An Introduction to EC7

Implications for the geotechnical engineer and best value in the procurement of site investigationsvalue in the procurement of site investigations

Eurocodes – What are they

Geotechnical and Structural Engineers

Eurocode 7 – What is it

Eurocode 7, is the new harmonised European code for geotechnical design.

• Part 1 “General rules”. Lays down the design principles and rules generally to be adopted.p p g y p

• Part 2 “Ground Investigation and Testing”. Requirements for the execution interpretation andRequirements for the execution, interpretation and use of results of laboratory and field tests.

What should it accomplishCommon approach across the member states.

It should help bridge the divide between geotechnical p g gand structural design.

It does this by the introduction of partial factors andIt does this by the introduction of partial factors and limit state design.

It presents a clear distinction between ULS and SLSIt presents a clear distinction between ULS and SLS.

It requires a more systematic approach to deriving material propertiesmaterial properties.

Introduces a degree of compulsion.

Waiting to see what everybody else does

Early Retirement

Waiting for you to tell me

EC i P dEC7 is a Post code -somewhere near Whitechapel?Whitechapel?

All very well in principle

New Geotechnical Design Principles Commitment to limit state design and the separation ofCommitment to limit state design and the separation of ultimate and serviceability condition.

Defines distinct actionsDefines distinct actions.

Use of "Characteristic“ to define values of ground ti f ith ti l f t t f d iproperties for use with partial factors to form design

values.

Application of separate partial factors to several aspects of uncertainty rather than a single lumped factor of safety applied to cover all uncertaintysafety applied to cover all uncertainty.

Communication between geotechnical and structural engineer is requiredengineer is required.

Changes for the Geotechnical Engineer

Planning – How much SI.

EC7 Part 2 doesn’t require tooEC7 Part 2 doesn t require too many changes to site practices, exceptions include SPT N values pand undisturbed samples (U100s).

Reporting will become more prescribed

Characteristic and Design Values

EC7 -1 states design values of geotechnical properties (Xd) shall be either derived from h i i l h ll b dcharacteristic values or shall be assessed

directly.

Characteristic values of a soil or rock shall be selected from a cautious estimate of a value ff ti th f th li it t taffecting the occurrence of the limit state.

This is where the designer has the opportunity to use his/her skills and judgements in the design process.

Geotechnical Design Methods

EC7-1 offers up to 4 methods for design checking.• Using calculations for ULS.• Using Prescriptive measures.• Using tests.• Using observational methods• Using observational methods.

Changes for the Structural EngineerCh t th d ifi ti l ti t• Changes to the scope and specifications relating to ground investigations.

G G• GIR You probably won’t see many changes to GIRs, which are roughly equivalent to an enhanced factual reportreport.

• GDR You should see substantial changes to interpretive or GDRs filtering through from nowinterpretive or GDRs filtering through from now onwards.

• EC7 1 makes compulsory the provision to the client• EC7 - 1 makes compulsory the provision to the client of a GDR, while EC7 – 2 requires the provision of a GIR to form part of the GDR.GIR to form part of the GDR.

Geotechnical Design Methods (DAs)

Geotechnical Design MethodsEC7-1 offers a variety of methods for design checkingEC7 1 offers a variety of methods for design checking. Using calculations for ULS, prescriptive measures, using tests & using observational methods.

ULS Design PrinciplesE t bli h A tiEstablish Actions Establish material (ground) propertiesEstablish (ground) resistancesEstablish (ground) resistancesSet up calculation models for the relevant ultimate and serviceability statesShowing in a calculation that limit states will not be exceeded

.

Characteristic and Design Values

Characteristic and Design ValuesCh t i ti l f il k h ll bCharacteristic values of a soil or rock shall be selected from a cautious estimate of a value

EC7-1 states design values of geotechnical properties (Xd) shall be either derived from characteristic values ( d)or shall be assessed directly.

Design Calculations

In ULS design calculations EC7 requires theg qfollowing equilibrium equation to be satisfied.

Ed ≤ RdEd ≤ Rd

Problems with Data

Even experienced engineers struggle to g ggreach a consensus.

By adopting a more rigorous statistical approach we should beapproach we should be able to be more consistent.

SPT N V lSPT N Values

Small data sets

Without prior knowledge statistical analysis gives pessimistic resultspessimistic results.

We do have tools thatWe do have tools that can combine or weight the results of small datasets with expected values.

Design example – clay soil vertical load only

Design example – clay soil vertical load only

Design example – clay soil vertical load only

Design example – dry sand vertical load only

Design example – dry sand vertical load only

Design example – dry sand vertical load only

Summary EC7 v BS Geotechnical Codes

EC7 embodies a design calc lation methodolog thatEC7 embodies a design calculation methodology that makes substructure design fully compatible with superstructure design using other ECs.p g g

EC7-1 explicitly identifies design limit states, and makes use of partial factors.p

The adoption of alternative methods for achieving a geotechnical design.geotechnical design.

EC7-1 makes compulsory the provision of a GDR, while EC7-2 requires the provision of a GIREC7 2 requires the provision of a GIR.

Unlike current codes, EC7 states that principles must be honouredhonoured.

C l iConclusions

Common approach across Europe and disciplinesCommon approach across Europe and disciplines brings obvious benefits. The adoption of EC7-1 as opposed to EC7-2 will The adoption of EC7 1 as opposed to EC7 2 will bring about the main changes.Greater consideration of limiting ground and foundation movements. It places an emphasis on risk management (identify assess and where necessary mitigate or(identify, assess and where necessary mitigate or avoid) ahead of construction. Most of it already considered good practice and y g pshould raise the bar for the industry.

C l iConclusions

Client education required.There is a much greater number of documents to

k i hwork with. Increase SI and Design costs.However should result in more detailed and betterHowever, should result in more detailed and better site investigations with more design effort. Reduction in construction costsRaise profile of industry and as such welcomed.

Thank youThank you