Evd is the dynamic deformation modulus (also known as the dynamic deformation module, dynamic modulus of deformation, dynamic stiffness modulus, composite stiffness, effective stiffness or surface modulus). Modulus is the most accurate and independent means for judging deformation and, thus, a material’s level of compaction. Evd is used to measure bearing capacity and compaction quality for subsoil’s and subgrade materials, unbound base layers, granular layers, backfilling materials, soil stabilisation with lime, cold recycling materials and pavements, cycle tracks and footpaths.

The soil receives an impact of maximum force Fs transmitted through the fall of the drop weight onto a circular plate of radius r, which is assumed to be rigid. When the device is calibrated, the force is selected such that the maximum normal stress σ under the load plate is 0.1MN/m2.

To calculate Evd, the deformability of the soil under a vertical load, as described above, with a settlement amplitude s (in mm) and the duration of impact ts:

Evd (MN/m2) = 1.5 x r x σ /s

For the 10kg drop weight and 300mm diameter plate Evd = 22.5/s
For the 15kg drop weight and 300mm diameter plate Evd = 33.75/s