Advantages of Gabion WallUpdated on March 5, 2011

Have you ever wondered when driving and you saw tones of stones or rocks filled in a basket of wire mesh? That structure is called the gabion wall.

You can see this structure near the stream, embankments or road.

What does the gabion wall do? And why use gabion wall? Well, one of the functions of gabion wall is for slope stability, which is to support and protect slope from erosion. Like other retaining structures, gabion wall has its advantages and limitations too.

Advantages1. Strong base that provides strength from being drag away by river or stream.

2. Reduce velocity of water as the energy dissipated by the rocks, thus reduce erosion.

3. Its flexibility gives allowance to small ground movement.

4. In most cases, as time goes, voids will be filled by vegetations and silt which will reinforce the structure and give extra strength.

5. Depends on the availability of material and equipments, handling and transporting material is easy and this reduce the time of construction.

6. Voids can be easily seen between the rocks which makes high permeability to the gabion wall. It allows water to flow through the structure which can maintain the water level in the ground (Groundwater level) to be low.

Limitations1. Aesthetic impression is minimal. In a town area, where slope is supported by

the gabion wall, the wire mesh basket can be seen and sometimes the rocks were surrounded by algae. However, there are some types of gabion wall that have high aesthetic impression and of course the cost will also be higher.

2. In a high velocity of flow, wire mesh could damage due to high impact of large object.

 

The advantages and limitations depend on the site condition, availability of material and equipment/machine, and also manpower. 

Site ConditionSite can be access by heavy machine. If it is near a river or stream, the depth of the river or stream should not exceed the depth that causes the machine to damage. The ground must also have a strength that is can support the weight of a heavy machine. For soft ground, if the cost is too high or if the volume is too large to remove the soft soil, then geosynthetic mattress might be required to increase the strength for the ground. 

Availability of MaterialLocation of quarry, and place for manufacturing the wire mesh which allows ease of transportation to the site is a good indicator of utilizing gabion structure.

Equipments / MachineThe accessibility of the site condition (ease of transportation to the site), and the equipment/machines are available at that area. 

ManpowerApart from operating the machines, most of the time filling and fastening the wire mesh basket is also done by hand.

There are more retaining structures other than gabion wall, such as reinforced concrete retaining wall and bored pile retaining wall. It requires a good decision making process to choose the best retaining structures. Analytical Hierarchy Process (AHP) is one of the decision making tool being utilized for decision making in this case.

Related Books

Pros And Cons Of Using Gabion Walls

HOW TO USE APPLICATIONS SECTION TO COMPLETE DESIGN SOLUTIONThe Applications sections within this web site have been configured to streamline the process of

designing Terra Aqua gabion products and solutions.

Read and review the text, photos, details, and information provided within the section.Read and review sample calculations provided.Run complete stability analysis with spreadsheet design calculator provided.Choose the appropriate cross sections and typical details provided.Provide plan view and profile view to correlate with typical section and cross sections.Go to the Technical Specifications page of this web site to choose the appropriate product specification and material type.Go to the Technical Specifications page of this web site and choose Project Specifications to complete the specifications section for gabion scope of work.

Terra Aqua’s gabion gravity retaining wall systems are monolithic gravity mass structures and follow standard design methods for gravity retaining walls. The following information is provided by Terra Aqua as a design guide to assist Professional Engineers, Government Agencies, Land Developers, and Contractors in the proper design, specification, construction and inspection of gabion gravity retaining walls.

Design ConsiderationsTerra Aqua always recommends that the soil data utilized for gabion wall design be based on a Certified Geotechnical Soils Report of the site location. Terra Aqua can provide a complete gabion retaining wall stability analysis upon request.

Terra Aqua gabion walls are constructed with natural stone. As drainage occurs soil particles are deposited into the small voids of the natural stone fill within the gabion wall allowing for pockets of vegetation to take root.

Pressure at the BaseThe total pressure of the gabion wall must be less than the anticipated bearing capacity of the soil under the base of the wall. The contact pressure on a flexible gabion footing is not distributed in a planar fashion, but decreases from a maximum at the point of application of the resultant to lesser values at the edges of the footing. The pressure at the toe of a gabion wall is, therefore, generally less than for a rigid wall.

The calculations for the subgrade reaction in flexible foundation are awkward and involve errors associated with evaluating the coefficient of subgrade reaction. The error in assuming this is on the safe side, since the reaction is assumed to have a planar distribution, as in rigid walls.

Foundation PreparationTerra Aqua gabion gravity retaining walls are typically placed directly on a graded soil foundation. To increase the bearing capacity, minimize differential settlement, and/or allow for additional drainage, a base layer of granular stone fill with consistent gradation ranging ½” – 11/2” may be placed and compacted to local standards 6” – 18” in depth as a founding course for gabion wall placement.

Foundation grade & Wall batter It may be determined, through an investigation and stability analysis, that additional stability of the gabion wall may be required to achieve acceptable factors of safety for sliding. One option to pursue prior to enlarging the gabion wall cross section for additional stability is to place the gabion gravity retaining wall on a 6 – 10 degree batter towards the retained slope. This will require the founding soils to graded and compacted to accommodate for the specified wall batter. 

Foundation below grade Terra Aqua gabion gravity retaining walls may be placed or keyed in below sub grade to prevent scour and wave action from undermining the toe of the structure. The rule of thumb for depth of placement below sub grade is approximately 2 times anticipated depth of scour.

Scour ApronA flexible double twisted mesh Terra Aqua gabion is designed to settle without fracture and adhere to the ground as scour occurs. Graded fill material ranging from 4"-8" for standard gabions and 3"-6" for reno mattresses will ensure uniform flexibility of the apron and will create a new state of equilibrium of the structure once settlement has occurred providing continued stability. Gabion

aprons are commonly used to protect the toe of a gabion retaining wall structure from scour that could cause undermining in channel works applications. It is recommended that the gabion apron be a minimum of 9"-12" in depth. The length of the gabion apron shall extend beyond the toe of the structure a minimum of 2 times the anticipated depth of scour. This will ensure that the gabion apron reaches just beyond the outer limit of the anticipated scour hole that may form.

The gabion apron will require minimal excavation and grade work. Generally the gabion apron is placed directly on the ground utilizing a geotextile filter fabric between the gabion apron soil interface to prevent and leaching of soils from underneath the apron. If the gabion apron is placed in relatively deep water, and efficient method of large scale placement is prefabricating the apron on a barge and then launching it into the water. The size of the gabion apron that can be placed by this method is limited only by the deck area of the barge. Gabions or reno mattresses may also be connected together filled and then placed into the water with a sling arrangement. This method is frequently used for building scour-resisting mats around bridge piers etc. Gabion aprons may be fabricated using Terra Aqua standard PVC gabion units or with Terra Aqua PVC reno mattresses.

Backfill & CompactionBackfill Material-Gabion gravity retaining walls, in comparison with reinforced soil walls, allows for a wider range of soil types to be utilized as backfill material. This is due to the gabion gravity walls configuration, typically low wall heights, and porous facing.   It is imperative to the overall long term performance of a gabion gravity retaining wall that the specified backfill material be properly placed and compacted. Poor compaction of backfill materials can lead to structural settlement, lateral wall movement, and result in insufficient shear strength to perform as designed. Specified backfill material shall be placed and compacted to minimum Standard Proctor 95% in lifts not to exceed 9” vertical and shall comply with local standards.

SOIL DATARecommendatio

nOf use for 

backfill

Soil Description

Soil Classification

Angle of Internal Friction

Unit weight of

Soil

Excellent Stone, Gravel, Sand

1 & 2 GP, GW, GM, GC, SW, SP 30-36 100-135

pcf

Good Clayey Sands, Silty Sands 3 SM, SC 28-32 110-130

pcf

Poor Soft Clay, Soft Silts 4 ML, CL, OL 25-30 110-125

pcf

Bad Stiff Clay 5 CL, CH 25-30 50-110 pcf

1. Clean sand, stone and gravel GW, GP, SW, SP2. Dirty sand and gravel of restricted permeability GM, GM-GP, SM, SM-SP3. Stiff residual silt and clays, silty fine sands, clays, sands and gravels CL,

ML, CH, MH,SM SC, GC.4. Very soft to soft clay, silty clay, organic silt and clay: CL, ML, OL, CH,

MH,OM.5. Medium to stiff clay deposited in chunks and protected from infiltration:

CL, CH

For type 5 material H is reduced by 4 ft resultant Acts at a height of (H-4)/3 above base. Adapted from Terzaghi and Peck

Filter Fabric Geotextile filter fabric is a vital component of any gabion gravity retaining wall. The void ratio of the stone fill confined within the gabion baskets allows for free drainage of the retained soils and requires a filter fabric be placed between the gabion wall and the specified backfill soil interface. The geotextile filter fabric will prevent loss of soil during drainage and drawdown. Gabion gravity retaining walls constructed without the placement of filter fabric will have a tendency to incur a loss of retained soils and grade elevation behind the gabion wall.  The type of backfill soil specified will determine the type, and placement of the geotextile filter fabric. Call Terra Aqua for recommendations on filter fabric.  

LayoutTo provide the maximum resistance to soil forces the gabion baskets shall be placed with the length dimension of the gabion unit running from the back of the gabion wall to the front face of the gabion wall. This will result in the internal diaphragms being placed perpendicular to the wall face and parallel to soil thrust. When gabion units shall be placed with the length dimension of the gabion unit running parallel with the length dimension of the wall the vertical seams shall be offset.

Compression Loads

For gabion gravity retaining walls that are 15’ – 30’ in height the gabion basket foundation and bottom courses shall be placed in 1.5’ vertical lifts to better absorb the compression and shear stresses. Terra Aqua’s double twisted mesh gabions shall withstand compression loads of 60,000 – 80,000 pounds per square foot. The shear modulus of elasticity shall vary between 5,000 – 8,000 pounds per square foot and is relevant to deformation.

Gabion Wall Face ConfigurationTerra Aqua gabion retaining walls can be designed and configured with a stepped front face or a smooth front face. When utilizing a gabion wall with a smooth front face, the gabion wall shall always be placed on a 6-10 degree batter and is not recommended for wall heights above 18’. Gabion walls with a stepped front face shall have a minimum 1’-1.5’ horizontal set back for each 3’ vertical lift.

Gabion Wall HeightTerra Aqua gabion gravity retaining walls can be designed and constructed up to approximately 30’, however due to the configuration of gabion gravity retaining walls their best suited for wall heights of 18’ or less. For wall heights of 18’- 36’ see the Stable Slope Section of this web site. 

Gabion Wall base width relative to wall height base width of a gabion gravity retaining wall is related to height of wall so as the wall height increases the base of the wall becomes wider to ensure structural stability. Terra Aqua has provided the diagram below to illustrate a starting point for design analysis to determine the base width relative to wall height. Terra Aqua recommends a conservative value of base width = 2/3 wall height. The stability analysis may determine that the gabion gravity retaining wall base width be less than or greater than ½ - 2/3 wall height.

GABION GRAVITY WALL SIZES & DIMENSIONS

GABION STONE FILL

Stone Fill Gradation for Gabion BasketsGalvanized/Galfan Gabions 8x10cm

4 inches – 8 inches      D50 6”

PVC Coated Gabions 8x10cm 4 inches – 8 inches      D50 6”Acceptable stone for gabion construction shall be hard, durable, equally graded, angular in shape,  and shall not be less than 4” in any given dimension and no larger than 8” in any given dimension. The specific gravity required for the stone fill shall be determined by the design and specified by the design engineer. Specific gravity for stone fill shall be no less than 2.5.

Unit weight of gabion stone fillTYPE OF ROCK LBS/CUBIC FT

BASALT 180

GRANITE 160

LIMESTONE 138

SANDSTONE 140

Unit weight of gabion stone fill- Based on a porosity of 0.30 or 30%

SPECIFIC GRAVITY OF MATERIALSBASALT 3.0

BRICK 2.0

BROKEN CONCRETE 2.4

GRANITIE 2.7

LIMESTONE 2.5

SANDSTONE 2.2

TRAP ROCK 2.7

SAMPLE CALCULATIONSProper design and construction of gabion retaining walls requires a thorough knowledge of the lateral forces acting between the retaining structures and the soil masses being retained. These lateral forces lateral forces are due to lateral earth pressure. Therefore, analysis and determination of lateral earth pressure are necessary to design gabion retaining walls.

The classical lateral earth pressure analysis and calculations are based on the Rankie theory by considering the soil in a state of plastic equilibrium, and the Coulomb theory by assuming a place failure surface. Both Rankine and Coulomb approached and developed lateral earth pressure problem with several essential assumptions such as an isotropic and homogeneous backfill soil, a plane backfill surface, a rigid failure wedge body etc…

As for the conditions which do not fit the Rankine and Coulomb theories such as irregular backfill surface, multiple soils etc… the Trial-Wedge (Limit Equilibrium) method, a graphical solution can be applied for estimating the lateral earth pressure, and an analytical solution based on the Theory of Elasticity can also be used. Currently these methods are practical and popular by utilizing a computer program. Terra Aqua can complete the global stability analysis upon request.

Terra Aqua Gabion Gravity Retaining Wall

Posted by: Ella Andrews , July 6, 2015

If you have been thinking about introducing some gabion walls to your property, as retaining walls or perhaps even some interesting outdoor seating, you might be wondering whether they really are the best choice. Like anything, these walls have their advantages and disadvantages. In order to determine whether gabions are the right choice for the project you have in mind, you will need to weigh these pros and cons against each other.

ProsThere are a number of advantages associated with the introduction of gabion walls, including:

Their strong bases, which prevent them from being dragged away during heavy downpours and even by vandals.They help to reduce the velocity of running water, as the rocks dissipate its energy, which helps to reduce erosion.The flexibility of the baskets and the rocks they contain allows from small movements as the ground below shifts.As time passes, gaps between the rocks will be filled by vegetation and silt, which will further reinforce the wall.Handling and transporting the materials is quite simple, which helps to reduce the time taken to build the gabions.Gaps between the rocks allow water to flow through the structure, helping to maintain a low groundwater level.

 

ConsThere are also a number of disadvantages associated with gabion walls that you need to be aware of:

In some cases, the aesthetic impression of the walls is minimal (as the wire basket can be seen and algae may be present).High velocity water could cause the gabion to be damaged through the impact of a large or heavy object.

It is important to keep in mind that the advantages and disadvantages will also depend on the condition of the site, the availability of materials and equipment, and the availability of manpower.

Site Condition – If the ground is relatively soft, you will need to create a concrete or stone base for the baskets to sit on top of (lest they sink into the mud). This can add significant time and cost. If the ground is relatively hard, you will be able to build the wall immediately.Availability of Materials & Equipment – If the supplier has baskets and rock in stock, you will be able to erect the gabions as soon as you get everything home. If they have to order materials in, you will have to wait until they’re delivered. Equipment may also be required.Availability of Manpower – Filling the baskets with rock is something that is done by hand, which can be time consuming (if you have a lot of baskets to fill) and can lead to injury if you’re not careful. If you have helpers, you will get the project done faster.

We hope that you have found the information provided above useful in determining whether gabion walls are the right choice for your upcoming project or not. Whilst these walls do look fantastic and can add a real sense of luxury to your property, it is important to note that they aren’t for everyone. If you have decided to introduce some gabions, it is important that you put the baskets together properly and fill them with the correct stone.