ALTERATIONS OF SOIL STRUCTURE UPON FREEZING AND THAWING AND SUBSEQUENT DRYING

Abstract

A laboratory investigation of a clay soil indicated that the percentage of aggregates < 1 mm in diameter might be increased, decreased or unaffected by freezing and thawing depending on the initial moisture content, the initial size of soil aggregates and the method of drying the sample. Little or no changes in aggregate size occurred if the initial moisture content was at 15 atmospheres. At 0.1 atm, aggregates which were initially coarse (> 4 mm) tended to break down slightly when exposed to alternate freezing and thawing followed by air-drying at room temperature. On the other hand, a substantial decrease in aggregates < 1 mm in diameter occurred when aggregates which were originally fine received the same sequence of treatments. However, if the samples were freeze-dried following the same treatments, all aggregates were reduced to < 1 mm in diameter. Similar trends were established with samples which were continuously frozen and when the initial moisture content was at 0.33 atm, although the magnitude of the change was much smaller. It is proposed that forces engendered during freezing disrupt aggregates, but this process is reversed during thawing and drying at room temperatures.