Gabion Wall Standard Design

Author: wenzhang1

May. 06, 2024

Gabion Wall Standard Design

Gabion Standard Design

                

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Fine Mesh Metals Ltd are not structural engineers. The designs on this page are suggestions based on industry standard designs. Gabion wall designs are very robust. These designs in general are the basis for any designs produced by structural engineers. However, there are ground types and situations where the deigns will not be sufficient. If your situation involves having a building, road etc on top of it, or you are putting them on very soft clay, then it would be advised to contact a suitably experienced and qualified Consulting Engineer, thus ensuring the most appropriate advice being provided and supported by professional indemnity insurance. This has implications in respect of Health and Safety being adequately addressed. The client has an obligation to ensure all persons engaged in the undertaking of the works are suitably experienced and qualified, thus being familiar with the construction process and associated risks to health and safety.

A Consultant engineer will require.

a.       A topographic survey to conclude wall height and any slope surcharge which could similarly influence the gabion arrangement.

b.      Proposed wall location.

c.       Ground investigation to conclude retained and foundation soils and associated geotechnical parameters.

This is an additional cost and we can direct you to a Consultant if you require.

The designs given on this page should not be used as a substitute for taking detailed and specific advice from a Consultant engineer. The recommendations and advice are given without Liability on the part of Fine Mesh Metals Ltd and should not be relied upon for any action or inaction.

Fine Mesh Metals Ltd shall not be liable to compensate any other party for any loss, including any consequential loss, arising from following the standard designs.

Standard Designs

The standard designs for gabion baskets are very robust, "Belt & Braces". In the Welded mesh variety sold by ourselves, we (at Fine Mesh Metals Ltd) have never seen a failure of a wall installed and filled correctly.

Affect of load behind wall:

A load such as a Carpark for normal vehicles adds a surcharge of 2.5kN/m2, which should not cause any issues with the standard designs.

A road behind the wall, which allowed access to HGVs, would increase the surcharge to 10kN/m2. We would  advise you take advice from a consultant if this is the case, or if a building is within 3m of the retained wall. This distance depends on the soil conditions.

Footings/foundation:

(Please see Note 1 below for a more detailed explanation)

Construction Design Standards suggest that a 500mm trench be dug to allow for future excavations in front of the wall. This also gets below the frost layer, and provides a toe in to stop the baskets slipping (this toe in is not normally used within the structural calculations for the standard designs). Another reason for this is that the top soil contains organic matter that may rot or compress. The majority of installations for short walls are started at ground level, it is down to the customer to make a decision on site looking at the ground conditions.

The worst material for gabion walls to sit on is soft clay. If the ground is likely to sink under baskets weight, a gabion retaining wall may not be possible.

100-200mm of hardcore (type 1) should be compacted with a vibrating plate as a footing for the gabion wall. If 200mm was put in the 500mm deep trench the baskets would start 300mm below ground.

Baskets should be lent back at 6 degrees. BS8002:2015(7.3) Cl. 5.3.3.2 states that A gabion wall should be built to a batter to increase its resistance to overturning and sliding. 

The Face of a gabion wall can be flushed or stepped. On taller walls baskets are stepped back to equalize the pressure between the heel and toe of the wall.

Gabions can be cut on site to achieve your required dimensions.

The standard thickness for walls up to 3m in height is 3mm. 4mm is the architectural spec, 5mm is what we would refer to as the military spec or for use on higher walls.

For inexperienced installers we recommend adding a 4mm face for walls 3m and below, this reduces the risk of bulging.

The selection of wire diameter is not straight forward. Below photos include examples of gabion retaining walls up to 10.0m high and constructed using various wire diameters.

BS8002:1994(7.1) comments that The life of a gabion wall is not necessarily limited by the effective life of the cage or basket if the shape of the wall is such that the stone filling remains substantially stable after failure of the cage

And Small gabion walls should be designed on the same principle as a gravity mass wall, no allowance being made for the strength or mass of the wire mesh.

Type of infill stone i.e. rounded or flat and quality of construction can greatly impinge upon the requirement for the stone filling to remain substantially stable after failure of the cage and for the wall to remain a coherent mass with no allowance being made for the strength or mass of the wire. A good standard of infill stone selection and placing notably in the manner intended to ensure the satisfactory performance and serviceability of the installation.

The selection of wire size is thus dependent upon:

  • Size and type of infill stone.
  • Standard of construction.
  • Wall height

The use of stone and construction practice not usually associated with gabion wall construction will have an influence on the performance, serviceability and overall life of the installation.

A cost saving option is to put a false partition in the front of the basket. This way the front can be hand laid with a high quality stone like slate. the back can then be back-filled with a low quality material for example reclaimed brick. However it is worth noting that it is unlikely that the use of low quality or smaller stone behind hand laying partitions would provide the stability of the specified gabion infill stone and as such the service life of the wall is likely to be affected.

Geotextile materials including that of Terram are permeable and will not prevent the passage of water through a gabion retaining wall.

The use of a gabion wall to support a building foundation would not be acceptable due to the flexible nature of a gabion. Alternative forms of building foundation should be considered in the event that the proximity of the building and associated traditional foundations are within the near vicinity of the rear of the gabion wall ,where soil strains and hence movements are likely to occur.

Considerations in Respect to Health and Safety

It is paramount when undertaking such works, to ensure that the construction can be undertaken with due regard for the health and safety for all concerned. In this regard the requirements of the Construction (Design and Management) Regulations 2015 herein referred to as CDM Regs apply. These requirements also apply to domestic clients. There have been many incidences of both injuries and fatalities associated with the undertaking of construction works in conjunction with excavations. These have occurred where vertical or near vertical excavated faces have been provided, and of which have either been unsupported or poorly supported, or where temporary unsupported excavated slopes or batters have been provided, which are too steep to remain stable. The influence of other factors which give rise to the potential for instability should also be included in considerations. These factors include, but are not limited to, water ingress, storage of materials, passage of vehicles.

The use of temporary propping to an excavated face in conjunction with earth retaining wall construction is generally not practical due to the restrictions presented working. The use of a temporary unsupported excavated slope or batter is typically employed and at a gradient of 45 degrees, albeit subject to site conditions. This scenario is the basis of calculation for the standard designs ,where the gap behind the wall is filled with angular material. The angular back-fill should be max of 40mm, so as to be compressed with a vibrating plate without needing heavier equipment, (type 1 would be suitable). If you wish to lawn on top of the back-fill 150-200mm of top soil would be advised with a geotextile underlay to stop the soil drying out. If you wish to plant shrubs a deeper soil pocket will be required. 

Highways classify angular back-fill as Class 6N which can be up to 125mm however this will require much heavier machinery to compress and will affect the design of the gabion wall.

1m high wall

A 1m high wall is very simple it can be made of 1m x 1m x 1m or 2m x 1m x1m baskets. The smaller is recommended if the length you have to cover is small as it will reduce transport costs. We can also use 1/2m deep baskets this will save on the cost of fill but will reduce the strength of the wall and is recommended only in situations where the bank is fairly stable. You can also use 1m high walls for terracing a garden in steps. We also provide sets of steps for this scenario.

It is standard to use 3mm wire thickness as the baskets have little weight exerted on them.

 

2m high wall



Gabion baskets are a mass retaining system thus, the higher the area that needs retaining, the heavier the wall must be. The standard design for a gabion wall is a pyramid. In general, for every 1m increase in wall height, the bottom row basket depth should be increased by half a metre.

For a 2m high wall the bottom row should be 1.5m deep and the top row should be 1m deep.

It is still standard to use 3mm wire thickness for both rows.


This can be made more stable by setting the top baskets slightly further back.

3m high wall

In this example the top 2 rows are the same as a 2m wall but with a .5m increase in the depth of the bottom row.

The bottom row is 2 metres deep middle row 1.5m deep and top row 1m deep. Normally we use 2m x 1m x 1m baskets bottom row 1.5m x 1m x 1m baskets in the middle row and 1m x 1m x 1m or preferably 2m x 1m x 1m baskets going sideways on the top row.

At this height there is quite a lot of weight exerted on the bottom row and unless the bracing ties are installed correctly there is a possibility that the face of the bottom row might bulge out. You may prefer to use 4mm thick wire on the bottom row rather than risk this. If the look of the wall is important than we would then put a 4mm thick face on the 3mm thick top row baskets. This will save on costs of having all baskets in 4mm.

Any higher than 3m you can still use the same principal of increasing the depth by .5m but it may be preferable to stagger the baskets back and getting a structural engineer to assess the stability of the site would be a preferable option.

Curved wall: Staggered effect using 1m or better .5m wide baskets



There are 2 types of curved walls inside and outside bends. When the wall curves around you when looking at it (inside bend ) this can be achieved easily using standard baskets angled away from each other. The wedge shaped gaps that are left are fixed using extra panels that are cut to size and wired in on site.

Outside curves are more difficult and require the gabion to be tapered inwards. This is achieved by taking the side panels off the baskets and sitting the baskets within each other. The lids can be folded or overlapped.

 

River erosion

Depending on the depth and speed of the river, different designs are appropriate. In general there is a worry that the river will undercut the baskets if using a standard wall. It is normal to use a gabion mattress (a short basket normally 3m x 2m x .3m high) that goes into the stream and underneath a standard wall. The standard wall does the retaining whilst the mattress stops the foundations being eroded.

It is recommended for installations that either will be or the likelihood exists for the gabions to be submerged either in standing or flowing water for a non woven needle punched geotextile permeable filter membrane be incorporated to the rear of the gabions. This will prevent the migration of fine particles from retained soils becoming washed through the gabions which could result in settlement or voids or cavities occurring with the potential for damage to any retained surfaces. A typical geotextile for this purpose is Terram T1000 or similar. However the actual material must be selected to ensure its characteristics are compatible with insitu soils. Geotextile membranes are available on our gabion pricing page.

 

Flood Protection

Gabion Baskets are permeable so that water can come through them, this stops a build up of water behind them and the ground becoming waterlogged. It is possible to stop water coming through by lining the baskets with a geotextile material, such as Terram. You can have a thin cladding wall basket in front of this so it is not visible. The flood protection offered is only as good as the installation and all joints must be sealed. Care must also be taken to ensure the plastic isn't torn or damaged. Water can still get around the sides of the baskets. This is only suitable in specific location.

Note 1

Considerations in respect of the noted 500mm trench is in respect of ‘Unplanned excavation’. BS8002(7.1) states:-

In checking the stable equilibrium and soil deformation, retaining walls should be designed assuming a depth of unplanned excavation in front of the wall. The depth of the excavation should be not less than 10% of the total height retained for cantilever walls or of the height retained below the lowest support level for propped or anchored walls, but the depth of the excavation may be limited to 0.5m. This recommendation for an addition excavation as a design criterion is to provide for unforeseen and accidental events. The recommended values should be reviewed for each design; more adverse values should be adopted in particular critical or uncertain conditions but smaller values may be adopted where adverse conditions are beyond reasonable doubt. Foreseeable excavations such as service or drainage trenches in front of a retaining wall, which may be required at some stage in the life of the structure, should be treated as a planned excavation. Actual excavation beyond the planned depth is outside the design considerations of this code.

The following is of note:-

  • In checking the stable equilibrium and soil deformation, retaining walls should be designed assuming a depth of unplanned excavation in front of the wall
  • This recommendation for an addition excavation as a design criterion is to provide for unforeseen and accidental events.
  • The recommended values should be reviewed for each design;
  • Foreseeable excavations such as service or drainage trenches in front of a retaining wall, which may be required at some stage in the life of the structure, should be treated as a planned excavation

 

BS 8002: 1994(7.1) has as noted been superseded and withdrawn and replaced by Eurocode 7 (7.2) and BS8002:2015(7.3).

The following is noted with reference to Eurocode 7(7.2) :-

Cl. 9.3.2.2 Ground Surfaces

(1)P Design values for the geometry of the retained material shall take account of the variation in the actual field values. The design values shall also take account of anticipated excavation or possible scour in front of the retaining wall.

Cl. 9.3.2.2 (2) discusses considerations in respect of cantilever and supported walls where stability is dependant upon ground resistance in front of the structure and lowering by an amount defined as Δa.

BS8002:2015(7.3) Cl. 4.6.4 – Unplanned Excavation comments on the requirements of Eurocode 7 Cl. 9.3.2.2 (2) i.e. notably in respect of cantilever and supported walls.

The design of gravity retaining walls e.g. gabion earth retaining walls are required to comply Eurocode 7 Clause 9 and Clause 4 and Clause 5 of BS8002:2015 notably Eurocode 7 Cl. 9.3.2.2(1)P in respect of unplanned excavation.

In the design of a gravity earth retaining wall e.g. gabion wall we are required to consider all aspects which would affect the normal serviceability and performance of the wall. Such considerations would include but not limited to:-

  • Ensuring that the wall formation level is not located in soil containing organic matter as such materials are subject to volumetric change due to degradation which could give rise to movement and potential instability in the wall. Similarly non engineered fill i.e. made ground which could include either non compacted or poorly compacted material and material subject to volumetric change due to degradation.
  • The wall formation is at a level where foundations soils are not subject to volumetric change due to frost heave and thaw, i.e. typically 450mm below ground level.

It is of note that a gabion earth retaining wall is flexible and can accommodate differential settlement and movement without structural distress. Criterion normally associated with rigid structures e.g. brick in particular the requirement to provide the foundation formation at a depth below a level where volumetric change due to seasonal variation in moisture can occur notably in clay soils where a minimum depth of 900mm is required, is not applicable to a flexible gabion earth retaining wall.

Any resistance to sliding provided by ground to the face of the wall is typically ignored in design due to the potential for such soils to be non-engineered, potentially partly organic and not always present when construction of the wall is completed.

The incorporation of the foundation formation at 0.5m below finished ground level to the face of the wall would satisfy the requirement to:-

  • Maintain stable equilibrium and soil deformation
  • Avoid potential disruption due to frost penetration
  • Typically be below the depth of any organic soil.

Commencement of construction of the gabion wall directly upon the excavated soil surface is likely to prove unacceptable due to excessive irregularity. The use of a well graded granular material such as SHW Type 1 compacted to ensure a dense stable mass or concrete would provide a suitable blinding/levelling medium and thus maintain acceptable wall alignment. Both materials can be considered non-frost susceptible and as such complying with the requirement to avoid potential disruption due to frost penetration.

Soils at and below formation level are significant in concluding the suitability of a mass gravity retaining wall including a gabion earth retaining wall. Some soils e.g. soft and very soft silts and clays and soils containing organic matter are unlikely to demonstrate satisfactory geotechnical characteristics necessary to provide and maintain the satisfactory design, performance and serviceability of the wall. Some loose cohesionless materials e.g. sands and gravels can similarly prove unacceptable unless treated.

 

Example Images of good stone placing in stepped and flush walls

A 6m high flush faced gabion wall

 

A 10m high flush faced gabion wall

A stepped gabion wall on a curve

A good example of stone placing when filling a gabion

If you want to learn more, please visit our website woven gabions.

Further reading:
5 Reasons ODM Star Pickets Outperform the Competition

A close up of a good gabion stone placing

Narrow gabion facing to sheet piling

Gabion Wall Frequently Asked Questions, Guidlines For ...

Gabion Wall Frequently Asked Questions

What Are Gabions?

Gabions are wire mesh containers constructed from galfan coated steel, filled with hard rock, stone or other materials including reclaimed and recycled aggregates.

Gabions are made up from various sized panels which are formed up into a box. The panels are connected together with either spiral / helical wire or with C-Rings applied by pneumatic hand tool.

Gabion walls are considered a gravity wall system.

Gravity walls depend on their own mass or weight to withstand pressures from behind the structure, in this case weight (rock) held within the gabion container.

The containers are linked together when assembled which creates an individual structure. Once the gabions are linked the strength of the structure increases significantly. This allows the user to form walls for retaining land, eliminate erosion, control water speed, support river banks and many other applications.

Gabion walls are popular in modern day landcape designs because they look fantastic, offer longevity, zero maintenance, eliminates drainage pressures plus they are cheap to install and are able to withstand significant pressures without deforming due to their flexibility.

Gabions have become popular as architectural features such as seating, cladding, pylons, feature walls, planter boxes and more.

Are Gabions Cost Effective

Gabions are considered a cost-effective solution to most situations. There are 2 main gabion types being woven diamond wire typically used in large scale civil projects (less expensive) and weld mesh type cages, made from 4mm welded panels commonly used for landscape and architectural applications where longevity and high aesthetics are important.

Century Gabions are weld mesh design, typically used by engineers, landscapers, architects and DIY users for their superior form and functionality.

What Type Of Rocks Do I Use?

For most gabion projects the recommended rock fill size range is between 75mm-150mm.

Generally a basalt rock would be used to fill gabions. Basalt is hard and durable, capable of withstanding weight loads typical with gabion structures.

For smaller non structural gabion projects, try using other types of rock or stone based on colour, texture or availability.

We suggest getting in touch with your local landscape yard or quarry to discuss suitability and availability based on geographic location.

How Long Do Gabions Last?

As noted above there are two types of gabion basket construction, woven and welded. Woven baskets are manufactured with 2.7mm wire while weld mesh gabions are manufactured with 4mm wire.

Woven baskets are less expensive however provide less life cycle.

The origin (country of manufacture) and coating type also plays a significant part in the life span of gabions.  As an example low cost gabions from China have much lower steel strength and low quality coating type and density.

Galvanised gabions may last from 5 to 10 years. where as Century Gabions with galfan coating will last anywhere from 50-100 years .

The 2 Common Coating Types

Galvanise

Galvanise coated wire is typically used in fencing and general purpose applications in Australia.

Galvanise coating works fine in light duty applications however does not meet industry standards for gabion structures. Effectively the galvanised coating has a short life cycle and this could prove catastrophic if the mesh panels fails after construction.

Tests have proven material which originates from China. shows significant corrosion after a short period of time and weld points were weak, in fact could be popped off the cross wire with little pressure.

Reports from engineers have been similar, in some instances gabion structures constructed with non compliant gabions have been removed from project sites for safety reasons.

If the material is imported from China it simply will not conform to Australian / International standards.

Our motto is : ” The Cost Of Replacement Is Far Greater Than Doing It Correctly First Time Round”.

If your unsure about quality while shopping around – request a manufacturers data sheet or mill data sheet.

There are numerous websites making false claims about quality and longevity of their mesh as being compliant to Australian Standards, we have learned that most are cheap imported galvanised fence panels.

Century Mesh & Century Gabions not only meets Australian standards but far exceeds them and we maintain direct relationships with the manufacturers for data sheets and certifications.

The below image shows rapid corrosion of galvanised mesh used in gabion wall. This corrosion was present in 3 years after installation.

Galfan Coating

Tech Guide | What Is Galfan Coating

Gabion Mesh Wire Diameter

Another mis conception is wire diameter. The industry standard is 4mm. 

In short Century Gabions have higher tensile strength, weld strength and shear strength than any other mesh on the market for gabions. Couple this with genuine galfan coating and 50×100 aperture and now we’re talking the highest spec batch manufactured mesh in Australia.

A 5mm option will only offer benefit provided it’s manufactured to the same spec as Century Mesh.

Most providers of 5mm gabions typically fall back under the umbrella of Chinese mesh. The increased diameter therefore offers no advantage.

The mesh remains very low carbon steel, low tensile strength, low shear strength, weak weld points and questionable coating type and coating density.

The below image shows 4mm galfan coated wire versus 5mm galvanised wire. Both items were tested in tidal water  side by side, same length of time, at the same location. The galvanised mesh shows significant corrosion

Galfan Coating

Tech Guide | What Is Galfan Coating

Do Gabions Need Foundations?

Gabions are most commonly laid onto compact road base so the gabion wall is fully supported. For most gabion wall projects 100mm depth of road base would be sufficient.

Where gabions are used to create a retaining wall 2-3 metres high or higher, its recommend the baskets are laid at a batter angle (leaning back) of around 6-10 degrees.

You can create this batter angle by using the base gravel. Its recommended the assembled gabions are placed onto the aggregate and checked for alignment before filling them with rock.

Another option is staggering or stepping them back, this step back could be anywhere from 300mm to 1m depending on project demands. An engineer should be consulted for design and construction plans where appropriate.

With increased popularity gabion fences and pylons are generally built on top of a concrete slab with internal steel posts running through the centre of the gabion for extra stability.

As most fences are low profile, say 300-500 depth with height of 2 metres the internal weight is to great for the gabion structure to be considered freestanding therefore the structure requires additional support internally.

What Size Gabion Baskets To Use?

As a guide a 2 to 1 ratio applies. 

If the gabion structure is retaining earth at 1m high the depth of the gabion needs to be 500mm.

As the height of the gabion increases, it may be possible to step the gabions back and possibly decrease the depth of the wall.

Another option is terracing the gabion wall. The structure can be built to a certain height and depth (using the 2:1 ratio) then leaving sufficient space, say 1-2metres between the top of the first gabion structure and the base of the second gabion structure.

Do Gabion Walls Require Planning Permission?

Consult your local council for height guidlines, in most states in Australia a wall can be constructed to 1 metre height without requiring council or engineering.

 

 

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