Dynamic Compaction

Densification of loose granular soils to improve strength and stiffness.

Loose, soft and variable near surface soils can cause excessive total and differential settlements that may damage buildings, services and infrastructure.  Dynamic compaction is ground treatment process that can address these challenges and, in some circumstances, can provide a more cost effective solution than deep foundations and alternative ground improvement systems.  

Dynamic compaction involves dropping a heavy mass from significant height utilising a free-fall mechanism on a crane.  The impact of the falling mass densifies loose granular soils and, with dynamic replacement in more clayey soils, creates localised craters into which sand or gravel can be placed and compacted.  Adoption of a suitable treatment grid spacing, falling mass and drop height can produce a density, strength and stiffness improvement across the project area, to depths in the order of up to 8m below the surface, thereby reducing total and differential settlements. 

The dynamic compaction solution has a number of applications which can offer significant benefits on construction projects over poor and variable ground strata.  These include;

  • Increased bearing capacity of the ground below shallow foundations and slabs.
  • Reduced total and differential settlements of structures.
  • Strength and stiffness improvement of the ground to limit the effects of disturbance and liquefaction during seismic events.
  • Improved uniformity in variable fill or granular ground strata to limit differential settlements below pavements and hard landscaped areas.

It must however be noted that the process causes significant ground vibration and this, in combination with noise factors, may preclude use of the system in built up areas and particularly where there are adjacent existing buildings that are susceptible to vibration damage.   

CMW work closely with specialist contractors who carry out dynamic compaction works and we have the experience and knowledge required to carry out design, specification, testing, value engineering and review processes of these ground improvement solutions.

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