A geogrid or geotextile is a very strong woven material that is sandwiched between courses of block and laid flat back into the excavated area behind the wall (a wall needing geogrid must be excavated much wider than the width of the wall units to accommodate the laying of the grid). Soil is placed over the top of the grid and compacted, essentially weaving the grid into the soil, making the wall unit and the soil behind it a unified retaining wall, capable of retaining much greater volumes and weights.

Retaining walls in excess of 4' or that have a surcharge applied to the top side of the wall (like a driveway, street or parking lot) need geogrid.