A gabion wall is a stack of wire mesh baskets filled with rock: galvanized wire of 2-3 mm in a 10 cm by 10 cm grid, filled with rock of 10-20 cm, stacked like bricks and tied to the course below with wire. Use rock bigger than the 10 cm mesh opening so stones cannot fall through, fill each basket in place, and set the bottom row on a level, compacted bed. The wall lets water seep slowly through, flexes with ground movement and suits stream banks and retaining walls.
Part of Flood Control and Drainage
A gabion is a wire basket filled with stone, used as a building block for walls that must be strong, permeable and flexible. It is the usual alternative to a masonry wall where ground can move.
The Wall Works Because It Lets Water Through And Bends Without Breaking
A masonry wall that holds water back builds up pressure behind it and cracks if the ground shifts. A gabion wall passes water slowly through its rock fill, so pressure does not build, while the soil and debris are held back. Its wire mesh lets the whole wall settle and bend with the ground instead of cracking. It is also very durable.
The wire is the weak link. Galvanizing protects it for years, but a wall in acid or salty water will corrode sooner, so use it for the life of the wire and plan its replacement.
What You Need
- Wire mesh — 2-3 mm galvanized wire in a 10 cm by 10 cm grid, formed into open-topped baskets.
- Rock — 10-20 cm across, hard and durable, such as quarry spall or river cobble. Reject stone that crumbles or splits when struck.
- Tie wire — to join baskets and lace courses.
- Pliers, gloves and a crowbar — for wire and rock work.
- A level bed — compacted and graded.
Method: Build A Gabion Wall
Step 1: Prepare the bed. Dig a level footing, compact it and shape it so the bottom row does not slide. A basket on a slope will slump.
Step 2: Set and tie the baskets. Place the baskets side by side and tie adjacent baskets together along every edge.
Step 3: Fill in place. Fill each basket with rock after it is positioned. Place the outside face by hand so the stones interlock, and fill the middle behind them. Overfill slightly, since the rock settles.
Step 4: Close and tie. Fold the lid over and wire it down. Tie across the basket from front to back at a few points so the face cannot bulge.
Step 5: Stack like bricks. Offset each course so joints do not line up, and tie it to the course below with wire.
Step 6: Backfill behind a retaining wall. Fill with free-draining gravel so water behind the wall can escape through it.
Worked Example: Check The Rock Against The Mesh
- Mesh opening: 10 cm.
- Rock size allowed: 10-20 cm.
- A 10 cm stone is no bigger than the opening, so it can pass through a stretched or open mesh. A 15 cm stone cannot.
So use the larger end of the range, 15-20 cm, for the face, and keep the 10 cm stones for the middle, where they are held by other rocks. As a size check on a basket 1 m x 1 m x 0.5 m: its volume is 0.5 m3, and with an assumed 35 percent void space the rock mass is 0.5 x 0.65 x 2,600 kg/m3 = 845 kg, assuming rock of 2,600 kg/m3. A filled basket weighs roughly 850 kg, which is why it is filled where it stands and never lifted full.
Common Mistakes
- Rock too small for the mesh — stones fall out. Use rock larger than the opening.
- Filling a basket then moving it — it is far too heavy and deforms.
- Untied courses — courses slide against each other. Tie them.
- Wall on a soft or sloping bed — it slumps or tilts. Prepare a level bed.
- No drainage behind a retaining wall — water builds up and pushes the wall out.
Safety
Wire cuts and heavy rock
Cut wire ends are sharp, and a filled basket weighs about 850 kg in the example above. Wear gloves, wear eye protection when cutting wire, lift rock with a partner or a lever, and never stand downslope of stones being placed. A wall at a stream bank means working beside moving water, and about 15 cm of fast-flowing water can knock an adult off their feet.
What’s Next
- Learn next: Riprap — loose rock armour instead of caged rock
- Combine with: Earth Berms — a gabion face on an earth bank