It is also used to confirm uniform compaction of over wide areas of ground, identifying poorly compacted areas and ineffective rolling of materials. The most popular Clegg instrument is one using a 4.5 Kg hammer.
Lightweight versions of the Tester available in 0.5 Kg and also 2.25 Kg weights are manufactured and are suitable for sports turfs whilst a heavy duty version is supplied for testing harder materials and road works.
The Tester consists of a compaction hammer operating within a vertical guide tube. When the hammer is released from a fixed height it falls through the tube and strikes the surface under test, decelerating at a rate determined by the stiffness of the material within the region of impact.
A precision accelerometer mounted on the hammer feeds its output to a hand held digital readout unit which registers the deceleration in units of Impact Value (IV). The IV indicates soil strength and shows good correlation with CBR test results.