EFFECT OF AGGREGATE STABILITY ON SOIL COMPACTION

Investigations of three differently textured and structured soils showed that soil compaction is a function of texture, structure, matric water potential and type and intensity of loading. Time-dependent consolidation and shear experiments revealed that fine-textured soil is more compressible than heavier soil. It also appeared, that compaction influences the mobilization of water (measured by micro-transducer tensiometers) and hydraulic conductivity, which together change the neutral stress (u) in the effective-stress equation of Terzaghi. Shear strength was much higher in structured soils than in non-structured soils. The influence of structure, i.e. the degree of aggregation, on the sensitivity to deformation was established by comparing the shear strength of the bulk soil (macroscale) with the shear strength of individual aggregates (microscale). For this purpose a new technique of measuring load-dependent aggregate stability in a shear box was developed, which allows one to compare the results directly with the results of shear box experiments of the bulk soil. It appeared that within small load ranges and below the preconsolidation load the aggregates are not destroyed. Disrupting the soil structure by high loads, especially when applied during adverse soil moisture conditions, makes the soil more susceptible to compaction.