Measuring In Situ Unit Weight and Moisture Content Using a Drive Cylinder, a Nuclear Density Gauge, and a Hybrid Nuclear-Electric Density Gauge

ABSTRACT Soil compaction is a critical aspect of the construction process that effectively enhances the strength and compressibility behavior of soils. Within the United States, traditional “spot-testing” quality assurance/quality control (QA/QC) monitoring of soil compaction commonly involves the use of a nuclear density gauge (NDG). However, despite the NDG’s relative ease of operation, the gauge uses two radioactive sources to infer a geomaterial’s unit weight and moisture content in situ, which necessitates that the gauge complies with various storage, transportation, and operation requirements laid out by the United States Nuclear Regulatory Commission (NRC). In response to these requirements, a new hybrid nuclear-electric gauge (termed the “EGauge”) has been developed for in situ “spot-testing” of soils for compaction QA/QC applications. As part of its operation, the EGauge uses a lower strength radioactive source to infer the soil’s moist unit weight, and it incorporates a dielectric moisture probe to infer moisture content in situ. Consequently, the EGauge emits significantly lower levels of radiation that are below the threshold levels requiring compliance with NRC regulations. Currently, few studies have been conducted comparing the NDG and the EGauge side-by-side. To contribute to these efforts, an experimental investigation was undertaken that tested both the NDG and the EGauge under a variety of soil compaction conditions using five soil types native to the state of Delaware. Direct measurements of in situ unit weight and moisture content were also obtained using the drive cylinder, which allowed for a comparison between the relative differences between direct and indirect measurements of field compaction control parameters. The results are presented in a side-by-side fashion between the two density gauges, allowing for direct assessment of the relatively new EGauge as compared with more established in situ compaction control tests, enabling the reader to assess the reliability of this emerging device.