The Rapid Impact Compaction for the soil improvement uses a hydraulic hammer mounted on an excavator. The hammer with a weight ranging from 5 up to 12 tons is dropped freely from a height of 1.2 m on a large circular foot. Impacts repeated at a rate ranging from 40 up to 60 blows per minute plunge the steel foot creating a crater.
The control system installed in the operator’s cab allows for controlling the compaction process and recording the parameters such as impact energy or foot penetration. It can also be used to change the height from which the hammer is dropped.
The compaction in the RIC technology is usually preceded by creating a test plot where the compaction is performed for various spacing and rates of blows. Then, the local compaction of the improved soil is tested and the optimal grid spacing and the number of blows per one point is determined. Depending on the soils, the number of blows varies between 10 and 40 per one point.
Rapid Impact Compaction is a shallow ground improvement and densification technique. This method densifies shallow, granular soils, which repeatedly strike an impact plate on the ground surface using a hydraulic hammer. The energy is transferred to the underlying loose soils and regroups the particles into a denser formation. The impact locations are located on a grid pattern and the spacing of those locations is calculated by the subsurface conditions and foundation loading and geometry.
RIC technique is performed at the surface of a terrain and it comprises of a heavy excavator which is equipped with a specially designed arm onto which the hammer is attached. Within the hammer, a 5 to 10 drop weight is hydraulically lifted till a required height after which the weight is dropped using a hydraulic acceleration. This whole process of lifting and dropping of the weight takes place with a frequency of 30 to 80 times a minute.
The RIC system uses "controlled impact compaction" of the ground using a 9-ton hammer dropped from height between 0.3 m to 1.2 m onto a 1.5 m diameter steel patent foot delivering about 26,487 to 105,948 Joules of energy per drop. RIC can be used to densify loose soils down to a depth of about 4 m to 6m. RIC consists of an excavatormounted hydraulic pile-driving hammer striking a circular plate (patent foot) that rests on the ground. The tamper typically strikes the plate at a rate of 40 to 60 blows per minute.
RIC can be used to improve bearing capacity and reduce liquefaction potential of loose soils. The compaction sequence is designed to work from the outside in, so that compaction of the lower zone soils occurs first followed by compaction of the upper zone. Data monitoring during the compaction process and the online display in the operator’s cab enables compaction control, an economic application of the compaction tool, and a work integrated quality control. The total impact depth of the impact foot, the number of blows, and the final settlement of the impact foot after a blow define the stopping criteria.
The way in which RIC improves the ground is a “top-down” process, compared to Dynamic Compaction (DC) which is a “bottom-up” process. The first few blows in rapid impact compaction create a dense plug of soil immediately beneath the compaction foot. Further blows advance this plug deeper, which compacts soil in a deeper layer. This process progresses until little further penetration of the compaction foot can be achieved with increasing blows.
