Guidelines for the Stabilization of Subgrade Soils in California

Subgrade is the soil or rock material underlying the pavement structure, and there is often substantial variability of engineering properties of subgrade soils over the length of a project. Depending on the existing soils and project design, the properties of the subgrade may need to be improved, either mechanically, chemically, or both, to provide a platform for the construction of subsequent layers and to provide adequate support for the pavement over its design life. This guideline, developed for the California Department of Transportation (Caltrans), is structured to lead the practitioner through the design and construction of stabilized subgrade layers. Lime or cement stabilization are the primary methods of subgrade stabilization used by Caltrans. This guideline also includes brief coverage of other cementitious additives (fly ash and kiln dust), as well as mechanical (compaction and material blending, but excluding geogrids and geofabrics) and asphalt stabilization methods.