Some Principles of Dynamic Compaction are as follows:-
• Dynamic densification
• Dynamic consolidation
• Dynamic replacement
Dynamic densification
When dynamic compaction is used on unsaturated granular
geomaterial,
• impact by a heavy tamper immediately displaces particles to a
denser state, compresses or expels air out of voids and reduces
the volume of voids
• under such condition, there is a ground depression without any
ground heave and a hard plug is formed under the tamper
Dynamic Consolidation
• Theory proposed by Menard and Broise (1975) to explain how
saturated fine grained soil can also be improved by dropping a
heavy tamper
• They attributed dynamic consolidation to four main
mechanisms
• Compressibility of saturated soil
• Liquefaction
• Change of permeability
• Thixotropic recovery
Compressibility of Saturated Soil
• Saturated fine grained soil is incompressible and cannot have
volume change under immediate loading (under undrained
condition)
• Menard and Broise (1975) attributed the immediate volume
change of saturated fine grained soil to the existence of
microbubbles in soils
Change of permeability
• Under high energy tamping, vertical fissures are generated
around the impact points
• The fissures significantly increase the permeability of fine
grained soil, which also accelerates the dissipation of excess
pore water pressure and consolidation
Thixotropic Recovery
• Due to disturbance of fine grained soil caused by tamping, there
will be reduction in strength
• This strength regains with time due to thixotropic recovery
• So fine grained soils should be evaluated atleast 30 days after
tamping
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