Impact Soil Tester  clegg




Newsletter 16                                                      June 1996


December 1995 saw the acceptance by the American Society for Testing and Materials (ASTM) of a new standard: D 5874 - Standard Test Method for Determination of the Impact Value (IV) of a Soil, available from the end of May 1996.

Note 1 of the new standard states that the equipment and procedures are similar to those developed by B. Clegg in the 1970s at the University of Western Australia and that Impact Value is also commonly known as Clegg Impact Value (CIV).

The definition given in D 5874 for Impact Value is "The value expressed in units of tens of gravities (g) derived from the peak decelration of a 4.5 kg (10 lbm) insrumented compaction hammer 50 mm (1.97 in.) in diameter free falling 450 mm (18 in.)." The apparatus for obtaining Impact Value is commonly known as a Clegg Impact Soil Tester or Clegg Hammer.

The Standard also defines Light Impact Value. This is derived from using a 0.5 kg hammer mass in place of the 4.5 kg mass which is dropped instead from a fixed height of 300 mm. The standard gives the notation for Light Impact Value as IV/L. This commonly is expressed as CIV/L.

The standard states that Impact Value "... 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, stabilised soil and recreational turf." 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 ..."

The standard allows for variations such as a different mass, drop height, etc., provided variations are reported accordingly. Therefore, the 20 kg "Heavy" or 2.25 kg "Medium" Clegg Hammers may be used under Standard D 5874.

D 5874 provides procedures for CIV testing in the field and in 152.4 mm (6 inch) test moulds as well as procedures for determining Target CIVs to achieve in the field through correlations with density and moisture content, CBR or by field trials.

ASTM Standards are available individually, on CD-ROM or in bound volumes of the ‘Book of ASTM Standards.’ Please contact us if you need information on how to obtain a copy of D 5874.
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