Dynamic Compaction

The Dynamic Compaction technique involves using a crane to drop weights of between 5 to 20 tons, from heights of up to 20m. As a result the technique is best suited to large, open sites where few obstructions are present.   

How the treatment works

The impact of the dropped weight induces settlement depths of up to 8m in most unsaturated soil types, including loose granular materials, made grounds and domestic landfills. The ground is treated by repeatedly dropping the weight onto individual footprints which are arranged on a grid pattern. Treatment is normally carried out on a number of 'passes' with the weight being dropped a set number of times on a regular grid pattern across the whole treatment area to constitute a 'pass'.

The number of drops, weights used and the height of the drops depends on the required post treatment bearing capacity, settlement performance and soil conditions. Between two and five passes are generally required with the first or earlier high energy treatment passes aimed at treating the deeper soil layer and a final low-energy contiguous tamping pass to compact the shallow near-surface soils disturbed during the earlier passes.

DC is most commonly used to prepare ground for foundation slabs for large buildings and external works.  

Benefits

• DC is a highly sustainable ground improvement technique and as excavation is not usually required it is suitable for use on contaminated or obstructed sites
• Levels can often be reduced by up to 10% of the depth of fill being treated thus reducing the amount of spoil requiring disposal
• Dynamic Compaction is frequently used for re-development of old domestic landfill sites, to collapse existing voids and accelerate the long-term settlement between piled structures and the surrounding hard standing areas
• Dynamic Compaction is extremely economical and can be used for large sites
• Although DC is generally not suitable for use within 30-50m of existing structures, it can be combined with Rapid Impact Compaction and vibro techniques to allow treatment to within 10m of sound buildings