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:
- 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
