Retaining Walls for Water
If a “water” retaining wall is what you need, then go with Allan Block – they have all the answers.
-Danelle
Reinforced Walls
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Retaining Wall for Water? Why Not?
Tuesday, January 5th, 2010
Special Retaining Wall Conditions
Thursday, July 30th, 2009I just wrapped up helping an engineer with his design and thought to myself “this is a great wall to blog about.” The wall was nothing spectacular, in fact, it was quite ordinary. All too often we get excited about those monster walls and forget that most of the walls built are less than 10 ft (3 m) tall. What made this wall interesting was the slope below the wall, a parking lot above the wall, and a very tight jobsite. For a detailed look at some of the conditions you need to watch for, see the Conditions page on the Allan Block website.
The first thing we addressed was the slope below the wall. A general rule of thumb is to bury additional block when there is a slope below the wall so you have a minimum level area, or bench, of 5 ft (1.5 m) extending from the toe of the wall horizontally to daylight.
In relation to this slope below the wall, we discussed the potential for a global stability problem. A global stability failure can be defined as the entire hillside slipping and sliding to the bottom of the slope which would obviously take the Allan Block wall with it. Global stability can also be a concern when building terraced walls, working in poor soil conditions, or building near water.
Wall Setback
Finally we discussed the surcharge from the parking lot. A surcharge can range from a sidewalk for a walking path, to a major freeway carrying thousands of vehicles per day. The wall design will be influenced by the expected load of this surcharge and its location in respect to the wall. When the engineer designed the wall in AB Walls 2007, he was sure to include the load from the commercial parking lot on the retaining wall.
Once the local engineer had the wall designed, he used the new “Send Info” button in AB Walls 2007 to send a preliminary material estimate to his local AB Sales Representative. In no time, the sales rep contacted the engineer with a couple AB Certified Contractors that were interested in bidding the job.
As I mentioned, this was by no means a monster wall, but it did demonstrate a few of the conditions that need to be considered when designing your retaining wall. For additional information, please visit allanblock.com or your local engineering professional.
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
