Soil Reinforcement Chart

When a Retaining Wall Needs Reinforcement

Match your wall to the conditions below to find which width and the number of layers of AB Reinforcement Geogrid you will need. To determine the number of rolls needed, multiply the length of your wall (in feet) by the number of layers needed, and then divide by 50 (the length of a roll of AB Reinforcement Geogrid). Typically most soils will be considered clay,for sandy conditions outlined in the table the soil must be a clean, granular material. Not sure what soil type you have?

Soil Reinforcement Chart for Residential Retaining Walls
Condition Above Wall	WALL HEIGHT**	AB Stones of the AB Collection only
		CLAY SOIL		SANDY SOIL
		No. of Layers	Width (W)	No. of Layers	Width (W)
	3 ft (0.9 m)	0	0	0	0
	4 ft (1.2 m)	2	3 ft	0	0
	5 ft (1.5 m)	3	3 ft	0	0
	6 ft (1.8 m)	4	4 ft	4	4 ft
	2 ft (0.6 m)	1	3 ft	0	0
	3 ft (0.9 m)	2	3 ft	0	0
	4 ft (1.2 m)	2	3 ft	0	0
	5 ft (1.5 m)	3	3 ft	3	3 ft
	6 ft (1.8 m)	4	4 ft	4	4 ft
	3 ft (0.9 m)	2	3 ft	0	0
	4 ft (1.2 m)	2	3 ft	0	0
	5 ft (1.5 m)	3	4 ft	0	0
	6 ft (1.8 m)	4	4 ft	4	4 ft
Condition Above Wall	WALL HEIGHT**	AB Collection (excl. AB Stones), AB Aztec, AB Europa Collection and AB Fieldstone Collection
		CLAY SOIL		SANDY SOIL
		No. of Layers	Width (W)	No. of Layers	Width (W)
	3 ft (0.9 m)	0	0	0	0
	4 ft (1.2 m)	2	3 ft	0	0
	5 ft (1.5 m)	3	4 ft	3	3 ft
	6 ft (1.8 m)	4	4 ft	4	4 ft
	2 ft (0.6 m)	1	3 ft	0	0
	3 ft (0.9 m)	2	3 ft	0	0
	4 ft (1.2 m)	2	3 ft	2	3 ft
	5 ft (1.5 m)	3	3 ft	3	3 ft
	6 ft (1.8 m)	4	4 ft	4	4 ft
	3 ft (0.9 m)	2	3 ft	0	0
	4 ft (1.2 m)	2	3 ft	2	3 ft
	5 ft (1.5 m)	3	4 ft	3	3 ft
	6 ft (1.8 m)	4	4 ft	4	4 ft
** Wall heights are for reference only.
This table is based on clay soil having an internal friction angle of 27° (Ref) or better and a sandy soil having an internal friction angle of 32° (Ref) or better. Soil reinforcement increases the strength of the wall by creating a reinforced mass of soil behind the blocks. The weight of the reinforced soil mass combines with the blocks for a heavier, stronger wall. The table is for estimating geogrid quantities only. For walls in the surcharge loading category above, on the last (top) layer of geogrid, it is typical to lengthen this grid by an additional 2 ft (600mm). To achieve these longer grid lengths, the Allan Block reinforcing grid must be installed perpendicular to the wall (rolled out from the front of the block to the back of the excavated area). * The surcharge loading category above assumes a solid surface such as concrete, asphalt or pavers having a suitable supporting subgrade.

Example:Using a block from the AB Collection, a 5 ft high wall (1.5 m) built in sandy soil with a level surface above the wall requires three layers of geogrid, 3 ft wide (0.9 m), but will require review by a local professional engineer.

AB Reinforcement Grid^™

AB Reinforcement Grid is biaxial which means it has the same strength in both directions and can be simply rolled out along the wall. It is available in 3 ft. and 4 ft. rolls and is 50 ft. long (0.9 m and 1.2 m by 15 m) and is best used for residential retaining walls under 6 ft. (1.8 m) tall as outlined in the table above.

Large roll geogrids are strongest along the roll or machine direction and are cut to the design length. They are best suited for retaining walls over 6 ft. (1.8 m) high.