How does it work?
The two methods utilize oscillations induced in a poker or mandrel to transmit vibrations into the soil and cause the reorientation of soil particles into a more compact state. Both methods involve penetration into the soil of the vibrating poker/mandrel to the design depth and subsequent withdrawal, on a grid pattern of treatment points to create blanket coverage of the area being compacted.
The distinguishing difference of the two methods is that the poker delivers horizontal oscillations into soil and the mandrel delivers vertical oscillations into the soil.
A variety of reasons exist for the horizontal oscillations delivering a more efficient and effective compaction; these include water jetting through the toe of the poker, the introduction of material around the poker as it is operated and the principal stress orientation in the soil. The mandrel, in contrast, relies solely on the vibratory effect of the vertical oscillations.
The superior efficiency of the horizontal oscillations is demonstrated by the higher levels of compaction achieved, despite generally operating at grid spacings double those of the vertical oscillations.