-
CIRIA C641 London, 2008
EC7 implications forUK practice
Eurocode 7 Geotechnical design
Richard Driscoll BRE
Peter Scott Buro Happold
John Powell BRE
Classic House, 174180 Old Street, London EC1V 9BPTEL: +44 (0)20
7549 3300 FAX: +44 (0)20 7253 0523
EMAIL: [email protected] WEBSITE: www.ciria.org
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Summary
The introduction of the Eurocodes represents for most civil and
structural engineers asignificant challenge in adapting to a very
extensive set of new design and constructionrequirements. This is
particularly so for geotechnical engineers in that Eurocode 7
andits associated new standards present some profound departures
from traditionalpractice. The aim of this publication is to provide
geotechnical engineers with anunderstanding of how the new
documents will affect their day-to-day activities. Muchinformation
on the detail of the new Eurocode system already exists, so this
bookfocuses on changes to common practice and their
implications.
The book takes the reader through a logical sequence of
activities, from site andground investigation to geotechnical
element design, to construction practicesintroduced by the new
European Execution Standards. It then concludes with anindication
of the likely timing of full implementation and a prediction of the
effect thatthe changes will have on geotechnical practice in the
UK.
The book seeks to give a clear overview of the main changes that
will arise, adding inappendices such detail of the Eurocode system
that is necessary to understand thesechanges. It illustrates the
changes with a set of design examples covering mainstreamdesign
challenges such as piles, retaining walls, embankments and slopes,
and hydraulicfailure.
The book is authored by three specialists who have worked
closely with thedevelopment and introduction of Eurocode 7 and its
application in the design office,and the content has been carefully
criticised by a panel of leading UK geotechnicalpractitioners.
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EC7 implications for UK practices. Eurocode 7 Geotechnical
design
Driscoll, R, Scott, P, Powell, J
CIRIA
C641 CIRIA 2008 RP701 ISBN: 978-0-86017-641-1
British Library Cataloguing in Publication Data
A catalogue record for this book is available from the British
Library.
Published by CIRIA, Classic House, 174180 Old Street, London,
EC1V 9BP
This publication is designed to provide accurate and
authoritative information on the subject mattercovered. It is sold
and/or distributed with the understanding that neither the authors
nor the publisher isthereby engaged in rendering a specific legal
or any other professional service. While every effort hasbeen made
to ensure the accuracy and completeness of the publication, no
warranty or fitness isprovided or implied, and the authors and
publisher shall have neither liability nor responsibility to
anyperson or entity with respect to any loss or damage arising from
its use.
All rights reserved. No part of this publication may be
reproduced or transmitted in any form or by anymeans, including
photocopying and recording, without the written permission of the
copyright holder,application for which should be addressed to the
publisher. Such written permission must also beobtained before any
part of this publication is stored in a retrieval system of any
nature.
If you would like to reproduce any of the figures, text or
technical information from this or any otherCIRIA publication for
use in other documents or publications, please contact the
Publishing Departmentfor more details on copyright terms and
charges at: [email protected] Tel: +44 (0)20 7549 3300.
CIRIA C641 iii
Keywords
Ground engineering, Eurocode, foundations, geotechnical design,
geotechnicalinvestigation, ground investigation and
characterisation, in situ testing andinstrumentation, piling, soil
structure interaction
Reader interest
Design of geotechnicalstructures, limit state design,Eurocodes
replace BritishCodes and Standards
Classification
AVAILABILITY Unrestricted
CONTENT Advice/guidance
STATUS Committee-guided
USER Client organisation, consultants,contractors ,
geotechnicalengineers, project managers,structural design
engineers
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Foreword
The creation of the structural Eurocodes has been in progress
for many years. Thesenew EU standards have now advanced to a stage
that warrants serious preparation fortheir implementation and the
consequences of withdrawal of corresponding nationaldocuments. For
a complex engineering discipline such as geotechnics, used to
thepiecemeal and evolutionary introduction of national codes and
testing standards, theintroduction of a significantly different
design philosophy for dealing with engineeringuncertainty and the
relatively rapid replacement of national documents representmajor
changes for the industry.
A recent report (Institution of Structural Engineers, 2004) has
highlighted thechallenges facing engineers in adapting to the
Eurocodes and has advocated thepreparation of guidance to ease
their passage into practice. This publication has beenproduced to
assist in this process by indicating the most important differences
thatgeotechnical engineers will encounter when implementing the new
suite of geotechnicalEurocode documents. It is not intended that
this publication teaches the reader how touse the Eurocode since
other referenced documents are available for this. However,
acertain amount of explanation for some of the features of Eurocode
design has beenfound necessary to assist in understanding the
differences to practice that the Eurocodewill bring.
The book lists all the documents that will eventually comprise
the full suite ofeuronorms covering geotechnical engineering. Many
of these documents are still inpreparation in several CENa
committees and working groups. However the maindesign code, EC7-1,
and several executionb standards have now been published byBSI.
This mixture of published and unfinished documents leads to a
rather confusingreference numbering system, with published BSI
documents designated by BS EN,published CEN documents by EN and
documents in preparation by prEN..For clarity and brevity, the
terms EC7-1 and EC7-2 have been used in this documentfor the two
parts of Eurocode 7. EC7-1 concerns geotechnical design and EC7-2
refersto ground investigation and testing. EC7-1 cannot be used
without EC7-2.
This book begins with a short introduction to explain its
purpose, content and style,and to identify the main changes that
EC7-1 will bring. In Chapter 2, it discusseschanges that may occur
in site investigation practice before concentrating on how
theEurocode may affect general geotechnical design philosophy in
the UK, with likelyconsequences, in Chapter 3. Chapter 4 focuses on
changes that are specific to the maingeotechnical elements that
require designing, such as piles, retaining walls and slopes,with
several worked examples demonstrating how the EC7-1 design
methodologymight differ from conventional practice. Chapter 5
briefly discusses differences ingeotechnical construction practice
that the new execution standards may introduce.
Precisely how the new Eurocode suite of documents will be
implemented in the UK isstill a matter for debate. The intention is
for packages of Eurocodes including, forexample, loading,
geotechnical, concrete, masonry and timber all necessary to design
acomplete building structure, to be available for full
implementation and consequentwithdrawal of national documents. It
may be obvious that the timing for this
CIRIA C641iv
a Comit Europen de Normalisation.
b Execution is defined as all activities carried out for the
physical completion of the work includingprocurement, the
inspection and documentation thereof .
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implementation is rather uncertain, though a prediction has been
made in Chapter 6,which also briefly discusses the regulatory
framework and how the new codes andstandards will apply within
it.
Finally, Chapter 7 comprises a short piece on the likely overall
effect of the Eurocodeon geotechnical investigation, design and
construction practice in the UK. Theappendices provide more detail
and further information. The intention is to keep thisbook as
simple and succinct as possible in discussing what is a complex
system of linkeddocuments and which introduces a partial factor
design philosophy to geotechnics. Thishas been carried out in
several ways:
1 Endnotes for each chapter are included at the end of the
book.
2 Text that quotes directly from the Eurocode has been
highlighted in bold, whileclause references are indicated in bold
italics.
3 Key conclusions from each chapter are summarised in a table at
the beginning ofthe chapter.
4 The examples have been formatted so that appropriate code
clauses are apparent.
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Acknowledgements
Research contractor
This publication is the main output from CIRIA research project
701. It was preparedby BRE in association with Buro Happold.
Authors
Richard Driscoll BSc MSc CEng FICE
Richard Driscoll is an associate of BRE and was the lead author
for this book. Richardworked at BRE for 27 years before retiring as
the head of ground engineering. Hespent many years as a BSI
representative developing EC7 and has co-authored a bookon the
subject.
Peter Scott BSc MSc CEng FICE MASCE FGS
Peter Scott is the technical head of the geotechnical group at
Buro Happold ConsultingEngineers. Peter has extensive experience in
geotechnical design for major projects inthe UK and abroad and was
responsible for providing the worked examples in the book.
John Powell BSc MSc DIC DSc(Eng) CEng MICE
John Powell is an associate director in the Geotechnics section
of Building Technologyat BRE. He chairs the BSI committee for BS
5930 and 1377 that is the mirrorcommittee for EC7 Part 2. He
represents BSI on the committee responsible for thedrafting of EC7
Part 2 and is the national technical contact for associated
technicalspecifications.
David Poh of Buro Happold Consulting Engineers assisted in the
preparation of theworked examples.
Following CIRIAs usual practice, the research project was guided
by a steering group,which comprised:
Steering group
Dr A Bond Geocentrix
Mr S P Corbet FaberMaunsell
Mr E S R Evans Network Rail
Mr J D Findlay Stent Foundations
Mr T Hayward Stent Foundations
Mr A Jukes Highways Agency
Mr A Kidd Highways Agency
Dr P Morrison Arup Geotechnics
Mr R Newman Tony Gee & Partners
Mr A S OBrien (chair) Mott MacDonald
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Dr M Pedley Cementation Foundations Skanska
Mr S G Smith Bechtel
Dr J Wilson Atkins
CIRIA managers
CIRIAs research managers were Mr Chris Chiverrell and Dr Andrew
Pitchford.
Project funders
This project was funded by:
The DTIs Partners in Innovation scheme
The Highways Agency
Network Rail
CIRIAs Core Programme Sponsors
Technical organisations
CIRIA and the authors gratefully acknowledge the support of
those fundingorganisations, the technical help and advice provided
by the members of the steeringgroup, and colleagues and specialists
for reviewing the document and for assisting theauthors in
co-ordinating and collating all the technical contributions.
Contributions do not imply that individual funders necessarily
endorse all views expressed inpublished outputs.
CIRIA C641 vii
Front cover photo: The piled wall for the new Wembley Stadium
(courtesy StentFoundations Ltd, a Balfour Beatty company). See Case
study in Appendix A5
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Contents
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . .ii
Foreword . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . .iv
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.vi
List of figures . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . .x
List of tables . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . .x
Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . .xi
Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . .xii
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.1
1.1 Purpose of this book . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . .1
1.2 The status of Eurocode documents . . . . . . . . . . . . . .
. . . . . . . . . . . . . . .3
1.3 Important features of EC7 . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . .3
1.4 The content of this book . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . .4
1.5 The style of this book . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . .5
1.6 Consultation . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . .5
2 Site characterisation and determination of ground property
designvalues . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.10
2.1 Summary . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . .10
2.2 Ground investigation and testing . . . . . . . . . . . . . .
. . . . . . . . . . . . . . .10
2.3 Ground identification and classification . . . . . . . . . .
. . . . . . . . . . . . . .13
2.4 Determining the design values of geotechnical parameters . .
. . . . . .13
3 The new principles of geotechnical design in Eurocode 7 . . .
. . . . . . . . . . . . . . .17
3.1 Summary . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . .17
3.2 Introduction . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . .17
3.3 Design by prescriptive measures . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . .18
3.4 Design using load tests and tests on experimental models . .
. . . . . . .19
3.5 Design using the Observational Method . . . . . . . . . . .
. . . . . . . . . . . . .19
3.6 Eurocode 7 general design principles . . . . . . . . . . . .
. . . . . . . . . . . .19
3.6.1 Limit state design . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . .19
3.6.2 Design requirements . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . .21
3.6.3 Design situations . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . .21
3.6.4 Durability . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . .21
3.7 Design by calculation . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . .21
3.7.1 The application of safety in limit state design
calculations . . . .21
3.7.2 ULS design calculations . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . .22
3.7.3 Actions and their effects . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . .22
3.7.4 Geotechnical resistances . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . .23
3.7.5 The GEO and STR ULS calculations . . . . . . . . . . . . .
. . . . . . .23
3.7.6 Serviceability limit state design . . . . . . . . . . . .
. . . . . . . . . . . . .24
3.7.7 The EQU limit state . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . .25
3.7.8 The UPL limit state . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . .25
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3.7.9 The HYD limit state . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . .26
3.8 The difference between DA-1 and traditional design
calculations . . .26
4 Specific changes in design principles with examples . . . . .
. . . . . . . . . . . . . . . .28
4.1 Summary . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . .28
4.2 Introduction . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . .28
4.3 Spread foundations . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . .28
4.4 Piles . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . .29
4.4.1 Specific changes/issues . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . .29
4.5 Retaining walls . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . .41
4.5.1 Specific changes . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . .41
4.6 Embankments and slopes . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . .72
4.6.1 Specific changes . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . .72
4.7 Hydraulic failure . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . .77
4.7.1 Introduction . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . .77
4.7.2 UPL design (see Clause 2.4.7.4) . . . . . . . . . . . . .
. . . . . . . . . . .77
4.7.3 HYD ULS design (see Clause 2.4.7.5) . . . . . . . . . . .
. . . . . . . . .80
4.7.4 Failure by internal erosion . . . . . . . . . . . . . . .
. . . . . . . . . . . . . .80
4.7.5 Failure by piping . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . .80
5 Carrying out the construction . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . .81
5.1 Summary . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . .81
5.2 Construction requirements in EC7-1 . . . . . . . . . . . . .
. . . . . . . . . . . . .81
5.3 BS EN execution standards discussed and compared
withrelevant BSs . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . .81
6 Implementing the new codes and standards in the UK . . . . . .
. . . . . . . . . . . . . .83
6.1 Summary . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . .83
6.2 Introduction . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . .83
6.3 National choice and the National Annexes . . . . . . . . . .
. . . . . . . . . .83
6.4 The retention of valuable national code and standards
material . . . .84
6.5 Time-scale and processes for change . . . . . . . . . . . .
. . . . . . . . . . . . . .84
6.6 Guidance material . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . .85
7 The impact of the geotechnical Eurocode system on UK practice
. . . . . . . . . . .86
7.1 Summary . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . .86
7.2 The impact of EC7-1 on design practice . . . . . . . . . . .
. . . . . . . . . . . .86
7.3 The impact of EC7-2 and associated documents on site
investigationpractice . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . .87
7.4 The impact on geotechnical construction practice . . . . . .
. . . . . . . . . .87
7.5 Overall impact . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . .87
References . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . .88
A1 Examples of the selection of characteristic ground property
values using allavailable site information . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.93
A2 Statistical methods . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . .96
A3 Design Approach 1 for GEO and STR limit state calculations .
. . . . . . . . . . . . . .97
A3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . .97
A3.2 Design Approach 1 . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . .97
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A4 Conflicts of construction practice and requisite amendments .
. . . . . . . . . . . .101
A5 Case studies using EC7 . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . .104
A6 The provenance of BS EN standards . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . .119
Endnotes . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . .120
List of figures
Figure 1.1 Diagrammatic representation of the suite of EU
geotechnical andstructural codes and standards . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . .9
Figure 2.1 Processing test measurements into design values of
groundparameters . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . .14
Figure 2.2 General procedure for determining characteristic
values from measured values . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . .15
Figure 4.1 Alternative procedures for pile design using profiles
of groundproperties . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . .31
Figure 6.1 Possible implementation timetable . . . . . . . . . .
. . . . . . . . . . . . . . . . . .85
Figure A1.1 UU txl. strengths (U100) for a site with 3 b/hs . .
. . . . . . . . . . . . . . . . .94
Figure A1.2 Corrected SPT N values for the site . . . . . . . .
. . . . . . . . . . . . . . . . .94
Figure A1.3 SPT inferred strengths . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . .95
Figure A1.4 Assessed characteristic strength profile . . . . . .
. . . . . . . . . . . . . . . . .95
Figure A1.5 Small building on estuarine beds near slope . . . .
. . . . . . . . . . . . . . . .95
Figure A5.1 Wembley Stadium site geology and topography . . . .
. . . . . . . . . . . .109
Figure A5.2 Undrained shear strength . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . .110
Figure A5.3 CPT cone resistance profiles . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . .111
Figure A5.4 Preliminary pile load tests . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . .112
Figure A5.5 Pile tests, observed versus predicted failure loads
. . . . . . . . . . . . . . .113
Figure A5.6 Pile load settlement behaviour (observed versus
predicted) . . . . . . .114
Figure A5.7 1.5 m diameter pile predicted load settlement (from
load tests on 0.45 m to 0.75 m diameter piles) . . . . . . . . . .
. . . . . . . . . . . . . . . . . .115
Figure A5.8 Wembley pile load test data compared with previous
publishedresults . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . .116
Figure A5.9 Predicted pile load settlement characteristics . . .
. . . . . . . . . . . . . . . .117
Figure A5.10 Test pile 7 measured, characteristic and factored
load settlement curves,compared with predicted behaviour . . . . .
. . . . . . . . . . . . . . . . . . . . .118
List of tables
Table 1.1 The content of BS codes and their correspondence with
the Europeandocuments . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . .6
Table 1.2 The content of BS codes and testing standards and
theircorrespondence with the European documents . . . . . . . . . .
. . . . . . . . .7
Table 2.1 Some of the changes introduced by EC7-2 . . . . . . .
. . . . . . . . . . . . . . .11
Table 2.2 Some terminological changes . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . .13
Table 5.1 Correspondence between BS codes and standards and
European codesand standards . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . .82
Table 7.1 Impact of EC7-1 on design practice . . . . . . . . . .
. . . . . . . . . . . . . . . . .86
Table A3.1 Values of partial factors recommended in EC7-1 Annex
A . . . . . . . .100
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Table A4.1 Conflicts between BS codes and those BS EN execution
standardsavailable in January 2005 . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . .102
Table A5.1 Summary of vertical pile tests . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . .106
Table A5.2 Flemings analyses (CEMSET), input parameters . . . .
. . . . . . . . . . .107
Table A5.3 Factors that may affect choice of factor of safety .
. . . . . . . . . . . . . . .108
Examples
Example 4.1 Design of a vertical, pre-cast concrete pile driven
into sand andgravel . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . .32
Example 4.2 Pile design incorporating negative skin friction
(downdrag) . . . . . . . .37
Example 4.3 The design of a cantilever retaining wall without
groundwater pressures acting . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . .43
Example 4.4 The design of a cantilever retaining wall with
groundwater pressuresacting . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .48
Example 4.5 The design of an embedded retaining wall with
groundwater pressures acting . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . .55
Example 4.6 The design of a cantilever retaining wall with
elevated groundwaterpressures . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . .65
Example 4.7 The design of a stable slope . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . .73
Example 4.8 An excavation below the water table, showing design
against uplift . .78
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Glossary
EC7 introduces terms and uses expressions that may require some
explanation. Thefollowing table indicates what meaning these are
intended to convey to the reader. Theinterpretations of the
terminology are largely those of the authors, often using text inBS
EN 1990: 2002 unless they include direct quotations from EC7.
Action 1 Set of forces (loads) applied to a structure
(directaction).
2 Set of imposed deformations or accelerations caused,for
example, by temperature changes, moisturevariation, uneven
settlement or earthquake (indirectaction).
Characteristic value Clause 2.4.5.2(2)P states that: The
characteristic value of ageotechnical parameter shall be selected
as a cautiousestimate of the value affecting the occurrence of the
limitstate. A fuller discussion may be found in Section 2.4.
Code Published guidance from a national standards body onhow
activities should be undertaken to achieve a requiredresult using
recommended best practice.
Comparable experience Documented or other clearly established
informationrelated to the ground being considered in
design,involving the same types of soil and rock and for
whichsimilar geotechnical behaviour is expected, and
involvingsimilar structures. Information gained locally is
consideredto be particularly relevant.
Derived value Value of a geotechnical parameter obtained by
theory,correlation or empiricism from test results. A
fullerdiscussion is found in Section 2.2.
Design situation Set of physical conditions representing the
real conditionsoccurring during a certain time interval for which
thedesign will demonstrate that relevant limit states are
notexceeded.
Design value Value of a variable used in the calculation of
thedimensions of or forces on or in, the structure to be built.
Effect of action Effect of actions on structural members (eg
internal force,bending moment, stress and strain) or on the
wholestructure (eg deflection, rotation).
Execution All activities carried out for the physical completion
of thework including procurement, the inspection anddocumentation
thereof.
Geotechnical action Action transmitted to the structure by the
ground, fill,standing water or groundwater (definition adapted
fromClause 1.5.3.7 of BS EN 1990).
Limit states States beyond which the structure no longer fulfils
therelevant design criteria.
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Nominal value Value fixed on non-statistical basis, for instance
onacquired experience or on physical conditions.
Partial factor A factor to either increase or decrease a
variable used inpart of the determination of the dimensions of or
forceson or in the structure to be built.
Representative value Value used for the verification of a limit
state. Aof an action representative value may be the characteristic
value.
Resistance Capacity of a member or component, or cross-section
of amember or component of a structure, to withstand actionsor
their effects without mechanical failure, eg bendingresistance,
buckling resistance, tension resistance.
Serviceability limit States that correspond to conditions beyond
whichstates specified service requirements for a structure or
structural
member are no longer met.
Standard Published instructions from a national standards body
onhow activities must be undertaken to achieve a
requiredresult.
Technical specification Published instructions from a standards
body on howactivities should be undertaken to achieve a
requiredresult.
Ultimate limit states States associated with collapse or with
other similar formsof structural failure.
Verification Design and checking.
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1 Introduction
1.1 Purpose of this book
A new European suite of geotechnical design, testing and
construction documents willin due course largely replace British
codes and standards. This book has been writtento identify and
explain to the general geotechnical practitioner in the UK the
keydifferences between the incoming and outgoing system and to
indicate what othercommonly used design documents1 will be
retained. The book does not provide aclause-by-clause commentary on
the main design Eurocode, EC7 Part 1 (this may befound elsewhere2),
nor is it intended to be a manual of good practice in
geotechnicaldesign. Rather, it highlights the important features of
the new Eurocode system andseeks to show how they may affect
practice. With accompanying illustrations in workedexamples, some
guidance is given on how to apply the systems Principles to
ensurethat designs will conform to the new requirements, and will
be built and maintained asthe Eurocodes intend.
The main changes to geotechnical practice introduced in the
Eurocodes areconcentrated in Eurocode 7 Geotechnical design Part 1:
General rules, which this bookconcentrates on3, and Eurocode 7
Geotechnical design Part 2: Ground investigation andtesting. It is
important to appreciate that the new European suite of
geotechnicaldocuments is a comprehensive, linked system of codes,
standards and technicalspecifications. These indicate how
information on the ground is to be acquired, how itis to be
interpreted and transformed into design parameters and the geometry
ofgeotechnical structures, and how these structures are to be built
and maintained, withsuitable monitoring and quality assurance.
There is a confusing plethora of alphanumeric references within
many of the newEuropean documents. For the purposes of simplicity,
this book refers to the two partsof Eurocode 7 as EC7-1 and EC7-2.
It should be understood that all Euronormspublished by CEN have the
prefix EN, those produced by ISO4 and adopted by CENhave the prefix
EN-ISO and all these documents, when published by BSI as UKversions
will be prefixed by BS EN etc. Further complication is introduced
by the useof pr EN to signify documents that are in
preparation.
Figure 1.1 illustrates the system of new European documents
while Tables 1.1 and 1.2show the current BS codes and standards and
their approximate relationships withthose European documents that
exist or are anticipated. There is direct correspondencefor some
documents (for example, some parts of BS 1377 are being and will
continue tobe replaced by an equivalent standard from CEN Technical
Committee 341, see Powelland Norbury, 2007 for examples) while in
most other cases there is limited overlapbetween the material (for
example, BS 8004 covers aspects of the construction(execution) of
pile foundations found in BS EN 1536:1999).
EC7 introduces a number of important changes in the codification
of design practices. Inparticular it:
presents, for the first time, a unified set of Principles for
all geotechnical design
bridges the philosophical divide between geotechnical design and
superstructuredesign that has existed since BS 8110, explicitly
employing limit state design andpartial factors, was introduced in
the UK
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makes a clear distinction between the avoidance of an ultimate
limit state (failure ofthe ground and collapse of all or part of a
ground-supported structure) and of aserviceability limit state
(undue movement and its consequences). Much routinegeotechnical
design has historically blurred these two requirements. The
Eurocodeshould prompt greater thought about designing to prevent
unacceptablemovement, which should be beneficial
requires more systematic thought about the degree of uncertainty
in the values ofgeotechnical material parameters for use in design
calculations5
introduces a degree of compulsion by indicating that certain
(Principle) activitiesshall be undertaken in both design and ground
investigation6.
EC7-1 is not only about carrying out design but is also about
checking7 that a designwill not reach a limiting condition in
prescribed design situations. The code does nottell the reader how
to design, rather it lays down a set of guiding design Principles,
liststhe many physical conditions that the ground and the structure
it supports mayexhibit, and states how the constructed outcome must
behave.
In common with the other structural Eurocodes, the foreword to
EC7-1 indicates that itserves as:
a means to prove compliance with the essential requirement of
mechanicalresistance and stability
a basis for specifying contracts for construction works.
Unusual forms of construction or design conditions are not
covered and additionalexpert consideration will be required by the
designer in such cases.
It is explicitly stated that appropriately qualified personnel
are to provide the inputdata for geotechnical designs and that the
design and ground investigations are to beperformed by
appropriately qualified and experienced personnel.
In addition to the above, this book has several further
aims:
to give readers a clear and simple understanding of the main
issues that they willneed to address when checking that their
geotechnical design conforms with theEurocode
to describe briefly the range of information presented in the
Eurocode suite, toclarify the meanings of some new terms, to
describe briefly the new design methodsand to present
easy-to-understand explanations of how the new methods workusing
design examples and a case study
to indicate the likely effect on geotechnical practice in the UK
of the move to theEurocode suite of documents, including how use of
the Eurocode will comply withthe requirements of the Building
Regulations and any other local regulations, suchas the London
District Surveyors rules.
The book has been written primarily for three groups of
readers:
1 The general geotechnical engineer who may often not have
routine recourse tocodes but who will, nevertheless, need to be
assured that a design complies with thecode requirements.
2 The non-geotechnically qualified engineer who carries out
simple design for smallprojects for which the ground conditions are
not regarded as problematical,whereby a geotechnical specialist may
not be required. Such projects often comprise
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small housing developments where the foundations may be
prescribed and whereother geotechnical structures require recourse
to relatively straight-forward design(such as small retaining walls
currently designed using BS 8002:1999).
3 The general engineer and building and construction
professional who may need tounderstand what the geotechnical
engineer is doing.
This book is intended to be a companion to the suite of European
geotechnicaldocuments and is not a substitute for them, in any
way.
1.2 The status of Eurocode documents
Once implemented in the UK, the Eurocode documents will have the
status of currentBS codes and standards. It is expected that all
references to BS documents in theBuilding Regulations and other
regulatory documents such as those of the HighwaysAgency and
Network Rail will be replaced by references to the new BS ENs.
TheEurocodes contain Principles that are mandatory ie they contain
the word shall,as highlighted later in this book. This means that
if and when the new BS ENs are usedto design or to check a design,
these mandatory requirements must be satisfied.
1.3 Important features of EC7
Scope
It is important to appreciate that EC7-1 applies to the design
of both new projects andthe repair and stabilisation of existing
geotechnical structures. It does not, however,specifically deal
with the re-use of existing foundations nor does it apply to
theassessment of existing structures.
EC7-1 and EC7-2 also apply primarily to greenfield sites, and
while clean fill iscovered, contaminated land is not.
Limit state design
Two different types of limit state are identified, each having
its own designrequirements:
ultimate limit states (ULS), defined as states associated with
collapse or with othersimilar forms of structural failure (eg
exceeding the bearing resistance of thefoundation). For
geotechnical design, it is particularly important to note
thatultimate limit states include failure by excessive deformation,
leading to ... loss ofstability of the structure or any part of
it
serviceability limit states (SLS), defined as states that
correspond to conditionsbeyond which specified service requirements
for a structure or structural memberare no longer met (eg excessive
settlement leading to cracking in the structure).
Limit states are generally avoided by considering design
situations in which adverseconditions apply (see Section 3.6.3).
The need to identify these design situations shouldhelp to develop
the routine use of risk assessment in geotechnics.
Uncertainty in ground parameter values and resistance
EC7-1 introduces the clear separation of actions and reactions
and the application ofpartial factors to characteristic values of
actions, ground parameters and resistances inplace of global
factors for dealing with all uncertainty and safety.
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Movement
Because of the explicit requirement to check serviceability
conditions, greater attentionwill need to be paid to settlements
and other movement. However, note that the codedoes not provide
explicit guidance on how to calculate movement. As will be
discussedlater, the separation of bearing capacity (a ULS) from
settlement (an SLS) means thatpartial factors applied in a ULS
calculation may not guarantee that settlements aresufficiently
small, particularly on soft ground. Clients should be confident
thatappropriately qualified and experienced personnel have been
involved in any EC7-1design calculations.
Compulsory reporting of information
The production and communication of the Geotechnical design
report and Groundinvestigation report are requirements of EC7.
Minimum contents for these reports arespecified and these comply
fully with obligations under CDM regulations.
Geotechnical models
EC7-1 deals with the design of different types of foundation,
retaining wall and othergeotechnical structures but the code does
not specify which soil mechanics theories orsoil behaviour models
to use, although it does suggest, in informative annexes8, meansto
determine, for example, the earth pressure acting on a retaining
structure or thestability of a slope.
A unifying set of design Principles
EC7-1 presents a unified set of Principles for design (see
Appendix A3). In contrast, BScodes have emerged over many years in
a rather piecemeal fashion, with a collection ofdifferent design
philosophies.
Terminology
EC7-1 introduces terms that are not widely used or defined in
the UK, at least by thegeotechnical engineering community. These
terms are briefly explained in the glossary,with some being more
fully covered in later chapters of this book.
1.4 The content of this book
Chapter 2 deals with important differences in obtaining design
parameters for use withEC7-1. For ground investigation, including
laboratory and field testing, EC7-2 dealswith basic ground data and
its interpretation with the resulting derived values beingpassed to
EC7-1 for conversion into a characteristic and hence design value.
Thedifferences from current practice in these processes are briefly
outlined.
Chapter 3 deals with the key differences in the general
Principles of design betweenEC7-1 and the BS codes of practice. The
alternative methods of design permitted inthe code are briefly
described after which design by calculation is discussed in
somedetail since it is here where the greatest changes from current
practice will be found.
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Of course, design calculations rely on the provision of
appropriate and suitablyaccurate input parameters. The chapter also
highlights important new concepts forarriving at suitably
conservative values of input parameters so that the design will
avoidthe occurrence of a limit state. The concept of characteristic
value of a parameter andhow it is acquired, starting with the
elements of a site investigation, is discussed, afterwhich the
obtaining of a design parameter value is considered.
Finally, the adoption in the UK of Design Approach 1 is outlined
(three alternativedesign approaches are permitted in the
Eurocode).
Chapter 4 briefly describes specific differences for common
design problems andillustrates them in typical worked examples and
a case history.
Chapter 5 describes the key differences involved in moving from
BS codes to the BSEN standards for execution (construction). The
resolution of any conflicts identifiedbetween the documents is
outlined.
Chapter 6 deals with the manner in which the Eurocodes will be
implemented in theUK. It briefly discusses how national preferences
for safety are incorporated into theNational Annexes for EC7-1 and
EC7-2 and explains how and when the Eurocodes arelikely to replace
the BS codes as references in Building Regulations and
otherregulatory and widely-adopted design documents9.
Chapter 7 discusses the manner in which the move to the
Eurocodes might affectgeotechnical practice in the UK, from changes
in site and ground investigation,through design calculations to
construction activities on site. Brief mention is made ofany
consequences for the economics of geotechnical works and any effect
onconstruction programmes.
There are a number of appendices that contain specific details
that have beenseparated from the main body of text to ease reading
and understanding.
1.5 The style of this book
Since the European geotechnical codes and standards have been
developed in asomewhat disconnected manner by several different CEN
committees, the emergingsuite of documents does not always appear
to conform to a logical pattern.Furthermore, EC7-1 itself does not
always follow the sequences of events that constitutedesign as
normally practiced in the UK. So this book does not follow the
order ofpresentation of material in the Eurocodes. Throughout, an
attempt has been made tokeep the narrative simple and focused on
how the Eurocode may introduce changes topractice.
1.6 Consultation
During the writing of this book, consultation has taken place
with a group ofgeotechnical design, construction and site
investigation specialists. While several in thegroup are familiar
with EC7-1, a concerted attempt has been made to address
thisdocument to people who have little or no knowledge of EC7.
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Table 1.1 The content of BS codes and their correspondence with
the European documents
CIRIA C6416
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Stan
dard
s fo
r th
e ex
ecut
ion
of s
peci
alge
otec
hnic
al w
orks
(CEN
TC2
88
)
B
S EN
14
475
:20
06
Rein
forc
ed fi
ll
pr
EN
14
49
0So
il na
iling
B
S EN
12
06
3:1
99
9Sh
eet p
ile w
alls
B
S EN
15
36
:20
00
Bore
d pi
les
B
S EN
12
69
9:2
001
Disp
lace
men
t pile
s
B
S EN
141
99
:20
05
Mic
ropi
les
B
S EN
15
37:2
00
0G
roun
d an
chor
s
B
S EN
15
38
:20
00
D
iaph
ragm
wal
ls
B
S EN
12
06
3:1
99
9
Shee
t pile
wal
ls
B
S EN
127
15:2
00
0G
rout
ing
B
S EN
127
16:2
001
Jet g
rout
ing
pr
EN
14
49
0So
il na
iling
B
S EN
14
67
9:2
00
5D
eep
mix
ing
B
S EN
147
31:2
00
5G
roun
d tr
eatm
ent b
yde
ep v
ibra
tion
B
S EN
15
237
:20
07Ve
rtic
al d
rain
age
B
S EN
14
475
:20
06
Rein
forc
ed fi
ll
Sect
ion
Ti
tle
1G
ener
al
2Pl
anni
ng o
f gro
und
inve
stig
atio
ns
3So
il an
d ro
ck s
ampl
ing
and
grou
ndw
ater
mea
sure
men
t
4Fi
eld
test
s in
soi
ls a
nd r
ocks
5La
bora
tory
test
s on
soi
ls a
nd r
ocks
6G
roun
d in
vest
igat
ion
repo
rt
Anne
x B
Plan
ning
str
ateg
ies
for
geot
echn
ical
inve
stig
atio
ns
EC7
-2
Gen
eral
issu
es c
over
ed
Ove
rall
appr
oach
Gro
und
inve
stig
atio
n
Des
ign
aspe
cts
ofco
nstr
uctio
n ac
tiviti
es
Des
ign
of s
peci
ficel
emen
ts
EC7
-1
Sect
ion
Ti
tle
1G
ener
al
2B
asis
of g
eote
chni
cal d
esig
n
3G
eote
chni
cal d
ata
4Su
perv
isio
n of
con
stru
ctio
n,m
onito
ring
and
mai
nten
ance
5Fi
ll, d
ewat
erin
g, g
roun
dim
prov
emen
t an
d re
info
rcem
ent.
(NNot
e: E
C7-1
doe
s no
t co
ver
the
desi
gn o
fre
info
rced
soi
ls o
r gr
ound
str
engt
hene
d by
naili
ng e
tc).
6Sp
read
foun
datio
ns
7Pi
le fo
unda
tions
8An
chor
ages
9R
etai
ning
str
uctu
res
10H
ydra
ulic
failu
re
11O
vera
ll st
abili
ty
12
Emba
nkm
ents
BS
code
BS
59
30
:19
99
Site
inve
stig
atio
n
Som
e of
tho
se b
elow
BS
60
31:1
981
Eart
hwor
ks
BS
80
06
:19
95
Stre
ngth
ened
/rei
nfor
ced
soils
and
othe
r fill
s
BS
80
04
:19
86
Foun
datio
ns
BS
80
04
:19
86
Foun
datio
ns
BS
80
08
:19
96
Safe
ty p
reca
utio
ns a
ndpr
oced
ures
for t
heco
nstr
uctio
n an
d de
scen
t of
mac
hine
-bor
ed s
hafts
for
pilin
g an
d ot
her p
urpo
ses
BS
80
81:1
98
9
Gro
und
anch
orag
es
BS
80
02
:19
94
Eart
h re
tain
ing
stru
ctur
es
Som
e
BS
60
31:1
981
Eart
hwor
ks
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Table 1.2 The content of BS codes and testing standards and
their correspondence with theEuropean documents
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CEN
ISO
sta
ndar
ds(s
ee A
ppen
dix
A6 fo
r an
exp
lana
tion
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hepr
oven
ance
of t
he d
iffer
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dard
s)
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EN IS
O 1
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88
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EN IS
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22
82
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BS
EN-IS
O 2
247
5-1
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06
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EN
-ISO
/TS
224
75
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00
6
DD
EN
-ISO
/TS
224
75
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007
CEN
ISO
/TS
178
92
-1*
CEN
ISO
/TS
178
92
-2*
CEN
ISO
/TS
178
92
-3*
CEN
ISO
/TS
178
92
-4*
CEN
ISO
/TS
178
92
-12
*
Not
e: T
here
app
ear
to b
e B
S EN
s in
exi
sten
ceth
at h
ave
been
dra
fted
by
com
mitt
ees
conc
erne
d w
ith a
ggre
gate
s. T
hese
will
nee
dto
be
revi
ewed
to a
sses
s th
eir
appl
icab
ility
toso
ils.
CEN
ISO
/TS
178
92
-5*
Labo
rato
ry a
nd fi
eld
test
ing
stan
dard
s an
d te
chni
cal s
peci
ficat
ions
(CEN
TC3
41
).N
ote:
Te
chni
cal S
peci
ficat
ions
ar
e id
entif
ied
by
TS
in t
he r
efer
ence
num
ber.
Geo
tech
nica
l inv
estig
atio
n an
d te
stin
g
Iden
tific
atio
n an
d cl
assi
ficat
ion
of s
oil:
Part
1: I
dent
ifica
tion
and
desc
riptio
n
Part
2: C
lass
ifica
tion
prin
cipl
es
Part
3: E
lect
roni
c da
ta e
xcha
nge
- soi
l
Roc
ks
Part
1: I
dent
ifica
tion
and
desc
riptio
n
Part
2: E
lect
roni
c da
ta e
xcha
nge
r
ock
Geo
hydr
aulic
test
ing
Gen
eral
Rul
es
Wat
er p
erm
eabi
lity
test
s in
a b
oreh
ole
with
out
pack
er
Wat
er p
ress
ure
test
in r
ock
Pum
ping
test
s
Infil
trom
eter
test
Wat
er p
erm
eabi
lity
test
s w
ith p
acke
r an
d pu
lse-
like
stim
ulat
ion
Sam
plin
g
prin
cipl
es
Sam
plin
g
qua
lific
atio
n cr
iteria
Sam
plin
g
con
form
ity a
sses
smen
t
Wat
er c
onte
nt
Den
sity
of f
ine
grai
ned
soils
Den
sity
of s
olid
par
ticle
s
Part
icle
siz
e di
strib
utio
n
Atte
rber
g lim
its
Incr
emen
tal l
oadi
ng o
edom
eter
test
EC7
-2
1G
ener
al p
lann
ing
of g
roun
din
vest
igat
ions
2So
il an
d ro
ck s
ampl
ing
and
grou
ndw
ater
mea
sure
men
ts
3Fi
eld
test
s in
soi
l and
roc
k
4La
bora
tory
test
s on
soi
l and
rock
5G
roun
d in
vest
igat
ion
repo
rt
Anne
x B
Plan
ning
of g
eote
chni
cal
inve
stig
atio
ns
Anne
x A
List
of t
est
resu
lts o
fge
otec
hnic
al te
st s
tand
ards
Anne
x L
Det
aile
d in
form
atio
n on
prep
arat
ion
of s
oil s
peci
men
sfo
r te
stin
g
Anne
x M
D
etai
led
info
rmat
ion
on te
sts
for
clas
sific
atio
n, id
entif
icat
ion
and
desc
riptio
n of
soi
ls
Anne
x N
Det
aile
d in
form
atio
n on
chem
ical
test
ing
of s
oils
Anne
x R
Det
aile
d in
form
atio
n on
com
pact
ion
test
ing
of s
oils
Anne
x Q
Det
aile
d in
form
atio
n on
com
pres
sibi
lity
test
ing
of s
oils
BS
code
BS
59
30
:19
99
Site
inve
stig
atio
n
BS
1377
:19
90
Met
hods
of t
est f
or s
oils
for
civi
l eng
inee
ring
purp
oses
Part
1G
ener
al r
equi
rem
ents
and
sam
ple
prep
arat
ion
Part
2Cl
assi
ficat
ion
test
s
Part
3Ch
emic
al a
nd e
lect
ro-c
hem
ical
test
s
Part
4Co
mpa
ctio
n-re
late
d te
sts
Part
5Co
mpr
essi
bilit
y, p
erm
eabi
lity
and
dura
bilit
y te
sts
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IRIA
-
CIRIA C6418
CEN
ISO
/TS
178
92
-11
CEN
ISO
/TS
178
92
-7*
CEN
ISO
/TS
178
92
-10
*
CEN
ISO
/TS
178
92
-8*
DD
CEN
ISO
/TS
178
92
-6:2
00
9*
CEN
ISO
/TS
178
92
-9
pr E
N-IS
O 2
2476
-1
BS
EN-IS
O 2
2476
-2:2
00
5
BS
EN-IS
O 2
2476
-3:2
00
5
pr E
N-IS
O 2
2476
-4
pr E
N-IS
O 2
2476
-5
pr E
N-IS
O 2
2476
-6
pr E
N-IS
O 2
2476
-8
pr E
N-IS
O 2
2476
-9
CEN
-ISO
/TS
224
76-1
0*
DD
CEN
-ISO
/TS
224
76-1
1:2
00
5
pr E
N-IS
O 2
2476
-12
pr E
N-IS
O 2
2476
-13
pr E
N-IS
O 2
22
82
-1
pr E
N-IS
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22
82
-2
pr E
N-IS
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22
82
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N-IS
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22
82
-4
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N-IS
O 2
22
82
-5
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N-IS
O 2
22
82
-6
pr E
N IS
O 2
2477
-1
pr E
N IS
O 2
2477
-2
pr E
N IS
O 2
2477
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pr E
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O 2
2477
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pr E
N IS
O 2
2477
-X
pr E
N IS
O 2
2477
-5
pr E
N IS
O 2
2477
-6
pr E
N IS
O 2
2477
-7
Perm
eabi
lity
test
Unc
onfin
ed c
ompr
essi
on te
st o
n fin
e gr
aine
d so
ils
Dire
ct s
hear
test
Unc
onso
lidat
ed t
riaxi
al te
st
Fall
cone
test
Cons
olid
ated
tria
xial
test
Elec
tric
con
e pe
netr
atio
n te
st
Dyn
amic
Pro
bing
Stan
dard
Pen
etra
tion
Test
Men
ard
pres
sure
met
er te
st
Flex
ible
dila
tom
eter
test
Self-
borin
g pr
essu
rem
eter
test
Full-
disp
lace
men
t pr
essu
rem
eter
Fiel
d va
ne te
st
Wei
ght
soun
ding
test
Flat
dila
tom
eter
test
Mec
hani
cal c
one
pene
trat
ion
test
Plat
e Lo
adin
g Te
st
Gen
eral
rul
es (p
erm
eabi
lity)
Perm
eabi
lity
test
s in
a b
oreh
ole
Wat
er p
ress
ure
test
s
Pum
ping
test
Infil
trom
eter
test
s
Clos
ed s
yste
ms
pack
er te
sts
Pile
load
test
s
tatic
axi
ally
load
ed c
ompr
essi
on te
st
Pile
load
test
s
tatic
axi
ally
load
ed te
nsio
n te
st
Pile
load
test
s
tatic
tra
nsve
rsel
y lo
aded
tens
ion
test
Pile
load
test
d
ynam
ic a
xial
ly lo
aded
com
pres
sion
test
Pile
Loa
d te
sr
rapi
d ax
ial l
oade
d co
mpr
essi
on te
st
Test
ing
of a
ncho
rage
s
Test
ing
of n
ailin
g
Test
ing
of r
einf
orce
d fil
l
Anne
x S
Det
aile
d in
form
atio
n on
per
mea
bilit
yte
stin
g of
soi
ls
Anne
x O
Det
aile
d in
form
atio
n on
str
engt
h in
dex
test
ing
of s
oils
Anne
x P
Det
aile
d in
form
atio
n on
str
engt
h te
stin
g of
soils
Anne
x C
Exam
ple
of g
roun
d w
ater
pre
ssur
ede
rivat
ions
bas
ed o
n a
mod
el a
nd lo
ngte
rm m
easu
rem
ents
.
Anne
x D
Cone
and
pie
zoco
ne p
enet
ratio
n te
sts
Anne
x E
Pres
sure
met
er te
st
Anne
x F
Stan
dard
pen
etra
tion
test
Anne
x G
Dyn
amic
pro
bing
Anne
x H
Wei
ght
soun
ding
test
Anne
x I
Fiel
d va
ne te
st
Anne
x J
Flat
dila
tom
eter
test
Anne
x K
Pl
ate
Load
ing
Test
Anne
x T
Prep
arat
ion
of s
peci
men
s fo
r te
stin
g of
rock
mat
eria
l
Anne
x U
Clas
sific
atio
n te
stin
g of
roc
k m
ater
ial
Anne
x V
Swel
ling
test
ing
of r
ock
mat
eria
l
Anne
x W
Stre
ngth
test
ing
of r
ock
mat
eria
l
Part
6Co
nsol
idat
ion
and
perm
eabi
lity
test
s in
hydr
aulic
cel
ls a
nd w
ith p
ore
pres
sure
mea
sure
men
t
Part
7Sh
ear
stre
ngth
test
s (t
otal
str
ess)
Part
8Sh
ear
stre
ngth
test
s (e
ffec
tive
stre
ss)
Part
9In
situ
test
s
Non
e
BS
80
04
:19
86
Foun
datio
ns
Not
e*
will
not
be
publ
ishe
d in
the
UK
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ensed copy:R
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IRIA
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Note The different sources of these documents are explained in
Appendix A6.
Figure 1.1 Diagrammatic representation of the suite of EU
geotechnical and structural codes andstandards
CIRIA C641 9
Geotechnicalprojects
Eurocodes:BS EN 1990:2002
Basis of structural designBS EN 1991-1-1:2002Actions on
structures
European standards forthe Execution of special
geotechnical works
Other structuralEurocodes
eg BS EN 1993-5:2007
ISO/CENStandards for
identification andclassification
Test standard fortechnical specificationsfor ground
properties
Geotechnical designEurocodes:
BS EN 1997-1:2004BS EN 1997-2:2007
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IRIA
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2 Site characterisation and determinationof ground property
design values
2.1 Summary
2.2 Ground investigation and testing
The processes for obtaining ground parameters to use in design
with EC7-1 arespecified in several parts of the suite of European
codes and standards, as indicated inTables 1.1 and 1.2. It is
evident that change over to the BS EN suite will entail
theacquisition of many more standards and a period of adjustment to
those documentsthat will replace BS 5930 and parts of BS 1377.
Table 1.1 lists the standards and technical specifications (TS)
that are being producedby CEN and ISO, which will replace UK codes,
standards and practice, covering thesame subject matter. Most of
the standards and TS documents are to be finalised or, insome
cases, drafted, so it is not yet possible to fully identify
conflicts with UKprocedures10.
The main areas in which EC7-2 differs from current BS codes and
standardsrequirements are listed in Table 2.1, from which it can be
seen that a fundamentalchange involves the introduction of some
compulsory activities (the word shall isused). This change has
consequences for the procurement of site investigation, for
theclear specification of who does what and for how information is
disseminated to allappropriate parties.
In fact, there are only two major changes to existing British
site investigation practice and itcan be expected that much if not
all of the good practice guidance contained in, forexample, BS 5930
will continue to apply in the future (see Section 6.4). The first
majorchange concerns the provision of a geotechnical investigation
report discussed later. The secondconcerns the effect of the
requirement in EC7-1 for much greater consideration ofsettlement
and deformation. This will entail much more attention being paid to
thedetermination of the deformational properties of the ground, a
difficult subject.
CIRIA C64110
1 EC7-2 makes compulsory the provision of a ground investigation
report to all relevant parties.
2EC7-2 is more prescriptive than BS 5930 in its planning and
execution requirements for groundinvestigation.
3
The emphasis in EC7-1 on better prediction of settlement and
deformation raises the importance of grounddeformation properties.
While the option is available in EC7-1 to use a reduced strength
value, akin to thestrength mobilisation factor used in BS 8002, the
need for better knowledge of the deformation propertiesof the
ground from additional and specific testing should presage a
profound change in UK geotechnicalpractice.
4Some parts of BS 1377 and BS 5930 have been and will continue
to be replaced by new BS ENdocumentation.
5 Some departures from BS 5930 terminology apply for soil and
rock descriptions.
6Design values of ground properties may be assessed directly as
an alternative to applying partial factors tocharacteristic
values.
7Procurement processes may need to be clearer about who does
what, quality assurance, professionalindemnity implications and
communication between interested parties.
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IRIA
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Table 2.1 Some of the changes introduced by EC7-2
CIRIA C641 11
EC7-2 novel feature Impact on practice as embodied in BS codes
and standards
Use of shall in Principle clauses,
rather than should11 (examplesfrom Section 2 Planning of
groundinvestigations)
if the main ground investigations do not supply the
necessaryinformation, complementary investigations shall be
undertaken.Clients may come to appreciate that, if they fund
morecomprehensive, initial investigations, they can avoid the
expense offurther investigation at a later stage
it is stated that investigations shall be planned and data shall
beadequate to manage risks12
the document states that a visual inspection shall be
undertakenbefore planning the investigation programme and used in
conjunctionwith a desk study
it also says that quality assurance systems shall be in place
for allaspects of the work13
the necessary number of specimens to be tested shall
bedetermined. Recommended numbers are contained in
informativeannexes but the status/validity of these will need to be
discussed inthe NA for EC7-2. It is unclear what the implications
might be if therecommendations are ignored and things go wrong
a table of applicability of various field tests is also
presented.
Section 3 on soil and rock samplingintroduces categories of
samplingmethod based on BS EN ISO 22475-114.
this implies that only certain sampling methods can be used to
obtainsamples of a certain quality class
the quality class relates to use in specific laboratory tests in
order togive the test results required for the selection of
characteristicvalues15.
Section 4 Field tests in soils androcks specifies that CEN
standardsshall be used when specifying tests.Conversion of test
results intoderived values is introduced
existing BS 1377 and BS 5930 sections specifying test methods
willbecome redundant where a corresponding standard exists. If
atechnical specification is listed for a particular test then
either this orthe BS can be used. See Table 1.2 for the tests
affected.
Section 5 Laboratory tests on soilsand rocks
general statements occur with shall throughout the section. Much
issimply good practice but if things go wrong then decisions
takenrelating to clauses saying shall will need to be justified
checks shall be made that the laboratory equipment used
isadequate, fit for purpose, is calibrated and within the
calibrationrequirements
there is a requirement that all test methods and procedures
shall bereported
a quality assurance system shall be in place in the
laboratory16
all descriptions shall be to BS EN ISO 14688-1:2002 and BS EN
ISO14688-2:2004
for the laboratory tests listed in Table 1.2 there will be no
withdrawalof corresponding BS documents as the CEN documents are
all onlytechnical specifications (TS) and EC7-2 allows the NA to
adoptNational Standards in preference. This will be the case in the
UK (onlythe TS for the fall cone will be adopted) (see NA to EC7-2
in 2009).
Section 6 Ground investigation reportdeals with what shall be in
the report
the report shall form part of the geotechnical design report
it shall state known limitations of the results
it shall include a presentation of all available information
andgeological features and a geotechnical evaluation of the
information
all methods shall be documented in accordance with the
relevantstandards
it shall include all relevant information on how the derived
valueswere arrived at.
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IRIA
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EC7-2 identifies an explicit hierarchy of investigations that is
also found in BS 5930:
geotechnical investigations17, which comprise the gathering of
all relevantinformation about the site18 and a ground
investigation
ground investigations, which comprise field investigations,
laboratory testing anddesk studies of geotechnical and geological
information
field investigations, which comprise direct investigations
(drilling, sampling and trialpits) and indirect investigations (in
situ tests, such as the CPT).
The code further distinguishes between investigations for the
purposes of design and forcontrol.
In a clear departure from most current practice, EC7-2 makes
compulsory theprovision of some form of ground investigation report
(GIR) as part of the geotechnicaldesign report. The code specifies
that the GIR should include:
a presentation of all available geotechnical information
including geological featuresand relevant data
a factual account of all field and laboratory investigations
a geotechnical evaluation of the information, stating the
assumptions made in theinterpretation of the test results
a statement of methods adopted (citing the relevant
standards)
all relevant information on how a direct assessment of design
values or derivedvalues (see below) were determined, including any
correlations used
any known limitations in the results.
The size of the GIR will depend on the complexity and value of
the project, varying froma single page for a simple footing to
volumes of pages for a major infrastructure project.
While listing the general information required to reach a
decision on the values ofgeotechnical parameters for a suitable
design, it could be argued that EC7 places toomuch emphasis on the
manipulation of test results and not enough on desk studies
andother means to determine information on such matters as:
site geology, geomorphology and overall stability
Mans influence on the site and the sensitivity of existing
structures
local experience and relevant published knowledge.
In addition to gathering all pertinent facts already known about
a site, determining theground properties for design using the
Eurocode suite could be seen as a logicalsequence of:
carrying out tests and interpreting the test results
determining derived values
collating all geotechnical and other relevant information about
the site
selecting characteristic values for factoring into design
values, taking account of therequirements of the project19.
The testing and interpretation elements of this sequence are
illustrated in Figure 2.1,which has been taken from EC7-2 and is
further explained in Figure 2.2. In both, theterm derived value is
used EC7-2 defines this as the value of a geotechnicalparameter
obtained from test results by theory, correlation or
empiricism.
CIRIA C64112Lic
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IRIA
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The processes for obtaining derived values are essentially the
same as current goodpractice EC7 may be seen simply as attempting
to codify these processes.
It is this derived value that is used in EC7-1 for selecting a
characteristic value fromwhich to determine a design value. The
selection is made in EC7-1 because, in the finalanalysis, it should
be the designers responsibility. This may generate difficulty for
theground investigation contractor in some instances. For example,
if the contractor isasked to provide characteristic rather than
derived values of ground parameters, it maybecome difficult or
risky unless there is sufficient information about the
designsituations and the limit states pertaining to the
project.
2.3 Ground identification and classification
For soil and rock descriptions (ISO-EN 14688-1, 14688-2 and
14689-1) somedifferences from BS 5930 terminology are apparent.
Examples that have required arevision of our current terminology
are shown in Table 2.2.
Table 2.2 Some terminological changes
(Fuller details can be found in Powell and Norbury, 2007 and
Baldwin, Gosling andBrownlie, 2007).
Some of the new field testing standards are likely to cover not
only equipmentspecification, sizing and operation but also to
introduce requirements for what might betermed fitness for purpose.
In these, the test specification is related to its applicationand
the required accuracy for the ground conditions, and for intended
use of theresults (this will become clearer as the documents are
completed).
As the various documents become available, detailed comparisons
with BS documentswill have to be undertaken to identify any
potential conflicts.
2.4 Determining the design values of geotechnicalparameters
One of the biggest changes for UK practice is the formalised
process in the Eurocodefor determining the design values of ground
properties using partial factors andcharacteristic values.
EC7-1 states that design values of geotechnical parameters (Xd)
shall either bederived20 from characteristic values using the
following equation:
Xd = Xk / M (Equation 2.2, BS EN 1997-1)
or shall be assessed directly (Clause 2.4.6.2(1)P).
where Xk is the characteristic value and M is the partial
material factor.
CIRIA C641 13
Old terminology New terminology
Slightly organic Low-organic
There are changes in the boundariesbetween the classes
Organic Medium-organic
Highly organic High-organic
Very soft, soft, firm, stiff and very stiff(terms used in BS
5930 to describeshear strength)
Now used to describe the consistency of silts and clays. Shear
strengthdescriptors become: vvery low, low, medium, high, very high
and extremelyhigh, (though maintaining the same strength ranges
used in BS 5930)
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Although the Eurocode clearly permits the direct assessment of a
design value, it placespriority on the use of factored
characteristic values. There are situations in which it ismore
appropriate to assess, for example, a strength where the critical
state strengthvalue will be used in the design. This may also apply
to the design values ofdeformation properties since these are
rarely measured and are commonly deducedfrom correlations with
strength.
In selecting the characteristic value, account should be taken
of a number of mattersthat are listed in EC7-1, which then defines
characteristic value as the characteristicvalue of a soil or rock
parameter shall be selected as a cautious estimate of the
valueaffecting the occurrence of the limit state.
Design values of parameters may be required for both ultimate
and serviceability limitstate considerations. It is important to
appreciate that, while the partial factor used toobtain the design
value will have different values for ULS and SLS, so also may
thecharacteristic value itself differ in calculations for these
limit states.
The meaning and selection of a characteristic value have been
debated for manyyears21. It is important to realise that, despite
the formalisation in the Eurocode, theselected value(s) is for the
judgement of the designer, having considered all
relevantinformation, including prior knowledge of the particular
site and all ground testingand assessment data. As the values of
the partial material factor M in Equation 2.2 arefixed in the
National Annex (see Section 6.3), the designer has control of the
designvalue through the selection of the characteristic
value22.
Much has also been said23 about the merits or otherwise of using
statistics in thedetermination of characteristic values and it is
important to appreciate that theEurocode does not require their
use.
Note: It is very important that the chosen correlation is
appropriate for the prevailing geologicalcondition.
Figure 2.1 Processing test measurements into design values of
ground parameters
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Figure 2.2 General procedure for determining characteristic
values from measured values
Selecting characteristic values
A list of the issues to be considered in determining
characteristic values is shown inFigure 2.2. An example of how a
characteristic profile of ground strength values mightbe obtained
for a particular site is given in Appendix A1. It is important to
appreciatethat the selections made in Appendix A1 are quite
subjective, so a risk-averse or risk-taking designer might make a
rather different selection which could be seen as aretention of the
status quo in UK practice.
Characteristic values of ground stiffness and weight
density24
The basis of structural design Eurocode, BS EN 1990, states that
The structuralstiffness parameters (eg moduli of elasticity )
should be represented by a meanvalue25.
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In problems involving ground structure interaction the stiffness
of the ground is oftena very important parameter26. In these cases,
the use of a mean value for groundstiffness is questionable27. As
EC7-1 does not define a characteristic value of groundstiffness, it
is suggested that its definition should follow that for strength ie
a cautiousestimate and not a mean value.
EC7-1s definition of characteristic strength value might be
assumed also to apply to theweight density of soil and rock.
However, the uncertainty about weight density isusually
sufficiently low that there is no need to make a distinction
between mean andcautious values.
Other attempts to deal with uncertainty in ground parameters
It is useful to compare the acquisition of conservative ground
parameters in EC7-1 withapproaches in other geotechnical design
codes and guidance for ensuring the necessarycaution in values for
use in design. Historically, CIRIA R104 (Padfield and Mair,
1984)suggested that design may be based on moderately conservative
values of parameters.Moderately conservative is defined as a
cautious estimate of the value relevant to theoccurrence of the
limit state which compares closely with the EC7-1 definition.
CIRIAC580 (Gaba et al, 2003) discusses these definitions.
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3 The new principles of geotechnicaldesign in Eurocode 7
3.1 Summary
3.2 Introduction
There are several key features of EC7-1 that make it different
from the current BSgeotechnical codes, these are:
unlike current codes, EC7 states that Principles shall be
honoured. BS codes stateonly that things should be done28
EC7-1 embodies a design calculation methodology that makes
sub-structure designfully compatible with superstructure design
using the other structural Eurocodes29
EC7-1 explicitly identifies design limit states30
EC7-1, in ultimate limit state design calculations, makes use of
partial factorsapplied to characteristic values of parameters, to
account more directly foruncertainty in the values of parameters
used in the calculations31 and to achievecompatibility with
structural codes that also conform to the basis of structural
designlaid down in BS EN 199032
the formal adoption of four alternative methods for achieving a
geotechnical design(see page 18)
EC7-1 makes compulsory the provision to the client of a
geotechnical design report,while EC7-2 requires the provision of a
ground investigation report, to form part ofthe geotechnical design
report.
Together, these provide a single set of guiding principles for
all geotechnical designsthat is absent in the current, diverse set
of BS design codes.
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1 Clear separation of ultimate (failure) condition from
serviceability (settlement and comfort) condition.
2Need to be aware of the important distinction between permanent
and variable actions, since differentvalues of partial factors
apply to each. Similarly for favourable and unfavourable
actions.
3Use of characteristic to define values of ground properties for
use with partial factors to form designvalues.
4Application of separate partial factors to several aspects of
uncertainty, rather than a single lumped factorof safety applied to
cover all uncertainty.
5Partial factor values have been largely selected to avoid
failure and are not necessarily sufficient to ensureacceptable
movement. A check on movements will often be required.