AASHTO TP 112:19(2020) Standard Method of Test for Determining In-Place Density and Moisture Content of Soil and Soil- – Aggregate Using Complex Impedance Methodology.
This practice describes the procedures for determining the density and moisture content of soil and soil-aggregate using a Complex Impedance Measuring Instrument (dM1). This practice describes three different electrode configurations to determine the density and moisture content. One tool utilizes soil penetrating probes and two additional tools are nonpenetrating surface electrodes. The CIMI measures the electrical properties of the soil being tested and correlates the electrical properties to the physical properties during a soil calibration procedure. The soil electrical properties are typically unique for the soil material. During the soil calibration procedure, a set of algorithms relates the electrical and physical properties of the soil using linear regressions. The subsequent electrical testing of the soil utilizes the established relationship of the electrical and physical characteristics to calculate the soil density and moisture content. The CIMI is solid state electronics that are calibrated at the time of manufacturing and no additional instrument is thereafter required. There is an instrument check box that can be attached to the soil sensor and tested to confirm that the CIMI is working properly.
Density—The total or wet density of soil and soil-aggregate mixtures is determined by applying a known frequency of alternating current and measuring it through the soil. The complex impedance is calculated based on the measurements and relationships previously established with a known soil model.
1.2.1. The density in mass per unit volume is determined by comparison of the readings calculated and the calibration with a representative soil model over a range of known densities.
Moisture—The moisture content of the soil and soil-aggregate mixtures is determined by applying
a known frequency of alternating current and measuring it through the soil. The complex
impedance is calculated based on the measurements and relationships previously established with
a known soil model.
The moisture content in mass per unit volume is determined by comparison of the readings calculated and the calibration with a representative soil model of known moisture content.
The equipment referenced in this method is fully described in ASTM D7698. The equipment uses probes driven to the depth of the soils or aggregates to be tested and measures the electrical properties.AASHTO TP 112 pdf download.