Dynamic compaction uses the energy from a falling weight in a pre-determined grid pattern to improve granular soils and fills.

Dynamic compaction technique illustration

Common uses

Increase bearing capacity
Decrease settlement
Mitigate liquefaction
Reduce sinkhole potential


Dynamic compaction is a ground improvement technique that densifies soils and fill materials using a drop weight. The drop weight, typically steel, is lifted by a crane and repeatedly dropped onto the ground surface. Vibrations transmitted below the surface improve soils at depth. The drop locations are typically located on a grid pattern, the spacing of which is determined by the subsurface conditions and foundation loading and geometry. 

Treated granular soils and fills have increased density, friction angle, and stiffness. In shallow karst geologies, dynamic compaction has been used to collapse voids before construction to reduce sinkhole potential. It has also been used to compact construction debris, urban fill, and sanitary landfills before constructing parking lots, roadways, and embankments. The removal of compressible, contaminated fills can sometimes be avoided.


Capable of compacting a wide variety of weak soils
Treated granular soils and fills have increased density, friction angle, and stiffness
Can improve soil conditions on marginal sites to extent that shallow foundations can be used without deep excavation or piling
Removal of compressible, contaminated fills can sometimes be avoided

Quality assurance

Typically, in situ testing by borehole or static cone penetrometer, allied with measurement of print volume and site surface settlement, is performed during the dynamic deep compaction.

The treatment pattern, energy level, number of passes, and phasing of passes must be designed to consider the soil conditions, type of development and required bearing capacity, and settlement characteristics. It is essential to thoroughly understand the soils before treatment and maintain close control during all phases of the work.