www.fugro.com The Dutch approach on Geotechnical Design by Eurocode 7 Adriaan van Seters Hein Jansen Fugro GeoServices BV The Netherlands Delft, Nov. 30 – Dec. 1, 2011 Safety Concepts and Calibration of Partial Factors in European and North American Codes of Practice
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www.fugro.com
The Dutch approach on Geotechnical Design by Eurocode 7
Adriaan van SetersHein Jansen
Fugro GeoServices BVThe Netherlands
Delft, Nov. 30 – Dec. 1, 2011
Safety Concepts and Calibration of Partial Factorsin European and North American Codes of Practice
www.fugro.comDate
Contents
Typical Dutch……� Design Approach 3 – why??� Piled structures – Cone resistance qc and EC7� Shallow foundations� Probabilistic Analyses for retaining structures� Calculation method for retaining structures� Slope stability� Summary
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Why Design Approach 3
� In 1970’s / 1980’s huge Water barriers in SW Holland
� Structures far outside the Technical State of the Art
� Extrapolation of knowledge was necessary
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Why Design Approach 3
For those structures … Probabilistic design
– Top safety event distributed into chances of failure for sub systems – Safety associated with uncertainty of loads and resistances– Resistance related to strength of materials
From 1990 � probabilistic design in Dutch codes
Partial factors on loads and materials – based on probabilistic analyses
1,64
Fav Fk
1,64
Xk Xav
%
Fσ Fσ RσRσ
X,F
dkarF FF =*γ mkard XX γ/=
StrengthLoad
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Pile foundations – Pile bearing capacity
� Pile bearing capacity based on CPT’s- Load tests in 1950’s - CPT is a “modelpile”- Tip and shaft resistance based on qc
(qc = cone resistance)
� Tip resistance qb, shaft resistance qs
– qb = αp * qc, qs = αs * qc
� Different pile types � different α-factorsαp - 0.6 to 1.0, αs - 0.6 % to 1.4 %
� Partial factor γt, γs;t
(same for all pile types)
� ξ3, ξ4 - values between 1.4 and 1.0(depend on no of CPT’s, since 1990)
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Pile Foundations - Design Approach 3
DA 3: Partial Factors γγγγ- A on Loads- M on Materials
Design Approach
Load/ Load effect A - Action
Material- Factor M- Material
Factor total Resistance R - Resistance
DA 1.1 > 1,0 = 1,0 = 1,0
DA 1.2 = 1,0 > 1,0 (q - last)
> 1,0 = 1,0
DA 2 > 1,0 = 1,0 > 1,0
DA 3 > 1,0 > 1,0 = 1,0
Piles in NL: q c is material parametermaterialfactor γγγγ on q c ���� DA3
Alternatively: factor on resistance ���� DA2
G, QvLoad(permanent, variable)
Resistance RsRb
Strengthϕ′, c′
MR
A
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Pile factors αααα
� Factors α are based on pile load tests in 1950’s –1980’s
� Dutch buildings � CPT’s every 25 * 25 m
� 2011: Pile load testing – seldom executed, no standard routine
� Recent discussion – Underperformance of precast concrete piles– New – untested – pile types
� Pile testing campaign required for all manufacturers
� Ready by 2016, otherwise 33 % reduction in bearing capacity/factor α
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Shallow foundations
In NL – Not many shallow foundations!
Bearing capacity formulaq = Nc * cu + γ * d * Nq + 0,5 * B * γ * Nγ