COMPACTION ENERGY RELATIONSHIPS OF COHESIVE SOILS

The energy requirements of laboratory methods of compaction that produce similar results with a sandy silty clay soil of low plasticity were investigated. The purposes were to provide insight into compaction energy relationships, to give a preliminary indication of the possible benefits of improved field compaction equipment design and operation, and to suggest directions for future studies. Three methods of compaction--impact, static, and kneading--were studied. The soil was compacted at three energy levels by the impact method, and for one energy level, nine combinations of rammer mass, number of tamps, and height of drop were used. The mositure versus unit weight relationships for the basic impact method were reproduced by a static compaction method and by a kneading method and the compaction energies determined. The compacted specimens were tested for as-compacted undrained strength. The static method is always the most efficient for the soil tested, but the relative efficiencies of the other methods vary with the mositure content of the soil, the rammer force per unit area, and the rate and duration of loading. In this study, the most efficient method was always at least three times as efficient as the lest efficient method with respect to the energy required to produce the same dry unit weight. A view of the compaction process for cohesive soils that considers energy and distinguishes between penetration due to densification and plastic deformation is presented.