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What’s going on behind the wall?

Thursday, April 23rd, 2009

Last 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:

  1. 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
  2. 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.
  3. 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

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Structural Testing Provides Support for Cost Efficient Designs

Thursday, January 15th, 2009

As an engineer, I tend to be conservative. I need some proof before I will stray from the most conservative design possible. The problem with a conservative design however, is that it tends to make the cost of a project much higher. Any time a new product is introduced to the marketplace, the engineering community naturally chooses the side of structural stability over a less costly design, and it was no different when Allan Block introduced the AB Fence System.

AB Fence Testing

AB Fence Testing

Allan Block agreed that a very conservative design approach should be used until the system underwent very thorough testing. Even with the conservative designs, the AB Fence System was a more cost friendly product than competitive fencing systems, but the AB engineers knew that the system had vastly greater structural capabilities than were being assumed in the engineering community.

So they teamed up with the University of Calgary and with Stork/Twin City Testing to put the system through rigorous testing to show the kind of loading it was actually capable of handling. The structural component testing and full-system testing outperformed even the expectations of the engineers at Allan Block. The result? Now a typical AB Fence design, while still very structurally sound, is much more cost effective. This makes the AB Fence system by far the best option for sound abatement, security fencing, and other applications for anyone who wants a reliable and safe structure without spending a fortune. And as an engineer, I’m all for that!

Steve

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