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