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9.3 Base for gabion walls

The compacted strip of crushed stone every gabion stands on. It stops a heavy basket from sinking or leaning.

Cross-section of a gabion basket 500 mm wide standing on a compacted crushed stone base 200 mm thick that reaches at least 50 mm past each side, on non-woven geotextile, set slightly below the ground. basket + 50 mm each side 1 Compacted base 0–32 mm, 200 mm 2 Geotextile non-woven, under the base 3 Gabion set level, slightly sunk
Cross-section of a garden gabion on its base.

At a glance

Difficulty
2 of 4
Time
Half a day for 5 m of wall
Tools
Spade, string line, rake, plate compactor or hand rammer, long spirit level, straight board
Parts
  1. 1  Geotextile
  2. 2  Compacted base
  3. 3  Gabion

What you need per metre of wall, 500 mm wide baskets, 200 mm base

MaterialSizeTypeAmount
Base 0–32 mm Crushed, with fines 250 kg
or 0–16 mm / 0–19 mm Crushed, with fines
Geotextile – Non-woven, separating 0.8 m²

Why crushed with fines?

0–32 mm

The fines fill the gaps, so the base compacts hard and stays flat under a heavy basket. A Canadian city builds its park gabion walls on 200 mm of compacted 0–19 mm crushed stone; a UK council asks for compacted well-graded granular fill.

not 16–32

Clean stone without fines rolls under load and cannot be screeded flat. Use clean stone behind a retaining wall to drain it (9.6), not under the baskets.

Step by step

  1. 1

    Mark out the base 50 mm wider than the baskets.

    Add at least 50 mm on each side; for a 500 mm basket, a 600 mm strip. For a retaining wall, use the width of the bottom basket.

    The strip marked with string
  2. 2

    Dig out topsoil and soft ground.

    Dig to firm ground, deep enough for the base plus a little of the basket. Garden walls are often set just below the surface; retaining gabions are buried 300–500 mm (9.6). Replace soft spots with compacted fill (2.3). Never build on frozen ground.

    The dug trench
    The dug trench Illustration
  3. 3

    Lay geotextile, then the base in layers.

    Non-woven geotextile keeps the soil out of the base. Spread the crushed stone in layers of about 100 mm and compact each one until the plate leaves no mark.

    Compacting the base
    Compacting the base Illustration
  4. 4

    Screed it level.

    Level along the wall and across it. For a retaining wall, let the base fall back into the slope, at most 1 in 10. On a slope along the wall, step the base in whole basket heights.

    Screeding the base
Specifications
PartMaterialThicknessHow
1 Geotextilenon-woven–Under the base and on buried faces
2 Base0–32 mm or 0–19 mm200 mmCompacted; at least 50 mm past the basket on each side
3 Subgradefirm soil–Firm and unyielding; soft spots replaced and compacted

Width

At least 50 mm wider than the basket on each side (Hertfordshire).

Thickness

200 mm of compacted 0–19 mm crushed stone under a park wall of 1.0 m baskets (Winnipeg). The council and highway drawings for retaining walls leave the thickness to the designer.

Level

Level for freestanding walls. For gabion retaining walls the prepared foundation may slope back at most 1 in 10 (Cessnock). Iowa DOT asks for a firm, unyielding subgrade compacted to 95 % of standard Proctor; no foundation work on frozen ground (UFGS).

Depth

Retaining gabions are buried 300–500 mm (Hertfordshire). Highway walls go 0.6 m into soil (FHWA E253-01); that is beyond garden scale. Playground baskets in Winnipeg sit 50 mm below the ground.

Sources

  1. Hertfordshire County Council, standard drawing HST-0600-001 Typical gabion retaining walls: fill graded 100–200 mm; welded mesh 75 × 75 mm; retained height 350–550 mm with one 1.0 × 1.0 m gabion, up to 1.5 m with a 1.5 m wide gabion under a 1.0 m one; gabions buried 300–500 mm; face batter 6°; foundation of compacted well-graded granular fill or concrete, at least 50 mm wider than the basket on each side; bracing wires after ⅓ and ⅔ of the height, end units braced both ways; no compartment more than 300 mm higher than its neighbour; exposed faces hand packed; vertical joints staggered; slight overfill where gabions are stacked; geotextile behind the gabions and on all buried faces
  2. City of Winnipeg, park landscape detail drawing L6 (tender 475-2016): freestanding park wall of 2.0 × 0.5 × 1.0 m baskets with 75 mm mesh, top 600 mm above ground; fill 100–200 mm field stone, no limestone; 200 mm of compacted 0–19 mm crushed base on non-woven geotextile; gabion seat of 0.5 × 0.5 m baskets on the same base with a timber top bolted to a steel plate; playground baskets set 50 mm below ground
  3. Cessnock City Council (NSW), AUS-SPEC 0294 Gabion walls and rock filled mattresses: rock sized for at least three layers in a gabion; 1 m gabions filled in three layers with bracing after the first and second; 500 mm gabions in two layers of 250 mm; bracing wires at 330 mm; exposed faces placed by hand; overfill 25–50 mm; prepared foundation sloping at most 1 in 10; geotextile between gabions and retained soil; heavy plant kept 1 m from the units
  4. Iowa DOT Standard Specifications §9050, Gabions and revet mattresses: lifts of at most 300 mm; stones turned by hand after each lift; connecting wires not needed in gabions up to 450 mm tall; two wires on each exposed face of each cell between lifts, about 300 mm apart; overfill 25–50 mm; firm, unyielding subgrade compacted to 95 % of standard Proctor
  5. US Department of Defense, UFGS 31 36 00 Gabions: rock 100–200 mm for gabions 500 mm and taller, large enough not to pass the mesh; at most 5 % oversize or undersize, undersize only inside, never on the face; room for three or more layers of rock per compartment; hard, angular to round, durable rock that does not break down in water or weather, with freeze-thaw testing; at most 5 % dirt, sand, clay and fines; 300 mm lifts, no cell more than 300 mm higher than its neighbour; stiffeners at ⅓ and ⅔ of the height; hand-placed visible faces; drop height at most 0.9–1.2 m; overfill 25–50 mm; no foundation work on frozen ground
  6. FHWA Federal Lands, standard drawing E253-01 Gabion retaining wall: rock-filled gabions weigh 110 lb/ft³ (about 1.75 t/m³); front face battered 1:12; underdrain at the back with outlets
  7. FHWA-RD-97-148, Granular base: natural aggregates weigh about 2.0–2.3 t/m³ in place
  8. EN 13242 Aggregates for unbound and hydraulically bound materials

Amounts: base 0.6 m × 0.2 m = 0.12 m³ compacted per metre of wall. Compacted crushed stone is taken as 2.1 t/m³, the middle of the 2.0–2.3 t/m³ range FHWA gives for natural aggregate in place: 250 kg. Geotextile 0.6 m wide plus overlap.

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