We all know any type of explosion generates vibrations and shock waves. Sometimes this energy can be used in compaction of foundation soil. The energy performs compaction like vibratory equipments used for usual compaction.
At first we will learn what types of explosives are used and where it should be buried. The explosive charges generally contain 30% gelatin dynamite of special types having ammonite and 60% dynamite. Normally the charges place at 2/3 of the thickness of required stratum to be densified for founding building structure.
The charges should be placed at (3-8) m interval and for a particular location 3-5 blasts are usually generated to have required compaction.
Now we will know the mechanism of compaction. This method of compaction is suitable for cohesionless soil of fully saturated condition. Shock waves generated by explosion results liquefaction to sand resulting a densification of the surrounding depositions. But in case of partial saturated soil capillary action obstruct the densification tendency by preventing soil particles to come close. So this method is not useful for partial saturated soils.
Now we have to know the zone of influence of explosion densification. Up to 25m depth is considered effective in blast operation. Uppermost soil up to 1 m depth is displaced in random manner leading improper densification. This random densified zone is compacted by usual compaction method (roller).
The following expression gives an idea about radius of influence(R):
Where M=mass of explosive charges (kg)
C=constant (considered 0.04 in case of 60% dynamite)