EC7 Geotech and Retaining.pdf

ICE Teesside Branch, NGG and IStructE
EUROCODE 7
Dr Ian Smith, Edinburgh Napier University
Retaining Walls and Geotechnical
Design to Eurocode 7
Dr Ian Smith
Head of School
School of Engineering and the Built Environment
Edinburgh Napier University

EUROCODE 7
This evening’s presentation
1. Introduction to the Eurocodes
2. Overview of Eurocode 7, EN 1997
3. Basis of Geotechnical Design
4. Geotechnical Design by Calculation
5. Retaining Wall Design
6. Conclusion

EUROCODE 7
The Structural Eurocodes
What are the
What are the Eurocodes
Eurocodes?
?
The structural Eurocodes are a European suite of codes for structural
design… developed over… 25 years
By 2010 they will have effectively replaced the current British Standards
They will be used as an acceptable basis for meeting compliance with UK
Building Regulations and the requirements of other public authorities
from:
National Strategy for Implementation of the Structural Eurocodes: Design Guidance
D. Nethercot et al, Institution of Structural Engineers (April 2004)

EUROCODE 7
Objectives of the Eurocodes
as a means to prove compliance of building and civil engineering works
with the essential requirements of mechanical resistance and stability and
safety in case of fire;
a basis for specifying contracts for construction works & related
engineering services;
a framework for drawing up harmonised technical specs for construction
products.
In addition, the Eurocodes are foreseen to:
• improve the functioning of the single market for products and engineering
services by removing obstacles arising from different nationally codified
practices for the assessment of structural reliability;
• improve the competitiveness of the European construction industry and
its professionals and industries, in countries outside the European Union.

EUROCODE 7
EN 1990 Basis of Structural Design
EN 1991 Eurocode 1 Actions on Structures
EN 1992 Eurocode 2 Design of Concrete Structures
EN 1993 Eurocode 3 Design of Steel Structures
EN 1994 Eurocode 4 Design of Composite Steel & Concrete Structures
EN 1995 Eurocode 5 Design of Timber Structures
EN 1996 Eurocode 6 Design of Masonry Structures
EN 1997 Eurocode 7 Geotechnical Design
EN 1998 Eurocode 8 Design of Structures for Earthquake Resistance
EN 1999 Eurocode 9 Design of Aluminium Structures
EN 1997 Eurocode 7 Geotechnical Design
Part 1: General Rules
Part 2: Ground
investigation and testing

EUROCODE 7

EUROCODE 7
Publication of Eurocodes
1975: ECC identify need to improve functioning of the single market for products and
engineering services
1989: ECC issue Council Directive 89/106/EEC
- known as Construction Products Directive
Passed to CEN for development
Eurocode Programme overseen by Technical Committee 250 (CEN/TC 250)
Each Eurocode produced by separate sub-committee
e.g. Eurocode 7 : CEN/TC 250/SC 7
Each Eurocode and National Annex published by national standards bodies,
e.g. BSI in UK
Eurocode programme developed by the Comité Européen de Normalisation (CEN)
– the European Committee for Standardisation.

EUROCODE 7
CEN Member States
• Austria
• Belgium
• Cyprus
• Czech Republic
• Denmark
• Estonia
• Finland
• France
• Germany
• Greece
• Hungary
• Iceland
• Ireland
• Italy
• Latvia
• Lithuania
• Luxembourg
• Malta
• Netherlands
• Norway
• Poland
• Portugal
• Slovakia
• Slovenia
• Spain
• Sweden
• Switzerland
• UK
(Comité Européen de Normalisation)

EUROCODE 7
CEN committee structure
CEN
CEN
TC 250
TC 250 TC….
TC…. TC…
TC…
SC 0
SC 0 SC 7
SC 7
SC…
SC…
SC 1
SC 1 SC…
SC…
e.g. Eurocode 7 : CEN/TC 250/SC 7

EUROCODE 7
Eurocodes Timeline
1989 – 1999
ENVs produced
1975 1980 1985 1990 1995 2000 2005 2010
• All European public-sector clients have been legally required to commission Eurocode-
compliant structural designs since March 2010.
• Private sector clients can continue to use any effective design methods. But, as most
existing codes will be withdrawn, Eurocodes will be only recognised codes available.
March
2010
Implmtn.
2002
ENs start
to appear
1989
Programme
passed to CEN
1975
EEC initiate
programme
1999
2011
Today

EUROCODE 7
Fundamental requirements
The structure and structural members should be designed, executed
and maintained in such a way that they meet the following:
• Serviceability requirement – the structure during its intended life,
with appropriate degrees of reliability and in an economic way,
will remain fit for the use for which it is required.
• Safety requirement – the structure will sustain all actions and
influences likely to occur during execution and use.
• Fire requirement – the structural resistance shall be adequate for
the required period of time.
• Robustness requirement – the structure will not be damaged by
events such as explosion, impact or consequences of human
errors, to an extent disproportionate to the original cause.

EUROCODE 7
National Annex
EN Title Page
EN Annexes
EN Text
National Title Page
National Foreword
Structure of a Eurocode Document

EUROCODE 7
EN Annexes
EN Annexes are either Normative or Informative.
Normative – contains information that must be followed.
Informative – contains supplementary information that may be
followed.

EUROCODE 7
National Annexes
• The “link” between Eurocode and national standards for member state.
• Contain rules and NDPs to ensure safety remains a national, and not a
European, responsibility.
• Foreword of each Eurocode lists paragraphs in which national choice
is allowed. However, the National Annex has limited overriding
authority to the Eurocode.
A National Annex cannot change or modify the content of the EN Eurocode
text in any way other than where it indicates that national choices may be
made by means of Nationally Determined Parameters.
Guidance Paper L: § 2.3.4

EUROCODE 7
National Annex
The National Annex flavours each Eurocode to each country’s needs.
A National Annex exists for each Eurocode Part.
National Annexes provide:
• Nationally Determined Parameters (NDPs)
• Country specific data
• Procedure to be used, where choice is offered
• Guidance on the informative annexes
• Reference to non-contradictory, complementary information (NCCI)

EUROCODE 7
1. Introduction to the Eurocodes ✔
2. Overview of Eurocode 7, EN 1997
6. Conclusion

EUROCODE 7
Eurocode 7: Geotechnical design
• Part 1: General rules
• Part 2: Ground investigation and testing
Published
December 2004
Published
November 2007

EUROCODE 7
National Annexes
• Part 1: Published November 2007
• Part 2: Published December 2009

EUROCODE 7
Development of Eurocode 7
• Agreement for geotechnical design more “challenging” than for
EN 1990, EN 1991 and material Eurocodes.
• EN 1997 was one of the later codes to be published.
• Unique in that some national practices maintained within
design process, e.g. the 3 Design Approaches

EUROCODE 7
Soil properties
8 features considered by drafters of Eurocode 7:
1. Soil properties determined by investigation,  EN 1997 Part 2
2. Undrained and drained conditions to be considered
3. Property characteristic value is “cautious estimate” of mean value
4. Soil variability is high,  judgement required for ‘k’ values
5. Strength related to normal stress ,  care required when applying
partial factors of safety to geotechnical loads
6. Soil can redistribute loading from weaker to stronger zones
7. Soil is compressible,  SLS usually controls design, though ULS
calculations usually performed in design
8. Soil stress-strain behaviour is complex,  few calculation models
provided in EN 1997

EUROCODE 7
Contents of Eurocode 7 Part 1
Foreword
1. General
2. Basis of Geotechnical design
3. Geotechnical data
4. Supervision of construction, monitoring and maintenance
5. Fill, dewatering, ground improvement and reinforcement
6. Spread foundations
7. Pile foundations
8. Anchorages
9. Retaining structures
10. Hydraulic failure
11. Overall stability
12. Embankments
Annexes A – J
167 pages

EUROCODE 7
Foreword
1. General
2. Planning of ground investigation
3. Soil and rock sampling and groundwater measurements
4. Field tests in soil and rock
5. Laboratory tests on soil and rock
6. Ground investigation report
Annexes A – X
196 pages

EUROCODE 7
Scope:
EN 1997-2 is intended to be used in conjunction with EN 1997-1 and
provides rules supplementary to EN 1997-1 related to:
• planning and reporting of ground investigations;
• general requirements for a number of commonly used laboratory and
field tests;
• interpretation and evaluation of test results;
• derivation of values of geotechnical parameters and coefficients.
Note: Establishment of characteristic values is covered in EN 1997-1.

EUROCODE 7
24 Annexes:
• Annex A List of test results of geotechnical test standards
• Annex B Planning of geotechnical investigations
• Annex C Example of groundwater pressure derivations based on a model and long term measurements
• Annex D Cone and piezocone penetration tests
• Annex E Pressure meter test
• Annex F Standard penetration test
• Annex G Dynamic probing test
• Annex H Weight sounding test
• Annex I Field vane test
• Annex J Flat dilatometer test
• Annex K Plate loading test
• Annex L Detailed information on preparation of soil specimens for testing
• Annex M Detailed information on tests for classification, identification and description of soil
• Annex N Detailed information on chemical testing of soil
• Annex O Detailed information on strength index testing of soil
• Annex P Detailed information on strength testing of soil
• Annex Q Detailed information on compressibility testing of soil
• Annex R Detailed information on compaction testing of soil
• Annex S Detailed information on permeability testing of soil
• Annex T Preparation of specimen for testing on rock material
• Annex U Classification testing of rock material
• Annex V Swelling testing of rock material
• Annex W Strength testing of rock material
• Annex X Bibliography

EUROCODE 7
• Reminder (Scope):
EN 1997-2 is intended to be used in conjunction with EN 1997-1
and provides rules supplementary to EN 1997-1.
• Part 2 does not cover standardisation of the geotechnical tests.
• Several ISO Technical Specifications play a part…
Eurocode 7 Geotechnical Design –
Part 2: Ground investigation and testing
EN ISO 22476
Field Testing
Parts 1 – 13
EN ISO 14688
EN ISO 14689
Identification and classification of
soil and rock
EN ISO 22475
Sampling and
groundwater
measurements
CEN ISO/TS 17892
Laboratory tests
Parts 1 – 12

EUROCODE 7
2.4.1 (2) It should be considered that knowledge of the ground
conditions depends on the extent and quality of the geotechnical
investigations. Such knowledge and the control of workmanship are
usually more significant to fulfilling the fundamental requirements than
is precision in the calculation models and partial factors.
EN 1997-1:2004 §2.4 Geotechnical design by calculation
In other words…
Design to EN 1997 depends as much on Part 2 as Part 1.

EUROCODE 7
European Geotechnical Codes
European Standards for
the Execution of Special
Geotechnical Works
Other structural Eurocodes
e.g. EN 1998, EN 1993-5
Geotechnical Design
(Eurocode 7: Parts 1 & 2) & NAs
Eurocodes:
EN 1990 Basis of Structural Design
EN 1991 Actions on Structures
Test Standards and
Technical Specs for
ground properties
ISO/CEN Standards
for identification &
classification
Geotechnical Projects

EUROCODE 7
Using Eurocode 7
Key aspects
• Limit state design to ensure serviceability limit states not exceeded
• Principles and Application Rules
• Characteristic values of geotechnical parameters
• Partial factors of safety
• Characteristic values → design values
• The 5 ultimate limit states
• GEO/STR limit states - Design approaches
• Serviceability limit state

EUROCODE 7
Limit state design
Serviceability limit states: (EN1990 §1.5.2.14)
“States that correspond to conditions beyond
which specified service requirements for a
structure or structural member are no longer met”
Ultimate limit states: (EN1990 §1.5.2.13)
“States associated with collapse or with
other similar forms of structural failure”

EUROCODE 7
Principles & Application Rules
The Principles (preceded by the letter P) comprise general statements and
definitions for which there is no alternative, as well as requirements and analytical
models for which no alternative is permitted unless specifically stated.
It is permissible to use alternative design rules to the Application Rules, provided
that it is shown that the alternative rules accord with the relevant principles and are
at least equivalent with regard to resistance, serviceability and durability which
would otherwise be achieved for the structure.
Note: If an alternative design rule is substituted for an Application Rule, the
resulting design cannot be claimed to be wholly in accordance with the Eurocode
although the design will remain in accordance with the Principles of the Eurocode.
All statements in each Eurocode are either:
 Principles (must be followed), or
 Application Rules (offer advice).

EUROCODE 7
2. Overview of Eurocode 7, EN 1997 ✔
6. Conclusion

EUROCODE 7
Basis of Geotechnical Design
EN 1997-1:2004
Section 2 Basis of geotechnical design
2.1 Design requirements
2.2 Design situations
2.3 Durability
2.4 Geotechnical design by calculation
2.5 Design by prescriptive measures
2.6 Load tests and tests on experimental models
2.7 Observational method
2.8 Geotechnical Design Report

EUROCODE 7
(1)P For each geotechnical design situation it shall be verified that no
relevant limit state, as defined in EN 1990:2002, is exceeded.
§2.1(1)
This section sets the scene for the design situations and identifies aspects to
be considered in the design, including: factors to be considered (e.g. site
conditions) (§2.1(2)); methods of verifying the limit states (§2.1(4)); and a
means of identifying the complexity of the design together with the
associated risks (§2.1(8)).
(4) Limit states should be verified by one or a combination of the following:
— use of calculations… (most common)
— adoption of prescriptive measures…
— experimental models and load tests…
— an observational method…

EUROCODE 7
Expanding on Clause §2.1(8), Eurocode 7 introduces the notion of three
Geotechnical Categories to establish the geotechnical design requirements
§2.1(10):
 Category 1 is for small projects with negligible-risk and where the
fundamental requirements will be satisfied on the basis of experience
and qualitative geotechnical investigations;
 Category 2 is for conventional structures (e.g. foundations, retaining
walls, embankments) with no exceptional risk or difficult soil or loading
conditions;
 Category 3 is for structures not covered by Categories 1 and 2 (e.g. very
large structures, structures involving abnormal risks).
Most routine geotechnical design work will fall into Geotechnical Category 2.

EUROCODE 7
2.2 Design situations
(1)P Both short-term and long-term design situations shall be
considered.
§2.2(1)
Section 2.2 of Eurocode 7 Part 1 gives guidance as to what to include in the
detailed specifications of design situations, such as: the actions, their
combinations and load cases, and the general suitability of the ground on
which the structure is located with respect to overall stability and ground
movements.

EUROCODE 7
2.3 Durability
(1)P At the geotechnical design stage, the significance of
environmental conditions shall be assessed in relation to
durability and to enable provisions to be made for the protection
or adequate resistance of the materials
§2.3(1)
Section 2.3 of Eurocode 7 Part 1 gives brief guidance on designing for the
durability of materials (such as concrete, steel and timber) used in the ground.

EUROCODE 7
2.4 Geotechnical design by calculation
Fundamental!
We shall look at this shortly…

EUROCODE 7
Other sub-sections of EN 1997-1:2004, Section 2
The remaining sub-sections of Section 2 of Eurocode 7 Part 1 are:
2.5 Design by prescriptive measures
2.6 Load tests and tests on experimental models
2.7 Observational method
2.8 Geotechnical Design Report

EUROCODE 7
3. Basis of Geotechnical Design ✔
6. Conclusion

EUROCODE 7
Geotechnical design by calculation
(1)P Design by calculation shall be in accordance with the fundamental
requirements of EN 1990:2002 and with the particular rules of this
standard. Design by calculation involves:
— actions, which may be either imposed loads or imposed
displacements, e.g. from ground movements;
— properties of soils, rocks and other materials;
— geometrical data;
— limiting values of deformations, crack widths, vibrations etc.;
— calculation models.
EN 1997-1:2004 §2.4.1(1)
Covered in Section 2.4 of Eurocode 7 Part 1

EUROCODE 7
Processes involved:
Establish design values of actions and
geometrical data
Establish design values of ground
properties and resistances
Define limit that must not be exceeded
(e.g. bearing resistance)
Perform relevant geotechnical analysis
Show, by calculation, that limit will not be
exceeded

EUROCODE 7
Actions:
• An action is given the general symbol, F.
• Actions can be permanent (persistent) or variable
(transient), accidental, or seismic.
• Persistent actions are denoted by FG. Transient actions are
denoted by FQ.
• Persistent actions can be either “favourable” or
“unfavourable”.
• Transient actions are always considered as unfavourable.

EUROCODE 7
Ground properties:
• Geotechnical parameters should be established with consideration
given to published data and local and general experience…
• Clauses 2.4.3(3) to (6) give guidance on how the parameters
should be considered in the design process.
• Material properties are given the general symbol, X.
• Characteristic values of material properties are given the general
symbol, Xk.

EUROCODE 7
Characteristic values of geotech parameters
(1)P The selection of characteristic values for geotechnical parameters
shall be based on results and derived values from laboratory and field
tests, complemented by well-established experience.
EN 1997-1:2004 §2.4.5.2(1)

EUROCODE 7
Characteristic values of geotech parameters
Cautious estimate
• Statistical methods not readily applicable to the determination of
characteristic values
• Notion of cautious estimate introduced
(2)P The characteristic value of a geotechnical parameter shall be
selected as a cautious estimate of the value affecting the
occurrence of the limit state.
EN 1997-1:2004 §2.4.5.2(2)

EUROCODE 7
Derived values
1.5.3 Specific definitions used in EN 1997-2
1.5.3.1 derived value
value of a geotechnical parameter obtained from test results
by theory, correlation or empiricism (see 1.6)

EUROCODE 7
Test results and derived values
F1 F2 L1 L2
Cautious selection
Geotechnical model and characteristic value of
geotechnical parameters
Application of partial
factors
Design value of geotechnical parameters
1 2 3 4
C1
C1 C1
C2
Information from other
sources on the site,
the soils and rocks
and the project.
Test results and
derived values
Correlations
Type of test (Field, Lab)
EN 1997-2
EN 1997-1

EUROCODE 7
Other means…
Statistical methods – can be used if sufficient geotechnical
measurements/results exist.
Except on projects where a large amount of high quality ground
investigation data is available, it is unlikely that statistical methods would
be adopted to select characteristic values of geotechnical parameters.
Standard tables of characteristic values, where available, may be
used in the selection of a characteristic value.
(12)P When using standard tables of characteristic values related to soil
investigation parameters, the characteristic value shall be selected as a
very cautious value.
EN 1997-1:2004 §2.4.5.2(12)

EUROCODE 7
Partial factors of safety
Provided in EN 1997-1
Nationally Determined Parameters (NDPs) provided in National Annexe
Symbols:
Actions: General: F Permanent: G
Transient: Q
Materials: General: M Soil properties: cu, , etc.
Resistance: General: R Bearing resistance: Rv
NB geotechnical engineers already use “” for unit weight (weight density).

EUROCODE 7
Design values
These are obtained by combining the characteristic value with the
appropriate partial factor of safety.
i.e.
characteristic value
design value
partial factor of safety

EUROCODE 7
Multiplied by F values
Representative action Fk
Design action Fd Design material property, e.g. c'd
Characteristic material property, e.g. c'
Divided by M values
Geotechnical Analysis
Design effect of actions, Ed Design Resistance, Rd
Verify
Ed ≤ Rd
Actions: (loads, forces etc.) Material Properties (c, tan , etc.)
and
The design is all about

EUROCODE 7
Characteristic
action
 representative
action
 design
action
 design effects of
action
(Fk) (Frep) (Fd) (Ed)
Design values of actions
Correlation
factor, 
Partial factor
of safety, F
i.e.
Frep = Fk   (  1.0;  = 1.0 for persistent actions)
Fd = Frep  F

EUROCODE 7
Design values of geotech params
i.e.
M
k
d
M
M


Partial factor of
safety, M
Characteristic geotechnical
Parameter
(Mk)
Design geotechnical
Parameter
(Md)

EUROCODE 7
Design values of geometrical data
(2)P In cases where deviations in the geometrical data have a significant
effect on the reliability of a structure, design values of geometrical data (ad)
shall either be assessed directly or be derived from nominal values using
the following equation (see 6.3.4 of EN 1990:2002):
ad = anom ± a
for which values of a are given in 6.5.4(2) and 9.3.2.2
EN 1997-1:2004 §2.4.6.3(2)

EUROCODE 7
Design effects of actions (i)
i) During the verification of geotechnical strength (i.e. GEO limit state) some effects of
the actions will depend on the strength of the ground in addition to the magnitude of
the applied action and the dimensions of the structure. Thus, the effect of an action in
the GEO limit state is a function of the action, the material properties and the
geometrical dimensions.
i.e.
Ed = E{Fd; Xd; ad}
where
Ed is the design effect of the action, and
Fd is the design action;
Xd is the design material property;
ad is the design dimension,
and where
E{…} indicates that the effect, E is a function of the terms in
the parenthesis.

EUROCODE 7
Design effects of actions (ii)
During the verification of static equilibrium (i.e. EQU limit state) some effects
of the actions (both destabilising and stabilising) will depend on the strength
of the ground in addition to the magnitude of the applied action and the
dimensions of the structure. Thus, the effect of an action in the EQU limit
state, whether it be a stabilising or a destabilising action, is a function of the
action, the material properties and the geometrical dimensions.
i.e.
Edst;d = E{Fd; Xd; ad}dst
where
Edst;d is the design effect of the destabilising action, and
Estb;d = E{Fd; Xd; ad}stb
where
Estb;d is the design effect of the stabilising action.

EUROCODE 7
Design resistances
Equation 6.6 in EN 1990:2002 indicates that the design resistance depends
on material properties and the structural dimension. However, in geotechnical
design, many resistances depend on the magnitude of the actions and so EN
1997-1:2004 §2.4.7.3.3 redefines Equation 6.6 to include the contribution
made by the design action. The clause actually offers three methods of
establishing the design resistance,
or or
Annex B of Eurocode 7 Part 1 offers guidance on which of the 3 formulae
above to use for each design approach.
 
d
d
d
d a
X
F
R
R ;
;

 
R
d
k
d
d
a
X
F
R
R

;
;

 
R
d
d
d
d
a
X
F
R
R

;
;


EUROCODE 7
The five ultimate limit states
Eurocode 7 lists five ultimate limit states to consider:
• Verification of static equilibrium (EQU)
• Verification of (structural) strength (STR)
• Verification of (ground) strength (GEO)
• Verification of resistance to uplift (UPL)
• Verification of resistance to heave failure due to seepage (HYD)

EUROCODE 7
Ultimate limit states
Loss of static equilibrium
EQU
EQU UPL
UPL
Uplift by water pressure
HYD
HYD
Hydraulic heave/erosion
GEO
GEO
Failure of the ground
STR
STR
Internal failure of structure
ULS for Stability:
ULS for Stability:
ULS for Strength:
ULS for Strength:

EUROCODE 7
Equilibrium (EQU) limit state
Loss of static equilibrium
Limit state is satisfied if the sum of the design values of the effects of destabilising actions
(Edst;d) is less than or equal to the sum of the design values of the effects of the stabilising
actions (Estb;d) together with any contribution through the resistance of the ground around
the structure (Td),
i.e. Edst;d ≤ Estb;d + Td.
EQU: loss of equilibrium of the structure or the
supporting ground when considered as a rigid body
and where the internal strength of the structure and
the ground do not provide resistance.

EUROCODE 7
Geotechnical (GEO) limit state
Failure of the ground
This limit state is satisfied if the design effect of the actions (Ed) is less than or equal to the
design resistance (Rd),
i.e. Ed ≤ Rd
GEO: failure or excessive deformation of the ground,
where the soil or rock is significant in providing
resistance.

EUROCODE 7
Structural (STR) limit state
Internal failure of structure
As with GEO limit state, the STR limit state is satisfied if the design effect of the actions (Ed)
is less than or equal to the design resistance (Rd),
i.e. Ed ≤ Rd
STR: failure or excessive deformation of the
structure, where the strength of the structural
material is significant in providing resistance.

EUROCODE 7
Uplift (UPL) limit state
Uplift by water pressure
This limit state is verified by checking that the sum of the design permanent and variable
destabilising vertical actions (Vdst;d) is less than or equal to the sum of the design stabilising
permanent vertical action (Gstb;d) and any additional resistance to uplift (Rd).
i.e. Vdst;d ≤ Gstb;d + Rd.
UPL: the loss of equilibrium of the structure or the
supporting ground by vertical uplift due to water
pressures (buoyancy) or other actions.

EUROCODE 7
Hydraulic (HYD) limit state
Hydraulic heave/erosion
This limit state is verified by checking that the design total pore water pressure (udst;d) or
seepage force (Sdst;d) at the base of the soil column under investigation is less than or equal
to the total vertical stress (σstb;d) at the bottom of the column, or the submerged unit weight
(G'stb;d) of the same column.
i.e. udst;d ≤ σstb;d or Sdst;d ≤ G'stb;d.
UPL: hydraulic heave, internal erosion and piping in
the ground as might be experienced, for example, at
the base of a braced excavation.

EUROCODE 7
ULS for retaining structures
(a) Overturning
(Eurocode 7 EQU limit state)
(b) Bearing failure
(Eurocode 7 GEO limit state)
(c) Forward sliding
(d) Ground failure
(e) Structural failure
(Eurocode 7 STR limit state)

EUROCODE 7
EQU limit state
Destabilising actions and effects
Representative destabilising
actions, Fdst; rep
Partial factors,
F dst
GEOTECHNICAL ANALYSIS
Design effect of destabilising
actions, Edst;d
Representative stabilising
actions, Fstb; rep
Design effect of stabilising
actions, Estb;d
Verify Edst;d ≤ Estb;d
Stabilising actions and effects
Design destabilising
actions, Fdst;d
Design stabilising
actions, Fstb;d
Partial factors,
F stb

EUROCODE 7
EQU limit state example
Pq
q
Pa
W
Overturning

EUROCODE 7
GEO limit state
Actions and effects
Representative
actions, Frep
Partial factors, F
GEOTECHNICAL ANALYSIS
Design effect of actions,
Ed
Characteristic material
properties, Xk
Design resistance, Rd
Verify Ed ≤ Rd
Material properties and resistance
Design actions, Fd Design material
properties, Xd
Partial factors, M

EUROCODE 7
GEO/STR Limit states
Three Design Approaches are offered - to reflect national choice
The design approach followed reflects whether the safety is applied to the
material properties, the actions or the resistances.
Design Approach 1: Combination 1: A1 + M1 + R1
†Combination 2: A2 + M2 + R1
Design Approach 2: A1 + M1 + R2
Design Approach 3: A* + M2 + R3
A*: use set A1 on structural actions, set A2 on geotechnical actions
† For axially loaded piles, DA1, Combination 2 is: A2 + (M1 or M2) + R4
The UK National Annex states that Design Approach 1 shall be used.

EUROCODE 7
GEO/STR Limit states
DA 1-1: A1 + M1 + R1 DA 1-2: A2 + M2 + R1
DA 1-1: A1 + M1 + R1
GEO/STR - Partial factor sets
Parameter Symbol A1 A2 M1 M2 R1 R2 R3
Permanent action (G) Unfavourable γG 1.35 1.0
Favourable γG 1.0 1.0
Variable action (Q) Unfavourable γQ 1.5 1.3
Favourable - - -
Accidental action (A) Unfavourable γA 1.0 1.0
Favourable - - -
Coefficient of shearing resistance (tan ') γ' 1.0 1.25
Effective cohesion (c') γc' 1.0 1.25
Undrained shear strength (cu) γcu 1.0 1.4
Unconfined compressive strength (qu) γqu 1.0 1.4
Weight density (γ) γγ 1.0 1.0
Bearing resistance (Rv) γRv 1.0 1.4 1.0
Sliding resistance (Rh) γRh 1.0 1.1 1.0
Earth resistance (Re) γRe 1.0 1.4 1.0

EUROCODE 7
Representation of degree of safety
Over-design factor:
Degree of utilisation:
d
d
E
R


d
d
R
E



EUROCODE 7
Gfav
Gunfav
Qunfav
Ed
Rd
Gunfav
Gunfav
Qunfav
Ed
Rd
sliding… … and bearing
GEO limit state examples

EUROCODE 7
3. Basis of Geotechnical Design ✔
4. Geotechnical Design by Calculation ✔
6. Conclusion

EUROCODE 7
Retaining wall design
(1)P The provisions of this Section shall apply to structures, which retain
ground comprising soil, rock or backfill and water. Material is retained if it
is kept at a slope steeper than it would eventually adopt if no structure
were present.
Retaining structures include all types of wall and support systems in
which structural elements have forces imposed by the retained material.
EN 1997-1:2004 §9.1.1(1)P
Covered in Section 9 of Eurocode 7 Part 1

EUROCODE 7
The limit states to be considered are listed in §9.2(1) and are:
• loss of overall stability;
• failure of a structural element such as a wall, anchorage, wale or strut
or failure of the connection between such elements;
• combined failure in the ground and in the structural element;
• failure by hydraulic heave and piping;
• movement of the retaining structure, which may cause collapse or
affect the appearance or
• efficient use of the structure or nearby structures or services, which rely
on it;
• unacceptable leakage through or beneath the wall;
• unacceptable transport of soil particles through or beneath the wall;
• unacceptable change in the ground-water regime.
EN 1997-1:2004 §9.2(1)
Limit states

EUROCODE 7
Gravity walls:
bearing resistance failure of the soil below the base;
failure by sliding at the base;
failure by toppling;
Embedded walls:
failure by rotation or translation of the wall or parts thereof;
failure by lack of vertical equilibrium.
EN 1997-1:2004 §9.2(1)
Plus…

EUROCODE 7
(a) Overturning
(Eurocode 7 EQU limit state)
(b) Bearing failure
(c) Forward sliding
(d) Ground failure
(e) Structural failure
(Eurocode 7 STR limit state)

EUROCODE 7
Must also consider overall stability (Section 11)…

EUROCODE 7
Future unplanned excavation
(2) In ultimate limit state calculations in which the stability of a retaining wall
depends on the ground resistance in front of the structure, the level of the
resisting soil should be lowered below the nominally expected level by an
amount Δa.
…
— for a cantilever wall, Δa should equal 10 % of the wall height above
excavation level, limited to a maximum of 0,5 m;
— for a supported wall, Δa should equal 10 % of the distance between the
lowest support and the excavation level, limited to a maximum of 0,5 m.
EN 1997-1:2004 §9.3.2.2(2)
(3) Smaller values of Δa, including 0, may be used when the surface level is
specified to be controlled reliably throughout the appropriate execution
period.
EN 1997-1:2004 §9.3.2.2(3)

EUROCODE 7
Gravity walls
When Rankine’s conditions do not apply...
Charts for both horizontal and inclined retained surfaces are given in Annex C.
Ka for a horizontal ground surface behind the wall
0.1
1
0 5 10 15 20 25 30 35 40 45
Design values of φ'
Ka
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
δ / φ' = 0
δ / φ' = 0.66
δ / φ' = 1
1.0

EUROCODE 7
Example
Retained fill:
c' = 0; ' = 32
 = 18 kN/m3
4.0 m
2.0 m
2.6 m
1.8 m
1.0 m Foundation soil:
c' = 0; ' = 28
 = 20 kN/m3
Surcharge, q = 20 kPa
3
1
2
= 22.4 kPa
= 26.7 kPa
34.1 kPa
= 6.2 kPa
7.4 kPa
h
a
K 
  q
a
K 
Check the overturning (EQU) and sliding (GEO) (using Design Approach 1) limit states.

EUROCODE 7
Embedded walls

EUROCODE 7
Embedded walls
d
Kpd0
O Ka(h+d0)
q = 10kPa
Kp(h+d)
Kad
d0
h
0.1h; > 0.5m
Pq1
Pq2
Pa1
Pp2
Pp1
Pa2
Cantilever wall – pressure distribution

EUROCODE 7
Embedded walls
Cantilever wall – simplified pressure distribution
Ka(h+d0)
Pp
Pa
R
Kpd0
h+d0
3
Pq

EUROCODE 7
Passive resistance
fav
G
k
p
d
p P
P ;
;
; 


Re
;
;

k
p
d
p
P
P 
Favourable action:
or
Resistance:

EUROCODE 7
Passive resistance
Design Approach
1 2 3
Combination 1 Combination 2
G;fav
1.0 1.0 1.0 1.0
Re
1.0 1.0 1.4 1.0
i.e. only concerns Design Approach 2

EUROCODE 7
Passive resistance
but what about for embedded walls?…
Single Source Principle…
NOTE Unfavourable (or destabilising) and favourable (or stabilising)
permanent actions may in some situations be considered as coming from a
single source. If they are considered so, a single partial factor may be
applied to the sum of these actions or to the sum of their effects.
EN 1997-1:2004 §2.4.2
Note to (9)P

EUROCODE 7
Passive resistance
Pp
Pa
“uncertainty” in Pp = “uncertainty” in Pa
i.e. if Pa is a permanent unfavourable action, so must be Pp
(Single source principle)

EUROCODE 7
Passive resistance
Design Approach
1 2 3
Combination
1
Combination
2
G;fav 1.0 1.0 1.0 1.0
G;unfav 1.35 1.0 1.35 1.0
Re 1.0 1.0 1.4 1.0

EUROCODE 7
Conclusion (Recap…)
1. Intro to Eurocodes
2. Intro to Eurocode 7
4. Geotechnical design by calculation
Actions, Ground properties, Characteristic values of geotechnical
parameters, Cautious estimate, Partial factors of safety, Design
values, Design effects of actions, Design resistances, Five Ultimate
limit states of Eurocode 7, Design Approaches (GEO), Over-design
factor and the degree of utilisation, single source principle
more…

EUROCODE 7
Conclusion (Recap…)
2.4.1 (2) It should be considered that knowledge of the ground
conditions depends on the extent and quality of the geotechnical
investigations. Such knowledge and the control of workmanship are
usually more significant to fulfilling the fundamental requirements than
is precision in the calculation models and partial factors.
4. Geotechnical design by calculation (continued)
In other words…
Design to EN 1997 depends as much on Part 2 as Part 1.

EUROCODE 7
Design to Eurocode 7
Many thanks for your attention.

EC7 Geotech and Retaining.pdf

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