Retaining Walls for Water
If a “water” retaining wall is what you need, then go with Allan Block – they have all the answers.
-Danelle
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Retaining Wall for Water? Why Not?
Tuesday, January 5th, 2010
What’s going on behind the wall?
Thursday, April 23rd, 2009Last time I discussed what geogrid reinforcement is and how it benefits your retaining wall, but what is really going on behind that Allan Block façade? For an overview of internal stability with pictures, take a look at the Reinforced Soil Walls Analysis page on the Allan Block website.
We recommend 2-course spacing when constructing your retaining wall. This helps to tie the reinforced soil mass together one cohesive mass to retain the soil behind. Typically, this 2-couse spacing will allow a lighter weight grid to be used because the forces are shared among more layers of grid. The closer the grid is placed together, the less each layer of grid needs to work to keep the wall standing tall.
When designing a wall using geogrid, there are three main factors that need to be reviewed:
- Grid Overstress: The grid will actually tear or rupture from the forces. This is corrected by adding more grid to the wall (single course spacing) or using stronger grid
- Pullout of Block: The grid pulling out of the block. With an Allan Block retaining wall, pullout of block is rare if built correctly due to the “rock-lock” connection which has extremely high connection strength.
- Pullout of Soil: The geogrid is being pulled from the soil due to the forced pushing on the wall. This can be corrected by using longer pieces of grid or placing the grid closer together.
Using geogrid reinforcement in your retaining wall design is a way to build taller walls that can support tremendous loads. When designing, keep in mind the wall’s internal stability by considering all of the forces acting on the individual layers of grid.
Tom
What is Geogrid?
Thursday, March 26th, 2009
AB 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 Working with Geogrid page on the Allan Block website.
The Magic of Geogrid
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.
For more information on using geogrid with your retaining wall, visit allanblock.com and view the AB Landscape Wall Guide, the AB Commercial Retaining Wall Manual, or the AB Engineering Manual.
Tom
