Generally, the soil types most favorable to the successful implementation of a dynamic compaction program are granular soils with a relatively low degree of saturation. Generally speaking, granular uncontrolled fill material or loose sands are the most applicable to improvement via high-energy compaction. However, several other soils types are also able to be adequately improved using dynamic compaction to a degree where the risk of post-construction settlement is significantly reduced. These materials include:
Urban or Uncontrolled Fills – Likely the most common soil condition for which dynamic compaction is utilized, dynamic compaction is especially effective at improving the reliability and overall engineering properties of a fill material that was placed without any sort of engineering controls. Often times, fill materials contain debris and other materials that if left in-place or unimproved, would create voids and lead to settlement of surface structures under new fill or structural loads.
Liquefiable or Loose – In many instances, settlement or bearing capacity of a structure is not the primary concern, but rather the potential for liquefaction during a seismic event. In these cases, dynamic compaction can be implemented to increase the density of granular soils below the water table, mitigating the potential for liquefaction-induced deformations during a seismic event.
Landfill Materials – At municipal solid waste sites, the dynamic compaction process can be very successful at reducing the void ratio of landfill material, thereby reducing the amount of oxygen present to degrade the material, which if left unimproved, can lead to long-term settlement of the soil mass.
Mining Spoils – Similar to general fill sites, mining spoils historically have been replaced in an uncontrolled fashion following strip mining operations at a site. In many instances, these uncontrolled deposits could be in excess of 50 or 60 feet deep. Dynamic compaction has been successfully implemented at many mine spoil sites where structures are to be constructed at the surface. Specifically, a 20 to 25-foot layer of material is improved at the surface, creating a soil “mat” that greatly irons out any settlement which may result as the lower mine spoils materials compress over time.
Collapsible Soils – Collapsible soils (otherwise known as Aeolian or wind-blown deposits) exist in many areas, particularly throughout the Midwestern and western United States. In a dry state, these soils have adequate bearing capacity and strength; however, have a tendency to collapse when they become saturated. By implementing dynamic compaction to improve these collapsible materials, the overall void ratio of the soil mass can be reduced, minimize the potential for collapse-related settlement issues.
Karst (Sinkhole) Sites – Karst is a geologic formation that occurs when cavities form in water soluble rock such as limestone or dolomite. The most common manifestation of a karst condition is the formation of sinkholes at the surface, as a result of soil migration into the underlying cavities in the rock. By introducing high-energy dynamic compaction drops across a site on a grid pattern, often times near-surface sinkholes can be exposed and remediated prior to surface construction.