EFFECTS OF CLAY TYPE AND RATE OF WETTING ON THE MELLOWING OF COMPACTED SOILS

Soil clays differing widely in mineralogy were individually mixed with sand and silt fractions from an Alfisol. The mixtures dominated by Ca 2+ were wet and dried ten times to simulate field conditions and promo te microaggregation of the soils. Compacted cores were prepared at fix ed water contents and tensile strengths of the cores were measured bef ore and after a number of wetting and drying cycles, wet at either fas t or slow rates. Compacted soils which were dominated by randomly inte rstratified minerals (RIM) exhibited higher tensile strengths before w etting and drying cycles. Tensile strengths of the compacted soils dec reased with increasing number of wetting and drying cycles to differen t extents for fast and slow rates of wetting. The results of the equil ibrium tensile strength and the mellowing ratio of the compacted soils in relation to the properties of the clay fractions, e.g. cation exch ange capacity (CEC), surface area and percentage of RIM and shrink-swe ll potential of the soils clearly showed that the higher the shrink-sw ell potential the higher the aggregation and soil softening. The degre e of reversibility of soil compaction by development of microcracks ca used by natural processes, e.g. wetting and drying cycles, increased a s the percentage of shrink-swell potential and rate of wetting increas ed.