application of different load factors depending on which of three ‘design approaches’is
being used. The National Annex documents (to be published separately from the Eurocodes)
which are to be used in each country to conform to their individual practices will address
within prescribed limits the design approach, partial factors, methods of calculating
settlement and the procedures to be used where alternatives to EC7 are needed. Design
Approach 1 with ‘partial factor combinations 1 and 2’is to be adopted in the UK in which the
factors are applied at source to actions and shear strengths, but the code notes that for pile
designthe partial factors must be applied to the bearing capacity or ground ‘resistance’. When
EC7 Design Approach 1 (DA1) is used, partial factor ‘combination 1’usually governs the
structural design values of actions for piles and ‘combination 2’the geotechnical sizing.
References are made to EC7 in the chapters of this book dealing with pile design and to
the BSEN standards for the execution of geotechnical works, but EC7 itself does not make
specific recommendations on methods of pile design. Essentially it prescribes the succes-
sion of stages in the design process using conventional methods to determine end bearing,
frictional resistance and displacement. References are therefore continued to BS8004 and
BS8110 alongside the appropriate Eurocode. At the time of preparing this edition the
application of EC7 is not mandatory in the UK, but in due course all geotechnical design
will have to conform. If the reader wishes to apply the EC7 rules to current designs, a
thorough study of the Designer’s Guide(1.5)which sets out the step-by-step design process
and takes account of the various qualifications to the application of the code rules is
recommended. Whether or not the Eurocode is used for design in preference to present
conventional methods it does provide a very useful design check, itemizing all the factors
which can influence economic foundation design.
As the British National Annex stating the partial factors to be used in designing piles is
not due to be published until 2008, the factors provided in the tables in Chapter 4 and used
in worked examples are those given in Annex A to EC7. The reader should therefore check
that the quoted values conform to the data in the National Annex when avaliable. Also,
engineers designing foundations in EU countries other than the UK should consult the
particular National Annexes for guidance on design procedures and partial factors. The
selection of characteristic parameters and the application of EC7 partial factors to ‘numerical
methods’for complex foundation design are yet to be decided and are therefore not dealt
with in this edition.
1.6 Responsibilities of engineer and contractor
In Britain and in many other countries piling is regarded as a specialist operation and the
procedure for calling for tendered prices for this work may result in a division of
responsibility which can lead to undesirable practices. When the engineer is wholly
responsible for design or supervision of construction, the type, width and overall length of
the piles will be specified based on the ground information. Detailed designs for concrete
piles showing the reinforcement, concrete mix proportions, cover and cube crushing
strengths will then be prepared. In the case of steel piles the standard sections, grade of
steel and welding requirements will be specified. The engineer will decide on the depth of
penetration of each pile from the results of preliminary calculations checked by field
observations during driving. Responsibility will be accepted by the engineer for paying the
contractor for any costs involved in shortening or lengthening piles, or of providing
additional piles should the ground conditions differ from those envisaged or should
General principles and practices 7