State of development of Eurocode 7- Geotechnical Design

FRANK, R. Soil Mechanics Teaching and Research Centre (CERMES, ENPC-LCPC), Champs-sur-Marne, France

ABSTRACT: This paper presents some aspects about the development of Eurocode 7 on geotechnical de­sign. Eurocode 7 consists of three Parts: General rules, Design assisted by laboratory testing and Design assisted by field testing. Part 1 (General rules) is presently being converted from a voluntary (ENV) to a full European Norm (ΕΝ) . After a historical note and a list of the current deadlines, the main features and con­tents of the three parts of Eurocode 7 are given. Liaisons with other European and international committees are summarised at the end.

I INTRODUCτιON

The system of Structural Eurocodes includes the 1 Ο following standards (ΕΝ for 'European Norm'): - ΕΝ 1990 Eurocode: Basis of structural design - ΕΝ 1991 Eurocode 1: Actions on structures - ΕΝ 1992 Eurocode 2: Design of concrete struc-

tures - ΕΝ 1993 Eurocode 3: Design of steel structures - ΕΝ 1994 Eurocode 4: Design of composite steel

and concrete structures - ΕΝ 1995 Eurocode 5: Design of timber struc­

tures - ΕΝ 1996 Eurocode 6: Design of masonry struc­

tures - ΕΝ 1997 Eurocode 7: Geotechnical design - ΕΝ 1998 Eurocode 8: Design of structures for

earthquake resistance - ΕΝ 1999 Eurocode 9: Design of aluminium struc­

tures Except for ΕΝ 1990, all Eurocodes are subdi­

vided into several parts. Eurocodes 2, 3, 4, 5, 6 and 9 are 'material' Euro­

codes, i.e. relevant to a given material. ΕΝ 1990 (Basis of design), Eurocode 1 (Actions), Eurocode 7 (Geotechnical Design) and Eurocode 8 (Earthquake resistance) are relevant to all types of construction, whatever the material.

Eurocode 7 on Geotechnical Design consists of three parts:

ΕΝ 1997-1 Eurocode 7: Geotechnical design -Part 1: General Rules

ΕΝ 1997-2 Eurocode 7: Geotechnical design -Part 2: Design assisted by laboratory testing

ΕΝ 1997-3 Eurocode 7: Geotechnical design -Part 3: Design assisted by field testing

lt is possible that, in the near future, the docu­ments for Parts 2 and 3 will be merged into one sin­gle document.

This Paper summarises some aspects of the de­velopment of Eurocode 7. ln the recent period, the development of Eurocode 7 was linked strongly to the development of ΕΝ 1990: 'Eurocode: Basis of structural design'. lt should be mentioned that ΕΝ 1990 is now ready and presently submitted to the formal final vote (CEN, 2001a} .

2 HISTORY OF EUROCODE 7 AND PRESENT DEADLINES

2. 1 History

The first Eurocode 7 Group, in charge of drafting a European standard on geotechnical design, was created in 1981. Under the Chairmanship of Ν . Krebs Ovesen (Denmark), it was composed of representatives of the National Societies for Geo­technical Engineering of the 1 Ο countries forming at that time the European Community (ί.e . Belgium, Denmark, France, Germany, Greece, lreland, ltaly, Luxembourg, Netherlands and United Kingdom).

ln 1987 a first model code on general rules for geotechnical design (corresponding to Eurocode 7-Part 1) was drafted and published (EC 7, 1990).

ln 1989, the task of drafting design codes for buildings and civil engineering works was trans­ferred to the Comite Europeen de Normalisation (CEN, European Committee for Standardization) and CENtτC 250 (τechnical Committee 250) in

87

charge of all the 'Structural Eurocodes' was created. ln particular, SC7, Sub-Committee 7, was in charge of Eurocode 7 on 'Geotechnical Design'. Today 19 national standards bodies are full members of CEN: the 15 countries of the Ευ , plus the 3 members of ΕFΊΆ , plus the Czech Republic. Other countries from Central and Eastern Europe are involved as observers. Ν . Krebs Ovesen was the first Chairman of CENΠC 250/SC7 until 1998. Since 1998, the au­thor is Chairman of SC7. His mandate is due to end in 2004.

ln 1993, SC7 adopted the ENV 1997-1 pre­standard: 'Geotechnical Design. Part 1: General Rules', prepared by ΡΤ1 (ENV, stands for European Norm Voluntary). ΡΤ1 (Project Team 1) was com­posed of Ν. Krebs Ovesen (Convenor, Denmark), Τ. Orr (Secretary, lreland), F. Baguelin (France), W. Heijnen (Netherlands), Ε . Maranha das Neves (Portugal), Β . Simpson (υΚ) and υ . Smoltczyk (Germany). ENV 1997-1 was olficially published by CEN in October 1994 in the English language (CEN, 1994). The versions in French and German , the two other languages of CEN publications, appeared in 1995-1996.

Eurocode 7 is composed of two other Parts: Part 2, devoted to geotechnical design assisted by laboratory testing and Part 3, devoted to geotechni­cal design assisted by field (in situ) testing. ΡΤ2 and ΡΤ3 drafted the corresponding ENVs (ENV 1997-2 and 1997-3) which were adopted by SC7 in 1997. This work was completed rather quickly (1994 to 1996) and faced no serious controversial issues.

With regard to ENV 1997-1 (General rules), it was clear, at that time, that (much) more work still needed to be done before reaching a full European standard ΕΝ (lor European Norm) acceptable to all member countries οΙ CEN. WG1 (Work Group 1) started the work in January 1997, slightly belore the official positive vote for the conversion into an ΕΝ was obtained (May 1997). ln WG 1, the 19 countries οΙ CEN are involved, Α. Anagnostopoulos and Μ. Kavvadas representing Greece.

Another important fact helped in obtaining this positive vote. lt was the recognition by CENΠC 250 that geotechnical design is unique and cannot be considered to be the same as other design practices needed in the construction industry. The methods commonly used vary from one country to the other and cannot be harmonised easily, simply because the geologies are different and form the rationale for the so-called Ίocal traditions' ... This recognition is confirmed by a resolution taken by TC 250/SC7 (Resolution Ν 87, meeting οΙ Paris, 6 September 1996): 'CENΠC 250 accepts the principle that ENV 1997-1 might be devoted exclusively to the lunda­mental ru les of geotechnical design and be supple­mented by national standards'.

The work for the conversion of ENV 1997-1 into ΕΝ 1997-1 is presently underway. The drafting of

the new document is the task of ΡΤ1 , created in 1998. ΡΤ1 is composed of υ. Smoltczyk (Conve­nor, Germany), C. Bauduin (Belgium) , G. Bosco (lt­aly), R. Driscoll (υΚ) and Β. Schuppener (Vice­Chairman οΙ SC7, Germany) .

The ENVs for Parts 2 and 3 (ENV 1997-2 and ENV 1997-3) were published by CEN, in 1999, in English (CEN 1999a, b), and, in 2000-2001 , in French and German. ΑΙ the time of writing (Septem­ber 2001 ), the result of the vote of the 19 members οΙ CEN for the conversion οΙ these two Parts into European Norms is pending.

2.2 Present deadlines :

lt is anticipated that SC7 will adopt in December 2001 the " final draft , of Part 1 (prEN1997-1) pre­pared by ΡΤ1 in English (CEN 2001 b).

The final editing and translation will probably take the whole of 2002 and it is expected that the 3 lan­guage versions (English, French and German) can be ready by December 2002, for the launching οΙ the formal vote by CEN early 2003.

ln case οΙ a positive vote, the publication οΙ the corresponding European Norm by each national standardisation body with its National Annex (in the official language(s) of the country) should be com­pleted by August 2005.

Then will start the so-called coexistence period (with other national standards). The exact ruling and length of this transition period for the whole system of Eurocodes are not yet fixed. For a given Euro­code, the date of withdrawal of all conflicting na­tional standards depend, in particular, on the state of development οΙ the other Eurocodes or Parts of Eurocodes needed to design a structure entirely ac­cording to the new Eurocode approach. Thus, 'pack­ages' have to be defined., i.e. sets of different Euro­codes (or Parts thereof) and, in principle, only when a whole package is ready can the corresponding na­tional standards be withdrawn. Moreover, the Ίegal '

status of standards/norms is different in each country and it is evident that the regulatory bodies of the various countries have an important role to play in order to make the use of the Eurocodes manda­tory. This is why, since 1999, a group of Eurocode National Correspondents (ENCs) formed by the European Commission is working in close link with CENΠC 250, in order to co-ordinate the implemen­tation of the Eurocodes into the national regulations. This group is presently drafting a 'Guidance Paper' with clear guidelines about the desirable 'coexis­tence' period(s) after a given package is entirely published. For the time being, a three year 'coexis­tence' period after publication of the last part is pro­posed. Thus, it is anticipated that the first 'package' ready will be the one for concrete bridges (including Eurocode 7 - Part 1) and that it will become manda­tory in August 2008, at least in certain countries.

88

With regard to Part 2 (laboratory testing) and Part 3 (field testing), the following deadlines are foreseen. lf the vote for the conversion is positive, the two PTs will begin the corresponding work in November 2001. The " first drafts » for Parts 2 and 3 (prEN 1997-2 and prEN1997-3) should be ready by December 2002 and the " final drafts , in July 2003. The final editing and translation could then be completed by January 2004.

3 CONTENTS OF DOCUMENTS

3. 1 Part 1 : General rules

The discussions inside SC7 for the conversion of ENV 1997-Part 1 into ΕΝ focused mainly on : - the definition of characteristic values for geo­

technical parameters; - load cases for checking the ultimate limit states

(ULS) in persistent and transient situations (cases Α, Β and C in ENV 1997-1);

- separate treatment for embankments and slopes, and drafting of a section (chapter) to include all clauses on site stability;

- new section on anchorages; - concerns from South European countries.

With regard to ULS in persistent and transient situations 3 alternative approaches are now possi­ble. Details can be found in the paper of Kavvadas et al. (2001) at this Conference

The document presently prepared for ΕΝ 1997-1 includes the following sections : - Section 1 General - Section 2 Basis of geotechnical design - Section 3 Geotechnical data - Section 4 Supervision of construction, monitor-

ing and maintenance - Section 5 Fill , dewatering, ground improvement

and reinforcement - Section 6 Spread foundations - Section 7 Pile foundations - Section 8 Anchorages (new) - Section 9 Retaining structures - Section 1 Ο Hydraulic failure - Section 11 Site stability (new) - Section 12 Embankments

Α number of Annexes are also included. Annex Α is an important one, as it gives the partial factors of safety for the 3 approaches for ULS in persistent and transient situations (as well as correlation fac­tors for the characteristic values of pile bearing ca­pacity). Annex Α is normative, but it only gives rec­ommended values for the partial or correlation factors. The exact values of the partial factors can be set by each national body in the so-called Na­tional Annex. All other Annexes are purely informa­tive. The list of the Annexes for ΕΝ 1997-1 is the fol­lowing : - Annex Α Safety factors for ultimate limit states

- Annex Β Background information on partial fac­tors for Design Approaches 1 , 2 3

- Annex C Sample procedures to determine limit values of earth pressures on vertical walls

- Annex D Α sample analytical method for bearing resistance calculation

- Annex Ε Α sample semi-empirical method for bearing resistance estimation

- Annex F Sample methods for settlement evalua­tion

- Annex G Α sample method for deriving pre­sumed bearing resistance for spread foundations on rock

- Annex Η Limiting foundation movements and structural deformation Annex J Checklist for construction supervision and performance monitoring

3.2 Parts 2 and 3: Laboratory and field tests

The role of Parts 2 and 3 of Eurocode 7 is to give the essential requirements for the equipment and test procedures; for the reporting and the

presentation of results; for their interpretation and, finally, for the derivation of values of geotechnical parameters for the design, consistently with the general rules of Part 1 .

They complement in this respect the require­ments of Part 1 in order to ensure a safe and eco­nomic geotechnical design. They are not (in princi­ple} recognised geotechnical test standards. Α new TC on Geotechnical testing and sampling has re­cently been created by CEN to consider this matter (τC 341).

3.2. 1 Contents of Part 2 : Design assisted by labo­ratory testing

The following subjects are treated in the present ENV 1997-2: - preparation of specimens for testing soi l and rock

material; - tests for classification, identification and descrip-

tion of soils; - chemical testing of soils and groundwater; - compressibi lity and strength testing of soils; - compaction testing of soi ls; - permeability testing of soils; - classification testing of rock material; - swelling testing of rock material; - strength testing of rock material.

3.2.2 Contents of Part 3: Design assisted by field testing

ENV 1997-3 includes sections on : - cone penetration testing CPτ(U) ;

- pressuremeter testing ΡΜΤ; - standard penetration tests SPT;

AQ

- dynamic penetration test DP; - weight sounding tests WST; - filed νane tests Fντ; - flat dilatometer tests DMT; - rock dilatometer tests RDT; - plate loading tests PL Τ; - groundwater measurements in soils and rock

These sections deal successiνely, for each test, with the equipment, the test procedure, the interpre­tation of the results, the reporting of the results and the deriνed νalues of geotechnical parameters.

Two additional sections are deνoted to : - planning of site inνestigations;

- soil and rock sampling. They are also obνiously releνant to laboratory

testing and explain partly the need for a single document for Parts 2 and 3.

ENV 1997-3 also includes a number of informa­tiνe Annexes with examples of deriνed νalues οΙ geotechnical parameters and coefficients.

4 LIAISONS

lnside the Eurocode system itself, there are, of course, many links between the different standards or parts of them. Eurocode 7 on Geotechnical de­sign is more precisely linked to the following ones : - ΕΝ 1990: Έurocode: Basis of structural design'

which defines the νarious limit states and design situations to be checked, and giνes the general rules for taking into account the actions on/from the structures and the geotechnical actions;

- ENV 1992-3: Design of concrete structures. Foundalions

- ENV 1993-5: Design of steel structures. Piles - ENV 1998-5 : Design of structures for earthquake

resistance. Foundations, retaining structures and geotechnical aspects. The other Technical Committees of CEN working

on standards of interest for Eurocode 7, and for which coordination must be ensured are : - CENΠC 341 on 'Geotechnical testing and sam­

pling', as mentioned earlier; - CENΠC 288 on Έxecution of geotechnical

works' ; - CENΠC 189 on 'Geotextiles and geotextile­

related products'; - CENΠC 227 on 'Road materials'.

Wilh regard to ISO, a strong liaison is kept with ΙSΟΠC 182 on 'Geotechnics', especially: - ΙSΟΠC 182/SC 1 Classification of soils; - ISOΠC 182/SC 3 Foundations retaining struc-

tures and earthworks. The Vienna agreement between CEN and ISO

being applied, SC3 is not presently working on the design of geotechnical structures (passiνe role) and CENΠC 250/SC 7 (Eurocode 7) has the lead. For classification and presentation of soils and rocks, it

is the contrary : ISOΠC 189/SC 1 is presently work­ing on it, and CENΠC 341 has the passiνe role.

5 CONCLUDING REMARKS

The work for the elaboration of a common frame­work for geotechnical design throughout Europe, i.e. Eurocode 7, started some 20 years ago. Giνen the progress recently achieνed, it seems reasonable to anticipate that the corresponding standards/codes will be aνailable soon.

Whateνer the future status of Eurocode 7 in the νarious countries, it will proνe to be νery lmportant for the whole construction industry. lt is meant to be a tool to help European geotechnical engineers speak the same technical language and also a nec­essary tool for dialogue between geotechnical engi­neers and structural engineers.

Eurocode 7 helps promote research. Obνiously, it stimulates questions on present geotechnical prac­tice from ground inνestigation to design models.

lt is our belief that it will also be νery useful to many geotechnical and structural engineers all oνer the world, not only in Europe.

REFERENCES CEN 1994. Geotechnical Design - General Rules.

Prestandard ENV 1997-1 . European Committee for Standardization (CEN): Brussels.

CEN 1999a. Geotechnical Design - Geotechnical Design assisted by Laboratory Testing. Pre­standard ENV 1997-2. European Committee for Standardization (CEN): Brussels.

CEN 1999b. Geotechnical Design - Geotechnical Design assisted by Field Testing. Prestandard ENV 1997-3. European Committee for Stan­dardization (CEN): Brussels.

CEN 2001 a. Eurocode: Basis of structural design . Final Draft prEN 1990 for formal νote, July 2001 . European Committee for Standardization (CEN): Brussels.

CEN 2001 b. Eurocode 7, Part 1: Geotechnical De­sign - General Rules. Final Draft prEN 1997-1, December 2001 , in prep., European Committee for Standardization (CEN): Brussels.

EC 7 1990. Eurocode 7: Geotechnics. Preliminary draft for the European Communities, Geotechnik, 1990/1.

Kaννadas, Μ., Frank R., Anagnostopoulos, Α . 2001 . Εφαρμογές των μεθόδων ανάλυσης γεωτεχνικών έργων μέσω οριακών καταστάσεων κατά τον Ευρωκώδικα 7 (in Greek - Applications of the ultimate limit state design in geotechnical projects using Eurocode 7). Proc. 41

h Hellenic Conference on Geotechnical & Geoenνironmen­tal Engineering, Athens, 30/5- 1/6/2001 , νοl. 2, pp. 17-24.