Rockfall Brochure Aug 2009 Maccaferri

8/12/2019 Rockfall Brochure Aug 2009 Maccaferri

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System solutions

Specific solutions

Specific problems

General issues

P r o b l e m s a n d S o l u t i o n s

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


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Risk analysis

SURFACE SLOPE INSTABILITY PROTECTION STRATEGY

PASSIVE PROTECTION SYSTEM

Control of instability effects

TRENCHES, ROCK FENCES ANDROCKFALL PROTECTION EMBANKMENTS

DRAPERY SYSTEMS SURFICIAL REVETMENTS

SOIL NAILING TIE BACK ANCHORS

ACTIVE PROTECTION SYSTEMInstability prevention

Roads, rai lways and urban areas are frequently subjected

to instabil ity of rock slopes. Such instabil it ies can affect

the superf ic ia l port ion of the s lope or involve i ts ent i re

global stabil ity. Rockfall systems can be designed to act

on the sur f ic ia l layer of th e s lope only or they can act

deeply with in the rock mass to consol idate large b locks

or s tabi l ize the whole s lope. A c lear d is t inct ion must

be made at the outset between sur f ic ia l protect ion,

appl ied us ing a combinat ion of s tee l meshes, s tee l

cables , cable pane ls and anchors (presented in th is

brochure) , and the works a imed stabi l iz ing the rock

s lope against g lobal instabi l i ty problems (not part of

th is brochure) . For the lat te r , the same superf ic ia l

protections are normally applied, together with solutions

spec i f ica l ly des igned for the g lobal s lope s tabi l i ty . I t i s

incorrect to assume that the same intervent ion

techniques dedicated to superf icial portion of the slopes

can be appl ied, without other w orks , for deep seated

instabi l i t ies . Sur f ic ia l ins tabi l i t ies are re lated to

a l te rat ions and deter iorat ion of the rocks due to p lant

root act ion, thermal expans ion, wind and sa l t e ros ion,

s lope excavat ion methods, f reeze and thaw processes ,

progressive weathering of joints within rocks, hydrostatic

pressures, seismic action and so on. Only in l imited cases

can these problems be reduced to a s imple so lu t ion.

Rather, quantitative r isk assessment should be undertaken

to adequate ly and e f f ic ient ly quant i fy the r isks

assoc iated with poss ib le lands l ides for a part icu lar s lope

or set of s lopes . The r isk assessment should weig h up

the probabil ity, magnitude and distr ibution of occurrences

and, on the other hand, take into account the unforseen

and undes i rable consequences of casualt ies , property

damage and loss of serv ice . R isk management should

focus on the ident i f icat ion of potent ia l key r isk factors

which are then logically evaluated in terms of probabil ity,

costs and other benef i ts , so as to manage the r isk in an

opt imal way.


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Rockfall barriersSimple drapery system

Rockfall protection embankmentsSurficial reinforcing systems

Rockfall protection

Passive systems are those which do not affect the

process of the rock detachment, but rather focus on

containing and intercepting fall ing and sl iding debris,

thereby averting danger to infrastructure and its users.

Passive systems include:

- S imple drapery systems

- Rockfall protection barriers

- Rockfall protection embankments

Activesystems are those that act to prevent and control

in a signif icant way rock detachments:

- Surficial reinforcing systems , where different kinds

of steel wire and steel cables form an armoured mesh

which is then f ixed to the rock slope through anchor bars.

- Pre-stressed and tie back anchors.

The planning, construction and maintenance of these

structures must take into account the durabil ity.

In accordance with these concepts, Maccaferris long-earned

experience in this f ie ld, coupled with its corporate

orientation towards research and innovation, has yielded

the development of the MAC.RO.System (MACcaferri

RO ckfall protection systems). MAC.RO. provides f lexible

solutions tuned to different problems and combines industrial

innovation and advanced research with project design.

Rockfa l l protect ion systems are a key e lement in the des ign and maintenance of road and ra i lway inf rast ructure

networks and have a d i rect impact on safety . For th is reason, a new approach that encompasses the overa l l ana lys is

of the rockfa l l s t ructura l sys tem, and not just the indiv idual components , i s necessary .

The word system is the best descr ipt ion, as i t embraces the d i f fe rent s t ructura l components that interact with

one another .

A ke y di st in ct io n must be ma de be twee n acti ve and pa ss iv e prot ec ti on sy stem s.

Cogne (AO) - Italy

Madeira - Spain

Belluno - ItalyScascoli (BO) - Italy


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0 10 20 30 40 50 60 70 80 90 1000 10 20 30 40 50 60 70 80 90 100

Galfan Zn-Al 5%-MM Alloy

Steel

Polymer sheathing

Galfan Zn-Al 5%

-MM Alloy

Steel

The MAC.RO. SystemThe concept behind a rockfa l l protect ion system is a

combinat ion of good p lanning with the r ight choice of

system components and mater ia ls . The choice has to be

based on the actua l forces the system wi l l have to

withstand, compared to the strength limits of the different

e lements of the system. As i t has a lways been with a l l

so i l s tabi l izat ion works , the bas ic concept Maccafer r i

comply with is the minimum energy leve l, i .e . an

intervent ion care fu l ly tuned to the problem, thereby

avoid ing over-des ign and unnecessary costs . Durabi l i ty

aspects of rockfa l l sys tems are regulated by the

Durabi l i ty and Construct ion Products Direct ive

89/106/EEC guide l ine . The per iod of t ime dur ing which

the system performs as expected is directly connected to

the durabil ity of the system components and the level ofmaintenance; a concept known as working design l ife.

Rockfa l l protect ion barr ie rs and sur f ic ia l sys tems are

non-easily replaceable systems, and therefore they

must have a 25 year work ing l i fe ; on the other hand,

re inforced earth embankments for rockfa l l protect ion

must be des igned for a minimum 50 year work ing l i fe .

Action

Trenches and walls at thefoot of a slope

Rock fences with high

energy dissipationcapacity

Rockfall protectionbarriers, made on-site

Simple drapery system

Surficial strengthening

Soil nailing

Deep consolidation, withnails and ties

Typical applications

Intercepting and stopping fallingrocks and boulders

Intercepting and stopping falling

rocks and boulders

Intercepting and stopping fallingrocks and boulders

Controlling rockfall, guiding fallingdebris to collect/ accumulation atthe foot of the slope

Consolidating the slopes surfaceand preventing possible rockdetachment

Global stabilisation of the slope

Stabilisation of huge rocks,individual or in groups, whichare prone to seismic shifting

Protection of roads running at thebottom of man-made cuttings

Protection of roads and buildings at

the foot of natural cliffs

Interception of falling rock pathsin rocky slopes

Protection of road cliffs andbuildings, also in combinationwith trenches and/or walls

Protection of road cuts andbuildings

Management of slope cuts

Natural cliffs, slope cuts

Passive

Active

Durability of facings and systemsVery aggressive environment (industrial, road and marine)

LossofCoating(gr/m

2)

Reinforced rockfall protectionembankments - required life-span

Rockfall protection -required life-span

Time

(years)

Zn-Al (5%) MM

polymer-

sheathed

Class A EN 10244

Zn-Al (5%) MM

Zn

300

275

250

200

175

150

125

100

75

50

25

0

Aim

Double knot to fix the overlappingrope in the HEA cable panel


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MAC.RO. System

LA.T.I.F. Trento - It aly

Universitdi Milan

Italy

CNR/ITC Milan - Italy

CETE - Lyon - France

ROCK FENCES

The solut ions provided by the MAC.RO.

system have been deve loped in col laborat ion

with noted research centres . In th is way

Maccafer r i not only prov ides products , but

a lso the fundamenta l technica l assessments

needed in order to achieve the opt imum

act ion p lanning.

Accessories

Steelgrid MO

Accessories

Steelgrid BO

HEA panel

ROCKFALL PROTECTIONEMBANKMENTS

SURFICIALSTRENGTHENING

SIMPLE DRAPERYSYSTEM

Terrameshdoubleface

SOILNAILING

Macmat R

Steelgrid BO

Accessories

OM CTR 30/04/A

CTR 20/04/A

CTR 20/04/B

CTR10/04/B

CTR 05/07/B

OM CTR 50/07/A

Pont Boset (AO) - Italy


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Rockfall catch fences

Soil nailing

Surficial reinforcing systems

Rockfall embankments

Simple drapery systems

Surficial reinforcingrevetments


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S imple mesh draper ies are usual ly insta l led a long rock

s lopes whose sur face can break down into f ragments

not smaller than the opening of the double twisted mesh

(60mm to 80mm) and not la rger than 0.5 metres in

diameter . On moderate ly s teep s lopes , or s lopes where

some vegetat ion may grow, the mesh should be kept as

c lose as poss ib le to the s lope. On v ery s teep or near ly

vert ica l s lopes , the mesh net must be ancho red at the

top and bottom of the c l i f f and le f t unanchored a long

the s lope. This a l lows smal l rocks and debr is to fa l l

safely to the foot of the cl if f , whilst remaining contained

between the rock face and the mesh. To l imit the

containment area between the mesh and rock face some

nai l ing or pegging of the mesh at interva ls between the

top and bottom anchorage may be necessary . The most

important aspect here is to have a safe and cont inuous

anchorage at the top and provide suf f ic ient space to

allow rocks and debris to move downwards. Our double-

twis t wire mesh is the idea l so lut ion due to i ts isot ropic

Simple drapery system

Guiding loose debris to fall safely behind the meshcollecting material at the foot of the slope.

Protection of infrastructure and buildings placed directlyat the foot of man-made cuts or natural cliffs.

Containment of small falling rocks from rock slopes proneto deterioration as a result of root action, thermal

expansion, winds, freeze thaw cycles, and hydrostaticpressures.

f lex ib i l i ty and the fact that i t wi l l not unrave l even in

the event of some wires acc identa l ly break ing. S ingle

twist mesh cannot provide the same level of safety in the

event of wire breakage, i r respect ive of the s t rength and

type of wire used.

Ancona - Italy

Cork - Ireland

Madeira - Spain


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Steelgrid MOMono Or iented

Fixed drapery systems

Anchor at the base of the slope

Bologna - Italy

The des ign of a drapery sys tem as a whole should be

undertaken only a f te r a rea l is t ic assessment of the s i te

condit ions have been establ ished, and in accordance

with the genera l p lanning guide l ines la id out in the

Eurocode des ign s tandards . The main contr ibut ing

factors that should be s t ressed and cons idered are :

- T he pe r ma nent l oads :

weight of the whole nett ing, with a recommended

part ia l safety factor of 1.35.

- T he va r ia bl e l oa ds:

weight of debr is p i led up at the foot and/or weight

of snow ( for s lopes less than 60) , with a suggested

safety factor of 3.

In genera l , the dynamic act ions produced by a rock

s l id ing between the drapery and rock face can be

dis regarded except in spec i f ic s i tuat ions in which the

rockfa l l sys tem has not been des igned or insta l led in

Maccaferri has developed Steelgrid, a new double twistedwire mesh with high tensile steel cables woven withinthe double mesh during the production stage. Theresulting product is midway between a cable reinforcedmesh and a steel cable panel, ideal as a surface revetment.However, the great economic benefit of Steelgrid isachieved from the fact that two different products canbe installed simultaneously (mesh and steel cables),reducing overall project costs and saving installationtime.

STEELGRID MO(Mono Oriented) consists of double twistedwire mesh where the usual selvedge wires are replacedby 8 mm diameter high tensile steel ropes. An additional8 mm diameter steel rope may be inserted longitudinallymidway between the selvedges in the woven mesh. Thissystem is the natural evolution of the typical simpledrapery system.

the correct way. Other than that, the main stresses are due

to the accumulation of debris at the foot of the slope.


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The volume of debris is evaluated not only in order to

design the drapery system, but also to determine the extent

and type of the most suitable rockfall system to be installed.

It is important to assess what the l ikely amount of

accumulated debris will be at the foot, since this will have

an impact on the admissible distance between the foot of

the slope and the road surface. In other words, the designer

should have a reasonable idea of the acceptable quantity

of debris, and refrain from drawing catastrophic scenarios

to justify the assumed requirement of a higher resistance

system. The f igures here show the volume of debris

corresponding to a base width of 1.00 metre in relation to

a accumulated height up to 3.00 metres.

Volume of debris at the foot of the slope

The force bear ing upon the drapery is a funct ion of the

s lope angle and must be eva luated us ing u l t imate l imit

state condit ions, taking into account the fr ict ion between

the debr is and the s lope and the previous ly ment ioned

safety factors .

Forces on the Drapery

Shear

Forceonfacing(kN/m)

Strainon facing

100

90

80

70

60

50

40

30

2010

0

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

Swm

= 80

= 70

= 60

Hd

Swm

1,00

Vd

1,8

1,6

1,4

1,2

1,0

0,8

0,6

0,4

0,2

0

Volumeatthefoot(m3/m)

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

HdVd

1,00

Torino - Italy

Bergamo - Italy

Eva luat i on o f

the su i tab i l i t y

o f the net

i n s imple

draper y

sys tems ,

us ing the

MACRO2.

sof tware


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A surf icial reinforcing system is aimed at the stabil ization

of the rock mass sur face layer conta in ing potent ia l ly

unstable rocks of a s ize typ ica l ly 1- 1.5 m 3. Th is type of

work can be c lass i f ied under the act ive sys tems rather

than the pass ive , a l though i t could be argued as a

combinat ion of both. I t should be h ighl ighted that a

"surface revetment insta l la t ion is d i f fe rent f rom the

global s tabi l i ty of the rock sur face. The lat te r, i f the

problem exists, must be addressed with deep penetrating

measures (e .g. so i l na i l ing, deep anchors ) , which may

then be coupled with a fac ing sy stem/drapery (made

with a ser ies of anchors , mesh and cables ) to achieve

sur face s tabi l i ty .

The complete system cons is t ing of anchors , s tee l cable

panels, steel cables and mesh netting, as detailed below,is a bas ic unit or ce l l enc losed between 4 a nchor

points . To determine the most su i table system, the

fo l lowing informat ion must be assessed:

- the s t i f fne s s o r rig id i t y o f the f ac ing (d rape ry )

- the fo rce s t ransm i t ted to the anchors .

Rock Slope SurficialReinforcing Systems

Prevent the possibility of rocks detaching a nd improvethe slope surface stability.

Consolidation of the shallow surface layer of the slope.

Protection of infrastructure and buildings placed directlyat the foot of man-made cuttings or natural cliffs.

Containment of large unstable rocks in slopes prone toweathering caused by root plant action, thermalexpansion, winds, freeze and thaw cycles, and hydrostaticpressures.

In these k inds of problems, i t i s c ruc ia l that the drapery

provides a h igh res is tance with minimal def lect ion in

order to l imit the d isp lac ement of the rock mass .

The s t i f fness of a drapery sys tem can be def ined as the

resistance to the displacement when the facing, anchored

in the s tandard manner, i s subjected to movement

perpendicular to the p lane of the system.

anchorage

metalcables

metal cables and double-twist mesh panels


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Steelgrid BOB i O r iented

HEA Panel

A steel cable or steel cable panel such as the HE Apanels

deve loped by Maccafer r i , i s more e f fect ive than woven

wire meshes on the i r own for s lope consol idat ion

appl icat ions , and th is is unre lated to the mechanica l

propert ies of wire . In addit ion, double-twis t wire mesh

is a lso more e f fect ive than s ingle tw is ted mesh, due to

i ts h igher s t i f fn ess . With th is in mind, Maccafer r i has

developed Steelgrid BO(Bi Oriented) combining benefits

of both. This geocompos i te is part icu l ar ly su i table in

rockfa l l protect ion as a sur f ic ia l re inforc ing system for

s lope consol idat ion appl icat ions . I ts great advantage

l ies in the abi l i ty to connect the integra l longitudina l

ropes to the top anchor cable , and the hor izonta l ropes

to the anchorage pattern a long the s lope. Furthermore ,

the woven s tee l ropes ins ide the wire mesh increase the

drapery s t i f fness , resul t ing in improved safety and more

ef fect ive fac ing.

Steelgrid BO (B i O r iented) cons is ts of 8 mm diameter

h igh tens i le s tee l ropes , in p lace of the convent ional

Types of facing

Bologna - Italy

Anchor and Steelgrid panels' junction

se lvedge wire , with a fur ther 8 mm diameter s tee l rope

inserted longitudina l ly midway between the se lvedges.

During the production stage, steel ropes are also inserted

transverse ly in the cross d i rect ion through the mesh

twist and secured to the edge ropes with ferruled loops.

Eva luat i on o f the f ac i ng behav iour

i n sur f i c i a l r eve tment s , us i ng the

MAC.RO. 1 so f tware


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24,4

13,5

4,6

11,9

8,0

1,3

Resistanceto tear

HEA Panel

High resistanceclips

Low resistanceclips

Resistanceto pull apart

kN kN

Typeof junction

0 5 10 15 20 25 30

HE A panels are manufactured from a single high tensile

steel rope, woven to form a panel diamond shaped mesh.

The meshes (where the cables over lap) are f ixed with

high-res is tance 3 mm wire knots.

HE A panels have been tested for the following features:

- re s i s tance o f the knot to tea r and pu l l apar t

- re s i s tance o f the knot aga ins t the open ing o f one

s ingle mesh in s tat ic condit ions

- de fo rmat ion o f the HEA pane l unde r s ta t i c load

- l o a d t ra n sm i t te d t o t h e a n ch o r s

CNR - ITC Milan - Italy

When high strength is required (> 192 kN)

When a facing with high stiffness is required

HEA steel cable panelsComparative tests carried out on tradit ional cable panels,

where the meshes are f ixed with c l ips, demonstrated

that Maccafer r i s HEA pane ls per form better and are of

better quality. In the case of the knot connection, after

the l imit res is tance is reached, the knot progress ive ly

unt ies i tse l f unt i l the break ing point of one of the wires

is reached. With t radi t ional c l ip connect ion systems, the

connect ion suddenly fa i ls when the l imit ing res is tance is

exceeded producing immediate unrave l l ing of the pane l .

Junction resistance

Resistance to mesh opening

Force

(kN)

70

60

50

40

30

20

10

0

clips

HEA knot

Displacement (cm)

Ancona - Ital y PONT BOSET - Aos ta Ital y

CERMETBologna - Italy


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70

60

50

40

30

20

10

0

Force

(kN)

Force developed at anchorages

0 500 1000 1500 2000 2500

Anchorage 1

Anchorage 2

Anchorage 3Anchorage 4

60

50

40

30

20

10

0

For

ce

(kN)

Displacement (cm)

10 20 30 40 50 60 70 800

HEA Panel

Steelgrid

Single-twist mesh,with high-resistance wire



Force developed at the anchors

Punch test resistance

Tests to determine the force d is t r ibut ion with i n an HEA

panel c lear ly show that h igher loads were recorded at

the pane l s corners . On the jobs i te , th is usual ly re f lects

the anchor pos i t ions .

Load-displacement curves from lab tests evaluate thestif fness of the surf icial reinforcing system, enabling

selection of the most suitable facing product in relation

to evaluated loads and maximum admissable displacement.


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Rockfall simulationwith rockfallinterception structure

Rockfa l l barr ie rs of var iable geometry ar e made of a

complex system of steel cable panels or r ing net panels,

a double-twis t wire mesh layer for the conta inment of

small rock fragments, steel cables connected to structural

e lements , posts, energy d iss ipator devices and anchors .

Rockfa l l barr ie rs d iss ipate energy with system

deformat ion, thus enabl ing the system to withstand

energies typ ica l ly in th e range of 500-5000 kJ .

Catch fencesIntercept and stop falling rocks

and boulders.

Protection of infrastructure and buildingsplaceddirectly at the footof man-madecuttings or natural cliffs.

Protection of the slope in the case of verywide cliffs.

Maccaferri supplies a system of barriersto cover

the full range of energy: from 500kJ up to 5000kJ.

These systems were deve loped through the

combinat ion of des ign and f ie ld tests , as required

by the of f ic ia l s tandards (ETAG 027-2008

Guide l ine for Euro pean Technica l Approva l of

Fa l l ing Rock Protect ion K i ts) .

Rockfall simulation

Brescia - Italy

Latina - Italy


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Rockfall protectionembankments

These pass ive systems are an idea l so lut ion when

superf ic ia l re inforc ing system cannot be insta l led (e .g.

for very wide s lopes) or intercept ion of fa l l ing rocks is

not poss ib le due to the whole s lope be ing i naccess ib le .

Nowadays , embankments are increas ingly bui l t us ing

re inforced soi l , enabl ing contractors to use loca l ly

ava i lable mater ia ls s i te won and creat ing a vegetated

embankment fac ing, which reduces the envi ronmenta l

impact of the system. Maccaferris Terrameshhas been widely used for suchworks where system effectiveness goes hand-in-handwith rapid building time.The double twist wire mesh units and integral soilreinforcement structural element, are pre-assembledduring the manufacturing process, dramatically reducing

the number of operations to be performed on site,reducing installation costs when compared to wraparound or separate component systems.

Intercept and stop falling rocks and boulders.

Reduce the environmental impact with re-vegetatingsolutions.

Protection of infrastructure and buildings placeddirectlyat the foot of man-made cuttings or natural cliffs.

Divert potential debris flows

Torino - Italy

Aosta - ItalyBelluno - Italy


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Aosta - Italy

Sassari - Italy

Aosta - Italy


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Maccaferri has developed new software to assist in theselection of the product used for flexible and softfacings.

Using load-displacement curves obtained by full scaletests on the products, the facing design can be achievedfollowing Eurocode directives. The facing product ischecked both at the ultimate limit state (related to thefailure of the system) and at the serviceability limitstate (related to the deformation of the product whenloaded).

Maccaferri has also developed a range of products(bolts, facing accessories) to fulfil the specificrequirements of flexible structural facing (mesh + deepnails) and soft facing (mesh + short nails).

Soil nailingSoi l Nai l ing is a techniq ue that can be used e i ther on

natura l or excavated s lopes . In so i l na i l ing, the soi l i s

re inforced by the insert ion of tendons.

A hard, f lex ib le (double twis ted wire mesh, HEA panels,

SteelGrid o r MacmatR ) or sof t (MacmatR ) fac ing

is used at the sur face of the s lope. The fac ing covers the

exposed face of the re inforced soi l and may provide a

stabil is ing function to retain the ground between the soil

na i ls , provide eros ion protect ion and have an aesthet ic

funct ion.

Usual ly the system provides s tabi l i ty whi le vegetat ion

becomes establ ished: in such way the system improves

the soi l shear s t rength, meanwhi le provid ing sur face

eros ion protect ion. Good pract ice is to vegetate the face

with grass and/or shrubs, and seeding can be carr ied out

by means of a seeded geotext i le or hydroseeding.

Improve the geo-mechanical characteristics of the soil

Connect the unstable surficial layers with the stabledeep slope

Rio de Janeiro - Brasile

Macerata - Italy

Anchor bars


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Rockfall Brochure Aug 2009 Maccaferri

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