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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](https://test.theconstructor.org/wp-content/uploads/2020/01/How-Dynamic-Compaction-Improve-Soil-Properties-413x380.jpg)
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](https://test.theconstructor.org/wp-content/uploads/2020/01/Dynamic-Compaction-Process-772x380.jpg)
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](https://test.theconstructor.org/wp-content/uploads/2020/01/Dynamic-Compaction-Grid-455x380.jpg)
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](https://test.theconstructor.org/wp-content/uploads/2020/01/How-Dynamic-Compaction-Densify-Soil-at-Great-Depth-418x380.jpg)
Deeper layers are compacted at wider grid spacing and upper layers are compacted with closer grid spacing.
![Dynamic Compaction of Soil](https://test.theconstructor.org/wp-content/uploads/2020/01/Dynamic-Compaction-of-Loose-Soil-692x380.jpg)
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](https://test.theconstructor.org/wp-content/uploads/2020/01/Schematic-Influence-of-Dynamic-Compaction-on-Soil-352x380.jpg)
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.