Standard Method of Test for Determining In-Place Density and Moisture Content of Soil and Soil– Aggregate Using Complex Impedance Methodology

Abstract

This practice describes the procedures for determining the density and moisture content of soil and soil-aggregate using a Complex Impedance Measuring Instrument (CIMI).

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.

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.

The correlation between the electrical properties measured and the known values developed in the laboratory soil model are used to determine the in-place density and moisture content.

SI Units—The values stated in SI units are to be regarded as the standard.

The inch-pound equivalents may be approximate.

It is common practice in the engineering profession to concurrently use pounds to represent both a unit of mass (lbm) and of force (lbf).

This implicitly combines two systems of units, that is, the absolute system and the gravitational system.

This standard has been written using the absolute system for water content (kg/m3) in SI units.

Conversion to the gravitational system of weight in lbf/ft3 may be made.

The recording of water content in pound-force per cubic foot should not be regarded as nonconformance with this standard, although the use is scientifically incorrect.

In the English system, the pound (lbf) represents a unit of force (weight).

However, the use of balances or scales recording pounds of mass (lbm), or recording of density (lbm/ft3) should not be regarded as nonconformance with this standard.

This procedure does not purport to address all of the safety concerns, if any, associated with its use.

It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.

See Section 6 for Hazards.