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Dynamic compaction is an efficient and cost-effective soil improvement technique that uses the dynamic effect of high energy impacts to densify weak soil. The dynamic effect is generated by dropping a static weight (15-40 tones) from a defined height (10-30 m).

The drop weight, which manufactured from steel; steel box and concrete, or reinforced mass concrete, is commonly manufactured from steel and cranes are used to lift and release it repeatedly from a certain height. These droppings exert a vibration on the soil and improves it at a depth.

The dynamic compaction is used to improve weak soil such as loose medium to coarse grained sand with salt or clay content. It effectively enhances the soil to a depth of 10m, but its influences reach till 12m depth. Not only does it utilized for settlement improvement and liquefaction mitigation but also for improvement of long-term performance, and backfilling landfill sites or collapsing cavities.

Purpose

The purpose of dynamic compaction technique is to transmit high energy waves through a compressible soil layer to improve Geotechnical properties of soil at greater depths.

How Dynamic Compaction Improve Soil Properties
Fig. 1: How Dynamic Compaction Improve Soil Properties

Dynamic Compaction Process

The concept of Dynamic compaction is simple but experienced engineers and good planning is essential. Dynamic compaction process includes lifting and dropping a heavy weight several times in one place.

Dynamic Compaction Process
Fig. 2: Dynamic Compaction Process

It is repeated on a grid pattern across the site. The spacing of grid patterns is determined based on underground condition, foundation loading, and foundation geometry.

Dynamic Compaction Grid
Fig. 3: Dynamic Compaction Grid

The resulting high energy impact transmits shock waves through the ground to the depth to be treated. This reduces air and water voids between soil particles resulting in enforced settlement.

How Dynamic Compaction Densify Soil at Great Depth
Fig. 4: How Dynamic Compaction Densify Soil at Great Depth

Deeper layers are compacted at wider grid spacing and upper layers are compacted with closer grid spacing.

Dynamic Compaction of Soil
Fig. 5: Dynamic Compaction of Soil

Advantages

  • Densify and compact soil to a depth of 12m
  • Effective in various soil conditions
  • Cost effective
  • Dramatic cost savings in excess of deep foundations and most undercut and replace options
  • Accelerate schedules
  • Mitigate soil liquefaction
  • Improves bearing capacity of soil
  • Decreases the volume of landfill waste
  • Reduces post-construction settlements
  • Environmentally friendly
Schematic Influence of Dynamic Compaction on Soil
Fig. 6: Schematic Influence of Dynamic Compaction on Soil

Disadvantages

  • It cannot be used within 30m from buildings and 15m from underground services.
  • Dynamic compaction is not appropriate if water depth is less than 1.5m.
  • It cannot be applied if soft cohesive soils are located in the upper part of the compaction.
  • Dynamic compaction is not effective when soils have fines content in excess of 20%.
  • Requires an intensive in situ testing programme to examine the result of compaction.

Applications

  • Densification of weak soil; fills, mine refuse, collapsible soils, sanitary landfills, and soils loosened by sinkholes.
  • Reclamation projects.
  • Treatment of industrial warehouses, port and airport platforms, roads and railways embankments, heavy storage tanks.

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Madeh Izat Hamakareem

Madeh Izat Hamakareem

EDITOR
Madeh is a Structural Engineer who works as Assistant Lecturer in Koya University. He is the author, editor and partner at theconstructor.org.

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