Cement Stabilization of Highly Organic Subgrade Soils to Control Secondary Compression Settlement

Many flexible pavements in western Palm Beach County, Florida, are underlain at shallow depths by thick deposits of organic soils and peats. These soils undergo long-term secondary compression as a result of sustained overburden pressure of the pavement and thereby cause excessive premature structural distress in the form of cracking, rutting, and differential settlement. Although cementitious materials have been successfully used to stabilize soft, expansive, and inorganic soils, research and experience regarding the stabilization of highly organic soils are limited. The authors' main motivation for doing this research was to investigate the effects of cement stabilization on the compressibility of soils consisting of organic content in the range of 67% to 90%. The undisturbed soil samples were collected from the subsurface of the SR-15 (US-98) roadway, which had experienced severe distress attributable to organic layers and had undergone frequent and costly rehabilitation in recent years. It was found that cement stabilization at dosages between 35% and 55% (by dry weight) drastically reduced the ratio of the secondary compression index to the primary compression index of the organic soils to values that resembled a nearly granular soil with desirable compressibility characteristics. This optimized mix design may provide appropriate guidelines for deep mixing methods in subsurface organic layers for the long-term preservation of roadways built over problematic soils.