September 11, 2015

What is Geogrid?

Geogrids are flexible, synthetic meshes which are manufactured specifically for slope stabilization and earth retention. These “grids” are available in a variety of materials, sizes and strengths. They can be made of high tensile strength plastics or woven polyester yarns and are typically packaged at the factory in rolls.

What does all that really mean, and how would you use it in your retaining wall?  To answer that, refer to the How Does Grid Work page on the Allan Block website.

Here is a simple demonstration of how geogrid helps your retaining and landscape walls.  I started with two 6 inch (154 mm) diameter columns of compacted sand around 8 inches (200 mm) tall.  The one on the right would not support a small block weighing about 22 lbs (10 kg) and simply fell into a big pile.  The one on the left held over 75 lbs (35 kg) before I stopped because I thought the point was made.  So, what was the difference between the two columns of sand? 

 Both were from the same bucket of sand with just enough water to make the sand stick together a little.  Both were compacted in about 2 inch (50 mm) lifts.  The difference – “geogrid” was added to the column of sand on the left.  For this demonstration, household screen was used to simulate geogrid and was placed after compacting each layer of sand.

If designed properly, and the installer follows the recommended geogrid spacing and compaction criteria, you can think of this mass of soil within the geogrid area as a single large block of soil.  This entire block of soil is going to resist the forces that are trying to tip the wall over, or slide it forward; much like a large block of concrete would act under the same conditions.