Effective Stress Theory of Soil Compaction

The shape of the moisture-density curve obtained from compaction tests has been explained in terms of capillarity and lubrication, viscous water, and physico-chemical interactions. None of these theories has been substantiated by diagnostic laboratory experiments and none has been extended to explain the effect, on the dry density, of foot pressure or number of stress applications. Probably the most important tool that has been used in the contemporary development of soil mechanics is the principle of effective stress. This principle has been used in analysis of the shearing properties of compacted soils and has been used, to a lesser extent, in analyzing the compaction process itself. However, it was not until recently (1960) that sufficient knowledge became available about the engineering properties of unsaturated soils to permit attempting a more definitive explanation of the shape of the moisture-density curve using the principle of effective stress. The effective stress theory developed herein is qualitative, as it has not been possible to determine the effective stresses and strains in the soil during compaction. Nevertheless, the theory provides an insight into the compaction process that was not available previously.