Retaining Walls and Geotechnical Design to Eurocode 7
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EUROCODE 7
Retaining Walls and Geotechnical Design to Eurocode 7 Dr Ian Smith Head of School School of Engineering and the Built Environment Edinburgh Napier University
Dr Ian Smith, Edinburgh Napier University
ICE Teesside Branch, NGG and IStructE
EUROCODE 7
This evening’s presentation 1. 2. 3. 4. 5. 6.
Dr Ian Smith, Edinburgh Napier University
Introduction to the Eurocodes Overview of Eurocode 7, EN 1997 Basis of Geotechnical Design Geotechnical Design by Calculation Retaining Wall Design Conclusion
ICE Teesside Branch, NGG and IStructE
EUROCODE 7
The Structural Eurocodes What are the 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)
Dr Ian Smith, Edinburgh Napier University
ICE Teesside Branch, NGG and IStructE
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.
Dr Ian Smith, Edinburgh Napier University
ICE Teesside Branch, NGG and IStructE
EUROCODE 7
The Structural Eurocodes 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 EN 1997
Eurocode 7 7 Eurocode
Geotechnical Design Geotechnical Design
EN 1998
Eurocode 8
Design of Structures for Earthquake Resistance
EN 1999
Eurocode 9
Design of Aluminium Structures
Dr Ian Smith, Edinburgh Napier University
Part 1: General Rules
Part 2: Ground investigation and testing
ICE Teesside Branch, NGG and IStructE
EUROCODE 7
The Structural Eurocodes
Dr Ian Smith, Edinburgh Napier University
ICE Teesside Branch, NGG and IStructE
EUROCODE 7
Publication of Eurocodes Eurocode programme developed by the Comité Européen de Normalisation (CEN) – the European Committee for Standardisation. 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 Dr Ian Smith, Edinburgh Napier University
ICE Teesside Branch, NGG and IStructE
EUROCODE 7
CEN Member States (Comité Européen de Normalisation) •
Austria
•
Latvia
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Belgium
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Lithuania
•
Cyprus
•
Luxembourg
•
Czech Republic
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Malta
•
Denmark
•
Netherlands
•
Estonia
•
Norway
•
Finland
•
Poland
•
France
•
Portugal
•
Germany
•
Slovakia
•
Greece
•
Slovenia
•
Hungary
•
Spain
•
Iceland
•
Sweden
•
Ireland
•
Switzerland
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Italy
•
UK
Dr Ian Smith, Edinburgh Napier University
ICE Teesside Branch, NGG and IStructE
EUROCODE 7
CEN committee structure e.g. Eurocode 7 : CEN/TC 250/SC 7
SC00 SC
Dr Ian Smith, Edinburgh Napier University
SC11 SC
CEN CEN
TC 250 250 TC
TC…. TC….
TC… TC…
SC… SC…
SC 77 SC
SC… SC…
ICE Teesside Branch, NGG and IStructE
EUROCODE 7
Eurocodes Timeline 1975
1980
1985
1990
1995
1989
1999
Programme passed to CEN
1975 EEC initiate programme
2000
2005
2002 ENs start to appear
2010
March 2010 Implmtn.
2011
1989 – 1999
Today
ENVs produced
•
All European public-sector clients have been legally required to commission Eurocodecompliant 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.
Dr Ian Smith, Edinburgh Napier University
ICE Teesside Branch, NGG and IStructE
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.
Dr Ian Smith, Edinburgh Napier University
ICE Teesside Branch, NGG and IStructE
EUROCODE 7
Structure of a Eurocode Document National Title Page National Foreword EN Title Page EN Text EN Annexes National Annex
Dr Ian Smith, Edinburgh Napier University
ICE Teesside Branch, NGG and IStructE
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.
Dr Ian Smith, Edinburgh Napier University
ICE Teesside Branch, NGG and IStructE
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
Dr Ian Smith, Edinburgh Napier University
ICE Teesside Branch, NGG and IStructE
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)
Dr Ian Smith, Edinburgh Napier University
ICE Teesside Branch, NGG and IStructE
EUROCODE 7
This evening’s presentation 1. Introduction to the Eurocodes ✔ 2. 3. 4. 5. 6.
Dr Ian Smith, Edinburgh Napier University
Overview of Eurocode 7, EN 1997 Basis of Geotechnical Design Geotechnical Design by Calculation Retaining Wall Design Conclusion
ICE Teesside Branch, NGG and IStructE
EUROCODE 7
Eurocode 7: Geotechnical design • •
Part 1: General rules Part 2: Ground investigation and testing
Published
Published
December 2004
November 2007
Dr Ian Smith, Edinburgh Napier University
ICE Teesside Branch, NGG and IStructE
EUROCODE 7
National Annexes • •
Part 1: Published November 2007 Part 2: Published December 2009
Dr Ian Smith, Edinburgh Napier University
ICE Teesside Branch, NGG and IStructE
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
Dr Ian Smith, Edinburgh Napier University
ICE Teesside Branch, NGG and IStructE
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 Dr Ian Smith, Edinburgh Napier University
ICE Teesside Branch, NGG and IStructE
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 Dr Ian Smith, Edinburgh Napier University
ICE Teesside Branch, NGG and IStructE
EUROCODE 7
Contents of Eurocode 7 Part 2 1. 2. 3. 4. 5. 6.
Foreword General Planning of ground investigation Soil and rock sampling and groundwater measurements Field tests in soil and rock Laboratory tests on soil and rock Ground investigation report Annexes A – X 196 pages
Dr Ian Smith, Edinburgh Napier University
ICE Teesside Branch, NGG and IStructE
EUROCODE 7
Contents of Eurocode 7 Part 2 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.
Dr Ian Smith, Edinburgh Napier University
ICE Teesside Branch, NGG and IStructE
EUROCODE 7
Contents of Eurocode 7 Part 2 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
Dr Ian Smith, Edinburgh Napier University
ICE Teesside Branch, NGG and IStructE
EUROCODE 7
Contents of Eurocode 7 Part 2 •
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
Dr Ian Smith, Edinburgh Napier University
CEN ISO/TS 17892 Laboratory tests Parts 1 – 12
EN ISO 14688 EN ISO 14689 Identification and classification of soil and rock
EN ISO 22475 Sampling and groundwater measurements
ICE Teesside Branch, NGG and IStructE
EUROCODE 7
Contents of Eurocode 7 Part 2 EN 1997-1:2004 §2.4 Geotechnical design by calculation 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.
In other words… Design to EN 1997 depends as much on Part 2 as Part 1.
Dr Ian Smith, Edinburgh Napier University
ICE Teesside Branch, NGG and IStructE
EUROCODE 7
European Geotechnical Codes ISO/CEN Standards for identification & classification Eurocodes: Test Standards and Technical Specs for ground properties
EN 1990 Basis of Structural Design EN 1991 Actions on Structures
Geotechnical Design (Eurocode 7: Parts 1 & 2) & NAs
Other structural Eurocodes
European Standards for the Execution of Special Geotechnical Works
e.g. EN 1998, EN 1993-5
Geotechnical Projects Dr Ian Smith, Edinburgh Napier University
ICE Teesside Branch, NGG and IStructE
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
Dr Ian Smith, Edinburgh Napier University
ICE Teesside Branch, NGG and IStructE
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” Dr Ian Smith, Edinburgh Napier University
ICE Teesside Branch, NGG and IStructE
EUROCODE 7
Principles & Application Rules All statements in each Eurocode are either: Principles (must be followed), or Application Rules (offer advice). 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. Dr Ian Smith, Edinburgh Napier University
ICE Teesside Branch, NGG and IStructE
EUROCODE 7
This evening’s presentation 1. Introduction to the Eurocodes ✔ 2. Overview of Eurocode 7, EN 1997 ✔ 3. 4. 5. 6.
Dr Ian Smith, Edinburgh Napier University
Basis of Geotechnical Design Geotechnical Design by Calculation Retaining Wall Design Conclusion
ICE Teesside Branch, NGG and IStructE
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
Dr Ian Smith, Edinburgh Napier University
ICE Teesside Branch, NGG and IStructE
EUROCODE 7
Basis of Geotechnical Design 2.1 Design requirements (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… Dr Ian Smith, Edinburgh Napier University
ICE Teesside Branch, NGG and IStructE
EUROCODE 7
Basis of Geotechnical Design 2.1 Design requirements 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. Dr Ian Smith, Edinburgh Napier University
ICE Teesside Branch, NGG and IStructE
EUROCODE 7
Basis of Geotechnical Design 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.
Dr Ian Smith, Edinburgh Napier University
ICE Teesside Branch, NGG and IStructE
EUROCODE 7
Basis of Geotechnical Design 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.
Dr Ian Smith, Edinburgh Napier University
ICE Teesside Branch, NGG and IStructE
EUROCODE 7
Basis of Geotechnical Design 2.4 Geotechnical design by calculation
Fundamental! We shall look at this shortly…
Dr Ian Smith, Edinburgh Napier University
ICE Teesside Branch, NGG and IStructE
EUROCODE 7
Basis of Geotechnical Design 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
Dr Ian Smith, Edinburgh Napier University
ICE Teesside Branch, NGG and IStructE
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
Dr Ian Smith, Edinburgh Napier University
ICE Teesside Branch, NGG and IStructE
EUROCODE 7
Geotechnical design by calculation Covered in Section 2.4 of Eurocode 7 Part 1 (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)
Dr Ian Smith, Edinburgh Napier University
ICE Teesside Branch, NGG and IStructE
EUROCODE 7
Geotechnical design by calculation 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
Dr Ian Smith, Edinburgh Napier University
ICE Teesside Branch, NGG and IStructE
EUROCODE 7
Geotechnical design by calculation 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.
Dr Ian Smith, Edinburgh Napier University
ICE Teesside Branch, NGG and IStructE
EUROCODE 7
Geotechnical design by calculation 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.
Dr Ian Smith, Edinburgh Napier University
ICE Teesside Branch, NGG and IStructE
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)
Dr Ian Smith, Edinburgh Napier University
ICE Teesside Branch, NGG and IStructE
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)
Dr Ian Smith, Edinburgh Napier University
ICE Teesside Branch, NGG and IStructE
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)
Dr Ian Smith, Edinburgh Napier University
ICE Teesside Branch, NGG and IStructE
EUROCODE 7
Test results and derived values Type of test (Field, Lab)
F1
Correlations
EN 1997-2
Test results and derived values
1
F2
L1
C1
C2 C1
2
3
L2 Information from other sources on the site, the soils and rocks and the project.
4
EN 1997-1 Cautious selection Geotechnical model and characteristic value of geotechnical parameters
Application of partial factors
Design value of geotechnical parameters Dr Ian Smith, Edinburgh Napier University
ICE Teesside Branch, NGG and IStructE
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) Dr Ian Smith, Edinburgh Napier University
ICE Teesside Branch, NGG and IStructE
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).
Dr Ian Smith, Edinburgh Napier University
ICE Teesside Branch, NGG and IStructE
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
Dr Ian Smith, Edinburgh Napier University
ICE Teesside Branch, NGG and IStructE
EUROCODE 7
Geotechnical design by calculation Representative action Fk
Characteristic material property, e.g. c'
The design is all about Multiplied by F values Actions: (loads, forces etc.)
and
Design action Fd
Divided by M values Material Properties (c, tan , etc.) Design material property, e.g. c'd
Geotechnical Analysis
Design effect of actions, Ed
Design Resistance, Rd Verify Ed ≤ Rd
Dr Ian Smith, Edinburgh Napier University
ICE Teesside Branch, NGG and IStructE
EUROCODE 7
Design values of actions Characteristic action
representative action
design action
(Fk)
(Frep)
(Fd)
Correlation factor,
i.e.
Frep = Fk
design effects of action (Ed)
Partial factor of safety, F
( 1.0; = 1.0 for persistent actions)
Fd = Frep F
Dr Ian Smith, Edinburgh Napier University
ICE Teesside Branch, NGG and IStructE
EUROCODE 7
Design values of geotech params Characteristic geotechnical Parameter (Mk)
Design geotechnical Parameter Partial factor of safety, M
(Md)
i.e.
Md
Dr Ian Smith, Edinburgh Napier University
Mk
M
ICE Teesside Branch, NGG and IStructE
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)
Dr Ian Smith, Edinburgh Napier University
ICE Teesside Branch, NGG and IStructE
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. Dr Ian Smith, Edinburgh Napier University
ICE Teesside Branch, NGG and IStructE
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. where where
Edst;d = E{Fd; Xd; ad}dst Edst;d is the design effect of the destabilising action, and Estb;d = E{Fd; Xd; ad}stb Estb;d is the design effect of the stabilising action.
Dr Ian Smith, Edinburgh Napier University
ICE Teesside Branch, NGG and IStructE
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,
Rd RFd ; X d ; a d
or
Rd
RFd ; X k ; a d
R
or
Rd
RFd ; X d ; a d
R
Annex B of Eurocode 7 Part 1 offers guidance on which of the 3 formulae above to use for each design approach.
Dr Ian Smith, Edinburgh Napier University
ICE Teesside Branch, NGG and IStructE
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)
Dr Ian Smith, Edinburgh Napier University
ICE Teesside Branch, NGG and IStructE
EUROCODE 7
Ultimate limit states ULS for Stability:
EQU
UPL
HYD
Loss of static equilibrium
Uplift by water pressure
Hydraulic heave/erosion
ULS for Strength:
GEO
STR
Failure of the ground
Internal failure of structure
Dr Ian Smith, Edinburgh Napier University
ICE Teesside Branch, NGG and IStructE
EUROCODE 7
Equilibrium (EQU) limit state Loss of static equilibrium
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.
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.
Dr Ian Smith, Edinburgh Napier University
Edst;d ≤ Estb;d + Td.
ICE Teesside Branch, NGG and IStructE
EUROCODE 7
Geotechnical (GEO) limit state Failure of the ground
GEO: failure or excessive deformation of the ground, where the soil or rock is significant in providing resistance.
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.
Dr Ian Smith, Edinburgh Napier University
Ed ≤ R d
ICE Teesside Branch, NGG and IStructE
EUROCODE 7
Structural (STR) limit state Internal failure of structure
STR: failure or excessive deformation of the structure, where the strength of the structural material is significant in providing resistance.
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.
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Ed ≤ R d
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Uplift (UPL) limit state Uplift by water pressure
UPL: the loss of equilibrium of the structure or the supporting ground by vertical uplift due to water pressures (buoyancy) or other actions.
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.
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Vdst;d ≤ Gstb;d + Rd.
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Hydraulic (HYD) limit state Hydraulic heave/erosion
UPL: hydraulic heave, internal erosion and piping in the ground as might be experienced, for example, at the base of a braced excavation.
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
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or
Sdst;d ≤ G'stb;d.
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ULS for retaining structures
(a) Overturning (Eurocode 7 EQU limit state)
(b) Bearing failure (Eurocode 7 GEO limit state)
(d) Ground failure (Eurocode 7 GEO limit state)
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(c) Forward sliding (Eurocode 7 GEO limit state)
(e) Structural failure (Eurocode 7 STR limit state)
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EQU limit state Destabilising actions and effects
Stabilising actions and effects
Representative destabilising actions, Fdst; rep
Representative stabilising actions, Fstb; rep
Partial factors, F dst
Partial factors, F stb
Design destabilising actions, Fdst;d
Design stabilising actions, Fstb;d
GEOTECHNICAL ANALYSIS
Design effect of destabilising actions, Edst;d
Design effect of stabilising actions, Estb;d
Verify Edst;d ≤ Estb;d
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EUROCODE 7
EQU limit state example Overturning
q
Pq W
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Pa
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GEO limit state Actions and effects
Material properties and resistance
Representative actions, Frep
Characteristic material properties, Xk
Partial factors, F
Partial factors, M
Design actions, Fd
Design material properties, Xd
GEOTECHNICAL ANALYSIS
Design effect of actions, Ed
Design resistance, Rd
Verify Ed ≤ Rd
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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: Design Approach 3:
A1 + M1 + R2 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. Dr Ian Smith, Edinburgh Napier University
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EUROCODE 7
GEO/STR Limit states GEO/STR - Partial factor sets Parameter Permanent action (G)
Variable action (Q)
Symbol
A1
A2
Unfavourable
γG
1.35
1.0
Favourable
γG
1.0
1.0
Unfavourable
γQ
1.5
1.3
-
-
-
γA
1.0
1.0
-
-
-
Favourable Accidental action (A)
Unfavourable Favourable
M1
M2
R1
R2
R3
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
DA 1-1:
A1 + M1 + R1
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DA 1-2:
A2 + M2 + R1
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Representation of degree of safety Over-design factor:
Degree of utilisation:
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Rd Ed Ed Rd
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GEO limit state examples sliding…
… and bearing
Gfav Gunfav
Qunfav
Gunfav Gunfav
Qunfav
Ed Ed Rd Dr Ian Smith, Edinburgh Napier University
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This evening’s presentation 1. 2. 3. 4.
Introduction to the Eurocodes ✔ Overview of Eurocode 7, EN 1997 ✔ Basis of Geotechnical Design ✔ Geotechnical Design by Calculation ✔
5. Retaining Wall Design 6. Conclusion
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Retaining wall design Covered in Section 9 of Eurocode 7 Part 1 (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
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Retaining wall design Limit states 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) Dr Ian Smith, Edinburgh Napier University
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Retaining wall design Plus… 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)
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Ultimate limit states
(a) Overturning (Eurocode 7 EQU limit state)
(b) Bearing failure (Eurocode 7 GEO limit state)
(d) Ground failure (Eurocode 7 GEO limit state)
Dr Ian Smith, Edinburgh Napier University
(c) Forward sliding (Eurocode 7 GEO limit state)
(e) Structural failure (Eurocode 7 STR limit state)
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Ultimate limit states Must also consider overall stability (Section 11)…
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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) Dr Ian Smith, Edinburgh Napier University
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Gravity walls When Rankine’s conditions do not apply... Charts for both horizontal and inclined retained surfaces are given in Annex C. 1.01 0.9 0.8 0.7 0.6 0.5 0.4 Ka 0.3
0.2 δ / φ' = 0 δ / φ' = 0.66 δ / φ' = 1 0.1 0
5
10
15
20
25
30
35
40
45
Design values of φ'
Ka for a horizontal ground surface behind the wall Dr Ian Smith, Edinburgh Napier University
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EUROCODE 7
Example Surcharge, q = 20 kPa 1.8 m
2
4.0 m 1
Retained fill: c' = 0; ' = 32 = 18 kN/m3
Ka h = 22.4 kPa
Ka q = 6.2 kPa
2.0 m 3
= 26.7 kPa 1.0 m
Foundation soil: c' = 0; ' = 28 = 20 kN/m3
7.4 kPa 34.1 kPa
2.6 m
Check the overturning (EQU) and sliding (GEO) (using Design Approach 1) limit states.
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ICE Teesside Branch, NGG and IStructE
EUROCODE 7
Embedded walls
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ICE Teesside Branch, NGG and IStructE
EUROCODE 7
Embedded walls Cantilever wall – pressure distribution q = 10kPa
h
0.1h; > 0.5m
Pq1
d
Pp1
d0 Kpd0
O
Kad
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Pa1 Ka(h+d0)
Pq2 Kp(h+d)
Pa2
Pp2
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Embedded walls Cantilever wall – simplified pressure distribution
Pq
Pp
Pa R
Kpd0
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h+d0 3
Ka(h+d0)
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Passive resistance Favourable action:
Pp ;d Pp ;k G ; fav or
Resistance:
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Pp ;d
Pp ;k
Re
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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
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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
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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)
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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
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ICE Teesside Branch, NGG and IStructE
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Conclusion (Recap…) 1. Intro to Eurocodes 2. Intro to Eurocode 7 3. Basis of Geotechnical Design 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…
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ICE Teesside Branch, NGG and IStructE
EUROCODE 7
Conclusion (Recap…) 4. Geotechnical design by calculation (continued) 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. In other words… Design to EN 1997 depends as much on Part 2 as Part 1. 5. Retaining Wall Design
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ICE Teesside Branch, NGG and IStructE
EUROCODE 7
Design to Eurocode 7
Many thanks for your attention.
Dr Ian Smith, Edinburgh Napier University
ICE Teesside Branch, NGG and IStructE
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