Using Electrical Density Gauges for Field Compaction Control

In the United States, the current state of practice for quality control of soil compaction is based upon measurements of soil density and soil moisture content at the time of compaction. The current approach that is used in the State of Delaware compares measurement of in situ soil density and moisture content with measurements of soil density and moisture content obtained from a standard-energy compaction test approach (1-Point Proctor Compaction). Measurement of in situ soil density and moisture content are typically obtained via measurements from Nuclear Density Gauges (NDGs). NDG test equipment uses a nuclear-based approach to obtain radioactive counts that are correlated to soil densities and moistures. The results of NDG test exhibit significant scatter when compared to previous in-situ density test standards (e.g. sand cone tests, "water balloon" tests, etc). Nonetheless this equipment has become the accepted industry standard for quality control of soil compaction, because tests are much faster and easier to perform than other density-based quality control tests. In addition to inherent inaccuracies with NDG test results, there are significant regulatory compliance issues that are present when dealing with NDG test equipment. The NDG itself contains radioactive material, which is heavily regulated by the Nuclear Regulatory Council. This regulation necessitates strict protection standards for employees working with this equipment (mandatory day-long training for all staff using the equipment, mandatory use and monitoring of nuclear dosimeter badges, significant security procedures related to storage of nuclear material/equipment, in-house Nuclear Compliance Regulatory officers, etc). Particularly for large-scale NDG operations, such as those at the DOT, these nuclear regulatory issues can present a significant obstacle to smooth day-to-day operations, and compliance can be difficult. New equipment that uses an electrically-based approach for measuring in situ soil density and moisture content has recently become available. This Electrical Density Gauge (EDG) equipment does not contain any nuclear material, and consequently does not have the same regulatory obstacles that are present with NDG. Additionally, this equipment may allow for more accurate measurements of in situ density and moisture content than those that are currently being made with the NDG (the accuracy of this equipment as compared to NDG is currently unknown). Electrical density gauges have the potential to replace nuclear density gauges for field evaluation of in situ soil density and moisture. Consequently, a study of the accuracy and effectiveness of the Electrical Density Gauge for compaction control of Delaware soils is needed. The program of research proposed will provide the necessary information to assess the benefits of this technology for the DOT.