Effect of Surfactant on Dry-Side Compaction of Silty Sand

Abstract

The use of surfactants with soil is an evolving practice that lacks a systematic theory to describe the mechanisms of behavior that influence the soil response. A technique has emerged from the theoretical modeling of partially saturated soils that allows near-optimum densities to be achieved with water contents well below optimum. The central theme of the model is a distinction between the intergranular stress caused by externally applied loads and the stress derived from internally distributed capillary stresses due to the presence of water menisci. A practical consequence of the theory is that resistance to compaction can be reduced by adding surfactant (soap) to the mix water to reduce the component of intergranular stress derived from capillary tension. The decrease in capillary tension permits greater dry-side compaction density and an increase in soaked California bearing ratio strength. Well-graded silty-sand data were used to compare the behavior of untreated specimens with that of specimens treated with a 4% by weight of water anionic surfactant. The treated specimens achieved dry densities near optimum with the use of 25% less total mix water. Differences in the California bearing ratio strength for the soaked and unsoaked specimens and comparison of specimens' swell during soaking support the concept that compaction was improved through reduction of capillary tension. This allows specified dry densities to be achieved using considerably less water, which is critical in arid environments, and translates into efficiency in cost and, more important for rapid military operations, in construction time.