Summary

Solifluction during the spring thaw was observed on a till slope of between 5° and 14° in the Okstindan Mountains, Norway. Stability analysis suggested that on the lower slope angles considerable artesian pore pressures would be necessary for failure by sliding to occur, but that on the 14° slope pore pressures only slightly higher than hydrostatic could generate shearing within the soil. However, excavation of a buried plastic tube in the 14° slope section revealed that over a five-year period no shear planes had developed in the soil, soil displacement decreasing gradually with depth and dying out at a depth of 500 mm below the surface. A total surface movement of 82 mm had occurred over the five year period. It was concluded that movement took place as a result of frost creep enhanced by short-term localized liquefaction at the thaw plane as the water-saturated soil resettled to fill the voids left by melting ice lenses. With the clearance of ground ice from the slope, drainage was no longer impeded, and the soil became freely draining and stable.

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