Soil (Sand) Separation Solutions for Florida projects

by George Charalambous, P.E., on February 09, 2021

For engineers and contractors who are working on Florida projects where the need for separation of granular fills from fine-grained soils arises, a complete understanding of the underlying design principles is critical to making the most effective and economical decisions. There are several misconceptions regarding the ability of geogrid to provide a separation function. Geogrid apertures are significantly larger than fine-grained soil particles, which has led to the false belief that geogrids cannot be used for separation.

The use of geogrids for stabilizing granular materials such as aggregate and sand is well documented. One aspect that is less well known is that Tensar TriAx Geogrids can also provide a separation barrier between these types of fills and natural subgrade materials, when established filter criteria are met.

Separation Field TestTensar Geogrids have been used for subgrade stabilization for over 30 years. During this time, they have been subjected to extensive testing by a variety of independent agencies to assess their stabilization and separation benefits, including studies at Montana State University and the U.S. Army Corps of Engineers. The ability of geogrid to maintain separation has also been demonstrated in the field. In the example shown here, the geogrid was placed over a fine-grained subgrade below the base course. After 11 years of use beneath heavy equipment and fully-loaded trucks, the base course was exhumed to observe if there was significant intermixing of the subgrade and aggregate fill material. The photo shows geogrid effectively maintained separation.

Filtration ImageThe successful use of TriAx Geogrids with clean, well-graded sand has also been observed on many projects across the State of Florida. On multiple occasions, TriAx Geogrids were installed directly on top of saturated in situ soils with a layer of clean sand to establish stability and maintain adequate filtration and separation, as shown here.

FG_MI_Install2FilterGrid: Another Great Alternative
Although TriAx Geogrids frequently provide adequate confinement of granular fill to achieve both filtration and separation, there are times when specifiers recommend a geotextile in conjunction with the geogrid. FilterGrid provides the superior performance of Tensar’s TriAx technology along with the added assurance of a non-woven geotextile – all in a single composite product.


Benefits of Using FilterGrid:

  • Simple and Efficient: Rather than installing a geotextile and TriAx intwo separate steps, FilterGrid deploys as a single layer, saving time and labor costs.
  • Economical: Optimizes the structural thickness to save time and money.
  • Multi-Functional: Provides stabilization, filtration, and separation of the granular fill material.

    Learn More: TriAx FilterGrid

Separation Solutions:

TX_FLY_FL_Filtration-Separation_GC_11.20Want to learn more about using TriAx Geogrid or FilterGrid for stabilization and separation? Download this flyer.


George Charalambous Headshot Hi, I'm George Charalambous, P.E., Senior Regional Manager for Tensar in the State of Florida. I encourage you to contact me for a free, no obligation project review to see how the use of TriAx Geogrid can save you money and reduce risk while also speeding up construction schedules and improving roadway performance. You can also schedule a presentation with me to learn more about Tensar Geogrid solutions.     

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