As suggested by Lars Forssblad (1981), the three main actions of compaction are static pressure, impact force and vibration.
Different compactors contain one or more modes of these actions.
For example, vibratory tampers perform mainly by the principle of impact while vibratory rollers work with principle of static pressure and vibration.
For sandy soils, vibration is adequate for normal compaction because the action of vibration sets the soil particles in motion and friction forces between soil particles are virtually demolished.
During this vibration motion, the soil particles rearrange themselves to develop a dense state.
For normal soils, it is necessary to combine the action of vibration together with static pressure to breakdown the cohesion forces between soil particles in order to allow for better compaction.
The static pressure of vibratory machines is adopted to exert a shearing force to eliminate the cohesion in clayey soils.