laboratory cyclic freeze-thaw and frost-heave tests conducted have shown that the mechanical properties of the clay soils, which are virgin unfrozen natural soil samples obtained from Northern Quebec, are sensitive to cyclic freeze-thaw. In the cyclic freeze-thaw tests conducted, scanning electron micrographs taken from samples after various cycles show that the original soil fabric becomes more disturbed after the first few cycles. Particles are re-arranged, and a regrouping of particles into larger stable (or apparently stable) soil fabric units are formed after a certain number of cycles. In essence, this study provides the experimental information concerning the cyclic freeze-thaw effects on mechanical properties for some high-clay content soils, not initially subject to freezing.