Significance and Use
5.1 Impact Value, as determined using the standard 4.5 kg (10 lbm) hammer, has direct application to design and construction of pavements and a general application to earthworks compaction control and evaluation of strength characteristics of a wide range of materials, such as soils, soil aggregates, stabilized soil and recreational turf. Impact Value is one of the properties used to evaluate the strength of a layer of soil up to about 150 mm (6 in.) in thickness and by inference to indicate the compaction condition of this layer. Impact Value reflects and responds to changes in physical characteristics that influence strength. It is a dynamic force penetration property and may be used to set a strength parameter.
5.2 This test method provides immediate results in terms of IV and may be used for the process control of pavement or earthfill activities where the avoidance of delays is important and where there is a need to determine variability when statistically based quality assurance procedures are being used.
5.3 This test method does not provide results directly as a percentage of compaction but rather as a strength index value from which compaction may be inferred for the particular moisture conditions. From observations, strength either remains constant along the dry side of the compaction curve or else reaches a peak and declines rapidly with increase in water content slightly dry of optimum water content. This is generally between 95 and 98 % maximum dry density (see Fig. 1 and Fig. 2). An as-compacted target strength in terms of IV may be designated from laboratory testing or field trials as a strength to achieve in the field as the result of a compaction process for a desired density and water content. If testing is performed after compaction when conditions are such that the water content has changed from the critical value, determination of the actual water content by laboratory testing enables the field density to be inferred from regression equations using IV, density and water content.
5.7 Impact Value may be correlated with an unsoaked CBR.
5.8 Impact Value may be expressed as a hammer modulus, analogous with elastic modulus or deformation modulus.
5.9 The light hammer uses the same accelerometer and instrumentation as the standard hammer. The smaller mass of 0.5 kg (1.1 lbm) results in more sensitivity for lower strength materials compared to the standard mass; that is, the zero to 100 IV scale is expanded with this lighter hammer mass and provides more definition on softer materials. To avoid confusion, the IV of the light hammer is notated as IV/L.
5.10 Light Impact Value has applications for recreation turf hardness evaluation, where the condition of the surface affects ball bounce characteristics, the performance or injury potential to participants, and where more sensitivity compared to the standard hammer is required or an imprint left by the 4.5 kg (10 lbm) hammer or other test methods is undesirable, such as on a golf putting green.
5.11 The medium hammer uses the same accelerometer and instrumentation as the standard hammer and provides a sensitivity between that of the standard hammer and light hammer. The IV of the medium hammer is notated as IV/M.
5.12 The Medium Impact Value has application to sand and earthworks, and natural turfgrass and artificial turf hardness evaluation, the last primarily in relation to performance or injury potential to the participants, and is preferable over the Light Impact Value in relation to thicker thatch and longer grass for such application.
5.13 The heavy medium heavy hammer uses the same accelerometer and instrumentation as the standard hammer, and tests through a larger zone both horizontally and vertically because of its larger diameter mass. The IV of the heavy medium hammer is notated as IV/HMH.
5.14 The Heavy Medium Heavy Impact Value has application to testing the same materials as those tested by the standard, light and medium impact soil testers, for evaluation of a layer of soil up to about 380 mm.
5.15 The heavy hammer uses the same accelerometer and instrumentation as the standard hammer, and tests through a larger zone both horizontally and vertically. The IV of the heavy hammer is notated as IV/H.
5.16 The Heavy Impact Value has application to testing the same materials as those tested by the standard, light, medium, and heavy medium heavy impact soil testers, but the greater mass of this impact soil tester provides less sensitivity of the output so is applicable for harder materials at the top end the scales or beyond the ranges of the lighter impact soil testers. The larger diameter mass of the heavy impact soil tester tests through a larger zone both horizontally and vertically than the smaller diameter impact soil testers.
Note 4: The quality of the results produced by this test method is dependent on the competence of the personnel performing it and the suitability of the equipment and facilities used. Agencies that meet the criteria of Practice D3740 are generally considered capable of competent and objective testing. Users of this test method are cautioned that compliance with Practice D3740 does not in itself ensure reliable results. Reliable results depend on many factors; Practice D3740 provides a means of evaluating some of those factors.
Scope
1.1 These test methods cover the determination of the Impact Value (IV) of a soil either in the field or a test mold, as follows:
1.1.1 Field Procedure A—Determination of IV alone, in the field.
1.1.2 Field Procedure B—Determination of IV and water content, in the field.
1.1.3 Field Procedure C—Determination of IV, water content, and dry density, in the field.
1.1.4 Mold Procedure—Determination of IV of soil compacted in a mold, in the lab.
1.2 The standard test method, using a 4.5 kg (10 lbm) hammer, is suitable for, but not limited to, evaluating the strength of an unsaturated compacted fill, in particular pavement materials, soils, and soil-aggregates having maximum particle sizes less than 37.5 mm (1.5 in.).
1.3 By using a lighter 0.5 kg (1.1 lbm) or 2.25 kg (5 lbm) hammer, this test method is applicable for evaluating lower strength soils such as fine grained cohesionless, highly organic, saturated, or highly plastic soils having a maximum particle size less than 9.5 mm (0.375 in.), or natural turfgrass.
1.4 By using a heavier 10 kg (22 lbm) or 20 kg (44 lbm) hammer, this test method is applicable for evaluating for harder materials at the top end the scales or beyond the ranges of the standard and lighter impact soil testers.
1.5 By performing laboratory test correlations for a particular soil using the 4.5 kg (10 lbm) hammer, IV may be correlated with an unsoaked California Bearing Ratio (CBR) or may be used to infer percentage compaction.
1.6 The values stated SI are to be regarded as the standard. The values stated in parentheses are given for information only.
1.7 All observed and calculated values shall conform to the guidelines for significant digits and rounding established in Practice D6026.
1.8 For purposes of comparing, a measured or calculated value(s) with specified limits, the measured or calculated value(s) shall be rounded to the nearest decimal or significant digits in the specified limits.
1.8.1 The procedures used to specify how data are collected/recorded or calculated, in this standard are regarded as the industry standard. In addition, they are representative of the significant digits that generally should be retained. The procedures used do not consider material variation, purpose for obtaining the data, special purpose studies, or any considerations for the user’s objectives; and it is common practice to increase or reduce significant digits of reported data to be commensurate with these considerations. It is beyond the scope of this standard to consider significant digits used in analysis methods for engineering design.
1.9 This standard 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.
Note 1: The equipment and procedures contained in this test method are similar to those developed by B. Clegg in the 1970s at the University of Western Australia, Nedlands, Australia. Impact Value is also commonly known as Clegg Impact Value (CIV).
