nuterra

DEEP DYNAMIC COMPACTION (DDC) FOR HAINES CITY NuTerra FACILITY

Madrid Engineering provided comprehensive geotechnical services for a new manufacturing facility in Haines City, Florida, assigning a unique “brute force” compaction method to prepare the site. Our…

Madrid Engineering provided comprehensive geotechnical services for a new manufacturing facility in Haines City, Florida, assigning a unique “brute force” compaction method to prepare the site. Our client, BCR Environmental, Corp. (BCR), agreed with the city of Haines City to construct a NuTerraTM Facility composting facility at the east side of the city.  This new facility is an environmentally beneficial regional bio-solids management facility delivering lower costs, enhanced regulatory compliance, and reduced liability.  For more details, please visit the website <http://bcrenv.com/about-us/featured-projects/haines-city-nuterra-facility>.

Madrid Engineering Group, Inc. (MEG) completed soil borings at several properties near an existing wastewater treatment plant, due to previous use of the site as an undocumented landfill.  The site that was ultimately selected has loose sand with pockets of municipal refuse (broken concrete, plastic, etc.) within the upper 15 to 20 feet.  The extensive loose material would have caused the foundation to settle several inches. MEG initially recommended over-excavating up to 20 feet below ground surface (bgs) and replaced with clean, compacted fill.  This approach was not economically feasible and would have required a significant amount of trucking in/out of the site, which would have significantly increased vehicle emissions for the site prep activity, always a concern for environmentally conscious professionals.  MEG then modified the recommendation to use a power sieve on-site to remove large debris and reuse the soil; however, this approach was still very expensive.

Finally, MEG recommended Deep Dynamic Compaction (DDC) to treat the upper 15 to 20 feet soil.  DDC consists of introducing multiple passes of high energy impacts on the proposed treated ground surface by dropping a heavy weight from a specific drop height.  The combination of weight and drop height is determined by desired treatment depth.  With this system, excavation is not necessary – it’s all done from the ground surface down. We noted that the soil from 15 to 20 feet was not as loose but required some densification, therefore MEG calculated a minimum project requirement of a 7.5 tons weight with a drop height of 20 feet to significantly densify soil to approximately 15 feet, based on multiple technical references.  Densification, Inc. (DI), a national geotechnical specialty contractor, was hired to perform DDC operations and finished the work on September 28, 2015.  DI used a 10-ton steel tamper and drop height of approximately 50 feet to perform the work.  The higher energy would definitely increase the depth of influence of the equipment beyond the theoretical minimum.  DI completed multiple passes over the site with their equipment, forming craters at each location and densifying the sand beneath and adjacent to each impact.

MEG performed a verification subsurface testing by drilling multiple SPT borings to 20 feet bgs after the DDC was completed.  The average SPT N-values of pre- and post-  DDC borings at different depths were then compared.  It was found that the N-values within the upper 3 to 4 feet (the approximate crater zone) show a reduction or negligible improvement (associated with the disturbance of the craters) and required recompaction (which was expected), while the N-values below 4 feet show significant increase (between 36% to 113%). The increased density zone appears to extend to at least 20 feet below ground surface (bgs).  Based these findings, MEG recommended the upper 3 to 4 feet of soil be roller compacted to 100% of the modified Proctor Maximum Dry Density prior to any subsequent fill placement.  MEG is currently performing Construction Material Testing services for the remainder of the project.