Dynamic Deep Compaction - Ground Improvement
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Dynamic deep compaction (DDC) is an important ground improvement technique, capable of compacting a wide variety of weak soils. The ground improvement results in increased bearing capacity and reduced settlement. In this way soil conditions on many marginal sites can be improved to the point where shallow foundations can be used without recourse to deep excavation or piling.
Whilst the principle of dynamic deep compaction is of considerable antiquity, it is only in the past 15 years that the technique has been seriously applied on a large scale to the solving of problems by ground improvement. Keller have been actively engaged in successfully applying the system internationally during this period, and are able to offer DDC alongside their other geo-technical techniques to provide a complete ground engineering service.
With DDC, the ground is subjected to repeated surface tamping using a heavy steel and concrete weight. Typically the tamper weighs between 5 and 20 tonnes, dropping in free fall from heights of up to 25 metres. The tamper is dropped a set number of times on a grid pattern over the site to form a pass. Two to five passes on a site, dependent on soil type and condition, can be required. The imprints formed at each drop position are infilled with granular material after each pass.
The treatment pattern, energy level, number of passes and phasing of passes must be designed to take into account the soil conditions, type of development and required bearing capacity and settlement characteristics. It is essential to have a thorough understanding of the soils prior to treatment, and to maintain very close geo-technical control during all phases of the work. Typically, insitu testing by borehole or static cone penetrometer, allied with measurement of print volume and site surface settlement is performed during the dynamic deep compaction contract.
