Field Implications of Current Compaction Specification Design Practices

The engineering properties of compacted soils are of primary importance in fill performance. However, for economic reasons, the achievement of a given relative compaction and compaction water content has become an end in itself for field compaction control. Although the profession has developed an understanding of the relationships between properties and compaction density water content, it has become routine practice to use some combination of precedence and code rather than desired material properties to establish compaction specifications. Because of the heavy emphasis placed on relative compaction, it is extremely important that geotechnical practitioners and earthwork contractors recognize the deviations in field density that can occur as a result of typical differences in the compaction processes and in the methods of compaction control encountered. Variations in both the field density and the laboratory-determined reference maximum dry density arise from numerous sources. A corresponding spatial variability of relative compaction should therefore be anticipated. This paper provides a comprehensive evaluation of potential problems in compaction control, and addresses the sources of field variability in relative compaction.