Site development often creates a detrimental impact to the environmental when poor soils or unsuitable fills are shipped off-site for disposal in a landfill. Since 1994, Densification Inc., a nationwide geotechnical specialty contracting firm based in Paeonian Springs, Virginia, has been providing property owners and developers with an attractive ground improvement alternative.
Specializing in a process known as dynamic compaction, Densification takes existing poor soils or loose fills and utilizes steel tampers, weighing 10 to 20 tons, to introduce multiple phases of high-energy drops across the site surface to consolidate and improve the soils in question. This process densifies the soil, improving the consistency and overall engineering properties of the soil mass.
Through this process, the need for off-site removal of existing soils for replacement with compacted granular fill or the installation of deep foundations can be eliminated or greatly reduced. “We’re a specialty geotechnical ground improvement contractor,” says Chris Woods, vice president of Densification. “We own 20 different size American crawler cranes, properly equipped for the dynamic compaction process, which can pick up weights up to 20 tons.”
Weighing in on a more sustainable alternative
By its nature, dynamic compaction is more environmentally friendly than the alternative of hauling out soils and laying new fill. “The traditional answer is usually to take out about 15 feet of soil, send it off to a landfill and bring in clean fill,” explains Woods. “From a sustainability standpoint, we’re improving on the soils that are already there and allowing contractors and developers to reuse the site without having to remove the poor soils before shallow foundation construction or the implementation of a deep foundation system.”
The steel tampers used in the dynamic compaction process generally results in 6-foot-in-diameter craters, ranging in a depth of 2 to 6 feet. Following each high-impact pass, the craters are graded by pushing the material surrounding the craters into the low points, leveling the site. Alternatively, imported granular material is used to backfill the craters in between passes.
Dynamic compaction is a very practical ground improvement approach, as it not only strengthens and compresses existing fill or natural soils; it also is similar to proof-rolling in that it exposes pockets of softer material that represent a worse condition that the surrounding soils. When these areas are identified during compaction, remediation can occur in one of two ways; either additional pounding can be carried out until the area is adequately densified, or soils can be undercut and replaced with compacted fill.
The degree and depth of the soil improvement achieved with dynamic compaction depends on the total amount of energy applied to the surface. This is a function of the drop height, drop weight, spacing of the grid pattern, and number of drop at each point. “The more energy imparted to the soil as part of the program, the greater the degree of improvement,” explains Woods.
Dynamic compaction is performed using a calculated grid pattern outlined on a CAD-generated drop plan drawing. The grid spacing, number of drops per impact point, drop height and total number of passes varies between site-specific soil conditions, but Densification has seen great success across a range of applicable soil types. Dynamic compaction can greatly improve urban or uncontrolled fills, liquefiable or loose soils, landfill materials, mining spoils, collapsible soils and even sinkhole sites.
Densification also serves as a geotechnical consultant on dynamic compaction-related projects, offering a practical point of view to project owners. “We have in-depth knowledge of dynamic compaction and other aspects of geotechnical consulting gained from decades of experience on more than 800 projects throughout the U.S. and around the globe,” says Woods.
One of the company’s landmark projects is the Prudential Center in Newark, New Jersey. “This is one of the more prominent dynamic compaction projects we’ve completed,” says Woods. “At the onset of the project, the owner was convinced the arena would have to be pile-supported, and so the dynamic compaction program saved millions in foundation costs.”
Home of the New Jersey Devils, the Prudential Center opened in October 2007. Locally known as “The Rock,” it was constructed on a shallow foundations system following the completion of Densification’s ground improvement program. “We improved 13 acres of urban fill, using dynamic compaction, which was an aggressive approach, given the sensitive urban environment.”
Woods says Densification is seeing more and more opportunities arise in its niche in a range of markets all over the world. “We’re doing a lot of work in upstate New York, Pennsylvania, West Virginia, and other states on strip mine sites once used for coal mining,” he says. “Natural gas companies are stepping in and wanting to establish compressor stations and pipelines. Often, these projects include 100 feet of mine spoil fill material from previous coal mining operations, much of which needs ground improvement to allow for construction.”
Another avenue where Woods sees growing potential is landfill sites. At municipal solid waste sites, dynamic compaction can be very successful at reducing the void ratio of landfill material, in turn reducing the amount of oxygen present to degrade the material. In instances where these soils are left unimproved, it can lead to long-term settlement of the soil mass, particularly under the application of new load.
“There is a great need for this service in many parts of the country, Florida in particular at the moment, to mitigate settlement associated with vertical construction on landfill sites,” says Woods. “We’re also looking at opportunities for expansion outside of the U.S., in the Middle East, Asia and recently, New Zealand. After the destruction of the Christ Church earthquake the need to ground improvement programs, which can successfully mitigate potentially liquefiable soils, has become an important issue. This ground needs to be densified in order to reduce the potential for such significant damage during seismic events.
As a member of the U.S. Green Building Council (USGBC), Densification continues to offer more environmentally-friendly solutions for owners and developers. With 21 years of experience in dynamic compaction and a long list of successfully completed challenging geotechnical projects, Densification Inc. remains an industry leader in improving sites from the ground down.
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