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Countdown to Eurocode 7: preparing Countdown to Eurocode 7: preparing for March 2010for March 2010

Andrew Harris Andrew Harris (Geomantix Ltd,(Geomantix Ltd,

Kingston University)Kingston University)

Outline of presentationOutline of presentation

General rules of Eurocode 7 for SlopesGeneral rules of Eurocode 7 for SlopesImplications of EC7 for slopesImplications of EC7 for slopesImplications of EC7 for slopesImplications of EC7 for slopes–– Stability of circular slip surfacesStability of circular slip surfaces

Current developments in EC7 and NCCI Current developments in EC7 and NCCI documentsdocumentsAdapting to EC7 and use of softwareAdapting to EC7 and use of softwareSummary of key pointsSummary of key points

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General rules of Eurocode 7 General rules of Eurocode 7 for Slopesfor Slopesfor Slopes for Slopes

Contents of EN 1997Contents of EN 1997--1 Sections 11 and 121 Sections 11 and 12

Section 11 Overall stabilitySection 11 Overall stabilitySection 12 EmbankmentsSection 12 Embankments

§§x.1 x.1 General (2/2 paragraphs)General (2/2 paragraphs)§§x.2 x.2 Limit states (2/2)Limit states (2/2)§§x.3 x.3 Actions and design situations (6/8)Actions and design situations (6/8)§§x.4 x.4 Design and construction considerations Design and construction considerations (11/13)(11/13)§§x 5 x 5 Ultimate limit state design (26/7)Ultimate limit state design (26/7)§§x.5 x.5 Ultimate limit state design (26/7)Ultimate limit state design (26/7)§§x.6 x.6 Serviceability limit state design (3/4)Serviceability limit state design (3/4)§§11.7 11.7 Monitoring (2)/Monitoring (2)/§§12.7 Supervision and 12.7 Supervision and Monitoring (5)Monitoring (5)

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Contents of EN 1997Contents of EN 1997--1 Sections 11 and 12 1 Sections 11 and 12 (cont)(cont)

ScopeScopeSection 11 covers overall stability of the ground Section 11 covers overall stability of the ground Section 11 covers overall stability of the ground Section 11 covers overall stability of the ground and movements in the ground related to and movements in the ground related to foundations, retaining structures, natural slopes, foundations, retaining structures, natural slopes, embankments, and excavationsembankments, and excavationsSection 12 covers embankments for small dams Section 12 covers embankments for small dams and infrastructureand infrastructure

Supervision, monitoring, and maintenanceSupervision, monitoring, and maintenance

Slopes must be monitored whenSlopes must be monitored when–– occurrence of limit states cannot be proven occurrence of limit states cannot be proven occurrence of limit states cannot be proven occurrence of limit states cannot be proven

sufficiently unlikely by calculation or prescriptive sufficiently unlikely by calculation or prescriptive measuresmeasures

–– assumptions made in calculations are not based on assumptions made in calculations are not based on reliable datareliable data

Monitoring should provideMonitoring should provide–– groundground--water levels or porewater levels or pore--water pressures for water pressures for gg pp pp

effective stress analysiseffective stress analysis–– lateral and vertical ground movementslateral and vertical ground movements–– depth and shape of existing slide (for remedial work)depth and shape of existing slide (for remedial work)–– rates of movementrates of movement

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Limits states for slopes and embankmentsLimits states for slopes and embankments

Limit states for slopes/embankments include:Limit states for slopes/embankments include:

Loss of overall stability Loss of overall stability of the ground and of the ground and associated structuresassociated structuresExcessive movementExcessive movementLoss of serviceabilityLoss of serviceability

Limits states for slopes and embankmentsLimits states for slopes and embankments

Section 12 adds for embankments:Section 12 adds for embankments:Internal erosionInternal erosionInternal erosionInternal erosionSurface erosion or scourSurface erosion or scourDeformations leading to Deformations leading to –– loss of serviceabilityloss of serviceability–– damage to adjacent structuresdamage to adjacent structures–– problems with transition zonesproblems with transition zones

Effects of freezing and thawingEffects of freezing and thawingg gg gDegradation of base course materialsDegradation of base course materialsDeformations due to hydraulic actionsDeformations due to hydraulic actionsChanges in environmental conditionsChanges in environmental conditions

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Design situationsDesign situations

Design situations must consider:Design situations must consider:–– Construction processesConstruction processesConstruction processesConstruction processes–– Previous or continuing ground movementsPrevious or continuing ground movements–– Effects of slope or embankment on existing Effects of slope or embankment on existing

structures or slopes structures or slopes –– VibrationsVibrations–– Climatic variationsClimatic variations

Vegetation and its removalVegetation and its removal–– Vegetation and its removalVegetation and its removal–– Human or animal activityHuman or animal activity–– Variations in water content or poreVariations in water content or pore--water pressurewater pressure–– Wave actionWave action

Design ApproachesDesign Approaches

Design Approach 1 applies partial factors to …Design Approach 1 applies partial factors to …–– actions in Combination 1 actions in Combination 1 –– unfavourable variable actions and material properties in unfavourable variable actions and material properties in

Combination 2Combination 2

Design Approach 2 applies partial factors to …Design Approach 2 applies partial factors to …–– effects of actions and to resistanceseffects of actions and to resistances–– but not to material propertiesbut not to material properties–– different factors for favourable and unfavourable actionsdifferent factors for favourable and unfavourable actions

Design Approach 3 applies partial factors to …Design Approach 3 applies partial factors to …–– material properties and a small factor to variable actionsmaterial properties and a small factor to variable actions–– but not to other actions or resistancesbut not to other actions or resistances–– in DA3, all actions are treated as ‘geotechnical’ when in DA3, all actions are treated as ‘geotechnical’ when

designing slopes and embankmentsdesigning slopes and embankments

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Design Approach 1 Combination 1 Design Approach 1 Combination 1 for slopes and embankments for slopes and embankments

Design Approach 1 Combination 2Design Approach 1 Combination 2for slopes and embankments for slopes and embankments

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Design Approach 2 Design Approach 2 for slopes and embankmentsfor slopes and embankments

Design Approach 3 Design Approach 3 for slopes and embankmentsfor slopes and embankments

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National choice of Design ApproachNational choice of Design Approach

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Partial factor groupingsPartial factor groupingsIndividual Individual partial factor partial factor or partial or partial factor factor

Design ApproachDesign Approach11 22 33Combination 1Combination 1 Combination 2Combination 2

factor factor ‘grouping’‘grouping’γγGG 1.351.35 1.01.0 1.351.35 1.0*1.0*γγG,favG,fav 1.01.0 1.01.0 1.01.0 1.01.0γγQQ 1.51.5 1.31.3 1.51.5 1.3*1.3*γγφφ = = γγcc 1.01.0 1.251.25 1.01.0 1.251.25γγReRe 1.01.0 1.01.0 1.11.1 1.01.0

1 351 35 1 251 25 1 4851 485 1 251 25γγGG x x γγcc x x γγReRe 1.351.35 1.251.25 1.4851.485 1.251.25γγGG x x γγcc / / γγφφ 1.351.35 1.01.0 1.351.35 1.01.0γγG,favG,fav x x γγcc / / γγφφ 1.01.0 1.01.0 1.01.0 1.01.0γγQQ / / γγGG 1.111.11 1.31.3 1.111.11 1.31.3**Factor from Set A2 on geotechnical actionsFactor from Set A2 on geotechnical actions

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Implications of EC7 for slopes Implications of EC7 for slopes p pp p

Key features of circular slip analysisKey features of circular slip analysis

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Bishop’s ‘Routine’ (aka ‘Simplified’) MethodBishop’s ‘Routine’ (aka ‘Simplified’) Method

⎧ ⎫⎪ ⎪

partial factors applied to material properties

( )

( ){ }

( )tan sec

tan1 tan

i i i i i i i i

i ii

c b W Q ub

FF

φ α

φα

⎪ ⎪⎪ ⎪⎪ ⎪⎪ ⎪′ + + −⎪ ⎪⎪ ⎪⎨ ⎬⎛ ⎞⎪ ⎪⎟⎪ ⎪⎜ ⎟⎪ ⎪⎜+ ⎟⎪ ⎪⎜ ⎟⎟⎜⎪ ⎪⎝ ⎠⎪ ⎪⎩ ⎭=

∑

∑ ( ){ }sini i i

i

W Q α+∑partial factors unfavourable

or favourable? partial factors unfavourable on variable actions

Applying partial factors to Bishop’s MethodApplying partial factors to Bishop’s Method

Applying partial factors is complicated by the Applying partial factors is complicated by the iterative nature of circular slip analysis (or iterative nature of circular slip analysis (or iterative nature of circular slip analysis (or iterative nature of circular slip analysis (or nonnon--circular)circular)It is unclear what parts of the equation are It is unclear what parts of the equation are favourable or unfavourable at any point in the favourable or unfavourable at any point in the analysisanalysis–– eg when eg when αα is negative the selfis negative the self--weight of the slip weight of the slip

reduces the overturning momentreduces the overturning moment

There is therefore no fully logical way of There is therefore no fully logical way of There is therefore no fully logical way of There is therefore no fully logical way of applying applying γγGG and and γγG;favG;fav

Applying different partial factors to different Applying different partial factors to different materials may result in a different mechanismmaterials may result in a different mechanism

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Current developments in EC7 and Current developments in EC7 and NCCI documentsNCCI documentsNCCI documents NCCI documents

Developments in EC7Developments in EC7

TC250 SC7 is the CEN committee responsible for EC7. The TC250 SC7 is the CEN committee responsible for EC7. The maintenance submaintenance sub--committee considers: committee considers:

ll i d i h h d l f h dll i d i h h d l f h d–– all matters associated with the development of the codeall matters associated with the development of the code–– Collecting errors and ambiguities in the current textCollecting errors and ambiguities in the current text–– ReRe--writing some sections where different EN documents writing some sections where different EN documents

contradict each other, e.g. Anchoragescontradict each other, e.g. Anchorages–– Producing corrigendum and eventually further versions of the Producing corrigendum and eventually further versions of the

codecodeETC10 is responsible for the evaluation of EC7 ETC10 is responsible for the evaluation of EC7 –– Assessing current best practice and interpretation of the codeAssessing current best practice and interpretation of the code–– Has produced a set of standard design examples for Has produced a set of standard design examples for

comparative purposescomparative purposesNo major changes currently proposed for Sections 11 and No major changes currently proposed for Sections 11 and 12 of EN 199712 of EN 1997--11

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ETC10 examplesETC10 examples

ETC10 has produced a set of examples for engineers to ETC10 has produced a set of examples for engineers to apply EC7 principles, please visit apply EC7 principles, please visit www.eurcode7.com/etc10www.eurcode7.com/etc10and attempt problems, closing date end of December 2009and attempt problems, closing date end of December 2009

NCCI documentsNCCI documents

Documents containing NonDocuments containing Non--conflicting complementary conflicting complementary information (NCCIs) are information (NCCIs) are being produced based on being produced based on current British Standards current British Standards and other recognised and other recognised guidance documents e.g. guidance documents e.g. CIRIA C580, Specification CIRIA C580, Specification for Highways Worksfor Highways WorksOf particular relevance to Of particular relevance to Of particular relevance to Of particular relevance to slope engineering are BS slope engineering are BS 6031 6031 -- Earthworks and BS Earthworks and BS 8006 8006 –– Strengthened Strengthened reinforced soils and other reinforced soils and other fills + BS5930, BS1377 etcfills + BS5930, BS1377 etc

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DPC BS 6031 DPC BS 6031 -- EarthworksEarthworks

A draft of BS 6031 has been produced but is now closed for public A draft of BS 6031 has been produced but is now closed for public commentcommentIt suggests that Design Approach 1 Combination 2 should be used It suggests that Design Approach 1 Combination 2 should be used It suggests that Design Approach 1 Combination 2 should be used It suggests that Design Approach 1 Combination 2 should be used for slopesfor slopes–– The overall stability of slopes should be checked against DA1 The overall stability of slopes should be checked against DA1

Combination 2. For completeness, DA1 Combination 1 should also be Combination 2. For completeness, DA1 Combination 1 should also be checked if the designer considers that the loading applied to the slope checked if the designer considers that the loading applied to the slope (other than the mass of the ground in the slope) might control the (other than the mass of the ground in the slope) might control the failure mechanism rather than the ground strength parametersfailure mechanism rather than the ground strength parameters (DPC (DPC BS 6031 BS 6031 §§7.3.3)7.3.3)

–– A minimum surcharge load of 10 kN/mA minimum surcharge load of 10 kN/m22 should be applied to the should be applied to the surface at the top of embankments and cuttings where the external surface at the top of embankments and cuttings where the external

i i h d l ff h bili f h li i h d l ff h bili f h l (DPC BS 6031 (DPC BS 6031 action might adversely affect the stability of the slope.action might adversely affect the stability of the slope. (DPC BS 6031 (DPC BS 6031 §§7.2.3)7.2.3)

Combination 1 should only be used where there are large external Combination 1 should only be used where there are large external forces acting on the slope. A three stage method has been forces acting on the slope. A three stage method has been suggested by Frank et al but this results in an equivalent factor of suggested by Frank et al but this results in an equivalent factor of safety of at least 1.35 for the effective stress casesafety of at least 1.35 for the effective stress case

DPC BS 6031 DPC BS 6031 –– Earthworks, partial factorsEarthworks, partial factors

The partial factors given in the NA annex to BS The partial factors given in the NA annex to BS EN1997 should be used in routine work coupled EN1997 should be used in routine work coupled EN1997 should be used in routine work coupled EN1997 should be used in routine work coupled with the other recommendations of EC7 for with the other recommendations of EC7 for selection of design parametersselection of design parametersBS 6031 points out that the partial factors may BS 6031 points out that the partial factors may not be adequate where the risk of any slope not be adequate where the risk of any slope failure is very high and may be too high for failure is very high and may be too high for situations where residual strength is adopted situations where residual strength is adopted –– in in situations where residual strength is adopted situations where residual strength is adopted in in this case it recommends this case it recommends γγφφ = 1.1= 1.1

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DPC BS 8006 DPC BS 8006 –– Strengthened reinforced Strengthened reinforced soilssoils

DPC BS 8006 statesDPC BS 8006 states–– BS EN 1997BS EN 1997--1:2004 does not cover the design and 1:2004 does not cover the design and BS EN 1997BS EN 1997 1:2004 does not cover the design and 1:2004 does not cover the design and

execution of reinforced soil structures; the values of execution of reinforced soil structures; the values of partial factors and load factors given in BS EN 1997partial factors and load factors given in BS EN 1997--1:2004 have not been calibrated for reinforced soil 1:2004 have not been calibrated for reinforced soil structures. BS EN 1997structures. BS EN 1997--1:2004 should not be used in 1:2004 should not be used in the design and execution of reinforced soil. In the UK, the design and execution of reinforced soil. In the UK, the design and execution of reinforced fill structures the design and execution of reinforced fill structures should be carried out in accordance with BS 8006should be carried out in accordance with BS 8006--1 and 1 and

h l fh l fBS EN 14475:2006. The partial factors set out in BS BS EN 14475:2006. The partial factors set out in BS 80068006--1 should not be replaced by similar factors in BS 1 should not be replaced by similar factors in BS EN 1997EN 1997--1:2004.1:2004. (DPC BS 8006 (DPC BS 8006 §§5.1)5.1)

Adapting to EC7 and use of Adapting to EC7 and use of softwaresoftwaresoftwaresoftware

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Adapting to EC7 and use of softwareAdapting to EC7 and use of software

Essentially if Design Approach 1 Combination 2 is Essentially if Design Approach 1 Combination 2 is used very little change is required except forused very little change is required except fory g q py g q p–– Multiplying unfavourable variable actions by 1.3Multiplying unfavourable variable actions by 1.3–– Ensuring that the characteristic parameters and the Ensuring that the characteristic parameters and the

design situation are appropriately conservativedesign situation are appropriately conservative

Software does not need to be modified Software does not need to be modified -- apply apply the partial factors to obtain design material the partial factors to obtain design material properties and variable actions. As long as the properties and variable actions. As long as the resultant factor of safety quoted by the program resultant factor of safety quoted by the program resultant factor of safety quoted by the program resultant factor of safety quoted by the program is ≥ 1.0 then the design complies with EC7is ≥ 1.0 then the design complies with EC7The above only checks the ULS limit state, where The above only checks the ULS limit state, where necessary the SLS limit state must also be necessary the SLS limit state must also be verified verified

Summary of key pointsSummary of key pointsSummary of key pointsSummary of key points

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Summary of key pointsSummary of key points

BS EN 1997 is already a current standard to which BS EN 1997 is already a current standard to which projects may be designedprojects may be designedp j y gp j y gBy March 2010 all conflicting standards will be By March 2010 all conflicting standards will be withdrawnwithdrawnFor slopes Design Approach 1 Combination 2 is For slopes Design Approach 1 Combination 2 is recommendedrecommendedCombination 1 may be ignored for slope design except Combination 1 may be ignored for slope design except where external loading is highwhere external loading is highCare should be exercised in using the BS EN partial Care should be exercised in using the BS EN partial factors for all design situations and risk levelsfactors for all design situations and risk levelsCurrent related BSs are being updated to remove Current related BSs are being updated to remove conflicts or withdrawnconflicts or withdrawn

To be kept upTo be kept up--toto--date on the developments of Eurocode 7 date on the developments of Eurocode 7 p pp p pp–– www.eurocode7.comwww.eurocode7.comFor discussion on the application of Eurocode 7 seeFor discussion on the application of Eurocode 7 see–– Bond & Harris (2008), Decoding Eurocode 7, Taylor and Bond & Harris (2008), Decoding Eurocode 7, Taylor and

FrancisFrancis–– Frank R., Bauduin C., Driscoll R., Kavvadas M. and Krebs Frank R., Bauduin C., Driscoll R., Kavvadas M. and Krebs

Ovesen N. Ovesen N. Designer’s Guide to EN 1997Designer’s Guide to EN 1997--1: Eurocode 7: 1: Eurocode 7: Geotechnical Design Geotechnical Design –– General Rules. General Rules. Thomas Telford.Thomas Telford.D t t f C iti d L l G t D t t f C iti d L l G t –– Department of Communities and Local Government Department of Communities and Local Government (2007). (2007). A designer’s simple guide to BSEN 1997. A designer’s simple guide to BSEN 1997. London.. London.. ((www.communities.gov.uk/planningandbuildingwww.communities.gov.uk/planningandbuilding).).

–– Driscoll R., Scott P. and Powell J. (2009) Driscoll R., Scott P. and Powell J. (2009) Eurocode 7: Eurocode 7: implications for UK practice. implications for UK practice. CIRIA C641.CIRIA C641.