Catalogue of Prefabricated Elements

Transcription

INTERNATIONAL NAVIGATION ASSOCIATION
CATALOGUE
OF
PREFABRICATED ELEMENTS
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Report of Working Group 36
of the
MARITIME NAVIGATION COMMISSION
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INTERNATIONAL NAVIGATION
ASSOCIATION
ASSOCIATION INTERNATIONALE
DE NAVIGATION
2005
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PIANC has Technical Commissions concerned with inland waterways and ports (InCom),
coastal and ocean waterways (including ports and harbours) (MarCom), environmental aspects
(EnviCom) and sport and pleasure navigation (RecCom).
This Report has been produced by an international Working Group convened by the Maritime
Navigation Commission (MarCom). Members of the Working Group represent several countries
and are acknowledged experts in their profession.
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The objective of this report is to provide information and recommendations on good practice.
Conformity is not obligatory and engineering judgement should be used in its application,
especially in special circumstances. This report should be seen as an expert guidance and state
of the art on this particular subject. PIANC disclaims all responsibility in case this report should
be presented as an official standard.
PIANC General Secretariat
Graaf de Ferraris-building – 11th floor
Boulevard du Roi Albert II 20, B.3
B-1000 Brussels
BELGIQUE
http://www.pianc-aipcn.org
VAT/TVA BE 408-287-945
ISBN 2-87223-152-8
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CONTENT
1. INTRODUCTION
1.1 Summary
1. INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1
1.2
1.3
1.4
1.5
1.6
The aim of the working group is to collect all the available
prefabricated elements up to date. This work is the basis for
the construction of a large Catalogue that can be updated
after distribution and reached by many professionals related
with ports and coastal engineering. Obviously, this catalogue will continue expanding in the future, so all engineers
are encouraged to cooperate and send new or different references of prefabricated elements.
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3
Terms of Reference . . . . . . . . . . . . . . . . . . . . . . . . .3
Members . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4
Work of the PIANC Working Group 36 . . . . . . . . .6
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . .6
Foreword . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6
2. ROLE OF PREFABRICATED ELEMENTS IN
MARITIME WORKS . . . . . . . . . . . . . . . . . . . . . . . . 6
Types of applications considered in this catalogue
For the last four decades, the use of prefabricated elements
in the construction of port and coastal structures has become
a very common practice. Prefabricated elements provide
important advantages, such as improved hydraulic performance when compared with natural materials, ecological benefits, cost reduction, construction efficiency, etc. As a consequence, numerous new prefabricated units have been designed for a wide variety of engineering applications, such
as breakwater protection, coastal erosion control, stability
of river banks, reflection damping on quays, attenuation of
waves, etc.
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2.1 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6
2.2 Types of application considered in this catalogue .7
2.2.1 Breakwaters . . . . . . . . . . . . . . . . . . . . . . . . .7
2.2.2 Revetments, seawalls & coast protection . .8
2.2.3 Quays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8
2.2.4 Bank protection . . . . . . . . . . . . . . . . . . . . . .9
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3. CONSIDERATIONS FOR SELECTION . . . . . . . 10
3.1 Prefabricated elements for breakwaters . . . . . . . . 10
3.1.1 Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
3.1.2 Structural integrity . . . . . . . . . . . . . . . . . . .12
3.1.3 Hydraulic performance . . . . . . . . . . . . . . . .13
3.1.4 Constraints . . . . . . . . . . . . . . . . . . . . . . . . .13
3.1.5 Maintenance . . . . . . . . . . . . . . . . . . . . . . . .13
3.1.6 Construction costs . . . . . . . . . . . . . . . . . . . 14
3.1.7 Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
3.2 Prefabricated elements for quays . . . . . . . . . . . . . 15
3.2.1 Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
3.2.2 Structural integrity . . . . . . . . . . . . . . . . . . . 16
3.2.3 Hydraulic performance . . . . . . . . . . . . . . . 16
3.2.4 Maintenance . . . . . . . . . . . . . . . . . . . . . . . . 16
3.2.5 Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
3.3 Prefabricated elements for revetments and seawalls 16
3.3.1 Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
3.3.2 Structural integrity . . . . . . . . . . . . . . . . . . . 17
3.3.3 Hydraulic performance . . . . . . . . . . . . . . . 18
3.3.4 Maintenance . . . . . . . . . . . . . . . . . . . . . . . . 18
3.3.5 Materials . . . . . . . . . . . . . . . . . . . . . . . . . . 18
3.4 Prefabricated elements for bank protection . . . . . 18
3.4.1 Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
3.4.2 Structural integrity . . . . . . . . . . . . . . . . . . .20
3.4.3 Hydraulic performance . . . . . . . . . . . . . . .20
3.4.4 Constraints . . . . . . . . . . . . . . . . . . . . . . . . .20
3.4.5 Maintenance . . . . . . . . . . . . . . . . . . . . . . . .20
3.4.6 Construction costs . . . . . . . . . . . . . . . . . . . 21
3.4.7 Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
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In this work, different applications of prefabricated elements in maritime and fluvial works are briefly described.
The structures are classified into four types:
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a) Breakwaters
b) Revetments and seawalls & coast protection
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c) Quays
d) Bank protection.
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For each of these four types of structures some relevant characteristics are described. This includes: types of prefabricated elements; structural integrity; hydraulic performance;
constraints; maintenance; construction costs and materials.
The catalogue includes all the names of prefabricated elements known to the members of the WG at the moment.
Some of them have additional characteristics like: shape,
photograph, etc.; type of work; reference projects; bibliography; invention and development and commercial references.
1.2 Terms of Reference
REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
In the last four decades the use of prefabricated elements in
the construction of port, coastal and waterway structures has
become a very common practice. Prefabricated elements
APPENDIX (IN CD FORMAT). . . . . . . . . . . . . . . . . . 22
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can represent important advantages not only from the structural point of view (hydraulic performance, stability under
extreme wave conditions) but also from many others (i.e.:
ecological benefits, cost reduction, construction efficiency,
material availability).
• commercial status (patent, information, commercial address, etc.).
The Catalogue does not include detailed information (performance indexes, response curves, etc.) about the technical
performances of the unit, but only gives references to the
most relevant published information. Therefore, the inclusion of a certain type of element in this PIANC Catalogue
should not be deemed as confirmation of its technical quality or suitability for any particular application.
As a consequence, a lot of new prefabricated units have
been designed for a wide variety of engineering applications (breakwater protection, coastal erosion control, stability of river banks, reflection damping on quays, attenuation
of waves, etc.).
1.3 Members
Coastal engineers and contractors are now facing the problem of identification and selection of the optimum product
for their specific work. Information on prefabricated elements is nowadays dispersed, not easily available and almost
impossible to be evaluated.
This Catalogue was produced by the PIANC Marcom Working Group no. 36.
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Members of the group have been the following:
Chairman:
Mr. José María Berenguer
BERENGUER INGENIEROS, S.L.
Costa Brava, 13
28034 Madrid
España
phone: +34 91 736 40 87
fax : +34 91 734 43 76
e-mail: [email protected]
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PIANC, as a non-profit international association, is in an
optimum position for producing a Catalogue of Prefabricated Elements for Coastal and Port Engineering. This
document, which includes a list of products, is useful for
managers, port authorities, engineers, scientists and other
professionals.
a) Breakwaters
b) Revetments and seawalls
Co-Secretary:
Mr. José Ramón Iribarren
SIPORT XXI, S.L.
Edificio Azasol, calle Chile, 8 of 104
28290 Las Matas (Madrid)
España
phone: +34 91 630 70 73
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c) Quays
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The catalogue is focused on prefabricated units used for the
construction of the following types of structures:
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d) Waterways banks
The task of the Working Group has consisted of collecting
and processing technical and commercial information on all
types of prefabricated units, developed for the above mentioned purposes, that fulfil two requirements:
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Co-Secretary:
Mrs. Paula Zambrana Berho
BERENGUER INGENIEROS, S.L.
Costa Brava, 13
28034 Madrid
España
phone: +34 91 736 40 87
fax : +34 91 734 43 76
1) Commercial or technical references exist; and
2) the element has been used in an actual work.
The work of the group is published as a Catalogue that will
include a standardised form for each type or unit comprising:
Members:
Mr.William N.H. Allsop
Howbery Park, Wallingford
Oxon
OX 10 8BA
phone: + 44 1491 82 22 30
fax: + 44 1491 82 55 39
• basic technical features (shape, dimensions, photographs, etc.)
• list of references on technical performance
• list of references of existing applications
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Mr. Frans Kapp
Entech Consultants Ltd.
P.O. Box 413
7599 Stellenbosch
South Africa
phone: + 27 21 883 92 60
fax: + 27 21 883-32 12
Mr. Arie Burggraaf
P.O. Box 32696
Braamfontein 2017
South Africa
phone: + 27 11 242 4029
fax: + 27 11 242 4029
Mr. Sverre Lorgen
SAM LORGEN AS
6002 Norway
phone: + 47 70 10 73 00
fax: + 47 70 10 73 01
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Mr. Hans.F. Burcharth
Sohngaardsholmsvej, 57
DK 900 Aalborg
Denmark
phone: + 45 96 35 84 82
fax: + 45 98 14 25 25
e-mail 1: [email protected]
e-mail 2: [email protected]
Mr. Romeo Ciortan
IPTANA
36-38 Bd Dimicu Golescu
7100 Bucharest
Romania
phone: + 401 210 3542
fax : + 401 312 1416
Ms. Kirsty J. McConnell
Howbery Park, Wallingford
OX 10 8BA Oxon
United Kingdom
phone: + 44 1491 82 22 30
fax: + 44 1491 82 55 39
Mr. Remouchamps
CAMET
Boulevard du Nord, 8
B-5000 Namur
Belgique
phone: + 32 81 77 29 70
fax: + 32 81 77 37 67
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Mr. Leopoldo Franco
Universitá di Roma, 3
Via Vito Volterra, 62
00146 Roma
Italy
phone: 39 06 551 73 458
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Mr. Billy L. Edge
College Station,
Texas Tx 77843 - 3136
United States of America
phone: + 19 79 845 4515 / 979 845 4516
fax: + 19 79 862 8162
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Mr. Luc Maertens
Avenue des Communautés, 100
1200 Brussels
Belgique
phone:+ 32 2 4026 563
cellular: + 32 475 490 206
fax: + 32 2 4026 530
Mr. P. Galichon
Port Autonome du Havre
P.O. Box 1413
F-76067 Le Havre CEDEX
France
phone: 33 35 21 7400
Mr. Krystian Pilarczyk
Vander Burghwegl, P.O. Box 5044
2600 GA Delft
The Netherlands
phone: + 31 15 25 18 427
fax: + 31 15 25 18 568/25 18 555
Mr. Minoru Hanzawa
2-7 Higashi-Nakanuki Tsuchiura
Ibaraki, 300 - 0006
Japan
phone: + 81 298 31 7411
fax + 81 298 31 7693
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1.4 Work of the PIANC Working Group 36
were mostly cast in-situ within wooden forms or sunken
ship hulls, large mortar blocks could also be prefabricated in
the dry above an emerging sand mound to be washed away
or within watertight caissons before sinking on a prepared
foundation surface.
Most of the information required for completing the Catalogue was intended to be gathered from the research of the
group members.
PIANC Marcom Working Group 36 has had the following
meetings:
As the capacity of lifting cranes increased in the 19th Century, heavier precast blocks could be placed for rubble mound
breakwaters or for blockwork seawalls and quaywalls. Their
shape was typically parallelepiped or cubic. At Leghorn
(Livorno) even the core of the curvilinear breakwater was
made with large regularly cut rock blocks in 1850. The size
of prefabricated blocks steadily increased up to 500t for the
solid cyclopean blocks used for vertical breakwaters in the
first part of the 19th Century. Parallelepiped blocks of 150t
were used for the protection layer of the Port of Bilbao rubble mound outer breakwater. A tailor-made crane must be
constructed for placing such artificial concrete units.
LONDON (United Kingdom) 26, September, 2001
Meeting during the International Conference on Breakwaters, Coastal Structures and Coastlines
BARCELONA (Spain) 5, April, 2002
Meeting at the Port of Barcelona
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1.5 Acknowledgements
The Chairman is grateful to the Barcelona Port Authority
for the attention to the Working Group 36 in the meeting at
the Port of Barcelona.
The 20th Century showed the revival and development of
the technology of cellular reinforced concrete caissons (prefabricated in yards and on fixed or floating platforms) and
the production of un-reinforced concrete blocks of various
shapes to be mainly used for breakwater armouring. In 1950
the first slender tetrapod block was developed. Economic
advantages in comparison with massive-type blocks promoted its use in a large number of breakwaters all around
the world.
1.6 Foreword
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Despite the work carried out by the Group, the present catalogue only includes a limited number of prefabricated elements that are commonly used in coastal and fluvial engineering.
The WG realize that there are a considerable number of elements that have not been included in the final list of the
Report. In most cases, this fact has been due to lack of information about the technical data of the unit or references
about actual applications.
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Another milestone occurred in the late 1970’s when the
massive Antifer cube and the slender Dolos were developed,
quickly followed by the hollow (multi-hole) block generation (Shed, Cob). Some catastrophic events occurred in the
1980’s mainly due to the structural failure of slender elements, and this led the research again towards bulky units.
Finally in the 1990’s other bulkier units like Accropode
(France), Core-loc (United States) were developed to optimise the hydraulic and structural properties for a stable,
durable, economic armour based on a single-layer design.
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That reason, together with the normal development of new
elements with time, should lead to a periodic updating of
the information contained in it. Therefore, the present report
must be considered as a first edition of a Catalogue on Prefabricated Elements that must be the starting point for future
and more complete publications.
In some cases it was even the contractor, instead of the designer, who proposed a new block shape to avoid payment
of royalties or to simplify the unit prefabrication, transport
and placement.
2. ROLE OF PREFABRICATED
ELEMENTS IN MARITIME WORKS
2.1 Background
The use of prefabricated elements for the construction of
quays developed on the basis of two new requirements;
deeper berths for larger ships and higher values of exploitation loads. Roman engineers constructed a quay of 7 metres
depth using large geometric rocks in the port of Cesarea
Maritima (1th Century, B.C.) Once the draught of commercial ships exceeded 6-7 metres depth in the 19th century,
performance limits of the quays existing in ancient ports,
made from natural materials, were exceeded. At this limit,
the use of artificial prefabricated concrete blocks becomes
Prefabricated elements have been used in maritime engineering since ancient times. Phoenician and Greek engineers
used cut rocks with regular placement to build breakwaters
and seawalls, sometimes fastening neighbouring blocks
with metal joints and clamps. The weight of the blocks typically did not exceed one tonne in order to allow easy handling with the lifting tackle available at the time. Later, the
Romans invented hydraulic cement and concrete technology
took its place in works at sea. Though concrete structures
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necessary for the construction of berthing gravity structures.
• requirement of high standards of quality in material and
construction methods
In the 20th century, the use of prefabricated concrete cellular
caissons has become the most widely used solution for large
and deep quays all over the world. The possibility of using
specialised construction facilities that allow time and cost
reductions and floating plant for transportation and placement, are important advantages of this technique. Several
types of caisson have been developed. Classification can be
made based on the horizontal section of the caisson (circular, parallelogram), the geometry of the cells (cylindrical,
parallelepipedic), the type of front face (ranurated, perforated, slotted, non-permeable, etc). Provided there are good
quality foundations, most of the quays in Europe are being
constructed with this technique.
• availability of suitable construction equipment
• narrow tolerances in put-in-place operations.
2.2 Types of application
considered in this catalogue
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In the last four decades the use of prefabricated elements in
the construction of port and coastal structures has become
very common practice. Prefabricated elements provide important advantages, such as improved hydraulic performance when compared with natural materials, ecological
benefits, cost reduction, construction efficiency, etc. As a
consequence, numerous new prefabricated units have been
designed for a wide variety of engineering applications,
such as breakwater protection, coastal erosion control, stability of river banks, reflection damping on quays, attenuation of waves, etc.
In estuaries and rivers, soft soil conditions led to solutions
based on rigid or flexible wall structures made with wooden
piles and plates. Higher loads and depths required by larger
cargo and ships required the use of metallic piles, sheet piles
or concrete prefabricated piles. Since the 19th century when
Mitchell-type metal piles were introduced in the construction of maritime works, manufacturers all over the world
have developed a wide variety of prefabricated elements.
As well as in the case of prefabricated caissons, the amount
of different designs exceeds the scope of the present catalogue.
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In this chapter, the types of application of prefabricated elements in maritime and fluvial works are briefly described.
The structures are classified into four types:
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a) Breakwaters
b) Revetments and seawalls & coast protection
Prefabricated elements have been used also as an alternative
for the protection of river banks and channels. Vegetation
cover and rip-rap were traditionally used for this purpose.
Geotextile techniques and protective layers of prefabricated
elements have become more and more commonly used for
this purpose.
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c) Quays
d) Bank protection.
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2.2.1 Breakwaters
Prefabricated elements have been commonly used for the
construction of the protective layer of rubble mound breakwaters. In some cases, artificial elements have also been
used for the core (Port of Gijón) or filter layers. On occasion, superstructures and parapets have been constructed
with massive regularly placed prefabricated units.
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In general, the major advantages of prefabrication in maritime works can be summarised as follows:
• standardised design and construction methods
• less variation in quality and easier and more efficient
quality control
Past PIANC Congresses, collected and resumed in PIANC´s
Centennial Jubilee Memorial Book, have illustrated the
technical debates about the applicability of different techniques. L.F.Vernon-Harcourt, H. Wortman, V. Benezit, J.
Lira, E.J. Castro, R. Iribarren, J. Larras, Hudson, A. Paape,
F. Abecasis, F. Vasco Costa, A. Torum, P.A. Hedar, and many
other excellent researchers and engineers established a solid
foundation for future development of coastal engineering.
• facilitates or eliminates formwork, especially underwater
• less dependence on weather conditions
• reduction of construction time
• reduction in cost.
Wave dissipating concrete blocks, such as Tetrapods and
Dolosse, are popular prefabricated elements used for some
time in rubble mound and composite breakwater construc-
On the contrary some disadvantages can be identified:
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tion. The main role of such concrete blocks is to reduce
wave reflections and wave forces acting onto caissons. Their
roles have proved to be reliable in the course of their history
of about 50 years.
• “Hard” measures: seawalls, revetments, groynes, detached breakwaters
Concrete blocks of relatively flat shape are major prefabricated elements used as cover layer in the structures of revetments, seawalls and other “hard” approaches to coast protection. They provide armour for slopes of natural soil and/or
rubble, protecting the structures from erosion and scouring
caused by wave attack. A wide variety of types of modular
blocks and cabled block types have also been developed and
patented in the last decades. Flexible materials have also
been used as a cover layer, e.g. bag blankets, stacked-bags,
fabric mattresses, and tubes, etc.
Recently, new types of breakwaters, such as vertical wave
screens and skirt breakwaters, etc., have been developed. A
wave screen is a porous vertical wall, usually constructed
using rectangular slats oriented in either a horizontal or
vertical direction and attached to vertical piles to support
structures. Wave screens can reduce wave transmission by
up to 80%. In addition, environmental considerations are
an important requirement for maritime structures. For example, a new type of submerged breakwater, so called artificial reefs, composed of purpose-designed concrete frame
units has been invented and their effectiveness in providing
a good environment for ecosystems has been proved in actual site applications.
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For the cover layer, stability against uplift forces and degradation of the subsoil are major aspects to be carefully considered in the design phases. Stone size and thickness of
under layer should be carefully selected.
In recent years, a wide variety of geotextiles has been developed and used as the filter layer of structures of revetments, seawalls & coast protection. Geotextiles generally
allow the installation of sublayers or cover layers beyond
conventional filter rules. Geotextiles are easily damaged,
especially during installation, and are rather difficult to repair. Therefore, special care must be taken when contacting
with the subsoil.
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Prefabricated large units have been traditionally used for the
construction of monolithic-type breakwaters. Many breakwaters in Japan, Italy and Spain are built based on the addition of large rectangular blocks or caissons. The floating
caisson technique, developed in the last half century, has
allowed the construction of breakwaters in deep water in a
very economical way, for example the South breakwater of
the Santa Cruz de Tenerife port (Spain) reaches the 60m water depth contour. A wide number of configurations of prefabricated units, aimed at improving hydraulic performance
(Jarlan-type, slotted-type, curved slit-type, multi-cellulartype, etc) have been developed recently, mainly in Japan.
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As for the design and construction of revetments using geotextiles, the documents, such as the PIANC reports of PTC I
WG4 and PTC II WG 21, can be used as guidelines.
2.2.3 Quays
2.2.2 Revetments, seawalls & coast protection
The use of prefabricated elements for the construction of
quays derived from three major aims:
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Coastal protection has long been a response in the fight of
man against wave action. Littoral erosion was recognized as
a loss of quality and surface of coastal lands. Former methods of coastal protection were always based on the “hardening” of the natural erodible materials. Large amounts of
rip-rap and rocks were placed along eroded shores. In most
cases, long-term evolution of the coast produces the progressive degradation and failure of this type of protection.
- to reach deeper depths for large vessels
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- to improve cost-effective construction methods
- to reduce wave reflection for wave disturbance purposes.
The most important developments for the first and second
aims were the development of the pile and sheet piling techniques, and the prefabricated caisson technique.
The conceptual comprehension of littoral processes by engineers in the 16th century promoted the adoption of new
types of remedial measures, such as groynes or detached
breakwaters.
Floating caissons, upright wave absorbing caissons and
modular blocks are popular prefabricated elements in quay
structures. Concrete sheet piles and concrete beams are also
found in quay structures. Other advantages of prefabricated elements in the construction of quays are derived from
improved technical performance (wave reflection), easier
construction methods, economics and lower environmental
impacts.
As coastal protection becomes a vital strategy for land protection and reclamation, cheaper and safer approaches were
required. At present, two major types of protection measure
can be applied:
• “Soft” measures: beach renourishment, algae plantation
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Gravity quays are used in loading and unloading vessels.
These structures, when backfilled with soil, rely on the
structure weight to resist the resulting earth pressure. The
most common types of gravity quay are those constructed
by concrete blocks, those developed with floating caissons
and, for smaller vertical structures, steel sheet piling backfilled with soil.
navigable channels to protect against boatwash and in canals
to provide a watertight surface and prevent leakage.
Steel piling is, therefore, the most common method but has
a limited life before decay sets in. A frequent problem in
many waterways today is the failure of sheet piling installed
decades ago. Given its disadvantages of high cost, limited
life span and the fact that it does not provide a habitat for
flora and fauna, sheet piling can only be considered effective when assessed against a very narrow range of criteria.
There is therefore a need to consider alternative methods of
bank protection which are more environmentally sensitive
and, ideally, of lower cost.
Caisson quays are prefabricated sand-filled concrete caissons. They have different sizes and forms. Usually, they
depend on the available formwork of the construction company. The foundation must support the structure and resist
sand scour and usually consist of a mat or mound of rubble
stone. Depending on site conditions, caissons are generally
suitable for depths from about 5 to 8 m and they can reach
depth up to 26 m. Beyond this limit, pressures upon the
foundation may exceed the acceptable values, if it is formed
by rock.
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Most canal banks have traditionally been protected by vegetation and stonework. Stone walls are used on most of the
English narrow canals and stone revetments on some of the
larger canals.
Traditional design methods for caisson quays take into account the verification of safety factors for the main failure
modes:
- Sliding
The intent is to select decision-making so that cost-effective solutions to bank erosion problems can be developed
through integrating engineering, ecological and economic
considerations.
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- Settlement or collapse of foundation
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- Overturning
In tidal rivers, the main methods in current use are concrete
revetments with Reno mattresses or stone rip-rap to protect
the toe of the bank, blockstone and sheet piling.
- Global failure (caisson-foundation failure).
Concrete unit revetments combine the advantages of individual concrete units or blocks that may be transported and
installed as modules with the coverage and protection of a
revetment. Revetments deflect wave energy, thus protecting
the bank from erosion.
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The failure modes are calculated for different action and
load combinations. Main variables affecting load combinations are: caisson weight, hydrostatic and dynamic wave
forces, earth forces, mooring loads, storage overload, machinery movement, overload acting upon the caissons.
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The design of the revetment can be an open joint revetment:
simple precast blocks laid with no positive interconnection
between adjacent blocks. Stability of the revetment is then
dependent on the stability of the individual blocks.
2.2.4 Bank protection
©
Bank erosion is a natural geomorphological process, which
occurs in all channels. It is one of the mechanisms by which
a channel adjusts its size and shape to convey the discharge
and sediment supplied to it from the surrounding land. As
a natural process, bank erosion is generally beneficial, particularly to the ecology of waterways. Erosion and deposition create a variety of habitats for flora and fauna, which
contribute to ecological diversity.
Alternatively, the blocks can be interlocked. Interlocking
blocks have positive interconnection between neighbouring
blocks, helping to distribute loads and providing some reduction in unit weight. The resultant revetment has restricted flexibility. Various forms of blocks are available, locking
in plan and in elevation.
However, erosion adversely affects riparian landowners
whose land is lost, particularly where houses, factories or
other buildings on the bank are damaged or destroyed. The
loss of the bank also affects those who use it for grazing,
fishing or recreation.
Blocks may also be held together by cables to form a large
flexible mat that may be laid by crane using a purpose-built
spreader frame. The blocks combine flexibility with restraint
under heavy loading. The mats are easy to lay underwater
and are less likely to be subject to progressive local failure.
Cables are made from steel or synthetic materials such as
polypropylene.
The predominant method of bank protection on many waterways all over the world has been sheet piling. It is used on
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3. CONSIDERATIONS
FOR SELECTION
Superstructure.
Armour units
3.1 Prefabricated elements for breakwaters
Toe block
Core
3.1.1 Types
Four broad categories of breakwater can be identified:
• Rubble mound breakwaters
SINGLE-LAYER (order) ARMOUR
• Vertical breakwaters
• Mixed-type breakwaters
Superstructure.
• Curtain-wall breakwaters.
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Armour units
Rubble mound breakwaters
Core
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As mentioned in Chapter 2, rubble mound breakwaters are
the most common type of breakwater in the world. They
have been widely constructed in several forms and designs.
Vertical breakwaters have also been commonly constructed
in some countries, in particular in Japan, Spain and Italy.
Mixed type breakwaters, consisting of an upright section
covered with a wave-dissipating layer of blocks, have recently been constructed, predominantly in Japan.
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SINGLE-LAYER (random) ARMOUR
In the case of rubble mound-type breakwaters, the use of
prefabricated elements has been primarily in the formation
of the armour layer with a view to improve its resistance
against wave action or to overcome lack of appropriate natural rock units. Numerous different artificial armour units
have been developed since concrete cubes were first used
with this purpose.
©
Prefabricated armour units can be sub-divided into the following categories, according to the type of placement:
- Double or multiple-layer armour units randomly placed
- Single-layer armour units orderly placed.
Four broad types of units exist, based on unit geometry:
- Massive or blocky units
Core
MULTI-LAYER ARMOUR
Bulky units as e.g. Accropode, Haro, Betas, Seabee and others, have been used as both multiple-layer and single-layer
armour. The stability of the armour layer is then based mainly on the high degree of interlock between adjacent units.
The recent trend of breakwater construction in deep water
and rough seas requires the use of large size blocks, and
another problem of the block strength has arisen lately.
- Bulky units
- Slender units
- Multi-hole cubes.
Armour units
Massive units, for example cubes, parallelepipedic and Antifer-type units, are usually placed as multiple-layer armour.
Resistance against wave action depends primarily on the
self-weight of the unit and the interlocking degree with adjacent units. If placed in a single layer, uplift forces caused
by water gradients must be compensated by self-weight and
friction forces.
- Single-layer armour units randomly placed
Superstructure.
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Mixed type breakwaters
Slender units are vulnerable to cracking and breaking because their limited cross-sectional areas, as a solution of this
problem various types of high-strength concrete and reinforcement have been considered (e.g. Dolos, Tetrapod).
Two different types of breakwaters fall into this category:
- Vertically composite caisson breakwater
Multi–Hole cubes, like Shed or Cob, are placed correctly in
patterns that exclude significant relative movements of the
blocks. Due to the slender structural members with rather
tiny cross sections, the limiting factors (excluding impacts)
for long-term durability are material deterioration, abrasion
on sandy coasts and fatigue due to wave loads.
- Horizontally composite caisson breakwater.
Caisson
Rock armour
Vertical breakwaters
Rock fill
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Vertical breakwaters are usually constructed with sand-filled
caissons made of reinforced concrete, but blockwork types
made of stacked precast concrete blocks are also used.
The caisson itself is the prefabricated element more widely
used for the construction of these types of breakwater. A
large number of different designs have been developed. Variations in the cross-section geometry (rectangular, semi-circular, trapezoidal, etc.), in the horizontal section (rectangular, cylindrical, triangular, etc.), in the geometry of the cells
(circular, square, hexagonal, etc.) or in the wall structure
(solid, perforated, slotted) leads to a broad classification.
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VERTICAL COMPOSITE BREAKWATER
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Concrete armour units
Scour protection
Fill
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In-situ cast
concrete cap
Caisson
Caisson
HORIZONTAL COMPOSITE BREAKWATER
Bedding layer
For the first type, the caisson, almost equal to the one used
for a simple vertical breakwater, is placed on a relatively
high rubble mound foundation.
CONVENTIONAL VERTICAL BREAKWATER
In the case of the horizontally composite type, the front of
the caisson is covered by armour units. This type is widely
used in Japan for shallow water zones. The armour reduces
wave impact forces on the caisson, wave reflections and
wave overtoppings.
©
In-situ cast
reinforced concrete
Block
Prefabricated units used for the cover layer are usually the
same as used for rubble mound breakwaters.
Curtain-wall breakwaters
Curtain-wall or wave screen breakwaters consist of an inclined or vertical curtain wall mounted on pile work. This
type of breakwater is applicable in mild wave climate on
sites with weak and soft subsoils. Almost all the principal
parts of a curtain breakwater (piles, curtain modules, connectors) should be prefabricated.
BLOCK WORK VERTICAL BREAKWATER
Generally speaking, vertical breakwaters are less economical than rubble mound structures in the case of shallow water but in deep water they become a cheaper solution.
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Assessment of stability of concrete armour units is primarily
based on methods originally developed for rock armour. R.
Iribarren and Nogales (1965) extended the formula originally developed by Castro (1935) to parallelopipedic blocks.
The prediction method of Hudson as given in the Shore Protection Manual (CERC, 1973, 1977, 1984) was originally
developed for rock armour. Extensive physical model testing over the years has derived values of the KD coefficient
for rock and a range of concrete armour unit types. These
are typically quoted by unit manufacturers, in design guidance available in the literature e.g. CIRIA/CUR (1984),
CUR (1995), SPM (2003) or in national design standards.
Further work on the assessment of armour unit stability
was undertaken by several researchers replacing Hudson´s
formula (see references). Due to the wide variety of units
available, and their varying response to wave conditions,
structure geometry and other variables, in many cases it is
necessary to undertake project-specific physical modelling
studies of armour stability.
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Useful information of all these type of breakwaters can be
found in the reports of PIANC Marcom WG 12 (1992) and
WG 28 (2003).
3.1.2 Structural integrity
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When using prefabricated units in marine construction, the
following should be considered:
Integrity of individual units
- Stability of the structure as a whole
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Structural stability
Prefabricated armour units are generally made of conventional unreinforced (mass) concrete, except some multi-hole
cubes where fibre reinforcement is used.
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- Integrity of the individual units.
As the size of individual units grows with the aim of resisting higher storm waves, some large rubble mound breakwaters have experienced damage due to the breakage of the
units. In most cases breakage took place before the hydraulic stability of intact units in the armour layer expired. It can
be deduced that there is an imbalance between the strength
(structural integrity) of the units and the hydraulic stability
(resistance to displacements) of the armour layer.
Prefabricated units may require careful placement with narrow tolerances to ensure integrity. Preparation of underlying material should ensure that the required tolerances are
met. It may be necessary to place prefabricated units on a
geotextile, particularly for those units where voids may be
large enough for underlying material to be lost. Guidance
is available on the use of geotextiles in the marine environment (PIANC, 1992).
The integrity of individual prefabricated units will depend
on concrete (or other material) quality, which should be adequate for use in the marine environment. Besides stresses
caused by mechanical and hydraulic loads, another problem
related to the structural integrity of concrete armour units is
the thermal stress developed during the process of curing.
Slender and big-size units are more sensitive to cracking
phenomena, due to the temperature gradients created by the
hydration process.
©
Stability of the prefabricated units is normally achieved by
selecting a unit size or weight that is sufficient to resist the
hydraulic loading the structure will experience. For large
concrete armour units used in breakwater and revetment
construction, stability may depend on some, or all, of the
following depending on the shape of the unit:
- weight or mass – as is the case for rock;
- interlock – due to complex geometry: this can bring
economies as less weight and hence material may be required;
Fatigue of concrete structures should also be considered
when repeated stress variations are significant. The waves
will cause pulsating and impact forces on the armour units
and thus significant stress variations.
- energy dissipation – this is often the case with hollow
blocks; and also with interlocking units where voids
between randomly placed units assist in dissipating
energy.
As discussed above, the units selected should be of adequate
size to ensure stability under hydraulic loading. Movement
of units under storm conditions may lead to abrasion or degradation, ultimately resulting in their failure. However, it is
Bblz-Marcom36+CR.indd 12
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advisable to limit the size of the slender-type units in order
not to exceed acceptable stress levels.
of layers of the armour. This tendency moves the structure
from a flexible to a rigid behaviour. As a consequence, failure modes may vary from gradual displacements to sudden
and global collapse. This failure mode must be carefully assessed in the design process of a breakwater protected with
a single layer armour.
In very dynamic environments, consideration should be given to the potential for abrasion by mobile sediment, which
may over time lead to a reduction in performance.
3.1.3 Hydraulic performance
Aesthetics
There are three major factors that should be considered
when evaluating the hydraulic performance of prefabricated
units for rubble mound breakwaters:
In some locations, prefabricated elements may be less preferable on aesthetic grounds than natural materials. In an attempt to overcome this, some types of units have been developed that either have a surface dressing of natural materials
or are finished to give the appearance of natural materials.
In other circumstances, local opinion may favour geometric
forms of construction using repeating shapes, that are easy
to form using, say, hollow cube armour placed in an orderly
way.
- the ability to attenuate wave run-up and overtopping
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- the ability to absorb the energy of waves as they break on
the slope, thus diminishing wave reflections
- the ability to control wave transmission.
The wave run-up level is one of the most important factors
affecting the design of coastal structures because it determines the design crest level of the structure in cases where
no or minor overtopping is acceptable.
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Environmental impact
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The coastal and fluvial zone is usually a fragile and limited
environment that can be affected in a serious and irreversible way. Fabrication of prefabricated elements in dedicated
locations away from areas to be protected can avoid or attenuate impacts on sensitive environment areas by factors
such as construction traffic, water quality, noise, air pollution, amongst others.
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The use of prefabricated armour blocks in breakwaters normally tends to increase the surface roughness and the porosity when they are randomly placed. Both factors result in
the reduction of wave run-up and wave reflections. If the
armour is formed by units placed in a certain pattern or in an
orderly way, both porosity and roughness may decrease. As
a consequence, run-up and reflections increase.
Maritime facilities and structures generally remain in service for long periods of time, during which their functions
must be maintained. It is thus essential not only to give due
consideration when initially designing the structures, but
also to carry out appropriate maintenance after the facilities
have been put into service.
Global porosity of the breakwater cross-section has an important influence on several hydraulic phenomena like armour stability, transmission, reflection or run-up. Singlelayer armour solutions normally result in a lower global porosity that must be compensated by increasing the porosity
or thickness of the inner layers, if high porosity is required
in the design.
In order to maintain the functions of maritime structures at
a satisfactory service level and to prevent deterioration of
the safety of such structures, maintenance including inspections, evaluations, repairs, etc. should be carried out, in line
with the specific characteristics of the maritime structures.
©
Vertical and upright breakwaters have several hydraulic
disadvantages over rubble mound breakwaters. They have
very high reflection and run-up coefficients, unless the crest
is sufficiently low to allow significant wave transmission.
Wave reflections induce agitation on the neighbouring water
areas and, frequently this becomes an important problem for
fishery activities, navigation and preservation of the ecological conditions of the sea bed.
Deterioration of the strength of concrete should be considered for concrete structures and the corrosion rate should
be considered for steel structures. For other materials, e.g.
geotextiles, the deterioration or damage of fabric material
caused by aging and/or chemical effects by acid or other
substances should be taken into account.
3.1.4 Constraints
Risk of failure
Repair of maritime structures can sometimes incur higher
costs than the initial construction. For example, it is usually very difficult or sometimes almost impossible to repair
the underlayer of revetments. When selecting prefabricated
elements, ease of repair and cost of maintenance should be
taken into account.
Historical trends in the construction of rubble mound breakwaters using prefabricated elements show a tendency to
reduce the total amount of concrete by reducing the unit
weight of the individual unit and / or limiting the number
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3.1.5 Maintenance
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When selecting and designing a structure, it is necessary to
give due consideration to the requirements for future maintenance and to select the types of structures and materials so
that future maintenance will be easily executed. This aspect
should be reflected in the detailed design.
may therefore present good technical solutions which use
less materials. Particular examples of this are randomly
placed concrete units for slope protection. They rely on their
complex geometry and interlock as well as mass to provide
stability and may therefore be more economical than a rock
solution where interlock is less and mass is the main factor
in providing stability.
With respect to prefabricated concrete armour elements, in
most cases huge problems are found for repairing broken
units if land access along the breakwater is not possible.
Substitution of deteriorated units is not always an easy task
when they are strongly interlocked.
Plant
It may be necessary to use specialist plant for placement of
prefabricated unit. Consideration should be given to whether this plant will be locally available.
3.1.6 Construction costs
Construction costs can be influenced by the following variables:
Logistics
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Elements may be delivered to site prefabricated or alternatively it may be necessary to fabricate the units close to (or
on) site, in a project-specific casting yard. Sufficient (level
and firm) land must be available for forming the units, removing moulds, curing and storage in sufficient quantities
to allow construction to proceed without delay.
Material availability
Prefabricated elements may be used where appropriate natural materials (e.g. narrow grade rock armour or wider grade
rip-rap) are not readily available. For example, for breakwater or revetment construction, prefabricated armour units
may be used where rock of adequate size, quantity or quality
is not readily available. Or perhaps, pre-cast concrete elements might be used for a wave screen where timber is not
available or might be rapidly damaged by borers.
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Fabrication cost and fees
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Consideration should be given to the cost of manufacturing
or hiring moulds for prefabricated units if they are to be cast
on site. It may also be necessary to obtain consent for use
of a particular unit and in some cases a licence fee must be
paid.
Construction access
Placement of prefabricated elements might be preferable to
in-situ construction where access is restricted to short durations by tide conditions or wave attack or where construction requires to take place under water.
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Materials to be used in structures and foundation works are
selected after giving due consideration to the external forces
acting on them, deterioration with time, lifetime of structures, shape of structures, workability, cost, impact on the
environment, and other matters.
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Tolerances
In order to obtain the required performance and structural
integrity from prefabricated units, it will often be necessary
to place them to narrow tolerances, specified grids. This
should be considered in conjunction with access, labour and
plant availability to ensure these requirements can readily
be achieved.
©
Concrete
Concrete is the most popular material in the field of prefabricated elements. Conventional unreinforced concrete is
used for massive and bulky units and steel bar reinforced
concrete is used for high interlocking blocks and vertical
wall blocks. Pre-stressed concrete is also used for concrete
sheet piles and beams. Recently, recyclable resources, such
as slag and/or coal ash, are considered as concrete materials
as replacing cement, sand or aggregate.
Labour
The degree of skill required for installation of prefabricated
elements should be carefully reviewed. Particular systems
may require careful installation to manufacturer’s specification. This may be important where unskilled labour is to be
used.
Unreinforced concrete is a brittle material with a low tensile
strength (1.5–3.0 Mpa) and a compressive strength, which is
one order of magnitude larger. As the reason for breakage of
units is due to tensile stresses it is therefore important that
tensile performance requirements are reflected in the specifications for concrete to be used in armour unit fabrication.
Hydraulic / structural performance
Many prefabricated units have been specifically developed
and optimised for hydraulic / structural performance and
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3.1.7 Materials
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3.2 Prefabricated elements for quays
Design and construction of caisson quays is very similar to
vertical breakwaters (see chapter 3.1). A large number of
different designs of caissons have been developed. As the
berth line has to be straight rectangular caissons are predominant. Main variations consist in the geometry of the
cells (circular, square, hexagonal, etc.).
A great number of structural parts in a quay can be prefabricated. Historically, piles were the first precast element to
be used with the purpose of enabling foundations in soft
ground conditions. Subsequently concrete caissons and
sheet piles were introduced.
3.2.1 Types
Concrete blocks of different forms have been developed for
the construction of blockwork-type quays, with the aim of
minimising wave reflections. In the case of cribwork-type
structures, designs have been dictated, primarily, by the use
of readily available construction facilities.
From the structural point of view, three broad categories of
quays can be established:
• Gravity quays
• Curtain-wall quays
Cribwork structures consist of the formation of a box by
interlocking prefabricated straight elements of steel or concrete and then in-filling to act as a gravity quay.
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• Open-Piled quays.
Gravity quays
Cellular and floating caissons, wave-attenuating blocks and
crib-pieces are usually prefabricated elements in gravity
quays.
Gravity quays are the most primitive but may be the most
economical type if sea bed soils are strong enough to resist
high foundation loads. Three main types can de identified:
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- Caisson quays
Steel sheet piles are widely used for the construction of curtain wall quays. A wide number of steel sheet piles have
been developed (Larssen, Hoesch, flat-web section, box section, Z-sections, I-sections, etc.) The use of steel sheet piles
as a prefabricated element in quay construction is described
in detail in PIANC Bulletin nº 59.
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- Blockwork quays
- Cribwork quays.
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Superstructure
Caisson
Curtain wall quays
Superstructure
Fill
Backfill
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Anchor
Steel sheet piles
Scour protection
Fill
©
Bedding
GRAVITY QUAY. Caisson-type
Superstructure
CURTAIN WALL QUAY
Dissipating block
Open piled quays
Fill
Bedding
Open-piled quays are commonly used in ports around the
world and are commonly used in soft soil areas. Piles are,
in some cases, prefabricated (steel tubes, pre-stressed concrete) and put in place by drilling or driving. Useful information on the use of prefabricated piles is contained in PIANC Bulletin nº 54.
Backfill
GRAVITY QUAY. Blockwork-type
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Hydraulic performance of the armoured slope under open
piled quays against the action of waves is very similar to
those described for breakwaters (see Section 3.1.3).
Superstructure
Pile
Slope protection
3.2.4 Maintenance
Fill
In order to limit deformations or settlements of structures
used for berthing, particularly in areas with a high degree of
exposure to hydraulic conditions or aggressive agents, regular inspections are required.
OPEN-PILED QUAY
The principal aims of the survey are to determine:
- the structural integrity of elements of the structure
- the appearance of deterioration processes
- indication of movements, deformations and settlement
Failure modes can be classified in two main groups:
- indication of scouring processes at the toe of the quay.
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Analysis of the structural stability of quays strongly depends
on the specific type.
- Overall stability modes
- Local failure.
3.2.5 Materials
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Reinforced concrete
Seaward overturning and sliding, together with global structure-soil slip and settlement are included in the first group.
Most of them apply for all type of quays.
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One of the main considerations in the design and production
of reinforced concrete is to achieve the appropriate cover
to reinforcement bars. The provision of a sufficient cover
thickness is the most positive way of reducing the risk of
corrosion damage. A nominal cover thickness of 50 mm is
considered to be a minimum and is only suitable for very
mild and controlled conditions. For severe exposure conditions it may be recommended to at least double the cover.
Different National standards and the publication EN 2061 (European Committee for Standardization, 2000) can be
used as guidelines.
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Local modes of failures are more in relation to the strength
of the prefabricated elements used in the formation of the
structure. Breakage of elements (blocks, piles, sheet piles,
etc.) depends mainly on the loads acting on and the strength
of the material used.
©
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Conventional unreinforced concrete, if well fabricated, usually shows an acceptable level of resistance against longterm loads such as corrosion or fatigue. Other material such
as reinforced concrete, pre-stressed concrete, timber or steel
are more sensible to deterioration (corrosion), in particular
in the intertidal and splash zones.
Reinforced concrete quality is also influenced by the cement
type, the mix quality as determined by the water-cement ratio and the placing tolerance that can be achieved.
3.3 Prefabricated elements for
revetments and seawalls
Gravity quays and curtain wall quays reflect some proportion of the wave incident energy. If significant, this process
can generate high levels of wave disturbance that can affect
the operation and safety of berthed ships.
3.3.1 Types
Slope revetments may be divided into several categories e.g.:
• Natural material (sand, clay and grass)
The energy of incident waves can be partly dissipated by
turbulence in holes and slots opened in the front face of
the quay. Changes in the wave phase can also contribute to
reducing wave disturbance. These two mechanisms are the
basis of the behaviour of attenuating solutions as e.g. attenuating blocks, perforated and slotted walls, non-straight
walls, etc.
16 16
• Protection by loose units (gravel, rip-rap)
• Protection by concrete or asphalt slabs
• Protection by interlocking units (concrete blocks and
mats).
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Concrete blocks of relatively flat shape are prefabricated elements that are commonly used as a cover layer in the structures of revetments, seawalls and coast protection. They
provide armour for slopes of natural soil and/or rubble, protecting the structures from erosion and scouring caused by
wave attack. A wide variety of types of modular blocks and
cabled block types have also been developed and patented
in the last decades. Flexible materials have been also used
as a cover layer, e.g. bag blankets, stacked-bags, fabric mattresses, and tubes, etc.
The stability of a revetment protection against the attack of
waves depends on such factors including friction, cohesion,
weight of the units, interlocking and mechanical strength.
The stability of the revetment strongly depends on the sort/
composition of the sublayers and the subsoil conditions. As
a consequence, they must therefore be regarded as a whole
system.
As a rule of thumb, the permeability of the different layers
of the revetment must increase from underneath to top. As
granular filters are mostly more expensive and difficult to
realize within the required limits, a geotextile may be substituted instead of a graded stone layer.
For the cover layer, stability against uplift forces and degradation of the subsoil are major aspects to be carefully considered in the design phases. Stone size and thickness of
under layer should be carefully selected.
Under wave attack, instability of artificially paved revetments occurs at the peak of the maximum down rush, where
uplift forces are higher, just before the arrival of the next
wave front. If the protection layer is pervious uplift pressures are strongly reduced. In this case, instability will occur due to the combined effect of uplift and impact forces
caused by wave breaking over the revetment.
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In recent years, a wide variety of geotextiles has been developed and used as the filter layer of structures of revetments,
seawalls & coast protection. Geotextiles generally allow the
installation of sublayers or cover layers beyond conventional
filter rules. Geotextiles are easily damaged, especially during installation, and are rather difficult to repair. Therefore,
special care must be taken when contacting with the subsoil.
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For the dimension of a revetment the following failure
modes must be taken into account:
• Sliding of the upper (prefabricated units) layer
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As for the design and construction of revetments using geotextiles, the documents, such as the PIANC reports of PTC I
WG 4 and PTC II WG 21, can be used as guidelines.
• Extraction of the units by uplift forces. Self-weight and
interlocking forces should be greater than uplift pressures caused by water gradients
• Global equilibrium (geotechnical instability). The revetment, as a whole, including sublayers and subsoils must
be in equilibrium.
In order to ensure that the structure remains stable the following issues should be considered in design.
Numerous proprietary concrete blockwork systems are
available for use as bank protection and revetment armour.
Design guidance for stability is often very specific to the
particular block type. Generic methods are available for determining the block size required for stability under wave
attack, based on physical model tests undertaken by Klein
Breteler & Bezuijen (1991) (also see PIANC (1992).
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Marine structures such as revetments, seawalls and coast
protection are often constructed from a core of granular fill
material, protected by a series of filter and armour layers.
In-situ material e.g. banks or coastal dunes, may be reprofiled before protective layers are placed. Alternatively, earth
retaining structures may be constructed, such as for quay
walls.
©
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• Water gradients due to incoming waves caused by wind
action or passing vessels may induce uplift forces acting
on the units.
It is essential to ensure that the core or in-situ material is
adequately compacted and that there are no voids, which
may lead to deformation or settlement of the structure during its life.
Klein Breteler & Bezuijen‘s method can be used to predict
block thickness for a wide range of support conditions, but
requires careful categorisation of underlayer materials. The
range of uncertainty in tabulated values of the stability coefficient Sb is relatively wide. In exposed locations, this can
result in blocks of significant thickness. Guidance should
therefore be sought from potential product suppliers who
may have product-specific design guidance that takes into
When designing filter, underlayers and armour layers, the
engineer should ensure that filter criteria are met to prevent
loss of fines from underlying material and adequate permeability to prevent build up of hydraulic pressures with the
structure.
Where the structure has a sloping face this should not exceed the natural angle of friction of the fill material.
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consideration the contribution to stability of other factors
such as interlocking, inter-block friction etc.
concrete, asphalt, geotextile, etc. Useful information about
the standards and specifications for these materials can be
found in several publications (SPM, 1984, TAW/CUR, 1984,
CIRIA, 1986, PIANC 1987a).
Where proprietary concrete blocks are to be used for bank
protection, they should be designed for stability under the
expected flow velocities. Guidance is given by 0CIRIA
(1987) on limiting flow velocities for various block thicknesses.
Prefabricated elements used in seawall and revetments are
usually made of conventional unreinforced concrete.
3.4 Prefabricated elements
for bank protection
Wave run-up and overtopping depends on several factors:
wave height (+) and period (+), angle of approach (-), surface roughness (-) of the upper layer, permeability of the
layers (-), slope and profile shape. In general, milder slopes
lead to lower run-up elevations.
The strategies for controlling bank erosion can be classified
into six types:
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1. Allowed natural adjustment; permitting erosion to continue and monitoring that the acceptable expectations
are being met.
Energy reflected from incoming waves generally increases
with the Iribarren number ( ). The wave reflection coefficient also increases with steeper slopes and diminishes as
the surface roughness and permeability increases.
2. Management; based on addressing the causes of the
problem.
3. Relocation; based on moving the affected activities to a
less vulnerable location.
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Prefabricated units with arms, legs, holes or protruding
forms contributes to attenuate the energy of the incident
waves, thus reducing reflection, run-up and overtopping.
4. Bioengineering; based on utilising the engineering role
of vegetation to stabilise the bank.
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3.3.4 Maintenance
5. Biotechnical engineering; based on combining the engineering role of vegetation with the structural benefits of
inert materials.
Multiple hydraulic interactions between inner fill, filter layers, protective layer, bed soil, joints and other variables that
converge in a revetment, mean that regular and frequent surveys should be carried out to ensure integrity of the structure.
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6. Structural engineering including not only bank reinforcement measures but also others oriented to control
the flow.
Surveys should check for the following:
The strategy chosen should take account of the consequences of bank failure. Where these are rated as severe, the risk
associated with the failure of any strategy is high. A low-risk
strategy is therefore appropriate. For example, where flood
defence is in question or navigation threatened, structural
engineering is likely to be the only appropriate strategy.
Where the consequences of bank erosion are less significant, a riskier solution may be more appropriate because of
its lower cost and, compared with structural engineering, its
greater benefit to ecological habitat and landscape.
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• Deformation of the revetment layer. This could warn
about the failure of the subsoil and inner layers. Core
material may be settling or flowing out through the filter
layers.
• Loose of revetment units. Due to the role of interlocking
on the stability of the outer layer of the protection, the
displacement of an individual unit could lead to rapid
failure. Substitution with prefabricated or cast-in-place
units may be required.
• Settlement of the crest level of the bank. This may indicate loose core materials, scouring of the toe or geotechnical instability of the bank.
Allowed natural adjustment should be the first option considered in any situation. It is particularly appropriate where
any other approach requires a level of investment, which
cannot be justified in economic or environmental benefits
or where the intervention would cause bank instability
downstream or upstream.
3.3.5 Materials
The following materials are commonly used in the construction of seawalls and revetments: sand, gravel, quarry rock,
industrial waste-products (slags, minestone, etc.), timber,
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Where natural adjustment is not acceptable, the second option should always be positive management of the bank.
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A structural engineering strategy, sometimes termed ‘hard
engineering’, includes the use of steel, concrete or timber
piling, often to create vertical banks. Other materials include rubber tyres and stones. It is particularly appropriate
wherever there is a risk of:
revetment. The revetment deflects wave energy, thus protecting the bank from erosion.
Bank protection using concrete units can be achieved by
three different approaches, as for coastal revetments discussed in Section 3.3.
• flooding of surrounding land
Open joint revetment
• damage to structures
Simple precast blocks are laid with no positive form of interconnection between adjacent blocks. Stability of the revetment is dependent on stability of individual blocks.
• damage to property, towpaths, roads, railways
• damage to canal lining with consequent loss of water in
the channel through leakage
Close-jointed block
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• rapid scour of the channel bed material.
Structural solutions are suitable where:
- flow velocities are extremely high
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- porewater pressures encourage movement of the lower
bank
Backfill
OPEN JOINT BANK PROTECTION
- strong tidal currents occur
Interlocking blocks
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- boatwash is high and cannot be reduced by management
of the volume of traffic and type of craft
Interlocking blocks have positive interconnection between
neighbouring blocks. The resultant revetment has restricted
flexibility. Geometry and physical size of blocks are factors that must be considered if there is a curvature required.
Blocks are laid by hand.
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- drawdown is frequent and rapid with large fluctuations
in flow depth.
3.4.1 Types
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Structural solutions for bank protection fall broadly into the
following categories:
Concrete block
• stone revetments, concrete bags and gabions
• timber and sheet piling
Free-draining material
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Fundation toe
• gravity walls and in situ concrete revetments
• concrete unit revetments.
The concrete unit revetment is one of the categories of the so
called “structural solution”.
INTERLOCKING BLOCKS BANK PROTECTION
Cable-tied
Within this category, a wide number of prefabricated elements have been developed under different trade names (see
below).
Blocks are held together by cables to form a large flexible
mat that may be laid by crane using purpose-built spreaderframe. The blocks combine flexibility with restraint under
heavy loading. The mats are easy to lay underwater and are
less likely to be subject to progressive local failure. Cables
Concrete unit revetments combine the advantages of individual concrete units or blocks that may be transported and
installed as modules with the coverage and protection of a
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are made from steel or synthetic materials such as polypropylene.
The roughness of the protection layer is one of the main
factors affecting current flow. Turbulence generated in the
water layer close to the surface of the bank induces loss of
energy and velocity.
Block
With respect to reflection and run-up of waves, trends are
similar to those outlined for coastal revetments (see Section 3.3.3).
Connecting cable
Filter
Prefabricated units with arms, legs, holes or protruding
forms contribute to attenuation of the energy of the flow or
waves.
Geotextile
3.4.4 Constraints
CABLE-TIED PROTECTION
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In the case of revetments constructed with concrete units,
attention must be paid to ensure that there is adequate drainage from the bank through the structure to prevent the buildup of porewater pressures, which can lead to the failure of
the complete bank along with the structure.
Two major types of loads may cause instability of a bank
protection:
For revetments with slopes steeper than 1 in 3 the geotechnical instability can be a decisive factor and should be examined properly.
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- wave attack caused by passing vessels or wind-generated waves
Concrete unit revetments often protect the bank without reducing the energy of the flowing water, and can result in the
transference of erosion problem to another bank section further downstream. Special attention must therefore be paid in
the protection of either ends of the structure.
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- shear forces generated by currents caused by river flow,
tidal variations and passing vessels.
The resistance behaviour of a bank protection under the attack of waves is similar to those described in Section 3.3.2.
As the stability of the protection strongly depends on the
sort/composition of the sublayers, the subsoil conditions
and the bed stability, it must, therefore, be regarded as a
whole system.
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From the aesthetic point of view, structural solutions based
on the multiple repetition of individual forms are poorly
evaluated. Vegetation raising in joints or holes can mitigate
against the visual impact of the structure.
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Water flowing over a bed of sediment at the toe of the bank
protection exerts forces on the grains that tend to move or
entrain them. If the resultant effect of disturbing forces
(drag and lift forces) becomes greater than stabilising forces
(gravity and cohesion) particles start to move and scouring
is initiated.
3.4.5 Maintenance
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Maintenance should focus on maintaining the overall integrity of the revetment. Three major modes of start of failure
must be observed in regular inspections:
- Deformation of the surface upper layer. This could be
evidence of the failure of the subsoil and inner layers.
Core material may be settling or flowing out through the
filter layers.
Shear stress forces induced by current flow also act on the
cover layer units. Connected or interlocking units can generally be lighter than loose or free units to achieve the same
degree of resistance. Stability of free placed blocks can be
improved by washing the joints by a granular grout. Regular
maintenance is essential if this is vital to the stability of the
structure.
- Loss of revetment units. Due to the role of interlocking
in the stability of the outer layer of the protection, the
displacement of an individual unit could lead to rapid
failure. Substitution with prefabricated or cast-in-place
units is required.
Exposed edges, such as bed protection at scour holes, edges
of a toe protection and transitions between adjacent revetment systems should be carefully assessed.
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- Settlement of the crest level of the bank. Loss of core
material, scouring of the toe or geotechnical instability
of the bank could be occurring.
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3.4.6 Construction costs
lines, Structures & Breakwaters ‘98, Institution of Civil Engineers, pp46-57, publn. Thomas Telford, London.
Generally speaking, revetments made of prefabricated elements are more costly than those made of natural materials,
unless no quarries are in the vicinity of the site.
Besley P. (1999) “Wave overtopping of seawalls: design and
assessment manual”, prepared by HR Wallingford limited
for the Environment Agency, R&D Technical Report W178,
Bristol, UK.
The cost of concrete unit revetments depends on several factors:
Burcharth, H.F., K. d’Agremond, Van der Meer, J.W.
(2000).
- Source of materials
- Suitable run length
Burcharth, H.F.(1984). “Fatigue in breakwater concrete armour units.” Proc. 19th International Conference on Coastal
Engineering, Houston, Texas.
- Machinery available for unit placing
- Manual labour required for underlayer preparation
CIRIA (1987) “Design of reinforced grass waterways”
H.W.M. Hewlett et al Construction Industry Research and
Information Association, Report 61, London, UK.
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- Dimensions and fabrication costs of the prefabricated
units.
CIRIA/CUR (1994) “Manual on the use of rock in coastal
and shoreline engineering” CIRIA Special Publication 83 /
CUR Report 154, CIRIA, London.
3.4.7 Materials
Material usually used in the construction of the prefabricated units for revetments is generally mass concrete. As no
relevant tensile stresses are expected from the flow action no
special strength performances are required for the concrete.
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Coastal Engineering Manual Part VI, (2002). U.S. Army
Corps of Engineers, Washington D.C.
CUR (1995) “Manual on the use of rock in hydraulic engineering” Report 169, Balkema, Rotterdam. ISBN 90 410
6050.
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Gabions are used for bank and slope protection with stones
as core material. Stone filled bags and nets are also used as
prefabricated elements for seawalls, coast and bank protection. In those types of elements, a smaller size of stones can
be utilized compared with those to be used individually.
Escarameia M. (1998) “River & channel revetments – a design manual” publn. Thomas Telford, London, UK. ISBN 0
7277 2691 9.
Gardener J.D. & Townend I.H. (1988) “Slotted vertical
screen breakwaters” Proc. Conf. Design of Breakwaters,
Eastborne, ICE, 1988.
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BIBLIOGRAPHY
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REFERENCES
Allsop N.W.H. (1995) “Vertical walls and breakwaters: optimisation to improve vessel safety and wave disturbance by
reducing wave reflections” Chapter 10 in Wave Forces on
Inclined and Vertical Wall Structures, pp 232-258, ed. Kobayashi N. & Demirbilek Z., ISBN 0-7844-0080-6, ASCE,
New York.
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Gardner J, Townend I.W. & Fleming C.A. (1986) “Design
of a Slotted Vertical Screen Breakwater” Chapter 138, Proceedings ICCE, Publn. ASCE, New York.
Goda Y. (1974) “A new method of wave pressure calculation for the design of composite breakwaters.” Proc. 14th
Int. Coastal Eng. Conf. ASCE, New York.
British Standards Institution (1991) “Maritime Structures Part 7: Guide to the design and construction of breakwaters”
BS 6349: Part 7.
Goda Y. (1985) “Random seas and design of maritime
structures” University of Tokyo Press, Tokyo.
British Standards Institution (2000) “Maritime Structures
- Part 1: Code of practice for general criteria” BS 6349:
Part 1.
Goda Y. (2000) “Random seas and maritime structures, 2nd
edition” ISBN 981-02-3256-X, World Scientific Publishing,
Singapore.
Besley P.B., Stewart T, & Allsop N.W.H. (1998) “Overtopping of vertical structures: new methods to account for shallow water conditions” Proceedings of Int. Conf. on Coast-
Hudson R.Y. (1974) “Concrete armour units for protection
against wave attack” Miscellaneous Paper H-74-2, Waterways Experiment Station, Vicksburg.
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Klein Breteler M. & Pilarczyk K.(1998) “Alternative Revetments”, Chapter in Pilarczyk K. W. (1998) “Dikes and
revetments – design, maintenance and safety assessment”,
Balkema, The Netherlands.
PIANC (1997) “Guidelines for the design of armoured
slopes under open piled quay walls” Report of Working
Group no. 22 of the Permanent Technical Committee, Supplement to Bulletin 96 Brussels, Belgium.
Kriebel, D. L. (1992) “Vertical Wave Barriers: Wave Transmission and Wave Forces” Chapter 100 in Proceedings of
23rd ICCE, publn. ASCE, NY.
PIANC (2003) “Breakwaters with Vertical and Inclined
Concrete Walls” Report of Working Group no. 28 of the
MarCom, Brussels, Belgium.
Pilarczyk K. W. (1998) “Dikes and revetments – design,
maintenance and safety assessment”, Balkema, The Netherlands.
Kriebel D.L & Bollmann (1996) “Wave Transmission Past
Vertical Wave Barriers”, Chapter 191, Proceedings 25th
ICCE, Orlando, publn. ASCE, NY.
Van der Meer J.W. (1988) “Rock slopes and gravel beaches
under wave attack” PhD thesis Delft University of Technology. (available as Delft Hydraulics Communication 396).
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McConnell K.J. (1998) “Revetments against wave attack: a
design manual” publn. Thomas Telford, London, UK. ISBN
0 7277 2706 0.
Van der Meer J.W. (1993) “Conceptual desing of rubble
mound breakwaters”, Publication no. 483. Delft Hydraulics.
Oumeraci H., Kortenhaus A., Allsop W., de Groot M.,
Crouch R., Vrijling H. & Voortman H. (2001) “Probabilistic
Design Tools for Vertical Breakwaters” Publn. A.A. Balkema, the Netherlands.
Van der Meer J.W. (1998) “Application and stability criteria for rock and artificial units”, Chapter in Pilarczyk K. W.
“Dikes and Revetments: Design, Maintenance and Safety
Assessment”, Publn. Balkema.
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PIANC Bulletin nº 54 (1986) “Steel sheet piles as prefabricated elements in harbour construction” S.Roth.
Van der Meer J.W., Tonjes P. & de Waal J.P. (1998) “A code
for dike height and examination” Proc. Coastlines, Structures and Breakwaters, Ed. N.W.H. Allsop, Publn. Thomas
Telford, London, UK.
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PIANC Bulletin nº 59 (1987)
PIANC (1992) “Guidelines for the design and construction of flexible revetments incorporating geotextiles in marine environment” Report of Working Group no. 21 of the
Permanent Technical Committee, Supplement to Bulletins
78/79, Brussels, Belgium.
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Morgan R.P.C., Collins A.J. and Hann M.J. (1999) “Waterway Bank Protection: a field manual”, Environment Agency.
R&D Publication 11 (Field Guide).
PIANC (1996) “Reinforced vegetative bank protections utilising geotextiles” Report of Working Group no. 12 of the
Permanent Technical Committee, Supplement to Bulletin nº
91, Brussels, Belgium.
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APPENDIX (IN CD FORMAT)
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Data tables for prefabricated elements
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Catalogue of Prefabricated Elements

Transcription

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