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

Process

Dynamic compaction is a ground improvement technique that densifies soils and fill materials by 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 prior to construction to reduce sinkhole potential. It has also been used to compact construction debris and urban fill as well as sanitary landfills prior to construction of parking lots, roadways, and embankments. The removal of compressible, contaminated fills can sometimes be avoided.

Advantages

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 take into account the soil conditions, type of development and required bearing capacity and settlement characteristics. It is essential to have a thorough understanding of the soils prior to treatment, and to maintain very close control during all phases of the work. 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 contract.