Geogrid & Wall Drainage

Geogrid and retaining wall drainage. Geogrid reinforces the soil behind a segmental retaining wall so the wall and the earth act as one mass rather than the blocks resisting the load alone. Above roughly 3 to 4 feet, most block manufacturers require it, and most engineered designs specify it.

Geogrid Basics

• Biaxial grid has similar strength in both directions, used for base stabilization over soft soil
• Uniaxial grid is far stronger in one direction, used for wall reinforcement running back into the fill
• Layer spacing and embedment length come from the wall design, not from a rule of thumb
• Grid must be pulled taut and covered with compacted fill, slack grid does nothing

Drainage Is What Actually Fails Walls

Most retaining wall failures are water failures, not block failures. Water builds up behind the wall, hydrostatic pressure develops, and the wall pushes out. Drainage aggregate, a drain pipe and non woven fabric that lets water through are what prevent that.

• Use non woven fabric behind walls, not woven weed barrier
• Woven fabric slows drainage and makes the problem worse
• Drain to daylight wherever possible
• See landscape and drainage fabric for the full range

When to Get an Engineer

Walls above about 4 feet, walls with a slope or structure above them, and walls holding back a driveway generally need an engineered design. Geogrid layout is part of that design. If you are unsure, that is the point to ask rather than guess.