implementation of eurocode 7 in french practice by means of...

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Implementation of Eurocode 7 in French practice by means of national additional standards

Jean-Pierre MagnanSébastien BurlonDepartment of Geotechnical engineering, Environment, Risks (GER)

Delft University of Technology - 30/11-01/12/2011: Workshop on Safety concepts and calibration of partial factors in European and North American

codes of practice

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Past/present versus Future

• Buildings- DTU (Unified technical documents)

� shallow foundations� pile foundations� retaining structures

- Recommendations

• Public works- CCTG (common technical clauses)

� foundations design (Fasc.62-V)� execution of works (Fasc.68)� earthworks

- Recommendations and guides- for designers- for « owners » (maîtres d’ouvrage)- for contractors

• Eurocodes (EC7-8.V)

• 6 national standards- shallow foundations- deep foundations- gravity walls- embedded walls- reinforced earth structures- earth structures

• Recommendations- (e.g.) micropiles- rigid inclusions- cyclic loads

• Guides

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Basic choices

� Design approach 2 + design approach 3 in some cases.

� Rely on proven methods used in our country (such as the use of pressuremeter).

� Open the list of accepted design methods to classical methods used in other countries.

� Do not rely on statistical concepts and analyses, but rather on experience and case histories.

� Yet accept methods strongly referred to in Eurocode 7 (e.g. model pile approach to pile design), but try to make them equivalent to concurrent alternative methods in all cases when they should be equivalent (typically only one or two tests or test profiles).

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National references for safety

Keep the present levels of safety in a renewed format.

1. New characteristic values ≡ existing design values

2. Partial factors should be equivalent to the global one

because existing safety levels were validated by designers, contractors, clients and insurances.

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Slopes and overall stability

Stability analyses refer to the model of a sliding block.

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Shallow foundations (ELU)

The preferred method is based on pressuremeter tests.

The traditional Nc, Nγ, Nq method is accepted.

A place for « one third of the limit resistance ».

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Pile foundations

The design method is based on pressuremeter tests (penetrometer tests, too).

We chose

- to import the « model pile » approach, though it is not used in France, and

- to keep as an alternative the traditional French method, based on the estimation of the « characteristic value » of the soil properties (equal to the former design values).

The two approaches were made equivalent by means of model factors.

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Axial load resistance

Rk Rd

Test

Model pile

Ground model

ξξξξmodel

model

ξξξξ

variability

ξ − spatial variability

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Deep foundations

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Deep foundations

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Gravity walls

Walls are designed by checking the usual failure mechanisms.

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Embedded walls

A distinction is made between usual embedded walls and multi-anchored walls (designed using Winkler type reaction model).

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Thank you for listening

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Which are the components of geotechnical decisions ?

60%

40%

Qs

Qb

Test results Calculation model Qs, QpCalibration: pile testsSoil properties

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Which are the components of geotechnical decisions ?

60%

40%

Qs

Qb

Test results Calculation model Qs, QpCalibration: pile tests

Test resultsSoil properties(Variations) Calculation model Criterion Max load

Calibration ?

Soil properties

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Where are uncertainties ?

60%

40%

Qs

Qb


Soil properties

Incl. Criterion

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Where are uncertainties ?

60%

40%

Qs

Qb


Test resultsSoil properties(Variations) Calculation model Criterion Max load

Calibration ?

Soil properties

Incl. Criterion

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But there are other departures from reality

Test results Soil properties are those of the soil before the pile

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But there are other departures from reality

Test results Soil properties are those of the soil before the pile

But piles cannot appear in the ground without having some influence !

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Closer to reality

Test results Driven piles are surrounded by a disturbed zone

This is accounted for by the methods calibrated against pile tests

What is the situation for numerical (e.g. finite element) models ?

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Closer to reality

Test results Driven piles are surrounded by a disturbed zone

This is accounted for by the methods calibrated against pile tests


Can we characterize the mechanical properties of disturbed soil ? And the extent of the disturbed zone ?

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Closer to reality

Test results Non displacement piles are less disturbing

This is accounted for by the methods calibrated against pile tests, too


Probably better.

But the question of the calculation model and soil parameters (even a representative value) remains.

What types of site investigations are needed and what can be reasonably expected ?What is the reliability of the tests ?

implementation of eurocode 7 in french practice by means of...

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