Dynamic compaction 1

[janithahb]

Dynamic compaction was used as a method of compaction in the construction which consist of a land reclamation using dredged sand from the sea. The material is granular. During the trial testings the test seemed to be performing well in improving up to depth required ( which is 4.5m).
Though the pilot test gave good results, when the compaction was carried out in areas where the reclamation carried out over a previously compacted area which lay 3m below newly reclaimed area, the CPT results indicated less improvement.
as a remedy i thought of increasing the energy per blow allowing the dynamic wave to penetrate the previously compacted area. since there are limitation to increasing the energy per blow since there are adjacent structures, are there any option doing using dynamic compaction as a compaction methods in improving compaction depth.

 

[BigHarvey]

If the mechanical characteristics of the soil have not improved as much as in the trial test there are two possibilities

1) the number of blows per print and/or the unit energy and/or the grid have been modified between trial test and production

2) the soil is not the same ( in reclaimed areas the fine content can increase when you increase the distance from the discharge point without precaution ). You can check that looking the FR value in the CPT soundings ( compare soundings before treatment or after treatment without mixing them, ground improvement makes FR decrease due to the change of horizontal stress level )

4.5 m is not very deep and shouldn't make any problem if you have a pounder of at least 10 to 12 tons dropped from at least 20 m.

If you have problems with vibrations, dig a trencg and/or revert to Rapid Impact Compaction.

 

[msquared48]

Seems like dynamic compaction should only be used in a situation where seismic activity is not an issue.

Seismic + water + sand = sand boils = further settlement = likely structural failure.

Mike McCann
MMC Engineering

 

[dgillette]

Actually, Mike, dynamic compaction is fairly common for preventing liquefaction, and SPTs show good densification as deep as 10 m, with the right soil. However, as BigHarvey indicates, adequate permeability and drainage during treatment are necessary if the pore water is going to be expelled. Wick drains have been used successfully for that purpose.