EC7 fundamental issues and its implications on users.pdf

Keynote lecture  Eurocode 7 – fundamental issues and some implications for users

Eurocode 7 – fundamental issues and some implications for users B. Simpson Arup, UK, [email protected]

Simpson, B (2012) Eurocode 7 – fundamental issues and some implications for users. Keynote Lecture, Proc Nordic Geotechnical Meeting 2012. DGF Bulletin 27.

ABSTRACT As Eurocode 7 becomes more widely used, questions raised by designers hae highlighted issues that require !urther debate and clari!ication. "ost o! these hae e#isted, in one !orm or another, !or many years, but the adent o! a new code, proiding a common language, has brought them

into sharper !ocus. Somealues o! these issues will be considered this paper$ the selection o! characteristic and design o! soil parameters, design in in situations dominated by water pressures, the releance o! the E%U limit state and the use o! numerical analysis !or U&S design. 'he selection o! parameter alues !or calculations !requently leads to debates among geotechnical designers. Eurocode 7 attempts, in an rather qualitatie way, to point towards a target reliability !or characteristic alues, while proiding a !ramewor( in which the precious e#pertise o! indiidual engineers can be !ully e#ploited. )roblems o! water pressures and the E%U limit state hae a lot in common$ how to ma(e proisions !or sa!ety in situations where !orces largely balance one another and material strength plays a small, but o!ten ital, part. *umerical models are now widely used to study sericeability, but their use in chec(ing ultimate limit states has been questioned+ how are partial sa!ety !actors to be applied, at what point in staged calculations, and can they be used with adanced nonlinear models o! soil behaiourEach o! these issues is discussed and some practical solutions suggested. Keywords: Codes of practice & standards; Design; Strength and testing of materials; Groundwater; Numerical modelling.

T$e paper refers to pre0ious pu%lications in /$ic$ more detail, and in some cases a more riorous account may %e found2 Sc$uppener et al ')**(-, Simpson and 3ocom%e ')*1*- and Simpson et al ')*11-. References to specific pararap$s in EC7 /ill %e s$o/n t$us2 4...5.

1 ITR!"#CTI! T$is paper considers topics t$at are currently under de%ate in relation to t$e application of Eurocode 7 &art 1 'E1((71 )**+, referred to $ere as EC7-. T$e issues raised are fundamental to eotec$nical enineerin, not artefacts of t$e ne/ code, t$ou$ t$ey may $a0e %een %rou$t to a $ead %y attempts to systematise eotec$nical procedures. T$e paper /ill pro0ide a re0ie/ of opinions on t$e issues discussed, and, /$ere possi%le t$e aut$or /ill i0e $is o/n opinion /it$ ustification.

) SA6ET 6!R8AT !6 EC7 T$e safety format in EC7 uses a limit state approac$. 9imit states are states of a construction %eyond /$ic$ t$e %e$a0iour is considered unaccepta%le. T$e aim of analyses is t$erefore to s$o/ t$at t$ese states /ill not %e e:ceeded.

1

Keynote lecture  Eurocode 7 – fundamental issues and some implications for users 'able . /actors proposed by 0E* !or the three 1esign Approaches. DA1 Actions

Soil

Permanent Variable tan ϕ'

Comb 2

unfav

Comb 1 1,35

fav unfav

1,5

1,3 1,25

DA2

DA3

1,35

1,35

1,5

1,5/1,3* 1,25

Piles

1,3

Effective cohesion

1,25

1,25

Undrained strength Unconfined

1,

1,

1,

1,

strength !eight densit" Spread

#earing

footings

$liding

Driven

#ase

1,3

1,1

piles

$haft %com&ression (otal/combined %com&ression

1,3

1,1

1,3

1,1

1,)

1,15

$haft in tension

1, 1,1

1,25

1,1

ote2 alues of all ot$er factors are 1.*. 6urt$er resistance factors are pro0ided for ot$er types of piles, anc$ors etc. ? 1. for structural loads< 1.@ for loads deri0ed from t$e round.

EC7 re;uires t$at %ot$ ultimate limit states '#9S- and ser0icea%ility limit states 'S9S- %e considered. 8ost of its te:t refers to #9S, for /$ic$ t$e main approac$ is %ased on use

applied to resistances rat$er t$an to material strent$s. T$ere are some situations in /$ic$ factorin loads at source leads to unreasona%le situations, especially in t$e

of partial factors. !pinions in Europe differ a%out /$ere and $o/ t$ese s$ould %e applied, and t$is is left to national c$oice< t$e 0alues to %e adopted for partial factors may also %e 0aried nationally. T$ree alternati0e ="esin Approac$es> $a0e %een de0eloped, com%inin partial factors in different /ays< t$e factor 0alues proposed in t$e European document are s$o/n in Ta%le 1, modified as noted %elo/ for "A1 Com%ination 1. In "esin Approac$ 1 '"A1-, t/o =com%inations> of partial factors are specified, and t$e desin must %e s$o/n to accommodate %ot$ com%inations. Essentially, t$ey are used in t$e same /ay as load com%inations, %ut t$e concept is e:tended to include material strent$s and resistances. &artial factors are enerally applied to eit$er loads '%efore com%inationor round strent$s '%efore calculation of resistances-, t$ou$ /it$ some e:ceptions. In countries t$at use "A1, t$e factors on round materials and strent$s are enerally set to 1.* in Com%ination 1, as s$o/n in Ta%le 1. 6or desin of piles and anc$ors, factors are

desin of retainin structures. 6or t$ese, EC7 allo/s t$e factors to %e applied to t$e effects of t$e loads, and t$is is used /$ere appropriate in =Com%ination 1> of "A1. In "A), partial factors are applied to loads and to round resistances. In a 0ariant of "A), "A)?, t$e e;uili%rium calculation is carried out usin unfactored '=representati0e>- loads, and t$e factors are applied to deri0ed load effects. It $as %een found t$at "A) and "A)? are unsuita%le for slope sta%ility pro%lems and for use of numerical met$ods, so most countries /$ic$ $a0e adopted "A) use "A@ for slope sta%ility and for numerical met$ods. In "A@, factors are applied to material strent$ and to loads simultaneously, in contrast to t$e t/ocom%ination approac$ of "A1 in /$ic$ t$ey are applied to t$e t/o separately and t$e results compared. A fe/ countries propose to use "A@ for all types of desins, /it$ factors ;uite different from t$ose s$o/n in Ta%le 1 in most cases.

)

Keynote lecture  Eurocode 7 – fundamental issues and some implications for users @ C3ARACTERISTIC A9#ES

A"

"ESI

to determinin c$aracteristic properties of materials in structural and eotec$nical desin.

2. Bac(ground in design practice 8any codes and te:t %ooDs tell t$e enineer $o/ to analyse results of specific, indi0idual tests and deri0e parameters t$at define t$e round, particularly its strent$ and deformation c$aracteristics, so t$at t$ese can %e used in calculations< some of t$is information is repeated in EC7 &art) 'E1((7)-. In practice, t$e eotec$nical process is more complicated t$an t$is, $o/e0er. A0aila%le information is often sparse in ;uantity, 0aria%le in ;uality and relia%ility, some of it from precise measurement at t$e rele0ant location in t$e round on t$e construction site, some inferred from a eneral understandin of t$e eoloy, some taDen from te:t %ooDs, papers or lecture notes, /$ere it may $a0e %een deri0ed %y %acD analysis of anot$er e0ent in a similar, %ut not identical situation some distance a/ay, and so on. T$ese sources may complement one anot$er, %ut t$ey may also %e found to %e inconsistent and contradictory.

2.3 1e!initions in E* 445 E 1((* contains t$e concept t$at material properties, or resistances, are first entered into calculations as characteristic alues 6(, to /$ic$ prescri%ed partial factors are applied to o%tain design alues 6d. T$is relations$ip is pro0ided in E;uation .@ of E 1((*2 Xd

=

ηXk/γm

'1-

/$ere η is a con0ersion factor relatin 0alues measured in tests to actual 0alues in t$e real construction, and γm is a partial factor for t$e material. E1((* notes t$at η may %e incorporated into γm 'i0in γ"- or into t$e c$aracteristic 0alue. T$us t$e c$aracteristic 0alues are used in t$e deri0ation of desin 0alues, /$ic$ incorporate all t$e safety elements re;uired %y t$e Eurocodes. To maDe t$is process /it$ prescri%ed partial factors useful, it is

6urt$ermore, e0endirectly, /$en rele0ant can %e measured per$apsparameters %y an in situ test, t$eir 0alues may %e c$aned %y t$e construction process itself, or %y some future e0ent suc$ as loadin or e:ca0ation. In structural desin, it is commonly t$e case t$at drafters of codes of practice $a0e more Dno/lede a%out t$e parameters of strent$ and loads rele0ant to a particular desin, and t$eir 0aria%ility, t$an does t$e desiner. 6or e:ample, code drafters may %e more Dno/ledea%le a%out /ind loadin, floor loadin, 0ariations in dimension of cast in situ concrete, or seismic loadin t$an is t$e desiner, and t$e same applies to t$e 0aria%ility of steel and concrete. 3o/e0er, in

necessary t$at c$aracteristic 0alues are defined as clearly as possi%le. E 1((* 4+.)5 says t$at t$e c$aracteristic 0alue of a material parameter /ill enerally %e a F fractile 0alue 'ie of test results-, unless ot$er/ise stated in t$e ot$er Eurocodes rele0ant to particular materials.

2.2 1e!inition in E07 T$e prime definition of c$aracteristic 0alue in EC7 is2 =T$e c$aracteristic 0alue of a eotec$nical parameter s$all %e selected as a cautious estimate of t$e 0alue affectin t$e occurrence of t$e limit state> 4).+..)')-5. EC7 re;uires t$at data from la%oratory and field tests s$ould %e =complemented %y /ellesta%lis$ed e:perience> 4).+..)'1-5. T$ese pararap$s maDe it clear t$at t$e c$aracteristic 0alues re;uired %y EC7 are to %e estimated, re;uirin a deree of $uman udement, and t$ey are to %e cautious, not simply =%est estimates>, =most pro%a%le> or statistically mean 0alues. T$ey are to %e cautious estimates of =t$e 0alue affectin t$e occurrence of t$e limit state>, t$at is, t$e

eotec$nical desin, t$e desiner Dno/s t$e location of t$e site, somet$in of its eoloy and round /ater conditions and t$e results, or paucity of results, of t$e round in0estiation, toet$er /it$ t$eir liDely relia%ility. T$is information 0aries considera%ly from one desin to anot$er and could not possi%ly %e Dno/n %y t$e code drafter. Because of t$is, t$ere are considera%le differences %et/een approac$es @

Keynote lecture  Eurocode 7 – fundamental issues and some implications for users 0alue actually operati0e in t$e round, not simply t$e 0alues measured in tests, and t$ey are to taDe into account /ellesta%lis$ed e:perience as /ell as test results made for t$e particular proect. Referrin to E;uation '1- a%o0e, taDen from E1((*, t$e re;uirement in EC7 for =t$e 0alue affectin t$e occurrence of t$e limit state> is e;ui0alent to incorporatin t$e con0ersion factor η, in t$is case relatin soil test results to real round %e$a0iour, into t$e c$aracteristic 0alue, as allo/ed %y E 1((*. &ararap$ 4).+.@'+-5 notes t$at assessment of round properties s$ould taDe account of =t$e effect of construction acti0ities on t$e properties of t$e round>. T$e =e:perience> to %e considered in estimatin t$e c$aracteristic 0alue is noted in 4).+..)'+-52 eoloical and ot$er %acDround information, suc$ as data from pre0ious proects. T$is pararap$ also lists t$e follo/in items as rele0ant to t$e re;uired estimate2 • t$e 0aria%ility of t$e measured property 0alues and ot$er rele0ant information, e.. from e:istin Dno/lede< • • •

•

0ariation seen in tests on small specimens. In t$ese cases, t$e c$aracteristic 0alue s$ould %e a cautious estimate of t$e mean 0alue for t$e Gone of round o0ernin t$e %e$a0iour of a eotec$nical structure at a limit state 4).+..)'7-5. T$is is illustrated in 6iure 1, /$ic$ s$o/s a %uildin to %e desined at t$e top of a slope formed in =estuarine %eds>, consistin larely of sands %ut /it$ some /eaDer clay inclusions. Considerin t$e o0erall slope sta%ility, any failure /ould $a0e to pass t$rou$ a maority of t$e sands, and could a0erae out t$e effects of t$e /eaDer clay Gones< so in t$is case t$e rele0ant c$aracteristic parameter, possi%ly ϕH, /ould %e a cautious estimate of t$e mean for t$e slip surface. 3o/e0er, in considerin t$e indi0idual pad foundations for t$e %uildin, it could %e possi%le t$at a pad /ould %e located almost e:clusi0ely on clay, so t$e c$aracteristic 0alue for t$e foundation desin /ould %e %ased on t$e strent$ of t$e /eaDer clay. Anot$er possi%ility is t$at t$e desiner c$ooses to $a0e round %eneat$ eac$ pad pro%ed to c$ecD for clay, and t$is is to %e

t$e e:tent of t$e field and la%oratory in0estiation< t$e type and num%er of samples< t$e e:tent of t$e Gone of round o0ernin t$e %e$a0iour of t$e eotec$nical structure at t$e limit state %ein considered< t$e a%ility of t$e eotec$nical structure to transfer loads from /eaD to stron Gones in t$e round.

du out if it 0alue is found. t$ata case, t$e c$aracteristic couldIn %e cautious estimate of t$e strent$ of parameters of t$e stroner sand. It can %e seen, t$erefore, t$at t$e c$aracteristic 0alue depends on t$e failure mode, t$e e:tent of t$e Gone of round affected, and t$e /ay it $as %een in0estiated.

2. Use o! statistics Alt$ou$ t$e definition of c$aracteristic 0alue in EC7 is not %asically statistical, statistical met$ods could %e useful in its assessment, and $elp to define t$e term =cautious>. &ararap$ ).+..)'11- says =If statistical met$ods are used, t$e c$aracteristic 0alue s$ould %e deri0ed suc$ t$at t$e calculated pro%a%ility of a /orse 0alue o0ernin t$e occurrence of t$e limit state under consideration is not reater t$an F.>. Aain, attention is dra/n to t$e real, o0erall %e$a0iour in t$e round – =o0ernin t$e occurrence of t$e limit state> – so t$e precedin pararap$s a%out mean 0alues in a Gone of influence still apply.

/igure . Building on estuarine beds.

Alt$ou$ t$e c$aracteristic 0alue is defined to %e =cautious>, not a statistical mean 0alue, it is noted t$at t$e round $as t$e a%ility to a0erae out some of t$e +

Keynote lecture  Eurocode 7 – fundamental issues and some implications for users T$e re;uirement to consider information from all a0aila%le sources also still applies. &ararap$ ).+..)'1*- says t$at if statistical met$ods are employed t$ey s$ould allo/ t$e use of a priori Dno/lede of compara%le round properties, and differentiate %et/een local and reional samplin. T$is re;uires ;uite ad0anced use of statistics. EC7 certainly does not encourae t$e replacement of /ell esta%lis$ed e:perience and /ellresearc$ed information %y simple statistical analysis of t$e immediately a0aila%le test results. e0ert$eless, statistical analysis of test results may pro0ide one source of useful information, to %e considered alonside ot$er a0aila%le sources. arious aut$ors $a0e considered statistical approac$es to a =cautious estimate of t$e mean 0alue for t$e Gone of round o0ernin t$e %e$a0iour of a eotec$nical structure at a limit state>. Sc$neider '1((7- suested t$at a 0alue taDen to %e *. standard de0iations from t$e mean of directly rele0ant test results could %e used. It can %e seen in 6iure ) t$at t$is is ;uite different from a F fractile of t$e test

com%ined %y statistics. T$e desiner must %e con0inced t$at a =cautious estimate of t$e 0alue affectin t$e occurrence of t$e limit state> is %ein adopted.

/igure 3. 1eriations o! 8characteristic alues9

results, %ein muc$ closeroftoort$ t$e mean of t$e results. In t$e conte:t American practice, "a$l%er and Ronold '1((@- and BecDer '1((- for more eneral use proposed t$e use of a =conser0ati0ely assessed mean> 'CA8- as t$e c$aracteristic 0alue, suc$ t$at for a normal distri%ution 7F of t$e measured 0alues /ould %e e:pected to e:ceed t$is 0alue. T$is re;uires an offset of *.( standard de0iations from t$e mean, for a normal distri%ution, as s$o/n in 6iure ). 6oye et al ')**- taDe up t$e same idea proposin to use a CA8 /it$ *F e:ceedance, e;ui0alent to *.+ standard de0iations %elo/ t$e mean of t$e test results for a normal distri%ution. 8ore recently,

Bored pile

/igure 2. Undrained shear strengths !rom borehole samples on site.

2.: A &ondon e#ample 6iure @ s$o/s t$e results of a series of undrained s$ear strent$ measurements in 9ondon Clay. T$e measurements /ere made usin unconsolidated undrained tria:ial tests. A statistical mean line $as %een dra/n t$rou$ t$e data and it is clear t$at undrained strent$ increases /it$ dept$. A c$aracteristic line is re;uired, and t$is s$ould depend on $o/ t$e c$aracteristic 0alues /ill %e used  /$at is t$e limit mode %ein considered 6or e:ample, if t$e undrained strent$ is needed for calculation

Tiete et al ')*11- $a0e discussed $o/ c$aracteristic 0alues can %e deri0ed for slope sta%ility pro%lems, taDin account of t$e coefficient of 0ariation of test results and t$eir spatial correlation. In t$e aut$orJs 0ie/, t$ese statistical approac$es are useful aids, %ut t$ey must ne0er %e allo/ed to replace or o0errule t$e use all information from all rele0ant sources, e0en /$en t$e sources are not easily 

Keynote lecture  Eurocode 7 – fundamental issues and some implications for users of t$e s$aft resistance of a pile, a 0alue suc$ as t$e Lcautious 'a0erae-J 0alue s$o/n on t$e fiure could %e used. 3o/e0er, for a mec$anism t$at mi$t taDe place in a small Gone of soil, suc$ as at t$e %ase of a pile, a more cautious 0alue  t$e Lcautious 'local-J 0alue  s$ould %e adopted.

/igure :. 0omparison o! results.

!n t$e %asis of t$ese inconsistent data sets, /$at 0alue s$ould %e used as t$e c$aracteristic undrained strent$ T$e 0alues measured in t$e tria:ial tests s$ould not %e inored, %ut t$e S&T results and t$e data from adacent sites s$ould also affect t$e decision. T$e c$aracteristic 0alue proposed for t$ese data is s$o/n on 6iure . T$is is less t$an t$e initial assessments in 6iure @, /$ic$ /ere %ased on t$e tria:ial results only, and is closer to a lo/er %ound of t$is particular set of tria:ial results.

/igure . S)' results !rom boreholes on site. 6rom t$ese %ore$oles, results from standard penetration tests /ere also a0aila%le, as s$o/n in 6iure +. In 9ondon Clay, t$ere is usually a constant factor %et/een standard penetration and undrained s$ear strent$ results< t$e factor is a%out +. to . 3o/e0er, if t$e mean line from t$e S&T results is transferred onto t$e undrained strent$ plot, as in 6iure , it appears t$at t$e normal correlation does not /orD. In fact, t$e measured undrained strent$s are remarDa%ly $i$2 t$ey are consistent /it$ 0ery lo/ /ater contents, /$ic$ /ere measured, %ut t$is mi$t simply mean t$at t$e samples $ad dried out on t$e /ay to t$e la%oratory, t$ou$ t$ere /as no reason to suspect t$is. 6iure  also s$o/s lines representin mean 0alues t$rou$ data from ot$er near%y sites, %ot$ for undrained s$ear strent$ and S&T results. T$e usual close correlation applies to t$ese, and it is clear t$at t$e undrained strent$s for t$e ne/ site are remarDa%ly $i$.

/igure ;. 0hosen characteristic alues.



Keynote lecture  Eurocode 7 – fundamental issues and some implications for users Enineers often need to follo/ t$is sort of process /$en tryin to interpret real data. It may %e t$at statistical met$ods could trace a similar loical se;uence. 3o/e0er, t$is /ould re;uire ;uite ad0anced met$ods and any statistical approac$ /$ic$ failed to taDe account of t$e di0erse array of data, typically a0aila%le, /ould %e $armful to t$e desin process.

enerally t$e strent$ to %e used in Eurocode 7 is t$e ma:imum a0aila%le to pre0ent collapse, not a 0alue mo%ilised in a /orDin state.

2.7 1esign alues o! ϕ= M$ereas t$e selection of c$aracteristic 0alues is common to all t$e "esin Approac$es of EC7, only approac$es "A1 and "A@ re;uire deri0ation of desin 0alues of material properties. T$is section is rele0ant to t$em. Eurocode 7 allo/s t/o alternati0e means of deri0in desin 0alues of material properties2 a- %y application of a partial factor γ", as discussed a%o0e. %- %y =direct assessment>, in /$ic$ case =t$e 0alues of t$e partial factors recommended ... s$ould %e used as a uide to t$e re;uired le0el of safety>. It is often asDed /$ere t$e use of a critical state anle of friction fits into t$is sc$eme. T$e suestion is made %y some t$at as t$e anle of friction cannot fall any lo/er t$is 0alue could %e used as a directly

2.; It is sometimes necessary to c$ose from one of t$e follo/in, dependin on circumstances2 • peaD, critical state or residual s$ear strent$ • ultimate strent$ or a =mo%ilised> 0alue • strent$ of intact material or strent$ on oints • strent$ at first loadin or after repeated loadin • stiffness of intact rocD or of t$e ointed material • stiffness on first loadin, or on unload reload In all cases, t$e ans/er of Eurocode 7 is2 =T$e one t$at is rele0ant to t$e pre0ention of t$e limit state under consideration.> EC7 does not differ in t$is respect from normal practice. 6or some particular situations, t$e code is a%le to specify /$ic$ of t$ese 0alues is rele0ant. 6or e:ample, /$ere concrete is to %e cast aainst round, /$ic$ mi$t t$erefore %e distur%ed, t$e critical state 0alue for t$e anle of s$earin resistance is re;uired 4..@'1*-, (..1'-5 . T$is ans/er to t$e ;uestion is not t$e same as2 =T$e one /$ic$ /ould %ecome rele0ant if t$e limit state /as not pre0ented.> 6or e:ample, in most plastic clays, if a slip occurred, t$e anle of s$earin resistance /ould e0entually fall to t$e residual 0alue. e0ert$eless, it is not necessary to desin for residual strent$ in clays /$ic$ $a0e not pre0iously slipped. Similarly, it may %e unnecessary to desin for critical state 0alues, t$ou$ %rittleness and ductility must %e considered, as noted in 4).+.1'1@-5 and 4).+.@'+-5.

assessed desin 0alue, re;uirin no furt$er γ". T$is /ould mean t$at no marin of safety /ould %e applied to t$e strent$ of soil %elie0ed to %e in an initially loose state. It is true t$at part of t$e uncertainty a%out ϕ= is t$e state of t$e soil, /$ic$ ele0ates its 0alue a%o0e t$e critical state 0alue. 3o/e0er, in t$e aut$orJs e:perience, round in0estiation is often inade;uate to i0e t$e desiners complete confidence in t$e actual nature of t$e soil, suc$ as its radin, apart from its state of compaction. !n t$is %asis, t$e desin 0alue of ϕ= for loose soil s$ould %e less t$an its anticipated critical state 0alue. T$e critical state 0alue is directly rele0ant to t$e strent$s of interfaces %et/een t$e round and concrete cast aainst t$e round 4..@'1*-, (..1'-5. In t$e aut$orJs 0ie/ it is arua%le t$at t$e reduction factor γϕ applied to t$is could %e less t$an t$e 0alue used enerally in t$e %ody of t$e soil, per$aps 1.1 instead of 1.), pro0ided its desin 0alue is still less t$an t$e desin 0alue for t$e %ody of t$e soil. 7

Keynote lecture  Eurocode 7 – fundamental issues and some implications for users 6or soil in a denser state, t$e desin 0alue in t$e %ody of t$e soil /ill normally %e o%tained from t$e c$aracteristic 0alue %y application of a partial factor γϕ. !ften, t$is /ill mean t$at t$e desin ϕ= /ill %e less t$an a cautious estimate of t$e critical state 0alue, ie ϕ=d > ϕ=(?γϕ  ϕ=crit,(. In t$e aut$orJs opinion, t$is is a 0ery useful additional safety c$ecD 'ie ϕ=d  ϕ=crit,(-, and it /ould %e ood if it /ere added, at least as an application rule, to EC7.

o0er0ie/ /ill %e pro0ided $ere in an attempt to $elp t$e reader understand t$e conclusions and remainin de%ate. Simpson et al discussed fi0e =simple> pro%lems intended to $i$li$t particular issues, toet$er /it$ t$ree more practical desins. T$is /orD is limited to considerin conditions of $ydrostatic /ater pressures or steady state seepae, in /$ic$ /ater pressures are specified in calculations, independent of t$e loadin and stressstrain %e$a0iour of t$e round. Situations in0ol0in t$e timedependent response of t$e round are not discussed.

2. /urther deelopment by S07 CENTC)*NSC7 $as set up E0olution roup 11 on =c$aracterisation>, c$aired %y 9o0isa 8oritG of S/eden. !ne of t$e tasDs of t$is roup is to consider t$e deri0ation of c$aracteristic 0alues.

.3 Cequirements o! E07 EC7 reconises fi0e types of ultimate limit states2 EO#2 loss of e;uili%rium in /$ic$ t$e strent$s of materials is insinificant STR2 failure of structural elements E!2 failure in t$e round #&92 failure due to uplift %y /ater pressure '%uoyancy3"2 $ydraulic $ea0e T$e particular pro%lems of 3" /ill %e

+ "ESIS "!8IATE" B MATER &RESS#RE

. ntroduction In sur0eys of 0ie/s on EC7, reater clarity of re;uirements for safety pro0isions in relation to /ater pressures is a fre;uent re;uest. As in t$e case of deri0ation of c$aracteristic 0alues, t$e aut$or %elie0es t$is re;uest reflects a pro%lem t$at predates EC7. CENTC)*NSC7 $as set up E0olution roup ( on /ater pressures, c$aired %y &rofessor or%ert ot of ermany. Mater pressures raise t/o particular pro%lems2 a- T$ey sometimes constitute lare forces t$at are critical to desin and $a0e /ell defined ma:imum 0alues, /it$ little real uncertainty. %- Besides constitutin forces, /ater pressures reduce t$e strent$ of frictional

discussed in +.( %elo/. STR and E! may occur toet$er and t$ey are c$ecDed usin load factors of 1.@ and 1. on unfa0oura%le permanent and 0aria%le loads, respecti0ely, /it$ 1.* and *.* on t$e e;ui0alent loads /$en actin in a fa0oura%le manner. T$e load factors used for #&9 are enerally lo/er2 1.1 for unfa0oura%le actions, enerally /ater pressure, and *.( for fa0oura%le, enerally /ei$t of a potentially %uoyant structure. T$e /ay in /$ic$ t$e STRNE! factors are to %e applied /$en /ater pressure is a leadin action is a particular point of de%ate. EC7 says2 =M$en dealin /it$ round /ater pressures for limit states /it$ se0ere

soils. T$us t$eyand $a0et$is a dou%le in soil mec$anics, is alsoeffect true of any partial factors applied to t$em. T$e issues raised %y desins dominated %y /ater pressure /ere considered %y Simpson , ot and 0an Seters ')*11- in a paper re;uested %y t$e EC7 committee CENTC)*NSC7. Reference to t$at paper is recommended for full details of t$e /orD, includin mat$ematics. A less mat$ematical

conse;uences 'enerally ultimate limit states-, desin 0alues s$all represent t$e most unfa0oura%le 0alues t$at could occur durin t$e desin lifetime of t$e structure> 4).+..1'-&5. otin t$at =desin 0alues> are 0alues t$at already incorporate safety, re;uirin no furt$er partial factors, t$is pararap$ indicates direct assessment of #9S desin 0alues on t$e %asis of t$eir p$ysical limits in e:treme, %ut credi%le 

Keynote lecture  Eurocode 7 – fundamental issues and some implications for users situations. 6or ser0icea%ility limit states, t$e desin 0alues are to %e less se0ere, correspondin to =normal circumstances>. E:pandin on t$is t/o pararap$s later, EC7 pro0ides an application rule2 ="esin 0alues of round/ater pressures may %e deri0ed eit$er %y applyin partial factors to c$aracteristic /ater pressures or %y applyin a safety marin to t$e c$aracteristic /ater le0el> 4).+..1'-5. It t$erefore appears t$at t$e desiner can c$oose %et/een direct assessment, factorin /ater pressures or adustin /ater le0els to deri0e #9S desin /ater pressures. An earlier pararap$ on actions is also important2 =Actions in /$ic$ round and free/ater forces predominate s$all %e identified for special consideration /it$ reard to deformations, fissurin, 0aria%le permea%ility and erosion> 4).+.)'(-&5. T$is $as attac$ed a sinificant note, outlinin t$e single source principle2 =#nfa0oura%le 'or desta%ilisin- and fa0oura%le 'or sta%ilisinpermanent actions may in some situations %e considered as comin from a sinle source. If t$ey are considered so, a sinle partial factor

If t$ese =secondary> actions or action effects are lare, failure could occur %ut t$e fault may %e seen to rest /it$ t$e o/ners or maintainers of t$e structure, or t$e 0andals< alternati0ely, t$e desiner s$ould $a0e foreseen t$em and /as /ron to omit t$em from t$e primary actions for /$ic$ t$e structure /as desined. 3o/e0er, if t$e secondary actions or action effects are small, t$e o/ner /ould reasona%ly e:pect t$e structure to %e sufficiently ro%ust to /it$stand t$em. In t$is conte:t, =lare> and =small> effects $a0e to %e uded in relation to t$e manitude of t$e primary actions. It follo/s t$at e0en /$ere t$ere is no real possi%ility of unfa0oura%le 0ariation of t$e primary actions, it may %e necessary to include some 0ariation of t$em in desin in order to accommodate t$e possi%le secondary actions t$at are not ot$er/ise included. T$e uncertainty of t$e /ay t$e actions produce effects /it$in a structure also $as to %e accommodated. T$e 0ariations could %e applied eit$er to t$e actions t$emsel0es, in deri0in desin

may applied to t$e sum of t$ese actions or to t$e%esum of t$eir effects.>

0alues, or to t$e action effects. . E#plicitly accommodate the worst water pressures that could reasonably occur As noted in +.) a%o0e, EC7 re;uires for #9S desin t$at t$e desin /ater pressures desin 0alues s$all represent t$e most unfa0oura%le 0alues t$at could occur durin t$e desin lifetime of t$e structure.

.2 Cobustness D allow !or secondary actions and action e!!ects E0en in cases /$ere t$e manitudes of t$e primary actions are fi:ed /it$ no possi%ility of unfa0oura%le 0ariations, desins s$ould %e sufficiently ro%ust to accommodate unDno/n and unpredicta%le secondary actions. 6urt$ermore, e0en /$ere t$e manitudes of actions are fi:ed, t$e 0alues of resultin action effects /it$in a structure may $a0e some uncertainty< t$at is, t$ere is uncertainty in t$e loadin model. In t$e cases considered $ere, t$e primary unfa0oura%le actions are deri0ed from /ater pressure, /$ic$ in some cases may $a0e 0ery clear limits. Secondary actions could include, for e:ample, sedimentation around a structure in /ater, e:ca0ation of t$e round a%o0e a structure relyin on t$e /ei$t of round, minor 0e$icle or s$ip impacts, considered too small to include in calculations, or 0andalism of 0arious Dinds.

/igure 7. raity wall retaining !ree water.

6iure 7 s$o/s a /all supportin /ater pressure. A drain is pro0ided, /it$ t$e intention t$at t$e dept$ of /ater %e limited to @m. 3o/e0er, if t$e drain s$ould %ecome %locDed and t$e /ater dept$ increases to +m, (

Keynote lecture  Eurocode 7 – fundamental issues and some implications for users

/igure . Submerged anchor bloc(.

t$e %endin moment in t$e /all is increased %y a factor of ).. Clearly, a desin t$at tooD t$e e:pected /ater dept$, @m, and applied a partial factor of 1.@ to t$e /ater pressure or %endin moment /ould %e inade;uate if t$e +m dept$ occurred. T$is e:ample illustrates /$y it is essential t$at desins e:plicitly accommodate t$e /orst /ater pressures t$at could reasona%ly occur.

illustrated in 6iure (. 8et$ods @ and + %ot$ follo/ t$e sinle source principle, noted in +.) a%o0e, %ut 8et$ods 1 and ) do not.

.: 'he single source principle 6iure  s$o/s an anc$or %locD, for /$ic$ t$e total /ei$t < is a permanent sta%ilisin 'fa0oura%le- force and t$e anc$or force / is a 0aria%le desta%ilisin 'unfa0oura%le- force. T$e c$aracteristic total density of t$e %locD is γc and t$at of t$e /ater γw. T$e /ater forces are taDen to %e permanent. T$e strent$ of t$e round or structure are not at issue, so t$e only ultimate limit state to %e considered for t$e anc$or %locD is uplift, #&9. 6or t$is, EC7 pro0ides t/o factors for permanent actions, a%%re0iated $ere as γ+dst 'enerally P 1- for t$e desta%ilisin force and

/igure 4. /actored water pressures on anchor bloc(. FaG 0haracteristic Fand "ethod G, FbG "ethod , FcG "ethod 3, FdG "ethod 2.

γ+stb 'enerally Q 1- for t$e sta%ilisin force< t$e factor for t$e 0aria%le desta%ilisin force is γ%+dst 'P 1-. It is clear t$at t$e c$aracteristic /ei$t of t$e %locD, .3:. *

γ ϕ  1+25 γ ϕ  1+5

1*m

5**

1***

15**

-.m/m

/igure U&S analysis o! m deep e#caation D bending4. moments.

;.: Staged construction umerical met$ods are often used to study t$e ser0icea%ility of desins for staed e:ca0ations. 6iure )1 s$o/s t/o alternati0e strateies t$at $a0e %een used to carry out #9S analyses /it$ factored soil strent$s. In Stratey 1, all soil strent$s from t$e start and t$rou$out t$e computation. In Stratey ), t$e computation is initially carried out /it$ unfactored strent$s, t$en, in separate %ranc$in computations, soil strent$s are factored at critical staes, considered separately. T$ese alternati0es $a0e %een discussed pre0iously %y many Bauduin et al ')***-, Simpson and

/igure 35. U&S analysis o! m deep e#caation D γ > .:.

desin is accepta%le or not, as in fact t$e met$od 'a- analysis s$o/ed it /as.

aGdc$i ')**@- and, in t$e conte:t of tunnel desin, C$eun et al ')**(-. Referrin to .@ a%o0e, met$od 'a- can %e used /it$ Stratey 1 or ), %ut met$od '%can only %e used /it$ Stratey ). Current opinion enerally fa0ours Stratey ), as confirmed %y recent discussions in EC7 E0olution roup +, for t/o main reasons. 'a- It is feared t$at applyin factors in earlier staes mi$t $a0e

;. 'he 8wrong9 !ailure mechanismA common o%ection to #9S computations, particularly to met$od '%-, is t$at /it$ factored strent$s t$ey i0e t$e =/ron> failure mec$anism. In fact, t$ere is no =correct> failure mec$anism, %ecause failure is not t$e =correct> state to occur. )*

Keynote lecture  Eurocode 7 – fundamental issues and some implications for users %%% St rateg& 1 %% % Comp#te #sing factored strengt$ 0actor material strengths

%%% %%% %%% %% %%% Str at eg & 2 %%% %%% %%% %% %%% %% Comp#te #sing c$aracteristic parameters

Comp#te #sing factored parameters

4nitial state

4nitial state7 8ould be critical for 3all bendin g moment

Ecavate to 5m  3all cantilevering

Ecavate to 5m  3all cantilevering

4nstall &ro& at m de&th

4nstall &ro& at m de&th

Ecavate to 1*m

Ecavate to 1*m

for 3all length, bendin g moment and &ro& force

.o further factors on strut forces or #s

6&&l" factors on strut forces or #s

.o further factors on strut forces or #s

and ϕ= it is reasona%le to taDe t$is as t$e factor on drained strent$, $o/e0er deri0ed. But more interpretation mi$t %e needed if t$e national anne: i0es t/o different 0alues. In any e0ent, it /ill %e important to asD /$et$er t$e strent$s calculated %y t$e model are more or less relia%le t$an t$ose used in normal practice. Some adustment to t$e factors s$ould %e made in t$e li$t of t$is.

8ould be critical

;.7 Undrained behaiour and consolidation Soils are essentially effecti0e stress materials respondin to effecti0e stresses, so ad0anced models of soil %e$a0iour are almost al/ays e:pressed in terms of effecti0e stress parameters. M$en soil deforms slo/ly enou$ t$at t$e deformation does not cause c$ane of /ater pressure, it is said to %e =drained>. M$en it deforms ;uicDly enou$ t$at no /ater can enter or lea0e t$e soil elements it is said to %e =undrained>. T$e undrained s$ear strent$ of soil, cu, can %e measured, and t$is results from its initial state and its effecti0e stress parameters 'e c=, ϕ=-.

/igure 3. Strategies !or analysis o! staged construction.

eit$er an unreasona%le or an optimistic effect on later staes< t$e aut$or supports t$is reasonin. '%- In some cases t$e #9S computations can %e run as aduncts to S9S computations< $o/e0er, t$is /ill not %e t$e case if desin situations for t$e t/o limit states re;uire differences of eometry 'suc$ as unplanned o0erdi-, loadin or /ater

Effecti0e stress parameters 'e c=, ϕ=- are sometimes called =drained> parameters. T$is is un$elpful terminoloy, since t$ese parameters o0ern %e$a0iour and can %e used in models or drained, undrained and partially drained states. Relia%le computation of undrained strent$ from effecti0e stress parameters is 0ery difficult, since it is affected %y many features of soil %e$a0iour, includin anisotropy and dilation. Because undrained strent$ can %e measured directly, /it$ moderate relia%ility, it is often prefera%le to input it directly as a parameter in numerical analysis t$an to try to compute it. 3o/e0er, t$is is not compati%le /it$ t$e use of effecti0e stress models. EC7 enerally re;uires a $i$er factor on undrained strent$ 'e 1.+ on cu- t$an on effecti0e stress parameters 'e 1.) on c=, tanϕ=-. T$e drafters assumed t$at effecti0e stress parameters /ould %e used only for drained states and did not comment on t$e use of approac$es t$at computed undrained strent$ for t$em. In numerical analysis, t$ere is t$erefore a temptation, for economy,

pressures. A t$ird possi%le reason is t$at only Stratey ) can %e run /it$ met$od '%-, suc$ as t$e &la:is cϕ reduction procedure.

;.; Use o! adanced soil models !or U&S 8odels of soil %e$a0iour muc$ more realistic t$an linear elastic8o$rCoulom% are increasinly used for S9S computations. Alt$ou$ some of t$ese, suc$ as t$e &la:is $ardenin soil models, $a0e simple strent$ parameters 'c=, ϕ=- as input, many do not 'e Camclay models or t$e BRICK model, Ellison et al )*1)-. &ractice to date $as %een to use only elastic8o$rCoulom% models for t$e #9S part of t$e computation, e0en /as an adunct to an S9S run t$at/$en usedt$is a more ad0anced model. EC7 pro0ides factors specifically for c=, ϕ= and cu, so if t$ese are not input parameters of t$e proram some deree of interpretation /ill %e needed. In t$e case of cu, t$is is t$e 'rele0ant- undrained strent$, so it /ould not matter $o/ t$is /as deri0ed. If t$e national anne: i0es t$e same 0alue for factors on c= )1

Keynote lecture  Eurocode 7 – fundamental issues and some implications for users to use an effecti0e stress model for undrained %e$a0iour /it$ a lo/er factor 'e 1.) on c=, tanϕ=- t$an /ould %e used if undrained strent$ /ere input directly 'e 1.+ on cu-. T$e aut$or considers t$is to %e potentially unsafe. T$e $i$er factor 'e 1.+- /as considered appropriate for c$aracteristic 0alues of cu %ased on measurement, /$ic$ is enerally more relia%le t$an 0alues computed from effecti0e stress parameters, so it is unreasona%le to adopt a lo/er 0alue for t$e latter. T$e conclusion to %e dra/n from t$is is t$at /$en undrained %e$a0iour is %ein modelled usin effecti0e stress parameters 'e c=, ϕ=- t$e partial factor applied to t$em s$ould i0e a reduction in undrained strent$ at least e;ui0alent to t$at re;uired %y EC7 for cu. T$is re;uires some testin, %ut as a first appro:imation t$e factor to %e applied to c=, tanϕ= mi$t %e a%out t$e same as t$at re;uired for cu 'e 1.+-. If timedependent consolidation is to %e modelled in a #9S numerical analysis, it /ill aain %e necessary to use an effecti0e stress model. T$e 0alues of partial factors to %e

and )7 to @)m deep to underside of %ase sla% '6i. ))-. T$e assumed e:ca0ation temporary /orDs consisted of t$ree le0els of temporary steel props. Mall t$icDness re;uired %y initial desin /as 1.)m. T$is /as su%se;uently increased to 1.m for consistency /it$ ot$er structures on t$e Italian $i$ speed net/orD and to account for a possi%le proloned cessation of /orD at final e:ca0ation stae '3ocom%e et al )**7-.

/igure 33. /lorence station cross section with design "ohr0oulomb soil parameters and stratigraphy.

Eurocode 7, "esin Approac$ 1 'EC7, "A1- /as adopted %y t$e desin team.

applied $a0e not yet %een considered.

"esin of t$e structure to Com%inations 1 and ) 'C1 and C)- /as more onerous t$an reulations applyin at t$e time in Italy. T$e current Italian national standard specifies desin of retainin structures and t$eir supports to C1 only /$ile C) is c$ecDed for lo%al failure due to collapse of t$e soil, not of t$e structure. It /as, $o/e0er, considered prudent for t$is proect t$at t$e structure %e c$ecDed for %ot$ com%inations in accordance /it$ EC7 "A1. T$e decision to use EC7 "A1 did not, $o/e0er, increase t$e num%er of analyses to %e carried out since C) /as needed in any e0ent to e0aluate t$e dept$ of em%edded /alls for lateral sta%ility.

7 CASE ST#"2 69!RECE 3I3 S&EE" RAI9 STATI!

7. ntroduction T$e analysis of a lare station %o: in 6lorence, Italy, desined to Eurocode is descri%ed %y Simpson and 3ocom%e ')*1*-, from /$ic$ t$e follo/in a%%re0iated 0ersion is dra/n. T$is case study presents salient features of t$e desin and t$e met$od adopted. &artial factors /ere applied to soil properties at all staes of e:ca0ation in t$e #9S analyses. Results are presented $ere of a su%se;uent comparati0e study into t$e effects of applyin partial material factors only at specific e:ca0ation staes. T$e proposed station lies on a $i$ speed rail line currently nearin completion %et/een 8ilan and aples and is situated ust nort$ of t$e $istoric centre of 6lorence. T$e Client for t$e station is Rete 6erro0iaria Italiana 'R6I- /it$ construction sc$eduled for )*1*. T$e structure is ++m lon, )m /ide

7.3 E!!ect o! !actoring at discrete stages In EC7 "A1, application of partial factors to soil properties is re;uired in #9S C), and t$ese factors /ere applied at all construction staes in t$e oriinal desin. Su%se;uently, an in0estiation /as carried out into t$e effects of applyin partial material factors only at specific e:ca0ation ))

Keynote lecture  Eurocode 7 – fundamental issues and some implications for users staes rat$er t$an at all staes. T$e results of t$ese C) analyses '/it$ factored soil %ut unfactored /all moments and s$ears- are also compared /it$ t$e results of C1 analyses 'unfactored soil, factored /all moments and s$ears-. T$e in0estiation considered t$ree propped e:ca0ation staes %ased on a 1.)m t$icD diap$ram /all, applyin t$e c$aracteristic 8o$rCoulom% soil parameters presented in 6iure )) in t$e pseudo finite element proram Oasys 6REM '&appin et al., 1(-. Bendin moments deri0ed usin 6REM are presented in 6iure )@. T$e #9S C1 results $a0e %een factored up %y t$e specified partial factor of 1.@ for comparison /it$ t$ose from #9S C). 8a:imum positi0e /all moments 'tension on e:ca0ated face- are marinally $i$er from C1 compared to t$ose from C) in /$ic$ partial factors are applied at all staes, t$e solid lines in t$e fiure. eati0e /all moments are, $o/e0er, reater in C) at t$e middle prop le0el 'U@1m-. T$is may %e a result of lo/er marin on lateral sta%ility and $i$er /all deflection durin t$e deeper

/igure 32. U&S wall bending moments

/igure 3. U&S prop !orces.

In t$e C) analyses /it$ soil strent$ factors only at discrete staes t$e desin prop forces are similar at t$e upper t/o le0els of props to t$ose from C) analysis /it$ partial factors at all staes. In t$e lo/est le0el of props, $o/e0er, t$e force is sinificantly reater if partial factors are applied only at t$is stae, possi%ly due to t$e effects of soil arc$in mentioned a%o0e.

staes of e:ca0ation C) compared to C1. Applyin partial in factors on soil strent$s in C) only at t$e respecti0e e:ca0ation staes a0e similar /all moments in staes 1 and ) to t$e C) analysis /it$ factors applied at all staes. Application of partial factors only at e:ca0ation stae @, $o/e0er, resulted in larer neati0e /all moments at t$e lo/est temporary prop, /it$ reater /all deflection t$an t$e analysis /it$ partial factors at all staes. Inspection of predicted soil pressures suests t$at /it$ partial factors applied durin staes 1 and ) more soil arc$in onto t$e $i$er props occurs, allo/in reater reduction of soil pressure %elo/ t$e acti0e limit t$an /$en partial factors are applied

7.2 0onclusions !rom case study 6or t$is particular study, t$e results o%tained /$en partial factors /ere applied at discrete staes /ere more se0ere t$an /$en t$ey /ere applied t$rou$out t$e computation. 8ore studies of t$is type are needed to determine /$et$er t$is is a eneral rule. In t$e opinion of t$e aut$or, $o/e0er, %ot$ types of analysis are 0alid c$ecDs on t$e code re;uirements. In a more

only in stae @. Results of t$e comparison in desin prop forces usin 6REM are presented in 6iure )+. T$e #9S C1 results $a0e aain %een factored up %y t$e specified partial factor of 1.@ for comparison /it$ #9S C). T$e C) forces /it$ factored soil strent$ at all staes are $i$er at t$e lo/er t/o le0els t$an t$ose from C1.

complete #9S analysis, %endin of t$e /all could %e included, and plasticity t$is /ould pro%a%ly i0e more similar %endin moments from t$e t/o C) analyses. T$e same may not %e true for t$e strut loads, $o/e0er, and since struts may pro0ide a some/$at %rittle response t$is remains an area to %e in0estiated.

)@

Keynote lecture  Eurocode 7 – fundamental issues and some implications for users E1((*. ')**)- Eurocode2 Basis of desin. BSI, 9ondon. 'BS E 1((*2)**)-. E1((71 ')**+=EC7>. Eurocode72 eotec$nical desin  &art 12 eneral rules. BSI, 9ondon. 'BS E 1((712)**+-. BSI ')**7- Eurocode 7  eotec$nical desin  &art )2 round in0estiation and testin. BSI, 9ondon 'BS E 1((7)2)**7-. 6oye, K.C. Salado, R. V Scott, B. )**. Resistance factors for use in s$allo/ foundation 9R6". W. eotec$. eoen0iron. En., 1@)'(-, 1)*– 1)1. ul0anessian, 3, Calaro, WA, 3olicDy, 8

 C!C9#"I RE8ARKS T$e paper $as discussed some of t$e current de%ates related to application of Eurocode 7, pro0idin tentati0e conclusions /$ere a0aila%le. 6or determination of c$aracteristic 0alues of material properties and of /ater pressures, some possi%le processes $a0e %een proposed, %ut t$e need to e:ploit enineerin insi$t and e:pertise $as also %een emp$asised. T$is is a

')**)- "esinersY uide to E 1((*  Eurocode2 Basis of structural desin. T$omas Telford. 3ocom%e, T., &elle/, A., 8cBain, R., and eo/, 3C. ')**7- ="esin of a ne/ deep underround station structure in 6lorence.> &roc. ZI ECS8E, 8adrid, ol ), pp 1*+( – 1*+. &appin, W.M., Simpson, B., 6elton, &.W., and Raison, C. '1(- =umerical analysis of fle:i%le retainin /alls.> Symposium on computer applications in eotec$nical enineerin. T$e 8idland eotec$nical Society, #K, April. Sc$neider, 3. R. 1((7. "efinition and determination of c$aracteristic soil properties. Contri%ution to "iscussion Session ).@, ZI ICS86E, 3am%ur. BalDema. Sc$uppener B., Simpson B., !rr T. 9. 9., 6ranD R. and Bond A. W. ')**(-. 9oss of static e;uili%rium of a structure – definition and 0erification of limit state EO#. &roc )nd International Symposium on eotec$nical Safety and RisD ISI6# )**(, ifu, Wapan, 'editors2 . 3ono, 8. SuGuDi, T. 3ara V 6. [$an, Taylor V 6rancis roup, 9ondon- 111) Wune, pp 111  11. Simpson, B and 3ocom%e, T ')*1*- Implications of modern desin codes for eart$ retainin structures. &roc ER)*1*, ASCE Eart$ Retention Conference @, pp.7*@, Seattle, Au )*1*. Simpson, B, ot,  V 0an Seters AW ')*11eotec$nical safety in relation to /ater pressures. &roc @rd Int Symp on eotec$nical Safety and RisD, pp *117, 8unic$. Simpson, B and aGdc$i, 8 ')**@- #se of finite element met$ods in eotec$nical limit state desin. 9S")**@2 International MorDs$op on 9imit State "esin in eotec$nical Enineerin &ractice.

particular c$allene for code drafters. &ro%lems affected %y t$e loadin of /ater pressure, or /it$ t$e %alanced loads from a sinle source considered %y EO#, re;uire 0ery careful assessment of safety. It $as %een suested t$at EO# s$ould %e rearded as =ust anot$er load case> rat$er t$an a different limit state. T$e use of numerical analysis is e:pected to %ecome increasinly common in eotec$nical desin, so it is important t$at modern codes accommodate t$is. Current discussions $a0e %een summarised and approac$es for analysin ultimate limit states $a0e %een presented. ( RE6ERECES Bauduin, C, "e os, 8 V Simpson, B ')***-. Some Considerations on t$e #se of 6inite Element 8et$ods in #ltimate 9imit State "esin. 9S")***2 Int. MorDs$op on 9imit State "esin in eotec$nical Enineerin, ISS8E, TC)@, 8el%ourne. BecDer, ".E. 1((. Ei$teent$ Canadian eotec$nical Collo;uium2 9imit states desin of foundations. I2 An o0er0ie/ of t$e foundation desin process. Canadian eotec$ W, @@'-, ((@. K C$eun, K Mest, 3 C eo/ V B Simpson ')**(- "o Eurocodes maDe a difference eotec$nics and Tunnellin, ol @, o. 1, pp@+7. Miley Interscience. . 'Report on Special MorDs$op on Conse;uences of Eurocode 7 on t$e desin of tunnels, Austrian Society for eomec$anics, SalG%ur, Austria."a$l%er, R and Ronold, K! '1((@- 9imit state desin of offs$ore foundations. &roc Int Symp 9imit state desin in eotec$nical enineerin, ol ), pp+(1**. "anis$ eotec$nical Society. "a$l%er, R and Ronold, K! '1((@- 9imit state desin of offs$ore foundations. &roc Int Symp 9imit state desin in eotec$nical enineerin, ol ), pp+(1**. "anis$ eotec$nical Society. Ellison, KC, Soa, K and Simpson, B ')*1)- A strain space soil model /it$ e0ol0in stiffness anisotropy. Xotec$ni;ue, in press.

)+