1、Standard Method of Test for Determining In-Place Density and Moisture Content of Soil and Soil-Aggregate Using Complex Impedance Methodology AASHTO Designation: TP 112-141American Association of State Highway and Transportation Officials 444 North Capitol Street N.W., Suite 249 Washington, D.C. 2000
2、1 TS-1b TP 112-1 AASHTO Standard Method of Test for Determining In-Place Density and Moisture Content of Soil and Soil-Aggregate Using Complex Impedance Methodology AASHTO Designation: TP 112-1411. SCOPE 1.1. This practice describes the procedures for determining the density and moisture content of
3、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
4、 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 algori
5、thms 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. 1.2. DensityThe total or we
6、t 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 ma
7、ss 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. 1.3. MoistureThe moisture content of the soil and soil-aggregate mixtures is determined by applying a known frequency of alternating current
8、 and measuring it through the soil. The complex impedance is calculated based on the measurements and relationships previously established with a known soil model. 1.3.1. The moisture content in mass per unit volume is determined by comparison of the readings calculated and the calibration with a re
9、presentative soil model of known moisture content. 1.4. 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 prope
10、rties measured and the known values developed in the laboratory soil model are used to determine the in-place density and moisture content. 1.5. SI UnitsThe 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 engin
11、eering 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. 2015 by the American Association of State Highway and Transportation Officials.All rights
12、reserved. Duplication is a violation of applicable law.TS-1b TP 112-2 AASHTO 1.6. 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/ft3may be made. The recording of water content in pound-force per
13、cubic foot should not be regarded as nonconformance with this standard, although the use is scientifically incorrect. 1.7. 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/f
14、t3) should not be regarded as nonconformance with this standard. 1.8. 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 a
15、pplicability of regulatory limitations prior to use. See Section 6 for Hazards. 2. REFERENCED DOCUMENTS 2.1. AASHTO Standards: T 99, Moisture-Density Relations of Soils using a 2.5-kg (5.5-lb) Rammer and a 305-mm (12-in.) Drop T 180, Moisture-Density Relations of Soils Using a 4.54-kg (10-lb) Rammer
16、 and a 457-mm (18-in.) Drop T 191, Density of Soil In-Place by the Sand-Cone Method T 265, Laboratory Determination of Moisture Content of Soils T 310, In-Place Density and Moisture Content of Soil and Soil-Aggregate by Nuclear Methods (Shallow Depth) 2.2. ASTM Standards: D4253, Standard Test Method
17、s for Maximum Index Density and Unit Weight of Soils Using a Vibratory Table D7382, Standard Test Methods for Determination of Maximum Dry Unit Weight and Water Content Range for Effective Compaction of Granular Soils Using a Vibrating Hammer D7698, Standard Test Method for In-Place Estimation of De
18、nsity and Water Content of Soil and Aggregate by Correlation with Complex Impedance Method 3. SIGNIFICANCE AND USE 3.1. The method is useful as a rapid, nondestructive technique for determining the in-place density and moisture content of soil and soil-aggregate based on electrical measurements. 3.2
19、. The test method may be used for quality control and acceptance testing of compacted soil and soil-aggregate mixtures for construction and for research and development. The nondestructive nature of the test method allows repetitive measurements at a single test location and statistical analysis of
20、the results. 3.3. It is difficult to address an infinite variety of soils in this standard. This test method does not address the various types of soils on which the CIMI method may or may not be applicable. 3.4. The procedures used to specify how data are collected, recorded, or calculated in this
21、standard are regarded as the industry standard. In addition they are representative of the significant digits that generally should be retained. 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-1b TP 1
22、12-3 AASHTO 4. INTERFERENCES 4.1. Variations in the test material with electrical impedance properties significantly different from construction soils and aggregate evaluated during soil model development, such as metal objects or organic material, may affect the accuracy of the test method. 4.2. La
23、rge air voids relative to the volume of material being tested, which may be present in the material being tested, may cause incorrect density measurements. 4.3. If the volume of soil material being tested has oversize particles or large voids in the electrical field, these irregularities may cause e
24、rrors in measurements of electrical properties. Where lack of uniformity in the soil due to layering, aggregate, or voids is suspected, the test site should be excavated and visually examined to determine if the test material is representative of the in situ material in general and if an oversize co
25、rrection is required. For the most accurate results, soils must be homogeneous and practically free of rocks that are in excess of 5 cm (2 in.) in diameter and construction debris. 4.4. Statistical variance may increase for soil material that is significantly drier or wetter than optimum moisture co
26、ntent (2.5 percent over optimum or 6.0 percent below optimum) as determined using T 99 or T 180. Based on experience, statistical variance may increase for soil material that is compacted to less than 88 percent of the maximum dry density as determined using T 99 or T 180. The CIMI is generally more
27、 accurate when the soil model range is broader than the range of soil density and moisture content being tested in the field. 4.5. All electrical values are equilibrated to 15.55C (60F). Temperature differences between the in-place soil being measured and the soil model may introduce an error. There
28、fore, the temperature is measured with a soil temperature probe for the soil model calibration and actual soil testing and the electrical soil signals are corrected by a temperature compensation algorithm. The equilibration is necessary because the soil temperature affects the electrical signals tha
29、t are measured. 4.6. The electrical properties of soil change considerably as soil temperature approaches the freezing point of the entrained water, therefore this test method only applies to soil and to soil-aggregate that is not frozen. 4.7. The use of a soil model that was generated from a differ
30、ent soil than that selected for unknown in-place measurements will result in errors in the determination of the density and moisture content of the tested soils. 4.8. Attempts to measure unknown in-place soils with a soil model that was generated from a limited range of wet density and/or moisture c
31、ontent values may introduce errors in density and moisture content determinations. 5. APPARATUS 5.1. Complex Impedance Measuring InstrumentAlthough exact details of construction of the apparatus and the electric circuits therein may vary, the system shall consist of the following: 5.1.1. Soil Sensor
32、 UnitA component of the CIMI that electronically combines the frequency source and the coplanar electrode pairs is shown in Figure 1. 5.1.1.1. Radio Frequency SourceTypically a 3-MHz frequency source is applied to the soil under test through coplanar electrode pairs in the instrument. The radio freq
33、uency current that passes through 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-1b TP 112-4 AASHTO the electrodes into the soil and the voltage that appears across the electrodes are measured. The e
34、lectrical phase relationship between the soil current and the electrode voltage is also determined. 5.1.1.2. AmmetersMeans for measuring the soil current. 5.1.1.3. VoltmeterMeans for measuring the voltage between electrode probes or coplanar electrodes 5.1.1.4. Phase Difference MeterMeans for measur
35、ing the phase difference between the electrode probes or the coplanar electrode voltage and soil current. 5.1.2. Display console unit. Note: The wires crossing in the diagram are not touching each other during use to prevent parasitic capacitance. Figure 1Diagram of a CIMI in Use with Electrode Prob
36、es 5.1.3. Software used to download and process the data for the generation of geotechnical engineering data. 5.1.4. Soil electrical probes (four required, equally dimensioned) of electrical conducting material suitable for driving into compacted material, typically constructed of common or stainles
37、s steel. 5.1.5. The length of soil electrical probes can vary typically having embedment lengths between 101.6 mm (4 in.) and 304.8 mm (12 in.) and diameters between 6.35 mm (1/4in.) and 12.7 mm (1/2in.). Because a portion of the probe must be above the surface to facilitate electrical clip connecto
38、r, the desired embedment depth must be clearly indicated with a scribed mark or change in geometry. 5.1.6. A template should be used to place the electrodes, as they are driven into the soil. The four probes are driven into the soil at 0, 90, 180, and 270 degrees in clockwise positions around the pe
39、riphery of the template. 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-1b TP 112-5 AASHTO 5.1.7. Surface coplanar electrode pair for measuring soil electrical properties beneath the electrode pair.
40、5.1.7.1. Figure 2 shows a pair of rectangular surface electrodes that are used to transmit and receive electromagnetic signals into the soil being tested. Each electrode is connected to a signal source generator and signal source measurement sensor. The depth of soil measurement is determined by wid
41、th w, length , and gap g. The calculated depth of investigation (b) is approximately equal to the electrode spacing gap g, but it is also somewhat dependent on width w and length . Figure 2Diagram of a Coplanar Electrode Pair Where Depth of Investigation Approximately Equals the Gap between the Elec
42、trode Pair 5.1.8. Figure 3 shows a pair of semicircular rod surface electrodes that are used to transmit and receive electromagnetic signals into the soil being tested is shown in Figure 3. Each electrode is connected to a signal source generator and signal source measurement sensor. The depth of so
43、il measurement is determined by the diameter of the rod, length , and electrode separation s. The calculated depth of investigation z, is approximately equal to the electrode separation s, but it is also somewhat dependent on length . 2015 by the American Association of State Highway and Transportat
44、ion Officials.All rights reserved. Duplication is a violation of applicable law.TS-1b TP 112-6 AASHTO Figure 3Diagram of a Semicircular Rod Surface Electrode Pair Where Depth of Investigation Approximately Equals the Gap between the Rods 6. HAZARDS 6.1. The radio frequencies and output power levels
45、of the CIMI are harmless according to the Federal Communications Commission (FCC). 7. CALIBRATION AND STANDARDIZATION 7.1. A soil model must be generated if one does not exist for the soil type being tested. 7.2. Choose the test method, or methods, in Section 2 for the basis of determining the in-pl
46、ace density of the soil model for calibration of the CIMI. Other methods may also be used if deemed appropriate. Assemble the equipment required for each test method. 7.3. Obtain a representative sample of soil from the site where in-place testing is conducted or from the borrow area planned as a so
47、urce of material. The sample should be a sufficient amount of soil for at least five compaction specimens; typically about 20 kg (44 lb) for material with maximum particle size less than 5 cm (2 in.). More material may be required if ancillary testing is planned such as Atterberg limits, particle si
48、ze analysis, etc. 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-1b TP 112-7 AASHTO 7.4. Use T 99 or T 180 for fine grained soils and soil rock mixtures that exhibit a clear maximum dry density, or A
49、STM D4253 or D7382 for predominantly granular material. 7.5. Select areas on the job site where the type of soil is consistent, and where differences in moisture content and compaction exist. Special preparation of spots of different densities or moisture contents should be prepared the day before, so as to allow stabilization of the soil moisture content. 7.6. The soil model must be developed using the same type of electrode pairs as will be used for test locations. 7.7. A matrix of six separate locations, all within the same soil material, shoul
