When constructing a base for a segmental retaining wall similar to Allan Block, it is typical to use wall rock for base material. For more information on wall rock see Chapter 2, Section 2.4. The base should be 12 in. (30 cm) wider than the block depth. Therefore, the base is typically 6 in (15 cm) deep by 24 in (60 cm). A larger base may be required for poor foundation soils. The wall unit should be centered on the base.
For deeper facing units such as AB Fieldstone, which creates a unit about 24 in. (60 cm) deep with the Long Anchoring unit (LAU), the typical base width would be 36 in (90 cm).
For walls with a deeper than typical minimum sized base, it is common to add a continuous longitudinal layer of geogrid, 3 in (7.5 cm) to 6 in (15 cm) above the bottom of the trench. This geogrid provides additional stability to the compacted base and helps to span lesser quality soils. (ref. BP, Chapter 2.8)
Allan Block is working to achieve our industry initiative of Zero Wall Failures. With our Best Practices Manual and experience in the industry we are trying to expand the knowledge base for the design of segmental retaining walls (SRW's) by communicating and educating the professionals in the industry. To see the full Best Practices Manual, visit allanblock.com to download today and keep an eye out for more industry Best Practice recommendations here.