Saturation-Based versus Proctor-Based Field Compaction Quality Control

Field compaction control is arguably the most common yet critical quality control procedure in geotechnical engineering. Since the early 1930s, the Proctor-based process for performing quality control of compacted soils has consisted of comparing the in-place dry unit weight (or density) and in-place moisture content of the soil with a laboratory reference. However, the current practice overlooks several facts that stand out by comparing compacted soil prepared in the laboratory versus compacted soil placed in the field. These issues mainly stem from overlooking the differences in the compaction energy in the lab versus what is applied in the field, and the unsaturated nature of compacted soil in assessing compaction performance. To address some of these issues, a new saturation-based framework for compaction quality control is compared to the traditional Proctor-based with the goal of providing practicing engineers with further insight into the key engineering attributes of compacted soils. The proposed saturation-based system builds upon advances in unsaturated soil mechanics and recent studies that relate normalized dry unit weight of the as-compacted soils that can significantly reduce the variation of laboratory-prepared reference specimens. The presented comparison is developed with the same field and laboratory data collected in most earth fill projects. For illustration purposes, the saturation-based framework is applied to a case history of compaction control data for an earth dam and compared to the conventional method.