R o a d w o r k s

Problems and Solutions R o c k f a l l P r o t e c t i o n

Rockfall Protection
Rockfall protection systems are a key element in the design
and maintenance of infrastructure networks and have a direct
impact on safety. For this reason, such systems need a new
approach that encompasses the overall analysis of the structural
system, and not just the individual components.
The word “system” is the best description, as it embraces the
different structural components which interact with one another.

A key distinction must be made between active and passive

protection systems.

“Passive” systems are those which do not affect the

process of the rock detaching, but rather focus on
containing falling debris, thereby averting danger for
the infrastructure and its users.
Passive systems include:
- drapery wire mesh
- rockfall protection barriers
- rockfall protection embankments

The “active” systems are those which act on the rock-

detachment process:
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- armoured mesh, where different kinds of metal wire and
cables form a mesh which is then anchored to the rock
slope.

The planning, construction and maintenance of these

structures must take into account their durability.
In accordance with these concepts, Maccaferri’s long-earned
experience in this field, coupled with its corporate
orientation towards research and innovation, yielded the
development of the MAC.RO. ™ System (MACcaferri ROckfall
protection systems), which provides a flexible response to
different problems, and combines industrial innovation,
advanced research and project design.

Italy

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CNR - ITC Milan Italy

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 ™
The MAC.RO. Action Aim Typical applications

System Trenches and walls at the

foot of a slope
Intercepting and stopping falling
rocks and boulders
Protection of roads running at
the bottom of man-made cuttings

The concept behind a protection system is the Rockfall protection barriers Intercepting and stopping falling Protection of roads and buildings
with high energy rocks and boulders at the foot of natural cliffs
combination of good planning and the right choice

Passive
dissipation capacity
of system components, which must be made as a Rockfall protection mesh Intercepting and stopping falling Closure of gorges in rocky slopes
function of the actual stress the system will have structures, made on-site rocks and boulders

to withstand, compared with the stress capacity Drapery wire netting Controlling rockfall, guiding Protection of road cliffs and
falling debris to collect/ pile up buildings, also in combination
of the various component materials. at the foot of the slope with trenches and/or walls
Just as for other soil stabilization activities, the
basic concept to comply with is the “minimum Soil reinforcement Consolidating the slope’s surface Protection of road cuts and
and preventing possible rock buildings
energy level”, i.e. a response commensurate with detachment
the problem, thereby avoiding overdesign and

Active
Soil nailing Global stabilisation of the slope Management of cuttings
unnecessary costs.
Aspects related to the durability of the systems Deep consolidation, with Stabilisation of huge rock Natural cliffs, cuttings
are regulated by the guideline, “Durability and nails and ties masses, individual or in groups,
which are prone to seismic
Construction Products Directive” 89/106/EEC. shifting
The concept of useful design life of a system, i.e.
the period of time during which the system
performs as expected, is strictly linked with the
durability of the system components, and, of Durability of facings and systems
course, with the level of maintenance. Very aggressive environment (industrial, road and marine)
Rockfall protection barriers and facings must be Rockfall protection - Reinforced rockfall protection
embankments - required life-span Class A EN 10244
conceived as “non-easily-replaceable systems”, required life-span

and therefore must have a durability of around Zn-Al (5%) MM

300
25 years, while structural works such as reinforced 275
earth embankments for rockfall protection must 250
Loss of Facing (gr/m2)

last for 50 years. 200

175
Zn
150
125
Zn-Al (5%) MM
polymer-
100
sheathed
75
50
25
0
Time
0 10 20 30 40 50 60 70 80 90 100 (years)

LA.T.I.F. Trento - Italy

Steel

Steel
Galfan Zn-Al 5%-MM Alloy

Galfan Zn-Al 5%
-MM Alloy
Polymer sheathing

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 The MAC.RO. ™ system includes:
- surface facings / protection
- rockfall barriers
- reinforced earth rockfall protection
embankments
Choosing between the available options,
and between the various solutions within
each option, must be in proportion to
the actual scale of the containment
problem being addressed.
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The solutions provided by the MAC.RO. ™ system have been developed in

collaboration with distinguished research centres. This way, Maccaferri
not only provides products, but also the fundamental technical assessments
which are needed in order to achieve the optimum action planning.

CNR/ITC - Milan - Italy Università di Milan - Italy

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 Drapery wire
mesh nets.
This system is typically applied to rock masses whose
surface can break down into fragments not smaller than
the apertures in the mesh, and in any case not larger than
0.5 metres in diameter.
On moderately steep slopes, or those where some
vegetation may grow, the mesh should be kept as close
to the slope as possible.
On very steep and/or near vertical slopes, the net must be
anchored at the top of the cliff, and left unanchored on
the rockwall, thereby allowing rocks to fall to the foot of
the cliff, and be contained between the rockwall and the
mesh.
A key factor here is to have a safe and continuous
anchorage at the top, from which space has to be allowed
for debris to fall down.
Our double-twist wire mesh is the ideal solution, both due
to its flexibility in all directions, and to the fact that it will
not unravel, even in the event of some of its wires accidentally
breaking. This problem used to be unsolvable, with old single-
twist mesh, as it cannot provide the same level of safety,
irrespective of the kind of wire used.

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Australia

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Fixed facing systems
An overall drapery mesh net system must
be sized after a realistic assessment of the
problem to be addressed, and in accordance
with general planning concepts laid out in
design codes.
The main stress factors to be taken into
account are:
- permanent stress factors:
weight of the whole netting, with a
recommended factor of safety of 1.35
- variable stress factors:
weight of debris piled up at the foot
and weight of snow (for slopes of less
than 60°), with a recommended factor
of safety of 4.
In general, the dynamic stress produced by a
rock during its fall should not be taken into
account, except in very peculiar situations.
Apart from cases in which system planning
and application have been inadequate, the
main mechanical stress comes from the debris
piled up at the foot of the slope.

W m : weight of the net

W d : weight of debris
Anchorage

fa
Italy

Net
W m cos βtanδ

H0

Wm
Wd cos βtanδ
Debris
Hd Hd
Φd β

Wd

Diagram of forces Drapery mesh net layout

Washington State Center Transportation

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Volume of debris at the foot
The volume of debris must be calculated, not only in order to have a sensible idea of the acceptable level of debris, and
design, the facing, but also to decide whether and to what extent correctly refrain from drawing catastrophic scenarios only to
of rockfall is acceptable. It is important to assess what the likely justify the presumed requirement of a higher resistance system.
amount of accumulated debris will be, and the acceptable amount The figure below shows the volume of debris for a foot width
in accordance with the distance between the foot of the slope of 1.00 metres (3.28 ft), and a possible max pile-up height of
and the adjacent road surface. In other words, the designer should 3.00 metres (9.84 ft).

Vd
Volume at the foot (m3/m)

1,8
1,6
1,4
1,2
1,0
0,8 Vd
Hd
0,6
0,4 1,00

0,2
0
0 1,00 2,00 3,00 Hd (m)

Italy

Strain on facing
The strain experienced by the
facing is a function of the slope Swm
angle, and must be calculated
using limit state conditions, taking 100
β = 80˚
Strain on facing (kN/ m)

into account the friction between 90

β = 70˚
the debris and the previously 80
mentioned factors of safety. 70
β = 60˚
60
50 Swm
Strain Hd
40 β
on facing
30
20 1,00
10
0
0 1,00 2,00 3,00 Hd (m)

Italy

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 Italy Italy

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 Slope reinforcement
Slope reinforcements are those actions aimed at consolidating
the surface of the rock mass and at containing possible rock
detachments (typically those of up to 1-1.5 m 3 (1.3 - 2 CUY)).
This intervention falls under the ‘active’ category rather than
‘passive’, although it could be argued as combining the two.
To be clear, a "surface revetment” is different from a whole
“rock surface” or slope stability solution.
The latter must be addressed - if it presents problems - with
deep-reaching overall stability solutions (e.g. soil nailing),
which may then be combined with a facing, (also made with
a series of anchorages, mesh and cables) to address the
surface stability.
The overall system made of anchorages, metal cable panels,
steel cables and mesh netting, is illustrated below, in which
the basic cell is a unit enclosed between 4 anchorage points.
In order to determine the right size of the overall system,
one must assess:
- the required rigidity of the structure
- the strain experienced by the anchorage points
In order to limit movement of the rock mass, it is crucial that
the surface facing provides a high resistance with minimum
deformation. The rigidity against deformation of the system is
the resistance that is applied when a deforming action occurs
metal cables and double-twist mesh panels
perpendicular to the plane of the system.

cliff
anchorage

metal
cables

USA

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HEA cable panels
HEA panels are made of twisted steel wire cables and high-
resistance 3 mm wire “knots”, for which the following forces
have been measured:
- resistance to tear and untwisting/unravelling
- resistance to the opening of one single mesh
in static conditions
- deformation under static load
- stress dissipation to the frame and anchorage points
Comparison with the same measurements taken on
traditional cable mesh panels connected with “studs” shows
that Maccaferri HEA panels are more reliable, in terms of
performance and quality.
With the knotted connection, when the limit resistance is
overcome, the knot progressively unties itself until the breaking
point is reached. However, with traditional stud connection
systems, the connection fails suddenly when the resistance limit
is exceeded. This produces immediate unravelling of the panel.

Knot resistance
Type Resistance Resistance
of knot to tear to untwisting
kN kN

HEA Panel 24,4 11,9

High resistance
stud 13,5 8,0
LA.T.I.F.
Low resistance
stud 4,6 1,3 Trento
Italy

Resistance to mesh opening

7000

6000

5000
Force (daN)

CNR - ITC
Milan
4000 Italy

3000

2000
studs
1000 HEA knot

0
0 5 10 15 20 25 30

Central deformation (cm)

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 Facing types
For slope reinforcement applications, a metal cable, or metal cable The resulting product is midway between a cable-reinforced
reinforced panel is a lot more effective than woven wire mesh mesh and a cable-panel surface revetment.
alone, without taking into account the mechanical properties of However, the great economic bonus of Steelgrid comes from the
the wire. (In any case, double-twist mesh has higher rigidity than fact that two different products can be installed at the same
single twist mesh, and is therefore more effective). time (mesh and metal cables). The following graphs and pictures
Maccaferri therefore has developed Steelgrid, a new double- show how the cables woven into the mesh enable the facing to
twist woven mesh into which metal cables are woven. distribute strain to the outer frame and anchorage points.

Steelgrid Cables woven into

type mesh the double-twist mesh

Steelgrid Cables
type mesh laid on on-site

Double-twist HEA type panel

metal mesh
1,50 m

3,00 m

3,00 m

3,00 m

Steelgrid type mesh facing 3,00 m

Steelgrid type mesh

facing and holding cables
3,00 m

Facing with HEA panels

and double-twist wire mesh

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Strain on anchorage points

7000

6000 Anchorage 1
Anchorage 2
5000
Anchorage 3
Force (daN)

Anchorage 4
4000

3000

2000

1000

0
0 500 1000 1500 2000 2500

Strain to anchorages (daN)

Facing deformation rigidity

6000

5000

4000
Force (daN)

3000

HEA Panel
2000
Steelgrid
1000 Single-twist mesh,
with high-resistance wire

0
0 10 20 30 40 50 60 70 80

Central Deformation (cm)

CNR - ITC
Milan
Italy

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Rockfall protection barriers
and embankments
These passive systems are an ideal solution when it is
not possible to intercept falling rocks or prevent them
detaching, due to the whole slope being too large, or
inaccessible.
These days, embankm ents are increasingly made with
reinforced earth, enabling builders to use local material,
reduce the footprint of the structure, and create a
vegetated embankment face, which minimises the
system’s environmental impact.
Maccaferri Terramesh ® solves many of these situations,
in which system effectiveness goes hand-in-hand with
rapid construction time.
The double twist mesh fascia unit and soil
reinforcement structural element are pre-assembled
during the manufacturing process, thereby
dramatically reducing the number of operations
to be performed on site.
Rockfall protection barriers are widely
used, in different configurations
according to the impact they have
to withstand, to the location, and
to the interaction with other
containment and support
structures, if present.

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Variable geometry barriers are made of a complex system
of metal cable and double-twist wire mesh panels for the
containment of small boulders.
The metal-cables connect to structural elements,
dissipation cables and anchorage lines with a high
deformation capacity enabling the system,
to withstand great energy (normally in
the range of 250-3000 kJ).

Maccaferri has developed a barrier system

(OM 250 to OM 3000) covering a wide energy
absorption spectrum.
These systems were developed through the
combination of planning and on-site tests, as
required by the strictest regulations.

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 ANY REPRODUCTION, INCLUDING PHOTOCOPY, FILM AND MICROFILM, IS FORBIDDEN. ALL RIGHTS RESERVED WORLDWIDE.

Officine Maccaferri S.p.A.

Via Agresti, 6 - P.O. Box 396
40123 Bologna - Italia
Tel. ++39 051 6436000
Fax ++39 051 236507
e-mail: comes.officine@maccaferri.com
Website: www.maccaferri.com

© 2004 Officine Maccaferri S.p.A. - Bologna - Italy - Print: Litografia Zucchini - Project: Grafica Monti - Photo: Archivio Officine Maccaferri