9 Garden walls and gabions
The base under a block retaining wall, and wire mesh baskets filled with stone (gabions): garden walls, low retaining walls, slim fences and screens, benches, planters and pillars. For gabions this chapter covers the stone, the base and the filling.
- 9.1Base for block retaining wallsThe strip under the first course of a block wall. 150 mm of 0–32 mm crushed, 600 mm wide.
- 9.2Choosing gabion fill stoneHard, frost-proof stone bigger than the mesh: usually 100–200 mm. Crushed packs tighter; rounded looks softer.
- 9.3Base for gabion wallsA level, compacted strip of crushed stone at least 50 mm wider than the baskets each side.
- 9.4Filling a gabion basketFill in thirds, brace after each third, hand-place the face and overfill 25–50 mm.
- 9.5Freestanding gabion wallsGarden and boundary walls built from standard 0.5 m wide baskets on a crushed stone base.
- 9.6Low retaining walls with gabionsUp to about 0.5 m of soil with one course; lean the face back, drain behind, and call an engineer above 1.2 m.
- 9.7Slim gabion fences and screensNarrow baskets held up by posts in concrete. Smaller mesh and smaller stone.
- 9.8Gabion benches, planters and pillarsSeats with a timber top, planters lined with geotextile, pillars anchored to a post.
The numbers in this chapter
| Part | Size | Rule |
|---|---|---|
| Fill stone (9.2) | 100–200 mm | Every stone bigger than the mesh opening |
| Mesh (9.2) | 75 × 75 mm | The common welded mesh for 100–200 mm stone |
| Base (9.3) | 0–32 mm or 0–16 mm | Compacted, 50 mm wider than the basket each side |
| Filling (9.4) | ⅓ · ⅔ · full | Brace after each third; overfill 25–50 mm |
| Weight (9.4) | 1.7–1.8 t/m³ | A filled basket, stone and voids together |
| Retaining (9.6) | 6° / 1:12 | Lean the face back into the slope |
Why gabions work
A gabion holds itself up by weight. The mesh keeps the stones together, the stones carry the load, and water runs straight through the gaps, so no pressure builds up behind it. That is also why the stone matters: it must be hard, it must not break down in frost or water, and it must be bigger than the mesh (UFGS 31 36 00). Everything in this chapter is garden scale. A retaining wall over 1.2 m, or one with a drive, a building or a steep slope above it, needs an engineer (9.6). For the block-wall version of a retaining wall, see 9.1; for drainage behind walls, 6.3. Every page cites its sources at the bottom: highway agencies, councils and US federal specifications, never basket makers.
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