Deformation and compaction of frozen soils

Compaction of frozen soils are known to give fills with low densities. Therefore, relatively large deformations and/or differential settlements often occur when such a fill thaws. The most important factors influencing the obtained dry density, and consequently the thaw deformations, are compaction effort, temperature, water/ice content and soil type. A laboratory test program was carried out in order to quantify the different factors influencing the obtained degree of compaction, as well as the related thaw deformations. Two different frozen soils were studied, a sand and a fine grained till. Soil cubes with the side length of 50 mm were frozen at the temperature of -10°C. The cubes were compacted in frozen condition into an oedometer cylinder with the diameter of 250 mm. After compaction thaw was induced by placing the oedometer in room temperature (+20°C). After thawing, a step-loading procedure was applied to the sample. Compression during thaw was in the order of 3–4 %, corresponding to 22–27% of the total recorded compression. After one freeze/thaw cycle, followed by the static oedometer testing procedure (to 640 kPa), the soil samples did only reach 37–64% of the compression which could be expected from dry densities obtained through a Proctor compaction procedure of the unfrozen soil. This implies further deformations to be expected, even though the soil was subjected to static load after thaw. The water content of the soil was found to be the most important factor for the obtained dry densities and thus for the thaw compression’s.