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European practice in ground anchor design related to the framework of EC7.
Pratique européenne pour le dimensionnement des tirants d’ancrage en application de l’EC7
Merrifield C.
Coffey Geotechnics, UK
Møller O.
Aarsleff, Denmark
Simpson B.
Arup, UK
Farrell E.
AGL Consulting, and Trinity College, Ireland
ABSTRACT: EN 1997-1:2004 (Eurocode7, Part 1 - EC7) is the European Standard for Geotechnical Design. Ground anchors are
addressed in Section 8 of this standard, EN 1537:1999 (execution)(under revision) and it is planned that testing will be covered by
prEN ISO 22477-5. EC7 Section 8 has been little used and is now under revision. Discussions between European experts on ground
anchors have highlighted the diversity of current design practices used in different countries. This paper explores this diversity and
highlights the variations in the approaches to the design and testing of ground anchors, dealing exclusively with grouted ground
anchors which are able to be tensioned. The existing practices of Denmark, France, Germany, Ireland and the UK are considered in
relation to the EC7 requirements for verification of ultimate and serviceability limit states. It is shown how the draft now proposed of
EC7 for the design and testing of anchors accommodates the approaches currently used in European countries within a single
framework.
RESUME : L’EN 1997-1:2004 (Eurocode 7, Par 1 - EC7) est la norme pour la conception des ouvrages géotechniques. Les tirants
d’ancrage sont traités dans le chapitre 8 de cette norme, dans la norme d’exécution EN 1537 :1999 en révision et dans le projet de
norme d’essais pr EN ISO 22477-5 en cours de rédaction. Le chapitre 8 de l’EC7 bien qu’encore peu utilisé, est en cours de révision.
Les discussions entre les experts européens sur les tirants d’ancrage ont mis en lumière la diversité des pratiques couramment
appliquées dans les différents pays. Cet article présente cette diversité et montre les différences d’approche tant au niveau de la
conception que des essais, en particulier avec les tirants d’ancrage scellés au terrain qui peuvent être mis en tension. Les pratiques
existantes au Danemark, en France, en Allemagne, en Irlande et au Royaume-Uni sont présentées selon les exigences de l’EC7 dans
le cadre d’une vérification aux états limites ultimes et de service. L’article montre comment le projet proposé pour l’EC7 concernant
la conception et les essais des tirants d’ancrage prend mieux en compte et de façon simple approches actuellement utilisées dans les
pays européens.
KEYWORDS: Anchors, Eurocode, Standards, Design
1 INTRODUCTION AND HISTORICAL CONTEXT
Ground anchor design as it is today has been derived from many
years of field tests, performance monitoring and field scale
research, resulting in an empirical approach of anchor
performance linked to soil parameters. Early use of anchors
included the application of rock bolts for roof stability in Poland
in 1918 and later in Czechoslovakia in 1926 to support an
inclined shaft. The mining industry led the field in anchoring
ground at this stage. Anchors were first introduced into civil
engineering in 1934 by the French engineer André Coyne who
devised strand anchors in sandstone to allow the raising of the
Cheurfas dam in Algeria. The first use of anchors in soil was by
Karl Bauer GmbH in Munich in 1958 to tie back retaining
walls. The site agent, noting the difficulty in withdrawing steel
drill casing developed a system which included 20m bars with
3m bond lengths installed with working loads of 25 tonnes.
Development of anchor design accelerated between 1966 and
1969 with the use of anchors in stiff clays, marl, fine to medium
sand and chalk (Littlejohn, 1970).
The developing design process was based on observations
from field anchor tests taken to failure and long term behaviour
of prestressed anchors. Empirical design rules with realistic
factors of safety were being produced relating ultimate pull-out
resistance to soil properties and anchor dimensions. The
relationship between soil parameters and anchor performance
was the basis of extensive research between 1970 and 1980,
when many of the empirical relationships were developed upon
which calculation of anchor/soil bond resistance, creep and
multiple interface resistance are based (Littlejohn, 2012).
The methods of designing the anchor to contribute to the
overall structural stability of, say, an anchored retaining
structure were based on limit equilibrium stability analyses
applying linear, active and passive pressure distributions.
Where the design required the minimisation of wall
displacement, the same approach was adopted using different
pressure distributions. With the relatively recent availability of
accessible FE approaches these conditions, taking into account
the effect of anchor prestress, are examined routinely today.
With the expansion of anchor use throughout Europe,
individual countries developed design guides and codes of
practice (BS8081, DIN 4125, SIA V 191, TA95 for example) to
promote safe design. Inevitably there were variations of design
practice between these standards reflecting regional practices.
In 1975, the Commission of the European Community initiated
an action programme to develop a set of harmonised rules for
the structural design of construction works based on Article 95
of the Treaty. This was transferred to CEN in 1989
guaranteeing them the status of European standards. EC7 (EN
1997-1:2004) was subsequently published and is intended to be
used as a general basis for the geotechnical aspects of the design
of buildings and civil engineering works. The design of anchors
is accommodated in Section 8, for which a new draft has
recently been prepared, which is referenced as EN 1997-
1:2004/prA1, to be published. Alongside EC7 two further
standards EN 1537 and prEN ISO 22477-5 have been developed
to provide rules for the execution of anchors and the testing of
anchors respectively. Whilst EN 1537 has been published for
European practice in ground anchor design related to the framework of EC7.
Pratique européenne pour le dimensionnement des tirants d’ancrage en application de l’EC7
Merrifield C.
Coffey Geotechnics, UK
Møller O.
Aarsleff, Denmark
Simpson B.
Arup, UK
Farrell E.
GL Consulting, and Trinity College, Ireland
ABSTRACT: EN 1997-1:2004 (Eurocod 7, Part 1 - EC7) is the E ropean Standard for Ge technical Design. Ground ancho s are
ddressed in Section 8 of is standard, EN 1537:1999 (exe ution)(un er revisio ) and it is planned that testing will be covered by
prEN ISO 22477-5. EC7 Section 8 has be n little used a d is now u der revision. Discu sions between European experts on
have ighlight d th diversity of curr nt design pra tices us d in different countries. This paper explores this diversity and
highligh s
variations in the approaches the design and testing of ground anchors, dealing exclusively with grouted ground
anchors w ich are able to be tensi ned. The existing prac ices of Denmark, Franc , Germany, Ireland and the UK are considered in
relation to the EC7 requirements for verification of ultimate and serviceability limit states. It is shown how the draft now proposed of
EC7 for the design and testing of anchors accommodates the approaches currently used in European countries within a single
framework.
RESUME : L’EN 1997-1:200 (Eurocode 7, Pa 1 - EC7) est l no me pour la conception des ouvrages géotech iq e . Les tirants
d’ancrage ont traités dans le chapitre 8 d cette norme, dans l orm d’exécutio EN 1537 :1999 en révi ion et dans le projet de
norme d’ sais pr EN ISO 22477-5 en cours de rédaction. L chapitre 8 d l’EC7 bien qu’encore peu utilisé, est en cours de révision.
Les discussions entr les experts e ropéens sur les tirants d’ancrag ont mis en lumièr la dive sité des pratiques couramment
appliqué s dans l s différents pays. Cet article présente cette diversité et montre les différenc d’approche ta t au niveau de la
conception que des essais, en particulier avec les tirants d’ancrage scellés au te rain qui peuvent être mis en tension. Les pratiques
exista t s au Dan mark, en France, en Allemagne, en Irlande t au Royaume-Uni sont résentées s lon les exig ces de l’EC7 dan
le cadre d’une vérification aux états limites ultimes et de service. L’article montre comment le projet proposé pour l’EC7 concernant
la conception et les essais des tirants d’ancrage prend mieux en compte et de façon simple approches actuellement utilisées dans les
pays européens.
KEYWO DS: Anchors, Eurocode, Standards, Design
1 INTRODUCTION AND HISTORICAL CONTEXT
Ground anchor design as it is today has been derived from many
y ars of fi ld tests, perform nce monitoring and field scale
research, r sulting i an empirical appro ch of anchor
performance link d to soil parameters. Early use of anchors
i lud t e application of rock bolts for roof stabil ty i Pola d
in 1918 and later in Czecho lovakia in 1926 to supp rt an
incl d shaft. The mining industry led the fiel in anchoring
ground at this stage. A chors wer first introduced i to civil
engineering in 1934 by the French engineer André C yne who
devised strand anchors in sandsto e to allow the r ising of the
Cheurfas dam in Algeria. The first use of anchors in soil wa by
Kar Bauer GmbH in Munich in 1958 to ti back retaining
walls. The site age t, noting the difficulty in withdrawing ste l
drill casing developed a system which includ d 20m bars with
3m bond lengths installed with working lo ds of 25 tonnes.
Development of anch r design accelerated between 1966 and
1969 with the use of anchors in stiff cl ys, marl, fine to med um
sand and chalk (Li tlejohn, 1970).
Th d velopi g de ign process was based on observ tions
rom field anchor t sts taken to failure and long ter behavi r
of prestr ssed ancho s. Empirical design rules w th realistic
factors of safety w re be ng produc d relating ultimate pull-out
resi tance to s il properties and anchor dimensions. The
relationship betw en soil pa ameter and anchor performance
as t e basis of extensive re earch betw en 1970 and 1980,
when many o th mpirical relationships w re developed upon
which calculation of anchor/soil bond resistance, creep and
multiple interface resistance are based (Littlejohn, 2012).
The methods of esigning h anchor to contr bute to the
overall structu al s ability of, ay, an anchored etaini g
structure w re based on limit equilibrium st b lity analyses
applying li ear, activ and passive pressure distributions.
Where the des g required the minimisa ion of wall
displacement, the same approach was adop ed using differe t
pr ssur distributi ns. With the r latively recent availability of
accessible FE ap roaches these onditions, takin into acc unt
the effect of anchor prestr ss, are exami ed routinely today.
W th the expansion of anchor use throughout Europe,
individual countr es developed d sign guides and codes of
ti (BS8081, DIN 4125, SIA V 191, TA95 f r example) to
promote saf design. Inevitably the e were variatio s of design
practice between these standards reflecting egional p actices.
In 1975, he Commission of he European Community in tiated
an action programme to develop et of harmonised rules for
the structural design of construction works b sed on Article 95
of the Treaty. This was transferr
to CEN in 1989
guaranteeing them the status of European standards. EC7 (EN
1997-1:2004) was subsequently published and is intended to be
u ed as a general basis for he geotechnical aspects of the design
of buildings a d civil engineer ng works. The design of anchors
is accommoda ed in Section 8, for wh ch a new dra t as
recently been prep red, which is referenced as EN 1997-
1:2004/prA1, to be published. Alongside EC7 two further
standa ds EN 1537 and prEN ISO 2247 -5 hav been developed
to provide rules for the execution of anchors and the testing of
anchors respectively. Whilst EN 1537 has been published for
