Clegg Impact Soil Testers

The original impact testers, the Cleggs, determine a soil 'impact value', which can be correlated to various strength properties.

Evaluation of relative strength determines suitability of compacted fill for carrying loads.

Operation

The tester measures the deceleration of a hammer free-falling onto the soil surface. The Impact Value is determined after four hammer drops to the same spot. Speed and ease of use enable many tests to be performed over a wide area. As many as 250 tests can be performed in a half-day.

Models.

Clegg Impact Testers are available in four models.
The Standard 10 lb (4.5kg) model with 18" (450mm) drop and 2" (50mm) diameter hammer face is the original version, in use for over 20 years for evaluation of compacted soil and pavement materials with aggregates below 1.5" (38mm).

The Light Hammer has a 1.1 lb (0.5kg) hammer and 12" (450mm) drop for use with fine grained cohesionless, saturated soils or highly plastic soils. This model is often used for measuring sports and recreational turf.

Midrange Model HM-702 has a 5 lb (2.25kg) hammer for soil applications between the Standard and Light Hammer models.

The 44 lb (20kg) Heavy Hammer Model with large 5" (130mm) diameter face and 12" (300mm) drop, tests to depths of 10" (250mm) or more. This model can be used to measure stiffness of underlying pavement layers and to estimate traffic-carrying potential of roads. Pavement deflection under wheel loads in correlation with Benkelman beam measurements can also be estimated with the HM-704.

Use of the standard model and the Light Hammer are described in ASTM D 5874.

The Standard model has a hardened strike face on the steel drop hammer which falls through an aluminium guide tube.
Peak values are shown on a digital display attached to the guide tube. For this model, one Impact Value unit on the 0-100 display scale equals ten "g" (gravitational deceleration).
A calibrating ring is provided, and a locking pin secures the unit for carrying.
An application guide is supplied, along with two 9V batteries.
The testers come in a sturdy road case.
(The Heavy Hammer model comes with an aluminum cart.)

See also:
Controls Impact Soil Tester
Shear vane testers
Auger Equipment
Scala Penetrometers
Pocket Soil Tester
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