Fiji Technical Workshop

Gabion Walls
May 2019

1
Objectives
» Improve our knowledge of gabion
properties
» Understand product applications
» Improve understanding of gabion wall
design

Agenda
» Introduction
» Steel Wire
» Double Twist
Mesh
» Mesh Products
» Characteristics
» Applications
» Design

2
Introduction
» First records of the use of this system go back more than 2,000 years, when Egyptians
used cylindrical willow baskets full of small stones to protect the banks of the River
Nile from erosion.
» Gabion structures are historically associated with military applications and hydraulic
structures.

Introduction
Officine Maccaferri was the first to undertake industrial production of gabions in 1894. The
first major work using factory made gabions was in 1894 on the River Reno (24,000 m3 in
34 days). It remains in use today.

1894 TODAY

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Steel Wire
Starting from the raw material there are the following production stages:
1. Wire Rods
i. Supplied in 1500 to 2000 kg coils
ii. Diameter 5.5-9,0 mm (±3%), according to EN 10017
2. Wire Drawing
i. Done in stages to reduce to required diameter for the mesh product
3. Coating
i. Heavy Zinc Coating or Zn-Al coating
ii. Polymer coating (by extrusion)

Wire Drawing Process

» After last reduction, drawn wire is coiled in rolls of approximately 1200 kg. The
smallest diameter possible is 1.6 mm, largest is 8 mm.
» The effect of wire drawing on steel is the
• Increase of breaking load index (fragility) from 35/40 up to 50/95 kg/mm²
• Decrease of the extension index (ductility) at 2/5%.

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Galvanization
» Galvanization is the process of applying a protective zinc coating to steel in order to
prevent corrosion
Steel Core

Fe-Zn Alloy

Zn

» Hot Immersion Zinc Coating consists of a zinc coating applied over base metal resulting
in a combination of qualities (against corrosion) not present in other coating systems.
Zinc Coating is therefore unique, different from any other process, because it coats base
metal (cast iron and steel) and reacts with its surface, combining with base metal and
creating a resistant intermediate layer that interacts with metal.

Durability Test
Accelerated Ageing Test on Zn Wire
KESTERNICH TEST (ISO 6988)
It simulates acid rain conditions by subjecting test specimens to
SO2 atmosphere as well as condensing moisture to evaluate
corrosion characteristics with time

SALT SPRAY TEST(ISO 9227)

It produces a corrosive attack (NaCl solution): the appearance of
corrosion products (oxides) is evaluated after a period of time.

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Wire Characteristics
1. TENSILE STRENGTH: it must be between 350 and 550 N/mm2 (EN 10223-3). This
characteristic is necessary to assure the wire resistance to the stresses received during
manufacturing processes and at the job site.
2. WIRE’S EXTENSION, measured on 250 mm long samples, it must not be less than 8%
(EN 10223-3). This characteristic is necessary to assure the wire’s malleability,
important in the manufacturing process (double twisting) and in use (flexibility).
3. COATING WEIGHT Minimum coating weight must not be less than those of class A of
EN 10244-2.

Wire Characteristics
4. COATING ADHERENCE to the wire (EN 10244 and
ISO 7989) must be such that, after the wire is wound
6 times round a mandrel of diameter 4 times (for
wire with a diameter <4mm) or 5 times (for wire
with a
diameter ≥4mm) that of the wire, it does not peel or
break in a way such that it could be easily removed by
one’s fingers.

This characteristic is necessary to define zinc adherence

to the wire and to make sure it is possible to twist the
wire during the production process and at the job site
Assessment of the adherence of the coating

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Wire Characteristics
5. TOLERANCE ON WIRE DIAMETER DIAMETER TOLERANCE
(mm) (mm)
Coated wires, especially the ones produced by the Hot
1.8 ± 0.05
Dip Process, are not perfectly even or free of
2.0 ± 0.05
irregularities.
2.2 ± 0.06
Wire diameter variations allowed are (T1 of EN 10218-
2.4 ± 0.06
2 and T1 of ISO 22034-2)
2.7 ± 0.06
6. COATING UNIFORMITY 3.0 ± 0.07
To determine zinc coating uniformity a Dipping Test 3.4 ± 0.07
is used, according to EN 10244-2 and ISO 7989-2. 3.9 ± 0.07
4.4 ± 0.08

Wire Characteristics
7. ZN MASS OF COATING
1. Gravimetric method (EN 10244, ISO 7989)
The metallic coating on a surface of known area is dissolved in
suitable solution (usually hydrochloric acid) to remove the coating
completely without attacking the surface of steel wire.

2. Gaseous volumetric method (EN 10244, ISO 7989)

The volumetric method for determining the mass of the coating depends
on the property by which a metal dissolved in an acid releases a quantity
of hydrogen proportional to the mass of metal dissolved, i.e. representing
the chemical equivalent of the metal in question.
The most practical method to verify the coating weight is the Zaba device
which is used in Maccaferri factories for periodic checks on the wire
quality

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Wire Characteristics
POLYMERIC COATING
» For the use in chemically aggressive environments or for the use
in permanent structures characterized by a long term service
life (>50 years), the wire is coated with a polymeric coating.
EXTRUSION PROCESS
» PVC grains are placed in the extrusion machine so as to melt and then are extruded around
coated wire

Wire Characteristics
POLYMERIC COATING
Diameter and coating thickness (EN 10218-
2)
Core diameter zinc or zinc alloy coated1) Organic coated wire minimum
diameter2)
mm mm
2.0 2.50
2.2 2.90
2.4 3.10
2.7 3.40
3.0 3.70
3.4 4.20
3.9 4.70
1) In accordance with T1 of EN 10218-2.
2) EN 10218-2.

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Double Twist Mesh
CHARACTERISTICS

The HEXAGONAL SHAPE of the mesh provides a better

distribution of the working tensions along the wires that
form the mesh.

Double Twist avoids spreading of the damage caused by the

accidental breaking of any wire or mesh.
B
r
o
k
e
n

» EN 10223-3: Steel wire and wire products for fencing and netting - Part 3: Hexagonal
steel wire mesh products for civil engineering purposes
» ASTM A 975: Double–Twisted Hexagonal Mesh Gabions and Revetment Mattresses

Double Twist Mesh

CHARACTERISTICS - DIMENSIONS
» Mesh size (M) is the average distance, measured at right angles between twisted sides
over 10 mesh
Table 2 EN 10223-3
MESH WIRE
Size Size
Diameter Diameter tolerances
Designation (M) Tolerances
mm mm mm mm
2.0 ± 0.05
2.2
6x8 60 -0/+8
2.4 ± 0.06
2.7
2.2/ 2.4
± 0.06
2.7
8x10 80 -0/+10 3.0
3.4 ± 0.07
3.9

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Double Twist Mesh
CHARACTERISTICS - EDGING AND SELVEDGING
1. EDGE WIRE: a terminal wire used to edge the wire mesh parallel to the double twist
by continuously weaving it into the wire mesh.
2. SELVEDGE WIRE: a terminal wire used to edge the wire mesh perpendicular to the
double twist by mechanically wrapping the mesh wires around it at least 2.5 times or by
inserting it throughout the twists and folding one mesh length.
MESH WIRE EDGE AND SELVEDGE
Diameter (mm) Diameter (mm)
2.0 2.4
2.2 2.7
2.4 3.0
2.7 3.4
3.0 3.9

Double Twist Mesh

CHARACTERISTICS - EDGING AND
SELVEDGING

Selvedging methods: by folding (left) and by wrapping (right)

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Double Twist Mesh
CHARACTERISTICS – TENSILE
STRENGTH

Standard testing machine

(Bellizzi factory)

Double Twist Mesh

CHARACTERISTICS – TENSILE
STRENGTH
WIRE AVERAGE MEASURED
MINIMUM TENSILE
STREGTH AS PER DOP’s TOTAL NUMBER OF TESTED
MESH TYPE DIAMETER TENSILE STRENGTH [kN/m] SPECIMENS
Φ [kN/m]
[mm]

2.00 37.0 30 58
2.20 42.3 37 198
6X8
2.40 49 - Tensile strength for the
2.70 63.3 55 153 different mesh/wire
2.00 30.0 26 15
combinations when tested
2.20 37.1 35 156
as per EN 10223-3
2.40 40.8 40 52
procedure
8X10 2.70 53.8 50 564
3.00 64.4 60 262
3.40 - 80 -
3.90 100.8 99 7

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Mesh Products
GABIONS
A double-twisted wire mesh container of variable sizes, uniformly partitioned into internal
cells, interconnected with other similar units, and filled with stone at the project site
L=Length (m) W=Width (m) H=Height (m) # of cells
2 1 0.5 2
1.5 1 1 1
2 1 1 2

Tolerances on dimensions are + 5% (length, width, height)

Mesh Products
GABIONS
A double-twisted wire mesh container of variable sizes, uniformly partitioned into internal
cells, interconnected with other similar units, and filled with stone at the project site

End Panels: panels that form

the sides of the Gabion unit.

Diaphragms: panels that

divide the gabion or the
mattress units into small
cells, placed in between the
end panels.

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Mesh Products
GABIO
NS BASE End Panels: fastened to the main wire mesh
panel by means of the loose ends of the cut
panel tightly twisted two times one around the
other around the edge of the side wires of the
END
main panel and the folded back.

DIAPHRAGM Diaphragms: connected to the main panel by

means of a spiral driven into the mesh end of
the diaphragm or using lacing clips

BASE

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Mesh Products
TERRAMESH SYSTEM
A modular system used for soil reinforcement applications; the facing section of the unit is
formed by connecting the back panel and 2 diaphragms to the main unit, thus creating
rectangular shaped cells used for stone confinement
L=Length (m) W=Width (m) H=Height (m)
3 2, 3 1
4 2, 3 1
5 2, 3 1
6 2, 3 1

Tolerances on dimensions are + 5% (length, width, height)

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Mesh Products
GREEN TERRAMESH
A single length of double twist mesh forms the base and upper reinforcing panels and the
facing unit. A bio-degradable or synthetic blanket is installed immediately behind the
sloping faces of the unit to control erosion and to promote rapid vegetation establishment
L=Length (m) W=Width (m) H=Height (m) Wire dia (mm)
2 2 0.6 / (70 )
o 2.2
3 3 0.76 / (70 )
o 2.7
4 3 0.73 / (65o) 2.7
5 3 0.70 / (60 )
o 2.7
6 3 0.58 / (45o) 2.7

Tolerances on dimensions are + 5% (length, width, height)

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 Mesh Products
MATTRESSES
A double-twisted wire mesh container uniformly partitioned into internal cells with
relatively small height in relation to other dimensions, having smaller mesh openings than
the mesh used for gabions.
L=Length (m) W=Width (m) H=Height (m)
LID 6 2 0.17
DIAPHRAGMS
6 2 0.23
Height
6 2 0.30)
Tolerances on dimensions are + 5% (length, width)
and + 2.5cm (height)

Mesh Products
MATTRESSES
» Maccaferri mattresses are called RENO mattresses
» Mattresses can be either with single diaphragms or with double diaphragms obtained
during production by folding the base mesh panel: this is the CASTORO mattress, that
only Maccaferri can produce.
Single CASTORO

» The mattress is divided into cells diaphragms positioned at:

• Standard 5 diaphragm mattress = 1m centres.
• 9 diaphragm mattress = 0.6m centres.

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Mesh Products
NETTING
According to EN 10223-3, the variations allowed for the netting width is ± “M”.
The maximum width of netting varies according to the loom’s maximum width. In our case
that is approximately 4.0 m .
L=Length (m) W=Width (m)
25 2, 3, 4
50 2, 3, 4
100 2, 3, 4

Tolerances on dimensions are + 5% (length, width)

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Mesh Products
FASTENING: LACING WIRE
Together with products, a sufficient quantity of wire is supplied for fastening and tying.
Lacing wire is used to assemble and interconnect empty units, to store and secure stones
filled units and for internal stiffeners (to support the facing and to connect the front panel to
the back panel of a gabion).
Lacing between netting must be made by passing a continuous wire through all meshes and
with a double turn every two meshes. Bracing wires are placed internally to ensure that
gabion faces have better rigidity thus avoiding deformation during the filling stage. Such tie
wires must extend over a complete mesh (two twists).

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Mesh Products
FASTENING: LACING WIRE
The amount of fastening or tie wire depends on the dimensions and weight of each unit and
follows the proportions below:
» Gabions = 5% of Mesh wire Lacing wire
Mesh diameter diameter
» Reno Mattresses weight Product type (uncoated) (uncoated)

= 3% of mm mm

weight
Mattresses 6x8 2.20 2.20
6x8 2.70 2.20
Gabions 2.70 2.20
8x10
3.00 2.40

Characteristics
TECHNICAL AND FUNCTIONAL CHARACTERISTICS
The good acceptance of Gabions in the various and different types of work for more than a
hundred years is due to a series of individual characteristics, all pertaining to the same
Gabion, which gives it enormous advantages compared to other solutions

1967 1976 1986

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Characteristics
MONOLITHICITY
»A Gabion structure is made by various elements linked through continuous fastening. The
soil trapped in the voids between stones and the eventual appearance of vegetation,
increases monolithicity, improving the static characteristics of the structure over time.
»Maccaferri Gabion works are therefore to be considered as one single, homogeneous and
monolithic structure.

Characteristics
FLEXIBILITY
»Flexibility, within technically acceptable limits, gives Gabion structures the capability of
deforming while maintaining its function whereas such situations would cause rigid or near
rigid structures to collapse.

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Characteristics
PERMEABILITY
» Empty spaces between stone fill in Gabions, allow fluid movement through them.
» For this reason Gabion works are not generally affected by hydraulic pressure thus work
much more efficiently under such circumstances.

Characteristics
VERSITILITY
»They can be either built manually or by mechanical. They can be built in any climate
»If an smooth surface is needed or desired, the final face can be covered with mortar. If
there is need for a rapid integration with local nature and environment, seeds can be
scattered inside Gabions.

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Characteristics
ENVIRONMENTAL INTEGARATION
»Gabion structures are the least damaging to the environment as they are built basically
with stone.
»They do not stop natural flows of water nor the flourishing of native vegetal species.

Characteristics
DURABILITY
»The double twist, in case of a break in any single wire, prevents the unraveling of mesh.
»Heavy Zinc-Al (Galmac) coating of wires assures that eventual deterioration of the netting
by rusting is very slow under normal conditions.
»Where corrosion is a more severe process, it is possible to considerably extend wire life by
making use of PVC coating.

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Applications

Applications
WEIRS WITH A VERTICAL DOWNSTREAM FACE
»These are usually built for flood control, water velocity reduction, material retention or
water storage.

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Applications
LONGITUDINAL WORKS
»Longitudinal works are structures that are erected and act in parallel with the flow of
water. They serve in various applications, such as:
1. Protection against erosion;
2. Water course control;
3. Normal flow control in canals;
4. Protection against floods.

Applications
DEFLECTOR WORKS(GROYNES)
»Deflective structures are used to correct or centre watercourse direction, sustain the
stability of banks subject to erosion, recreate other areas already affected by erosion, or
deepen the centre of the watercourse to promote navigation.

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Applications
PROTECTIVE LININGS
»Used in downhill linings, canals, retention basins, temporary defenses, embankment
protection, etc.

Applications
PROTECT STRUCTURES
»Used to provide erosion protection and retain soil around culverts, bridge abutments, rail
etc.

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Applications
GRAVITY WALLS
» Structures that work mainly through the action of their own weight.

Applications
REINFORCED SOIL WALLS
»Terramesh® System: which features external faces stone filled as with Gabions and mesh
panel to form a reinforced soil mass.

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Gabion Design

Gabion Design
Gravity Walls
• Structures that work mainly through the action of their own weight .

27
Gabion Design
Rock
Gradation
Gabion rocks shall range between 100mm and 200mm. The
range in sizes may allow for a variation of 5% oversize
and/or 5% undersize rock, provided it is not placed on the
gabion exposed surface.

Gabion rocks shall be hard, angular to round, durable and of such quality that they shall
not disintegrate on exposure to water or weathering during the life of the structure.

Gabion Design
Standard unit weights of suitable gabion rocks (grock)
Rock Type Density (kN/m3)
Basalt 29
Granite 26
Hard Limestone 26
Sandstone 23
Soft limestone 22

The actual unit weight of a gabion structure is determined by:

ggabion = grock (1 - n) , where n = index of voids (porosity).
n value for gabions is 0.25 - 0.35

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Gabion Design
Typical Failure Modes of Mass Gravity
Walls

Gabion Design
Analysis of Soil Pressure Coulomb Wedge Theory

Depends on
equilibrium of the “wedge”
of earth which is assumed
to be rigid
& on which the
frictional forces
&
soils own weight are
acting

29
Gabion Design
Limit
Equilibrium

𝑆𝑡𝑎𝑏𝑖𝑙𝑖𝑠𝑖𝑛𝑔 𝑓𝑜𝑟𝑐𝑒 𝑅𝑒𝑠𝑖𝑠𝑡𝑖𝑛𝑔 𝑚𝑜𝑚𝑒𝑛𝑡

𝐹𝑆 𝑆𝑙𝑖𝑑𝑖𝑛𝑔 = ≥ 1.5 𝐹𝑆 𝑂𝑣𝑒𝑟𝑡𝑢𝑟𝑛𝑖𝑛𝑔 = ≥ 2.0
𝑆𝑙𝑖𝑑𝑖𝑛𝑔 𝑓𝑜𝑟𝑐𝑒 𝑂𝑣𝑒𝑟𝑡𝑢𝑟𝑛𝑖𝑛𝑔 𝑚𝑜𝑚𝑒𝑛𝑡

Gabion Design
Limit Equilibrium

Meyerhof Theory

Middle Third Rule (𝑀𝑟 − 𝑀𝑜)

𝑑=
𝑁
𝐹𝑜𝑢𝑛𝑑𝑎𝑡𝑖𝑜𝑛 𝑠𝑡𝑟𝑒𝑠𝑠 = 𝑁 1 + 6𝑒
𝐵 𝐵
𝑝 𝑙𝑖𝑚
𝜎𝑎 𝑑 𝑚 =
3

30
Gabion Design
Limit
Equilibrium

Analysis of intermediate layers

for:
• Allowable shear
• Allowable compressive stress

Gabion Design
Limit Equilibrium

𝑅𝑒𝑠𝑖𝑠𝑡𝑖𝑛𝑔 𝑚𝑜𝑚𝑒𝑛𝑡𝑠
𝐹𝑆 𝐺𝑙𝑜𝑏𝑎𝑙 𝑠𝑡𝑎𝑏𝑖𝑙𝑖𝑡𝑦 = ≥ 1.3 − 1.5
𝑂𝑣𝑒𝑟𝑡𝑢𝑟𝑛𝑖𝑛𝑔 𝑚𝑜𝑚𝑒𝑛𝑡𝑠

31
Gabion Design
Stepped inside gabion
walls

BIDIM GEOTEXTILE

Gabion Design
Stepped outside gabion walls

BIDIM GEOTEXTILE

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Gabion Design
Design Recommendations

Walls stepped outside are

preferable.
If stepped inside, they often
require a batter of 6 degrees

Avoid irregular wall rear surfaces

Gabion Design
Design Recommendations

check overall stability! do not use foundation keys, extend foundation

>2D

use apron instead of direct foundation

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Gabion Design
Design Recommendations

Configurations like this shall be checked

against slope stability, not as conventional
retaining walls.

 > 80 deg

Gabion Design
Design Recommendations

34
Gabion Design
Design Recommendations

Frankton Wall Failure

» Erosion of cut slope over the years posing threat to property

35
Frankton Wall Failure
Wall
failure

Frankton Wall Failure

Causes of wall failure

Slenderness of wall Use of fine grained

backfill material

36
 Re-construction using similar gabion layout
but having an Expanded polystyrene (EPS) blocks as backfill behind wall

Gabion Design
Design Recommendations
Use of Filter Fabrics
A proper filter fabric (non woven)
may be recommended along the wall
rear face, not on the foundation.
Parameters for the geotextile to look
at, are the weight, the punching
resistance and the permeability
Water
Enter water table when a free water
surface is present.
Water levels shall be lower than the
wall height.
Check accuracy of water profile data
entered

37
Questions?

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