Gabion and crib retaining walls
Gabion baskets and crib walls hold back ground by weight and by being free draining, which makes them well suited to slopes and wet sites. We design them as gravity structures with the stability and drainage checks that prove they work, for clients across the UK.
Do gabion walls need a structural engineer?
For low decorative baskets a supplier detail may be enough, but as soon as a gabion or crib wall retains a real height of ground, supports a surcharge or sits on a slope it needs stability calculations. We design it as a gravity retaining structure and check sliding, overturning, bearing and slope stability to Eurocode 7.
How gabion and crib walls work
A gabion wall is a stack of steel wire baskets filled with hard, angular stone, and a crib wall is an open framework of interlocking timber or concrete units filled with granular material. Both are gravity retaining structures: they hold back the soil by their own considerable weight and by the friction between courses, so the design is about mobilising enough mass and width for the height being retained rather than reinforcing a thin stem. Because they are built from discrete units they can also flex and settle a little without cracking, which suits variable ground.
Their great advantage is that they are free draining. Water passing through the retained soil runs straight out through the stone fill instead of building up behind a solid face, so the hydrostatic pressure that fails so many masonry and concrete walls simply does not develop. That makes gabions and cribs a natural choice for wet ground, watercourses, embankments and slope stabilisation, as well as landscape walls where the stone-filled or planted face is wanted for its own sake.
Designing for stability
Even as a gravity structure the wall has to be proven against the same failure modes as any retaining wall. We check sliding along each course and along the base, overturning about the front toe, and the bearing pressure the wall imposes on the ground beneath, all to Eurocode 7 with the retained soil and any surcharge from ground, traffic or buildings above. The width at the base is set so the resultant of the weight and the earth thrust stays within the middle of the base and no course wants to slide or tip.
Gabion and crib walls are usually built with a batter, a backward lean or a stepped face, which throws the weight back over the retained soil and improves stability for a given volume of fill. On sloping sites we also check the overall stability of the whole slope, because a wall that is internally stable can still slide if the ground it sits on fails on a deeper surface. The stone grading, basket mesh and wire coating are specified to suit the exposure so the wall keeps its strength over its design life.
Fill, facing and detailing
The performance of a gabion depends on the fill and the baskets. We specify hard, durable, angular stone in a grading that locks together and will not wash out through the mesh, a heavily galvanised or polymer-coated wire to resist corrosion, and the lacing or fastening between baskets that ties the stack into one mass. A geotextile filter is detailed on the retained face so fine soil cannot migrate into and through the stone over time, which would otherwise let the ground behind slump.
Detailing sets how the wall meets the rest of the site. We design the foundation or levelling course the wall sits on, the transition where a gabion wall meets a building or a different wall type, and any planted or vegetated crib face where a green finish is wanted. The calculations and drawings are prepared to Eurocode 7 and delivered to clients across the UK, so a landscape or groundworks contractor can build the wall correctly wherever the site is.
What we check.
The points our calculations resolve for a project like this.
- Gravity stability against sliding, overturning and bearing
- Free-draining stone fill removing hydrostatic pressure
- Batter or stepped face to throw weight back over the soil
- Overall slope stability on sloping and embankment sites
- Stone grading, mesh and wire coating for the exposure and life
- Geotextile filter stopping fine soil migrating through the fill
From enquiry to sign-off.
Enquiry
Send drawings or describe the problem. We confirm the scope, the deliverables and a target timescale.
Information
We agree the survey, drawings or data we need and any site access required.
Engineering
Design, calculation or assessment to the relevant Eurocodes and UK National Annex.
Issue
A clear, defensible report or set of calculations, with assumptions and limitations stated.
Common questions
Do gabion walls need a structural engineer?
For low decorative baskets a supplier detail may be enough, but as soon as a gabion or crib wall retains a real height of ground, supports a surcharge or sits on a slope it needs stability calculations. We design it as a gravity retaining structure and check sliding, overturning, bearing and slope stability to Eurocode 7.
Why do gabion walls not need separate drainage?
Because the stone fill is free draining, water in the retained soil passes straight through the wall instead of building up behind a solid face. That removes the hydrostatic pressure that fails many solid walls, which is why gabions suit wet ground and watercourses. We still detail a geotextile filter so fine soil is not washed through.
How high can a gabion wall be built?
Gabion and crib walls can be built to several metres, but the base has to get wider and the batter steeper as the height grows, because they resist the soil by weight alone. Beyond a certain height a reinforced soil or reinforced concrete solution can become more economic, and we advise where that crossover falls for your site.
What stone should fill the baskets?
Hard, durable, angular stone in a grading that locks together and is too large to wash out through the mesh, typically a clean crushed rock. The exact size suits the basket and the exposure. We specify the stone, the wire coating and the geotextile so the wall keeps its strength and shape over its life.
Tell us what you are building.
Send the drawings or describe the project. We confirm scope, deliverables and a realistic timescale.
Start a project