30/03/2011. Eurocode 7 Today and Tomorrow. Ground structures t Slope and Retaining wall design in the Netherlands. Contents

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Hein Jansen Fugro Ingenieursbureau BV The Netherlands Contents

Probabilistic Analyses for retaining structures Partial

1 Eurocode 7 Today and Tomorrow Ground structures t Slope and Retaining wall design in the Netherlands Adriaan van Seters Hein Jansen Fugro Ingenieursbureau BV The Netherlands Contents Design Approach 3 Safety and reliability in EN-1990 Probabilistic Analyses for retaining structures Partial Factors Calculation method for retaining structures Example Slope stability Date 1

2 The Netherlands use Design Approach 3 OB 3: partial factors on : - A on Loads and Load effects - M on Material strength A q surface Load (var.) F A Load Effects Loads A Soil strength R Resistance E pas φ, c M Also for SLOPES 3 Material Factors applied to Sheetpiles (45-ϕ /2) ϕ (45+ϕ /2) Characteristic values ϕ char Design values ϕ d tanϕ d = tanϕ char / γ ϕ PAO BP5 4 2

3 Safety and Reliability in Eurocode 7 old NEN 6700 new Eurocode 0 (NEN-EN 1990) Class β Class β Example 1 3,2 Family house CC1/RC1 3, ,4 Buildings < 3 stories 3 3,6 CC2/RC2 3,8 Offices, apartments Traffic bridges High rise buildings > 70 m - - CC3/RC3 4,3 Stadions, Concert halls Primary dikes, railway bridges Distinction between CC/RC-Classes in Eurocode EN-1990 given by LOADFACTORS γf (for Class CC2/RC2) for: CC1/RC1: γ = 0,9 * γf CC3/RC3: γ = 1,1 * γf FOR GROUND STRUCTURES SLOPES, SHEET PILES Eurocode EN 1990: Loadfactors to be used are according SET C permanent loads γ = 1.0 variable loads γ = 1.3 Medium Clay Stiff Clay Radius : 44,00 [m] Safety : 1,23 Main load = soil weight both stabilising and destabilising Therefore γ = 1.0 is correct, but no difference for various CC/RC-Classes In NL Differentiate in Material Factors per CC/RC 0,000 PAO BP5 6 3

4 Probabilistic Analyses in 1990 and 2005 σ b 0,5 anchor 2,7 8,0 1,5 5,0 Sand 5,50-8,0- Clay 8,5- Sand 12,0- σ b Clay Sand Configurations analysed Probabilistic Analyses Probabilistic analyses Level II and Level III (Monte Carlo) stochastic parameters (geometry, soil parameters) average value μ and standard deviation σ ( variation coefficient V = σ / μ) Combined with Reliability index β = 3,33 / 3,8 / 4,3 (EN 1990) influence factors α follow from probabilistic analyses 4

5 Probabilistic Analyses Probabilistic analyses influence factor α is dependent on: influence of parameter on failure mode type of failure mode number of stochastic parameters 2 ( ( α ) = 1. 0 Partial factors Partial factor V γ = 1 α β V formula based on characteristic (5 %) values of parameters sheet pile design in sand: probabilistic analyses result in α ϕ = 0.7 to 0.8 for friction angle ϕ with V ϕ = 0.1 γ ϕ = = 1,

6 Partial Factor for ϕ General trend V = 0.1 assumed variation for tan (ϕ) gamma 2,0 19 1,9 1,8 1,7 1,6 V = 0,1 1,5 1,4 1,3 1,2 1,1 1,0 0,0 0,2 0,4 0,6 0,8 1,0 alfa alfa = 0.75 beta = 3,3 beta = 3,8 beta = 4,2 Partial Factor for c General trend V = 0.2 assumed variation for cohesion c gamma 2,0 1,9 1,8 1,7 V = 0,2 1,6 1,5 1,4 1,3 1,2 1,1 1,0 0,0 0,2 0,4 0,6 0,8 1,0 alfa beta = 3,3 beta = 3,8 beta = 4,2 6

7 Partial Factors for Retaining Walls (flexible) Soilparameter Symbol Set M2 Reliability Class RC1 (β = 3,3) RC2 (β = 3,8) RC3 (β = 4,3) Friction angle tan ϕ' γ ϕ 1,15 1,175 1,20 Effective cohesion γ c 1,15 1,25 1,40 Undrained γ cu 1,5 1,6 1,65 Shear strength Volume unit weight γ g 1,0 1,0 1,0 Geometric offsets: retaining height: 10 % extra, max 0.5 m (acc EC7) waterlevel: extra 0.25 m difference between both sides DIMENSIONING OF SHEETPILE WALL Use Beam-Column method with linear soil springs k d For each calculation phase 5 calculations ULS - Vary spring stiffness (high/low) and vary waterlevel at excavation (high/low) 4 calcs SLS-calculation 7

8 CALCULATION SCHEME Phase Scheme A Always design values (d) Incl Material Factors 1 d 2 d 3 d d Scheme B Design values (d) in applicable phase, but characteristic values (char) in previous phases char d char d char d c a d d char d Scheme A too conservative Scheme B enough safety (ex 1 case), based on PROB sums PAO BP5 15 EXAMPLE Phases 1. Excavate to NAP + 0,7 m 2. Install Anchor 3. Excavate to NAP -6,0 m (wet) 4. Underwater concrete + pump out water F A + 1,0 m -6,0 m - 10,0 m 10 kpa AZ 18 NAP + 2,0 m + 0,5 m Sand Clay Peat Silt Sand silty Clay, sandy Gravel Sand PAO BP5 16 8

9 EXAMPLE PHASE SLS [char-values] ULS scheme A ULS scheme B ULS = SLS x 1,2 M rep F A;rep 1. Excavate to 0.7 m 2. Install anchor 3. Excavate to 6m 4. Under water concrete + pumping PAO BP5 17 EXAMPLE PHASE SLS [char-values] ULS scheme A ULS scheme B ULS = SLS x 1,2 M rep F A;rep 1. Excavate to 0.7 m 2. Install anchor 3. Excavate to 6m 4. Under water concrete + pumping PAO BP5 18 9

Under water concrete + pumping 139 116 260

10 EXAMPLE PHASE SLS [char-values] ULS scheme A ULS scheme B ULS = SLS x 1,2 M rep F A;rep 1. Excavate to 0.7 m 2. Install anchor 3. Excavate to 6m 4. Under water concrete + pumping PAO BP5 19 Slope Stability 10

Reliability Class RC1 RC2 RC3 1,2 1,25 1,3 1,3 1,45 1,6 1,5 1,75 2,0 1,0 1,0 1,0 Material factors are

11 Partial Factors - Slopes SOIL PARAMETER Symbol Slope Stability Set M2 Default EC7 Friction angle tan ϕ γ ϕ 1,25 Cohesion c γ c 1,25 Undrained shear strength c u γ cu 1,4 Volume unit weight γ g 1,0 Reliability Class RC1 RC2 RC3 1,2 1,25 1,3 1,3 1,45 1,6 1,5 1,75 2,0 1,0 1,0 1,0 Material factors are based on PROB sums in the 90 s Developments in Geotechnics. With Trial and Error. EUROCODE 7 But now with Eurocode 11

12 Thank You 12

Safety Concepts and Calibration of Partial Factors in European and North American Codes of Practice

Safety Concepts and Calibration of Partial Factors in European and North American Codes of Practice The Dutch approach on Geotechnical Design by Eurocode 7 Adriaan van Seters Hein Jansen Fugro GeoServices