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Dynamic deep compaction (DDC) is an important ground improvement technique, capable of compacting a wide variety of weak soils. The 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.
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This is a method of improving the ground from the surface for industrial or commercial development. Dynamic compaction can improve granular soils to depths of 5-10 metres. Stone piles extend the method to more cohesive soils. The procedure is to drop heavy weights of several dozen tonnes repeatedly onto the soil from a height of several dozen metres.
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This is a method of improving the ground that involves compacting by hammering the earth in a matrix or in stages depending on the type of soil and the degree of improvement required.
It is generally used on low-power granular soils and landfills as the kinetic energy transmitted during the hammering reaches a few metres down. .
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The technique consists of methodically and repeatedly dropping heavy steel weights onto the surface of soils requiring improvement. The resulting impacts create powerful compression and shear stresses that reach considerable depths and induce volume reduction within the soil masses, improving their geotechnical properties. Using specially modified powerful crawler cranes, the weights or tampers are hoisted and released as a quasi free fall. The weight of these tampers usually varies between 10 and 18 tonnes, but with special hoisting systems it can reach 30 tonnes or more to achieve greater improvement depths. The tampers are typically dropped from 10 to 25 metres above the work platform.
The energy applied to the ground upon impact is measured in tonne-metres (t-m) and the magnitude of the energy per drop is a determinant factor in the degree and maximum depth of improvement achieved. Other significant parameters affecting both the depth and degree of improvement are the overall design of the energy application program, the proper phasing of the work, the right number of impacts per grid point, and the close monitoring of the soil response as work progresses. The increase and the subsequent rate of dissipation of pore pressures, the variations of induced settlements throughout the site, heaving, etc. are all elements which must be closely monitored and evaluated throughout the treatment.
Dynamic Compaction is an extremely rapid technique compared to other methods, and in loose granular soils of 12 metres or less, it is unquestionably the most economical of all existing soil improvement techniques.
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This method is also known under the name of Heavy Tamping and it is employed in order to reduce the risk of liquefaction. It consists in the repeated application of a high-density impact on the surface of cohesion-less soils. This method induces the soil liquefaction and increases the relative density until reaching a potential range of non-liquefiability. The maximum effectiveness of the method is 30 m.
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Compaction Grouting uses controlled displacement to increase the density of soft or loose soils. It is typically used for settlement control, structural re-leveling, and remediation of sinkholes. A small diameter (2" - 4") steel casing is advanced through the zone to be improved, and a stiff mortar-like grout is injected at high pressure to displace and compact and the surrounding soils. Pumping is continued as the grout casing is withdrawn, forming a larger diameter (12" - 18") column of interconnected grout bulbs. As they form, they intensely compact the soil around them. Compaction
piles can be formed in the same manner to create a continuous structural support for
foundations.
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Definition:
compaction of the ground using an important mass with or without incorporation of materieux (gravel)
Characteristics:
the vibrations peuvetn êter followed and the lawsuit can be adapted to guarantee a maximum amplitude of vibrations
Scope of application:
reduction of compressings
exploitation of the recently embanked grounds
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The improvement of poor soils by depth vibrators is an innovation of Keller. For the treatment of non-cohesive and cohesive soil formations different types of depth vibrators and various techniques are available. Together with the different methods of soil improvement a wide range of pile foundations and similar foundation techniques are available.
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