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SUMMARY Soil samples from Germany, Israel and USA were moulded at water contents around the lower plastic limit and compacted with uniaxial pressures c . 20‐200 kPa. The samples were stored at constant water content. At intervals after moulding, the strengths of sub‐samples were measured with a small penetrometer. The soils showed increases in strength with time. Two types of behaviour were observed and explained by a simplified theory for soil strength. With the German and Israel soils, penetrometer strength increased by the same absolute amount irrespective of compaction pressure. This indicates that new particle‐particle bonds were being formed at a rate which was not affected by compaction. With the USA soils, the ratio of penetrometer strength/initial strength increased with time and was independent of compaction pressure. This indicates that existing particle‐particle bonds were being reinforced by a cementation mechanism. Evidence is presented which suggests that age‐hardening by this second mechanism may be inhibited by soil organic matter.
Dexter et al. (Wed,) studied this question.