Authored By: Bryan Gee
There have been many innovations in geosynthetic technology since the first use of geotextiles in the 1960s, both in the geosynthetic materials themselves and our understanding of their proper application. As our understanding of the functions of different geosynthetic materials has developed, it has led to the creation of geocomposite materials which combine these functions.
Geogrids and geotextiles each have important functions. One of the most important geosynthetic functions, which can be accomplished using both geogrids and geotextiles, is the separation of fine-grained subgrade soils, like silts and clays, from granular layers. In the case of geogrids, separation depends on the relative size and gradation of both the granular material and the fine-grained soil. With proper design, a well-graded aggregate placed over a stiff, stable geogrid will function as a filter, preventing migration of fine-grained soils. This will provide the best solution in most cases for long-term separation of fine-grained soils from granular material.
However, in some cases, filtration cannot be achieved, due to the combination of the gradation of the subgrade soils and the available granular material. In other cases, the designer does not have sufficient data on the subgrade soils to determine if filtration can be achieved. When faced with these issues, the best solution may be the use of a geotextile to ensure that separation is maintained. Geotextiles provide separation based on the openings in the fabric, which allow water to pass through the material while being small enough to restrict the passage of fine-grained soil particles. In most cases, the fabrics used for separation are light (4 to 8 ounces/square yard) non-woven geotextiles.
Because fine-grained subgrades requiring separation are almost always unstable as well, the stabilization function of geogrids is also needed. So in cases where a geotextile is specified to ensure separation, it is often installed under a geogrid, which stabilizes the granular layer above to provide a stable surface. When using this approach with separate geogrid and geotextile materials, this results in one or more added construction steps.
Tensar has introduced TriAx FilterGrid, which combines TriAx Geogrid with a non-woven geotextile, to allow the installation to be achieved in a single step instead. Now, in cases where both a geogrid and a geotextile are required, contractors can save time and labor by installing them together. And TriAx FilterGrid is built to make sure that full interlock of the aggregate with the geogrid is maintained, so the stabilization of the layer is not compromised.
Geosynthetic technologies offer some of the greatest potential benefits for infrastructure improvement. By developing TriAx FilterGrid, a composite material that combines multiple functions in a single step, Tensar has added another tool for engineers and contractors to build better.
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