1

Session 5

Factors Affecting Eurocode 7Geotechnical Design Triangle

Associated CEN Standards

Implementation and Future Developmentof Eurocode 7

2

Session 5a

Factors Affecting Eurocode 7and

Geotechnical Design Triangle

3

3 Challenges in PreparingEurocode 7

To prepare a geotechnical standard that:

1. Harmonized geotechnical design with structural design - Consistent with EN 1990

2. Took account of special features of soil and geotechnical design

3. Was acceptable to the European geotechnical engineering community- Accommodated different national design practices

4

Consistent with EN 1990

Based on limit state design method

Have partial factors applied to characteristic values

Use partial action factors in EN 1990

Provide partial material factors

Characteristic value and partial factors reliability based

5

Special Features of Soil and Consequences for Eurocode 7

SoilNatural2 or 3 phase

Non-homogeneous

High variability

Frictional

High ductility

Compressible

Non-linear

SteelManufactured Single phase

Homogeneous

Low variability

Non-frictional

Less ductile

Non-compressible

Linear

Comparison between Soil and Steel

Consequences for EC7Properties determined not specifiedNeed to consider water as well as soil – effective stresses control behaviour Characteristic value not 5% fractile of test resultsNeed judgement selecting characteristic valueLoads affect resistances so need care factoring permanent loadsCauses load redistribution in structures so lower partial factors may be appropriate on structural loadsDesign often controlled by SLS – not by ULSSLS calculations often difficult – design using ULS calculation

6

National Design Practice

Throughout Europe, there are different national geotechnical design practices involving:

Ground investigation methodsSoil testing methodsGeotechnical design methods

Due to different:Ground conditionsClimatic conditionsDesign traditions

Due to different regulatory regimes and cultures, e.g.In Germany the calculation methods are prescribed in the national standardsIn the UK, the calculation methods are not prescribed and the standards have no legal status but codes represent good practice

Different design practices needed to be accommodated

National Design Practice accommodated by:Focussing on principles of geotechnical designAllowing each country to produce a National Annex with non-conflicting complementary information

7

Issues in Development of Eurocode 7

Six issues arose during the development of Eurocode7Scope of Eurocode 7

Definition of the characteristic value of a geotechnical parameter

Partial factor on permanent loads

Application of partial factors to material parameters or resistances

Treatment of water pressures and forces

Accommodation of national design practice

8

Scope and Style

Eurocode 7 differs from other Eurocodes in its scope and style because geotechnical design is different from structural design

The importance of geotechnical investigations and testing is emphasised

There is a Part 2 on “Ground investigation and testing”

There are no calculation models in the code text

Important statement in EC7 (2.4.1(2)) concerning knowledge of ground conditions and precision in calculation models:

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 than is precision in the calculation models or the partial factors

9

Definition of the Characteristic Value

The definition of the characteristic value of a geotechnical parameter is given in Eurocode 7 (Clause 2.4.5.2(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

The zone of ground governing the behaviour of a geotechnical structure at a limit state is usually much larger than a test sample or the zone of ground affected in an in situ test. Consequently the value of the governing parameter is often the mean of a range of values covering a large surface or volume of the ground. The characteristic value should be a cautious estimate of this mean value (Clause 2.4.5.2(7) – Application Rule)

Agreeing this definition for the characteristic value of a geotechnical parameter was important for the development of Eurocode 7 and was innovative, enabling Eurocode 7 to be consistent with the basis of design in EN 1990 for manufactured structural materials

Characteristic value is not the 5% fractile of a set of test results

10

Partial Factors on Permanent Loads

Originally a partial factor of unity on permanent loads was argued for geotechnical design by the Eurocode 7 committee

Based on geotechnical design experience, particularly in Denmark

Led to introduction of Design Cases A, B and C in ENV with partial factor of unity of on permanent loads for geotechnical designs to Eurocode 7 to be compatible with other structural Eurocodes using Case B with partial factor on permanent loads of 1.35

At the EN stage, Cases B and C became Design Approach 1, Combinations 1 and 2

11

Partial Factors on Material Parameters or Resistances

Partial factors to material parameters or resistancesRequired by some countries in order to have Eurocode 7 acceptedAccommodated by introduction of 3 Design Approaches

DA1DA2DA3

12

Treatment of Water Pressures and Forces

Water pressures and forces very important in geotechnical designs

Can be most significant

Led to introduction of two hydraulic failure ultimate limit states –UPL and HYD - with separate sets of partial factors

Although water pressures are forces, i.e. actions, it is often better to consider worst possible groundwater level – i.e. use a geometric allowance – rather than apply a partial factors to water pressures

This is an area of on-going debate

13

4 Aspects of Soil MechanicsProfessor John Burland, in his Invited Lecture on The Teaching of Soil Mechanics at the IX ECSMGE in Dublin in 1987, identified four aspects of soil mechanics which, by means of the Soil Mechanics Triangle, he showed were linked

The four linked aspects of Soil Mechanics are:

– The ground profile– Soil behaviour– Applied mechanics– Empiricism, well-winnowed

experience

• Well-winnowed experience is a metaphor from grain industry:– Separating grain (good) from chaff (bad) by a current of air– It is experience where only those practices that have proved to be successful and

reliable are retained while those that have proved to be not reliable are rejected

The Soil Mechanics Triangle

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Interaction between Structural and Geotechnical Engineers

In 2006 Professor John Burland, in the context of a lecture on the interaction between structural and geotechnical engineers, expanded the Concept of the 4 Aspects of Soil Mechanics

Ground profileAdded

• Genesis/geology• Soil description

Soil behaviourAdded

• ObservationApplied Mechanics changed to Appropriate ModelAdded

• EvaluationEmpiricismAdded

• Precedent

GENESIS/GEOLOGY

IDEALISATION FOLLOWED BY EVALUATION

CONCEPTUAL OR PHYSICAL MODELLING ANALYTICAL MODELLING

LAB./FIELD TESTING OBSERVATION/ MEASUREMENT

PRECEDENT EMPIRICISM

WELL-WINNOWED EXPERIENCE

SITE INVESTIGATION SOIL DESCRIPTION

GENESIS / GEOLOGY

PRECEDENT

SOIL DESCRIPTION

EVALUATION

OBSERVATION

The Geotechnical Triangle

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Geotechnical Design Components

displacements)(imposed loads or

Actions

movements

Geometry

Limiting values for

Ground properties

Code of Practice(safety factors)

Calculation model

Design

Geotechnical design components

GeometryGround propertiesActions (loads)Calculation models

All relevant limit statesULS and SLS

Safety elementsPartial factorsLimiting values of deformations

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4 Aspects of Geotechnical Design

Similarly the components of geotechnical design can be grouped into 4 aspects:

Problem geometry– To which geometric allowances are applied

Loads and material properties (Actions and Resistances)– To which partial factors are applied

• Calculation models– To which model factors may be applied

• Relevant to all of these is the geotechnical complexity• To which is applied risk analysis• Comparable experience

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The Geotechnical Design Triangle

Four Aspects of Geotechnical Design

Geometrical DataGround profile, structural dataNominal values, Geometrical allowances

Loads (Actions), Geotechnical ParametersGeotechnical investigations, Lab./field testing, Derived parametersCharacteristic values, Correlation factors

Limit State DesignConsideration of limit statesCalculations, Prescriptive measures,Load or model tests, An Observational methodPartial factors, Combination factors, Allowable deformations

Design ComplexityComparable experienceRisk assessmentGeotechnical Categories

- GROUND PROFILE - STRUCTURAL GEOMETRY

- CONSIDERATION OF LIMIT STATES - CALCULATIONS - PRESCRIPTIVE MEASURES - LOAD OR MODEL TESTS - AN OBSERVATIONAL METHOD

- GEOTECHNICAL INVESTIGATIONS - LAB./FIELD TESTING - DERIVED PARAMETERS

DESIGN COMPLEXITY

NOMINAL VALUES

GEOMETRIC ALLOWANCES e.g OVERDIG

GEOTECHNICALPARAMETERS

GEOMETRICALDATA

LOADS

- COMPARABLE EXPERIENCE

CHARACTERISTIC VALUES CORRELATION FACTORS, ξ

PARTIAL FACTORS, γ COMBINATION FACTORS, ψ ALLOWABLE DEFORMATIONS

LIMIT STATE

DESIGN

RISK ASSESSMENT

GEOTECHNICAL CATEGORIES

The Geotechnical Design Triangle

GROUND PROFILE /STRUCTRURAL DATA

NOMINAL VALUES/GEOMETRICAL ALLOWANCES

- GEOTECHNICAL INVESTIGATIONS- LAB./FIELD TESTING- DERIVED PARAMETERS

CHARACTERISTIC VALUES/CORRELATION FACTORS, ξ

PARTIAL FACTORS, γCOMBINATION FACTORS, ΨALLOWABLE DEFORMATIONS

- CONSIDERATION OF LIMIT STATES- CALCULATIONS- PRESCRIPTIVE MEASURES- LOAD OR MODEL TESTS- AN OBSERVATIONAL METHOD

RISK ASSESSEMENTGEOTECHNICAL

CATEGORIES

DESIGN COMPLEXITY

- COMPARABLE EXPERIENCE

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Experience“Experience” is in both The Geotechnical Triangle and The Geotechnical Design Triangle

“Experience” is a term very commonly used term in geotechnics

However it is not well-defined

Eurocode 7 provides the following definition for comparable experience:

– Documented or other clearly established information related to the ground being considered in design, involving the same types of soil and rock and for which similar geotechnical behaviour is expected, and involving similar structures. Information gained locally is considered to be particularly relevant

Experience is linked to “Precedent”, which is also in the Geotechnical Triangle

Many existing national geotechnical codes contain valuable information and design practices that are based on national experiences – this is well-winnowed experience

It was considered important that this experience should not be lost with the introduction of Eurocode 7

Hence it has been agreed that the Eurocodes may be supported by national standard providing non-conflicting complementary information (NCCI)

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Well-Winnowed Experienceand Eurocode 7

Since work on Eurocode 7 started in 1981, it has progressed through a number of stages

Model codeENV Stage (trial code)EN Stage

Many geotechnical engineersFrom different parts of EuropeWith different experiences

Many drafts preparedMany comments receivedMany design examples

Based on more geotechnical experience than any previous geotechnical code

Hence it is now well-winnowed

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Discussion

Any Questions

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Session 5b

Related CEN Standards

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Related CEN Standards

Parts 1 and 2 of EN 1997 refer to many CEN standards for:Geotechnical investigation and testing

Execution of special geotechnical works

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The CEN Standards for

Geotechnical Investigations and Testing

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CEN and ISO StandardsCEN has three committees preparing standards covering different aspects of geotechnical engineering– TC 250/SC7: Geotechnical design

– TC 341: Geotechnical investigation and testing

– TC 288: Execution of special geotechnical works

Under Vienna Agreement, CEN and ISO (International Standards Organisation) cooperate in preparation of standards – i.e. do not produce separate standards for same area

– Hence some geotechnical and investigation standards are being produced by ISO TC 182: Geotechnics and are also being published as CEN standards

Many CEN geotechnical standards have already been published as ENs, and hence as Polish and other national standards, while others are still being prepared

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Standards for Geotechnical Design and Investigation and Testing

TC 250/SC7: Geotechnical Design– 1997 Geotechnical Design 2 Parts

• Part 1: General rules• Part 2: Ground investigation and testing

TC 341: Geotechnical investigation and testing– 14688 Identification and classification of soil 3 Parts– 14689 Identification and classification of rock 2 Parts– 17892 Laboratory testing of soil 12 Parts– 22282 Geohydraulic testing 6 Parts– 22475 Sampling methods and groundwater measurements 3 Parts– 22476 Field testing 13 Parts– 22477 Testing of geotechnical structures 8 Parts

Total of 47 parts

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CEN Standards forExecution of Special Geotechnical Works

TC 288: Execution of special geotechnical works13 standards:

– 1536 Bored piles– 1537 Ground anchors– 1538 Diaphragm walls– 12063 Sheet pile walls– 12699 Displacement piles– 12715 Grouting– 12716 Jet grouting– 14199 Micropiles– 14475 Reinforced fill– 14490 Soil nailing– 14679 Deep mixing– 14731 Ground treatment by deep vibration– 15237 Vertical drainage

Hence the total planned number of new CEN geotechnical standards from these three TCs is

– 2 (TC 250) + 47 (TC 341) + 13 (TC 288) = 62

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Other Related CEN StandardsCEN has established four other committees whose work is related to geotechnical engineering– TC 89: Thermal performance of buildings– TC 154: Aggregates– TC 277: Road Materials– TC 396: Earthworks

TC 89 has produced one standard part:– EN ISO 13793 Thermal design of foundations to avoid frost heave 1 Part

TC 154 and TC 277 have produced many standards which have already been published as ENs

TC 396 only formed in 2009 and so has not yet produced any standards– 5 Working groups established

- General matters- Classification systems for Earthwork purposes and characterisation of

excavatability- Construction procedures- Quality control and monitoring - Hydraulic fill

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Road Material and Aggregate StandardsTC 154 Aggregates

– 932 Tests for general properties of aggregates 6 parts– 933 Tests for geometrical properties of aggregates 11 parts– 1097 Tests for mechanical and physical properties of aggregates 10 parts– 1367 Tests for thermal and weathering properties of aggregates 6 parts– 1744 Tests for chemical properties of aggregates 6 parts– 13242 Aggregates for unbound and hydraulically bound materials

for use in civil engineering work and road construction 1 part– 13383 Armourstone 2 parts

TC 277: Road Materials– 13285 Unbound mixtures – specification 1 part– 13286 Unbound and hydraulically bound mixtures 20 parts

Part 1: Test methods for laboratory reference density and water content –Introduction, general requirements and sampling

Part 2: Test methods for the determination of the laboratory reference density and water content – Proctor compaction

Part 46: Test method for the determination of the Moisture Condition Value

TC 89, TC 154 and TC 277 give 64 more standard parts

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Standards for Identificationand Classification of Soil

CEN ISO Standards3 parts of 14688: Geotechnical investigation and testing - Identification and classification of soil

– EN ISO 14688-1:2002/AC:2005 - Part 1: Identification and description– EN ISO 14688-2:2004 - Part 2: Principles for a classification– prCEN ISO/TS 14688-3 - Part 3: Electronic exchange of data on

(Under drafting) identification and description of soil

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Standards for Identificationand Classification of Rock

CEN ISO Standards2 parts of 14689: Geotechnical investigation and testing - Identification and classification of rock

– EN ISO 14689-1:2003 - Part 1: Identification and description– prCEN ISO/TS 14689-2 - Part 2: Electronic exchange of data on (Under

drafting) identification and description of rock

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Standards for Laboratory Testing of SoilCEN ISO Standards

12 parts of 17892: Geotechnical investigation and testing - Laboratory testing of soil

– Part 1: Determination of water content– Part 2: Determination of density of fine-grained soil– Part 3: Determination of particle density - Pycnometer method– Part 4: Determination of particle size distribution– Part 5: Incremental loading oedometer test– Part 6: Fall cone test– Part 7: Unconfined compression test on fine-grained soils– Part 8: Unconsolidated undrained triaxial test– Part 9: Consolidated trail compression tests on water-saturated soils– Part 10: Direct shear tests– Part 11: Determination of permeability by constant and falling head– Part 12: Determination of Atterberg limits

– All parts published as CEN ISO/TS with same date: 2004/AC:2005– CEN defines a TS as a normative document where the state-of-the-art is not yet

stable enough for confirmation as an EN

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Standards for Geohydraulic Testing

CEN ISO Standards6 parts of 22282: Geotechnical investigation and testing - Geohydraulic testing

– Part 1: General rules– Part 2: Water permeability tests in a borehole without packer– Part 3: Water pressure test in rock– Part 4: Pumping test– Part 5: Infiltrometer test– Part 6: Water permeability tests in a borehole with packer and pulse -

litre stimulation

They have been published in 2008 (Parts 1 and 2) and in 2007 (Parts 3, 4, 5 and 6) by CEN as prEN (draft European Standard – a standard under development) and by ISO as DIS (Draft International Standard) for approval). They all have a Foreseen Date of Availability (FDAV) of 07-2010

Since the 22282 parts have not yet been published by CEN as ENs or TSs, they are not referred to in EN 1997 Parts 1 or 2

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Standards for Sampling Methods and Groundwater Measurements

CEN ISO Standards

3 parts of 22475: Geotechnical investigation and testing - Laboratory testing of soil

EN ISO 22475-1:2006 Technical principles for execution

CEN ISO/TS 22475-2:2006 Qualification criteria for enterprises and personnel

CEN ISO/TS 22475-3:2007 Conformity assessment of enterprises and personnel by third party

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Standards for Field Testing of Soil

CEN ISO Standards13 parts of 22476: Geotechnical investigation and testing: Field testing

– prEN ISO 22476-1 Electrical cone and piezocone penetration tests– EN ISO 22476-2:2005 Dynamic probing– EN ISO 22476-3:2005 Standard penetration test– prEN ISO/DIS 22476-4:2007 Ménard pressuremeter test– prEN ISO/DIS 22476-5:2008 Flexible dilatometer test– 22476-6 Self-Boring pressuremeter test– prEN ISO/DIS 22476-7:2008 Borehole jacking test– 22476-8 Full displacement pressuremeter test– prEN ISO/DIS 22476-9:2009 Field vane test– CEN ISO/TS 22476-10:2005 Weight sounding test– CEN ISO/TS 22476-11:2005 Flat dilatometer test– EN ISO 22476-12:2009 Part 12: 2004 Mechanical cone penetration test (CPTM)– 22476-13 Plate loading test

– The parts of 22476 are at different stages of development

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Status of CEN/ISO Field Testing StandardsThree parts, 2, 3 and 12, as full EN standards

– 2: Dynamic probing– 3: Standard penetration test– 12: Mechanical cone penetration test (CPTM)

Two parts as CEN ISO TSs– 10: Weight sounding test– 11: Flat dilatometer test

Three parts as prEN and ISO/DIS, “Under approval” with Foreseen Dates of Availability (FDAVs)

– 5: Flexible dilatometer test - FDAV 11-2010– 7: Borehole jacking test - FDAV 11-2010– 9: Field vane test - FDAV 01-2012

One part as prEN and ISO/DIS, “Under approval” with no FDAV– 4: Ménard pressuremeter test

One part as prEN ISO “Under drafting” with an FDAV– 1: Electrical cone and piezocone penetration tests - FDAV 01-2012

Three parts not yet listed by CEN– 6: Self Boring pressuremeter test– 8: Full displacement pressuremeter test– 13: Plate loading test

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Execution Standards13 standards with the umbrella title Execution of special geotechnical workshave been prepared by TC 288 and published by CEN– EN 1536:1999 Bored piles– EN 1537:1999/AC 2000 Ground anchors– EN 1538:2000 Diaphragm walls– EN 12063:1999 Sheet pile walls– EN 12699:2000 Displacement piles– EN 12715:2000 Grouting– EN 12716:2001 Jet grouting– EN 14199:2005 Micropiles– EN 14475:2006/AC:2006 Reinforced fill– FprEN 14490 Soil nailing– EN 14679:2005/AC:2006 Deep mixing– EN 14731:2005 Ground treatment by deep vibration– EN 15237:2007 Vertical drainage

All parts are current ENs except 14490 Soil Nailing, so should be national standards Status of 14490 is “Under approval” and FDAV is 05-2010The execution standards have only been published by CEN, not by ISO, and so are not under the Vienna Agreement

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Standards for Testing of Structures

EN ISO Standards

8 parts of 22477: Geotechnical investigation and testing - Testing of geotechnical structures

– ISO/DIS 22477-1 Pile load test by static axially loaded compression test – 22477-2 Pile load test by static axially loaded tension test – 22477-3 Pile load test by static transversely loaded tension test – 22477-4 Pile load test by dynamic axially loaded compression test – prEN ISO 22477-5 Testing of anchorages – 22477-6 Testing of nailing – 22477-7 Testing of reinforced fill – 22477-8 Pile testing - Statnamic testing

All parts of 22477 are under development. Only Part 5 listed on CEN website and listed as “under drafting”

Not referred to in EN 1997 Parts 1 or 2

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CEN Standards Referred to in Eurocode 7

Part 1: Geotechnical design– EN 1536 Bored piles

– EN 1537 Ground anchors

– EN 12063 Sheet pile walls

– EN 12699 Displacement piles

– EN 13793 Thermal design of foundations to avoid frost heave

Part 2: Ground investigation and testing– EN ISO 14688 Identification and classification of soil (Parts 1 and 2)

– EN ISO 14689 Identification and classification of rock (part 1)

– EN ISO 22475 Sampling methods and groundwater measurements (Part 1)

– EN ISO 22476 Field testing (Parts 1, 2, 3, 4, 5, 6, 8, 9, 12, 13)

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Conclusions

Eurocode 7 will become the geotechnical design code for all public works in Europe from March ’09

Many supporting referenced CEN investigation, testing and execution standards have already been published as national standards

Existing standards will no longer be maintained but may be revised to provide NCCI

40

Session 5c

Implementation and Future Developmentof Eurocode 7

41

Implementation of Eurocode 7

To use Eurocode 7 (EN 1997) in practice, each country has to select values of the partial factors for geotechnical designs in its country

These, and any other aspects of Eurocode 7 left for national determination – e.g. which Design Approach to use - are known as nationally Determined Parameters – NDPs

The NPDs are published in a country’s National Annex to a Eurocode

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Planned Implementation of the Eurocodes

Plan:From 31st March 2010 the Eurocodes will be implemented in all 29 CEN countries as national standards, with National Annexes giving the nationally determined parameters (NDPs) - next month !

Eurocodes will supersede and take precedence over existing national geotechnical standards

Hence, from 31st March 2010, all publicly funded projects must be designed to the Eurocodes

It is likely that all private projects will also be designed to the Eurocodes after 31st March 2010

Existing national standards may be revised to provide non-conflicting complementary information (NCCI)

It is intended that most of the other CEN standards referred to in the Eurocodes will also be published as national standards by 31st March 2010

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Actual Implementation of Eurocodes

Joint Research Council (CEN and EU) set up to manage the implementation of the Eurocodes is determined to implement them on 31st March 2010

BUT Austria and Germany (and other countries?) have requested a postponement of the date of withdrawal of existing standards due to:

the many corrigenda and amendments that have been made to the Eurocode parts since they were published, and

the need to have so many supporting CEN supporting standards to be implemented as national standards

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Selection of DAs by 29 CEN Countries

after Schuppener, July 2008

Total

Slopes

Retaining structures

Piles

Shallow foundations

DA3DA2*DA2DA1ALLNo or

Incomplete answers

Design Situation

IRL

IRL

IRL

IRL

BG, CY, CZ, IS, LV, H, MN

EST, F, I

L, SF

A, D, E, GR, PL, SK, SLO CH, DK, NL, S

NA

NL, S, SK

E, FB, EST, LT, P, UK

A, CH, D, E, EST, F, GR, I, L, NL, PL, S, SF, SK, SLO

A, CH, D, GR, L, NL, PL, RO, S, SF, SK, SLO

B, I, LT, P, RO, UK

B, LT, P, RO, UK

A,CH, D, E, EST, F, GR, L, SF, SLO

7 1 5-6 2-16 4-14

DK

DK

DK

DK

B, LT, RO, P, UK

* Partial action factor applied to action effect rather than to the actions

PL

PL

PL PL

45

Thank You

Thank you

Any questions?

Discussion

46