How each method applies energy
Dynamic Compaction drops a heavy weight in free fall from a crane. Each drop delivers a large amount of energy, so relatively few drops are applied at each point, in phases on offset grids.
Rapid Impact Compaction uses a hydraulic hammer striking a steel foot that stays in contact with the ground. Each blow delivers less energy, but blows follow one another quickly, and the rig records the foot penetration for every blow.
Side-by-side comparison
| Factor | Dynamic Compaction | Rapid Impact Compaction |
|---|---|---|
| Energy per impact | High: free-fall weight | Lower: hydraulic hammer on a foot in contact |
| Depth of improvement | Deeper | Shallow to moderate |
| Control at each point | Drops and crater depth recorded per print | Blows and penetration data-logged per point |
| Flying debris | Exclusion zone needed | Minimal: the foot stays on the ground |
| Equipment and access | Heavy crawler crane; large open site | Excavator-mounted rig; more mobile, suits smaller areas |
| Suitable soils | Granular soils and fills | Granular soils and fills |
Both methods respond poorly in saturated fine-grained soils (clays and silts), where impact energy raises pore-water pressure instead of densifying the soil.
The main selection factors
- Required depth of improvement, from the design and the site investigation.
- Soil type, fines content and groundwater level.
- Distance to structures, buried services and site boundaries.
- Size and shape of the treatment area, and access for the equipment.
- Programme and the working platform available.
- How the result will be verified and what the acceptance criteria are.
Using both on one site
The two methods are often complementary. On some projects DC is used in open areas where depth is needed, and RIC is used close to boundaries or existing assets, where vibration must be kept lower.
What neither method replaces
Both methods still need a site investigation, a trial area and verification testing, because the achievable depth and the production parameters are established on site.