Basis of design

Eurocode 7 requires embedded walls to be designed with sufficient embedment to prevent rotational and vertical failure. The wall's cross-section and any supports it relies upon must be verified against structural failure (see Section 12.7). Furthermore, embedded walls must not fail due to overall instability of the ground in which they are installed.

[EN 1997-1 ยง9.7.2(1)P, 9.7.4(1)P, 9.7.5(1)P, and 9.7.6(1)P]

Regrettably, Eurocode 7 gives little detailed guidance on the design of embedded retaining walls. Traditional national practice will therefore still have a large role to play in their design for the foreseeable future.

This book does not attempt to provide complete guidance on the design of retaining walls, for which the reader should refer to any well-established text on the subject.3

12.3.1 Role of CIRIA C580 in UK practice

The UK National Annex to BS EN 1997-14 lists CIRIA report C5805 as a source of 'non-conflicting, complementary information' (NCCI) which can be used to provide detailed guidance on the design of embedded retaining walls. However, CIRIA C580 was written before publication of the final version of EN 1997-1 and several of its recommendations contradict Eurocode 7.1

For example, C580 presents three design approaches (A, B, and C) which are unrelated to the three Design Approaches (1, 2, and 3) in Eurocode 7 Part 1. The partial factors recommended in C580 differ from those given in EN 19971 and the UK National Annex. CIRIA's guidance on the structural design of embedded walls is based on existing British Standards, such as BS 59506 and BS 8110,7 and not on their Eurocode replacements.

C580's Design Approach A employs 'moderately conservative' soil parameters, groundwater pressures, loads, and geometries. As discussed in Chapter 5, the moderately conservative approach - which was originally documented in CIRIA Report 104 (the predecessor to C580) - adopts parameters that have similar reliability to Eurocode 7's characteristic values

Proposals have been made to update CIRIA C580 to remove these conflicts.

(based on a 'cautious estimate'). Approach B employs 'worst credible' parameters, which have significantly higher reliability than characteristic values. Approach C, which should only be used as part of the observational method of design,8 employs 'most probable' parameters with slightly lower reliability than characteristic values.

The differences between the partial factors recommended by CIRIA C580 and those specified in the UK National Annex to Eurocode 7 - for ultimate limit states (ULSs) GEO and STR and serviceability limit states (SLSs) - are summarized in the table below. The requirements of Eurocode 7 take precedence over those of CIRIA C580.

Limit Design Approach Partial factors

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