For many years this process has been used to achieve ground compaction and consolidation to considerable depths - providing a suitable base on which to support structures.

A solid steel tamping weight is dropped onto the ground from a sufficiently great height to achieve the necessary compaction. The resulting high energy impact transmits shock waves through the treated ground. This reduces voids between soil particles resulting in enforced settlement, thus reducing long term settlement.

The treatment is carried out in a series of impact positions on various grid patterns which are arranged so that compacted zones beneath the weights overlap to ensure the whole area has been treated. As a result, foundation loads can be supported without shear failure or excessive settlement. This technique is used in conjunction with good control and insitu testing procedures.

This treatment technique is not as widely used as stone columns due to three main factors:

• The range of soil types suitable for improvement is less wide than that for stone columns e.g. soft clays and silts or sites with a high water table are unsuitable
• Dynamic compaction sets up much higher levels of vibrations than stone column installation. Typically dynamic compaction can be carried out within 15m from existing services and 30m of existing buildings

Cost Advantages

• Lower cost per square metre than stone columns

Sites where dynamic compaction would have a cost advantage over stone columns include:

• Large greenfield/brownfield sites
• Sites where there are a significant amount of underground obstructions. These would require extensive preparatory earthworks by the Main Contractor to prepare the site for the stone columns or piles