How much compaction force is needed?

A rule of thumb is that a compactor will compact 1 inch of material for every 1,000 pounds of compaction force it exerts. You should also consider the machine's vibration frequency, measured in vibrations per minute. Higher vibration frequency (around 5,700 vpm) is good for compounding thin layers of material.

The compaction effect of the Rapid Impact Compactor is characterized by pulse-shaped loading of the ground and is achieved by a specific number of blows. The ground to be improved is both compacted and displaced depending on the soil type, thus, causing plastic deformations in the near-field while elastic waves are generated in the far-field. The nature of vibration excitation (transient or periodic) is one of the limiting factors for the allowable impact on buildings and human beings and has to be taken into account for the assessment of standardized limit values. 

RIC utilises a 7 tonne hydraulic piling hammer repeatedly hitting a heavy 1-1.5m diameter steel foot. Recurring blows at each treatment position create imprints, which are subsequently filled with granular material. The pattern is then repeated at offset locations in order to provide treatment depths of around 3m. 

Use within 30 feet of a Building – Because Rapid Impact Compaction provides a low magnitude of impact loading at a very high frequency, the peak particle velocity remains relatively low (less than 2 inches per sec) at a distance of 30 feet from the source. This is different from Deep Dynamic Compaction which has a low frequency and a high magnitude of loading so vibrations are greater from DDC when compared to RIC.

One advantage of RIC is that the drop height and number of blows can be varied based on the soil conditions. Through a test program, we will work with the Geotechnical Engineer of Record (GER) to determine the appropriate improvement criteria and RIC set-up for various areas of the site. For a site with a mixed soil profile and varying thicknesses of sand and clay, the ability to accurately control the amount of energy delivered to the ground is critical as it allows one to improve the loose overlying loose soil without liquefying the fine grained soils below – providing more uniform compaction.

The RIC compactor is mounted on a excavator so that moving around the site is easy. The compactor consists of a 7.5-ton weight falling approximately 36 inches onto an anvil in contact with the ground at a rate of approximately 40-90 blows per minute thereby compacting approximately 800 sf of area per hour. Onboard diagnostics equipment allows the compaction effort to be stopped when optimum compaction has been achieved.