Dynamic Compaction for New Development on Old Landfills

February 10, 2016

Dynamic Compaction used by SCS Engineers at the Procacci Sweetwater project site in Miami, FL.

Dynamic compaction is a construction technique that increases the density of soil/waste deposits by dropping a heavy weight at regular intervals to consolidate and improve the geotechnical characteristics of the deposit so that it can be suitable for redevelopment. This construction technique can be used to transform otherwise undevelopable property, such as old landfill areas, into developable property.

Most soil types can be improved by dynamic compaction; the method is particularly well suited to non-organic, irregular fill, where variable characteristics such as solid wastes are present. Field conditions and several other parameters are considered when designing and implementing dynamic compaction programs to keep costs in line. The primary considerations include, but are not limited to, waste delineation, distance from the ground surface to ground water, waste thickness, minimum energy, and selection of dynamic compaction parameters.
The following factors and associated costs should be evaluated if dynamic compaction is to be considered:

  • Test pits to determine lateral extent of fill below surface
  • Drilling investigation to ascertain thickness of waste or debris
  • Depth to water table
  • Survey of existing ground surface
  • Design plans, permitting, and bidding
  • Mobilization of dynamic compaction contractor and earthwork contractor
  • Purchase and placement of soil to establish the minimum 5-ft distance to ground water
  • Flagging drop locations
  • Performing dynamic compaction
  • CQA monitoring
  • Performing vibration measurements
  • Purchase and placement of soil in craters and preparing the ground surface after each pass
  • Survey of the final surface
  • CQA report summarizing activities and observations

Major change orders and environmental impacts can be expected if the plan does not address these factors.
If you decide to consider dynamic compaction in your redevelopment project, having onsite construction quality assurance monitoring during the process is important. CQA monitoring will verify that the work is implemented as designed and permitted, and that proper techniques are used to make sure the proper distribution of energy into the ground is taking place. The CQA monitor will also check to see that the final configuration of the fill is achieved, a safe working environment is maintained., and that ground vibrations are monitored near adjacent structures to to prevent structural damage.

For developments involving construction of buildings over a dynamically compacted areas, a combustible gas barrier layer is generally required below the building footprint to safely collect and vent subsurface combustible gases (i.e., typically methane) to the environment. Construction costs associated with a combustible gas barrier layer should include the following:

  • Removal of any near-surface wastes below building footprint for installation of a methane barrier layer
  • Disposal of excavated waste
  • Construction of a 1-ft sand layer (gas collection layer) below the barrier layer
  • Construction of collection pipes in the sand layer below the barrier layer
  • Construction of the barrier layer
  • Construction of a 1-ft thick sand layer (cushion layer) above the barrier layer
  • Backfilling the excavation to the building foundation level

In summary, dynamic compaction is a proven geotechnical construction engineering method that can be used to improve certain landfill areas to support redevelopment. SCS Engineers has completed many projects of this nature and is ready to serve and help to bring your project in service.

Related Article

Pursuing Dynamic Compaction, by Ali Khatami, Ph.D., Bruce Clark, P.E., and Myles Clewner, L.E.P., Waste Age
Sample Case Studies
Environmental Due Diligence – Procacci Site, Sweetwater, Florida

Landfill Engineering and Consulting – Medley Landfill, Miami-Dade County, Florida

Landfill Site Redevelopment for the City of Industry, California


Contact Dr. Ali Khatami

Ali Khatami, PhD, PE, LEP, CGC, is a Project Director and a Vice President of SCS Engineers. He is also our National Expert for Landfill Design and Construction Quality Assurance. He has nearly 40 years of research and professional experience in mechanical, structural, and civil engineering.

Dr. Khatami has acquired extensive experience and knowledge in the areas of geology, hydrogeology, hydrology, hydraulics, construction methods, material science, construction quality assurance (CQA), and stability of earth systems. Dr. Khatami has applied this experience in the siting of numerous landfills and the remediation of hazardous waste contaminated sites.

Dr. Khatami has been involved in the design and permitting of civil/environmental projects such as surface water management systems, drainage structures, municipal solid waste landfills, hazardous solid waste landfills, low-level radioactive waste landfills, leachate and wastewater conveyance and treatment systems. He has also been involved with the design of gas management systems, hazardous waste impoundments, storage tank systems, waste tire processing facilities, composting facilities, material recovery facilities, landfill gas collection and disposal systems, leachate evaporator systems, and liquid impoundment floating covers.

See his full resume.

Posted by Diane Samuels at 6:00 am