C1 GENERAL C1.1 Scope

C1.1.1 Scope of Eurocode 7

Eurocode 7, to be used in conjunction with Eurocode 1, applies to the geotechnical aspects of design of buildings and civil engineering structures for strength, stability, serviceability and durability. It provides rules for calculating design earth pressures, and, in this respect, acts as a loading code for use with other Eurocodes. It also gives some minimum standards for construction requirements.

It does not cover seismic design, which is the subject of Eurocode 8 and in 9.1(1) it is stated implicitly that dykes and dams are also excluded. EC1, 1.1 states that it does not completely cover structures which require unusual reliability considerations, such as nuclear structures. By implication, this applies to the full suite of Eurocodes.

C1.1.2 Scope of ENV 1997-1 See A2.3.

C1.1.3 Further parts of Eurocode 7

Parts 2 and 3 of EC7, for laboratory and field testing, respectively, have been accepted as pre-standards (ENVs, early 1998). Besides providing basic descriptions of the performance of tests, these documents indicate how parameters required for design may be derived from the test results. Their status, contents and further development are discussed in A2.5 and D2.3.

C1.2 References

The reasons for noting the two ISO documents on Units and Symbols is not stated in the text. In practice, there is no need to refer to them.

C1.3 Distinction between principles and application rules

At this point Eurocode 7 repeats the definitions, given in Eurocode 1, of principles and application rules. Throughout the text, the modal verb ‘shall’ is used in principles, whilst ‘should’ is used in application rules. The following explanation is taken from ‘Harmonised editorial style for Eurocodes’ issued by CEN/TC250 in January 1996:

a Principles are requirementsfor which ‘shall’ is appropriate;

b Application Rules are recommendationsfor which ‘should’ is appropriate;

c for permissiveprovisions ‘may’ is appropriate;

d in statements of possibilitythe appropriate form is ‘can’;

e ‘may’ is used only to allow, never as an alternative for ‘might’ or ‘can perhaps’;

f ‘can’ is never used to allow or authorise, but only to state a fact.

Occasionally, EC7-1 uses the form ‘shall normally’ in principles. This is intended to indicate a requirement which is mandatory unless the designer can justify a claim that the circumstances are exceptional.

In this commentary, the words ‘must’ and ‘recommended’ are used to convey the opinions of the authors, as explained in A3.3.

C1.3(5)

Eurocode 7 gives precise calculation rules for relatively few situations, though it does provide formulae for bearing capacity factors and coefficients of earth pressure (Annexes B and G). In cases such as these, simpler formulae could be used provided it was shown that they give results at least as conservative. For example, it might be convenient for a designer to use established charts in place of the rather complex formulae provided in the code. This paragraph may become more important in the future if more detailed calculation rules are included in the code.

C1.4 Assumptions

It is an underlying assumption of the Eurocode system that structures are designed by appropriately qualified and experienced personnel and that

construction is carried out to standards which are accepted as good practice in western Europe. The factors of safety proposed do not provide for deviation from these assumptions. The Site Investigation Steering Group (1993) provide recommendations on appropriate qualifications for personnel involved in geotechnical work.

It is not entirely clear who is to make the assumptions listed in this clause, and why. Firstly, they are assumptions made by the code drafters. This means that the code does not make any provision for non-compliance with the assumptions listed. For example, the code makes no provision for lack of necessary maintenance in a completed structure or for poor standards of construction. Features such as these are not allowed for within the margins of safety specified by the code.

The designer is permitted to make the assumptions which are listed, though he also has influence, to some degree, over ensuring compliance with them. This is particularly true for the first three assumptions: data collection, qualifications of the designer and communication within the design and construction team. He may have little or no power to ensure compliance with the remaining assumptions which concern actions taken after design, but he should at least be satisfied that compliance with these assumptions is practical and clearly intended at the time of design.

C1.5 Definitions

C1.5.1 Terms common to all Eurocodes

Much of the terminology of limit state design is defined in EC1 and not repeated in EC7. In fact, repetition of any kind is avoided as far as possible. It is therefore essential that users of EC7 have EC1 available. Some of the

common terminology of limit state design is noted in A2.8.

C1.5.2 Special terms used in ENV 1997-1 C1.5.2(1)P

Comparable experience: documented or other clearly established information related to the ground being considered in design, involving the same types of soil and rock and for which similar geotechnical behaviour is expected, and involving similar

structures. Information gained locally is deemed to be particularly relevant.

Besides using theory and calculations, geotechnical engineering relies heavily on experience. However, experience which is only partly understood and partly applicable can be very dangerous. This paragraph demands clear communication of experience so that it is sufficiently objective to be both understood and challenged by all competent parties.

It is recognised as part of the sound geotechnical process that the performance of similar structures in the locality of a new design will be investigated, and lessons will be learnt from both success and failures. In British practice, this is often achieved by a visit to local Building Control offices.

The emphasis on relevant, and especially local, experience occurs repeatedly in the document. It is hoped that the required documentation of experience will make it more readily available to all comers. ‘I can’t explain why – it’s just my engineering judgement’ is not good enough!

Ground: soil, rock and fill existing in place prior to the execution of the construction works.

‘Ground’ is taken to mean the material which was present on site without the control of the geotechnical designer. It will normally need to be investigated. It may include fill as well as natural ground. Fill ‘placed during execution of the construction works’ is included within the definition of ‘structure’.

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Three other verbs are used repeatedly in the text, and it would be beneficial if they were defined:

‘Considered’. This verb means that the engineer has given attention to an item, and should generally make a note of the fact, possibly by no more than a tick on a check list. The consideration may be very brief, leading to an immediate conclusion that the item is not significant for the design in hand.

The verb ‘consider’ often does not imply the need for calculation, though this may be appropriate in some cases.

‘Assess’. A quantity is said to be ‘assessed’ when a numerical value is determined by an engineer. This process may involve calculation, but not necessarily so. It could include processes of rough estimation or

determination simply on the basis of comparable experience. In most cases this refers to prediction of the likely behaviour of a structure.

‘Evaluate’. This verb is used to mean ‘derive a value’ for a parameter. In most cases this refers to derivation of characteristic values for material properties.

C1.6 SI units

C1.7 Symbols common to all Eurocodes See C1.5.1.

C1.8 Symbols used in Eurocode 7

Geotechnical symbols have generally followed the recommendations of the International Society for Soil Mechanics and Foundation Engineering (ISSMFE (1977)). In particular, the symbol c_uis retained for undrained shear strength in preference to s_u. The symbol γis also retained for unit weight, despite possible conflict with the symbol for partial factors.