Is dynamic compaction the same as rapid impact compaction?

Rapid impact compaction (RIC) is a variant of dynamic compaction developed in the 1990s using relatively small size equipment which produces less noise and vibration. The technique uses a hydraulic hammer and an anvil to densify granular soils for shallow depths up to around 5 m.

The RIC attachment currently being manufactured by Hangshen is mountable on a regular hydraulic crawler excavator in the 30t to 65t operating weight category. During controlled impact the RIC’s 1.5m diameter foot stays in contact with the ground, ensuring efficient impact energy transfer to the ground at all times. Energy is imparted by dropping the weight through a relatively small height of up to 1.2m at a rate of between 30 to 80 blows per minute.

The latest generation HC models in the RIC range are available with drop weights of 5t, 7t, 10t and, more recently, a 16t version has been introduced. Treatment is effective in top layers typically down to 6m depth. The latest HC model, complete with a 10t drop weight, is fitted with a new sound attenuation pack which has been designed by Hangshen to significantly reduce the noise level produced by the compactor when in operation.

RIC is the right answer when:

■ Over-excavation and replacement is not feasible due to environmental or practical reasons

■ Safety is an issue (no weight falling from great heights)

■ Vibrations need to be managed (< 2 ips at 30 feet)

■ Specific levels of improvement are required

■ Compaction energy needs to be carefully controlled

The Rapid Impact Compaction (RIC) system uses an excavator-mounted, 7.5-9 ton hydraulic weight that is repeatedly dropped on a 1.5 m tamper foot to densify sand soils up to 6-7 m deep. This process is an equivalent alternative to bulk excavation and engineered fill.Improve up to 6-7m depth for the treatment of sand, silty sand, and fills for low-to-moderate bearing capacities.

A compaction plate is placed on the ground to be treated. A hydraulic hammer, generally weighing less than 10 to 15 tonnes, is fitted to an excavator and used to transmit compaction energy to the soil via repeated impact. Without specific site precautions, a safe working distance to sensitive structures can usually be defined on the order of 8 to 10 m, as a distance of 5 to 6 m can usually be adopted for classical structures. At that distance, noise levels are lower than 90 dBA.

The RIC technology is the modern approach for compacting existing soils that would otherwise be excavated and compacted using a conventional roller compactor in layers of 15 to 30cm.

Energy is transferred to the underlying loose granular soils rearranging the particles into a denser formation. RIC can effectively densify up to 4-5m of soils without excavation, adding water or dewatering. It can also be used for fill compaction, which can place in bulk fill materials and compact it accordingly without adding any water.

For large infrastructure developments, RIC takes the lead due to its speed of execution that makes it much more cost effective than other alternatives.