EN Eurocode 7. Section 8 Anchorages Section 9 Retaining structures. Brian Simpson Arup Geotechnics

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of information workshop 1 EN 1997-1 Eurocode 7 Section 8

1 EUROCODES Background and Applications EN1997-1: Anchorages and Retaining structures Brussels, February 2008 Dissemination of information workshop 1 EN Eurocode 7 Section 8 Anchorages Section 9 Retaining structures Brian Simpson Arup Geotechnics

2 BP106.9 EN Geotechnical design General Rules 1 General BP111.5 BP112.6 BP124-T Basis of geotechnical design 3 Geotechnical data 4 Supervision of construction, monitoring and maintenance 5 Fill, dewatering, ground improvement and reinforcement 6 Spread foundations 7 Pile foundations 8 Anchorages 9 Retaining structures 10 Hydraulic failure 11 Overall stability 12 Embankments Appendices A to J 2

3 BP124-F3.6 8 Anchorages 8.1 General 8.2 Limit states 8.3 Design situations and actions 8.4 Design and construction considerations 8.5 Ultimate limit state design 8.6 Serviceability limit state design 8.7 Suitability tests 8.8 Acceptance tests 8.9 Supervision and monitoring 3

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7 7

8 8

9 9

10 8 Anchorages Section depends on EN Execution of special geotechnical work - Ground anchors Not fully compatible with EN1537. Further work on this is underway. BS8081 being retained for the time being. 10

11 EN1537:

12 EN1537:1999 Execution of special geotechnical work - Ground anchors 12

13 EN1537:1999 Execution of special geotechnical work - Ground anchors - provides details of test procedures (creep load etc) 13

14 Partial factors in anchor design 14

15 Partial factors in anchor design 15

16 EUROCODES Background and Applications EN1997-1: Anchorages and Retaining structures Brussels, February 2008 Dissemination of information workshop 16 EN Eurocode 7 Section 8 Anchorages Section 9 Retaining structures Brian Simpson Arup Geotechnics

17 EUROCODES Background and Applications EN1997-1: Anchorages and Retaining structures Brussels, February 2008 Dissemination of information workshop 17 EN Eurocode 7 Section 9 Retaining structures Fundamentals Design Approaches Main points in the code text Examples: Comparisons with previous (UK) practice Comparison between Design Approaches Lessons from the Dublin Workshop

18 EUROCODES Background and Applications EN1997-1: Anchorages and Retaining structures Brussels, February 2008 Dissemination of information workshop 18 EN Eurocode 7 Section 9 Retaining structures Fundamentals Design Approaches Main points in the code text Examples: Comparisons with previous (UK) practice Comparison between Design Approaches Lessons from the Dublin Workshop

Genting Highlands BP87.59 BP106.30 BP111.

19 Genting Highlands BP87.59 BP BP BP BP BP124-F3.9 BP BP145a.8 19

Genting Highlands BP87.60 BP106.31 BP111.

20 Genting Highlands BP87.60 BP BP BP BP BP124-F3.10 BP BP145a.9

21 BP87.61 BP BP BP BP BP124-F3.11 BP BP145a.10 FOS > 1 for characteristic soil strengths - but not big enough 21

BP106.33 BP111.25 BP112.46 The slope and retaining wall are all part of the same problem. BP87.

22 BP BP BP The slope and retaining wall are all part of the same problem. BP87.62 BP BP124-F3.12 BP BP145a.11 Structure and soil must be designed together - consistently. 22

ISGSR2007 - First International Symposium on Geotechnical Safety and Risk Approaches to ULS

23 ISGSR First International Symposium on Geotechnical Safety and Risk Approaches to ULS design The merits of Design Approach 1 in Eurocode 7 Brian Simpson Arup Geotechnics BP145a.1 23

24 EUROCODES Background and Applications EN1997-1: Anchorages and Retaining structures Brussels, February 2008 Dissemination of information workshop 24 EN Eurocode 7 Section 9 Retaining structures Fundamentals Design Approaches Main points in the code text Examples: Comparisons with previous (UK) practice Comparison between Design Approaches Lessons from the Dublin Workshop

25 BP111.5 BP112.6 BP124-T1.31 EN Geotechnical design General Rules BP General 2 Basis of geotechnical design 3 Geotechnical data 4 Supervision of construction, monitoring and maintenance 5 Fill, dewatering, ground improvement and reinforcement 6 Spread foundations 7 Pile foundations 8 Anchorages 9 Retaining structures 10 Hydraulic failure 11 Overall stability 12 Embankments Appendices A to J 25

26 9 Retaining structures 9.1 General 9.2 Limit states 9.3 Actions, geometrical data and design situations 9.4 Design and construction considerations 9.5 Determination of earth pressures 9.6 Water pressures 9.7 Ultimate limit state design 9.8 Serviceability limit state design 26

27 9.2 Limit states 27

28 9.2 Limit states 28

29 9.3.2 Geometrical data 29

30 9.3.2 Geometrical data 100% 100% 10% 10% 30

31 9.4 Design and construction considerations 31

32 9.4 Design and construction considerations 32

33 9.4.2 Drainage systems 33

34 9.5 Determination of earth pressures 34

35 9.5 Determination of earth pressures 35

36 9.5.3 Limiting values of earth pressure Annex C also provides charts and formulae for the active and passive limit values of earth pressure. 36

37 Annex C Sample procedures to determine limit values of earth pressures on vertical walls Based on Caquot and Kerisel (and Absi?). No values for adverse wall friction, which can lead to larger K a and much smaller K p. 37

38 Wall friction Adverse wall friction may be caused by loads on the wall from structures above, inclined ground anchors, etc. 38

39 C.2 Numerical procedure for obtaining passive pressures Also provides Ka Programmable formulae (though not simple) Incorporated in some software (eg Oasys FREW, STAWAL) Precise source not known (to me), but same values as Lancellotta, R (2002) Analytical solution of passive earth pressure. Géotechnique 52, Covers range of adverse wall friction. Slightly more conservative than Caquot & Kerisel when φ and δ/φ large but more correct? 39

40 Ka, Kp charts in Simpson & Driscoll 40

41 Comparison with Caquot & Kerisel Ka(C&K) / Ka(EC7) % Kp(C&K) / Kp(EC7) % 41

42 9.7 Ultimate limit state design 42

43 9.7.2 Overall stability 43

44 9.7.3 Foundation failure of gravity walls 44

45 9.7.4 Rotational failure of embedded walls 45

46 9.7.5 Vertical failure of embedded walls 46

47 9.7.6 Structural design of retaining structures 47

48 9.7.6 Structural design of retaining structures 48

49 9.7.7 Failure by pull-out of anchorages 49

50 9.8 Serviceability limit state design 50

51 9.8.2 Displacements 51

52 EUROCODES Background and Applications EN1997-1: Anchorages and Retaining structures Brussels, February 2008 Dissemination of information workshop 52 EN Eurocode 7 Section 9 Retaining structures Fundamentals Design Approaches Main points in the code text Examples: Comparisons with previous (UK) practice Comparison between Design Approaches Lessons from the Dublin Workshop

53 BP BP m propped wall BP

54 BP BP BP124-F3.15 BP m propped wall - data BP78.26 CASE: DA1 DA1 EC SLS Unplanned overdig (m) Dig level: Stage Stage Characteristic φ' ( ) γ (or M) on tan φ' Design φ' δ'/φ' active δ'/φ' passive K a Factor on K a Design K a K p Factor on K p Design K p Excd. side Retd. side 1.0 γ Q

55 BP BP BP BP124-F3.16 8m propped wall - length and BM BP78.28 CASE: DA1 DA1 EC SLS Unplanned overdig (m) Design φ' Design K a Design K p Excd. side Retd. side 1.0 γ Q Computer program STW STW F Data file PROP11 PROP1 BCAP3A Wall length (m) 15.1 * 17.9 * 17.8 ** Max bending moment (knm/m) Factor on bending moment ULS design bending moment (knm/m) * Computed ** Assumed

56 BP BP124-F3.17 BP BP Redistribution of earth pressure BP87.75

57 BP BP BP BP124-F3.18 Compare CIRIA 104 BP

58 10kPa (13kPa) 0-8m (-8.5m) φ = 24 (19.6 ) 58

59 xbcap5-feb07c Event 3 Run 3 Increment 1 11: : Bending moment Scale x 1:101 y 1:13681 y coordinate (x = m) 630kN/m Bending moment [knm/m] 59

60 BP BP BP BP124-F3.19 8m propped wall - length and BM BP78.32 CASE: CIRIA CIRIA BS DA1 DA1 EC7 DA1 DA1 DA1 DA1 Fs Fs SLS Unplanned overdig (m) Design φ' Design K a Design K p Excd. side Retd. side γ Q Computer program STW STW STW STW STW FREW FREW FREW FREW SAFE Data file PROP4 PROP5 PR1B-03 PROP11 PROP1 BCAP3A BCAPBA BCAP1A BCAP4A XBCAP5 Wall length (m) 20.4 ** 14.1 ** 17.9 * 15.1 * 17.9 * 17.8 ** 17.8 ** 17.8 ** 17.8 ** 17.8 ** Max bending moment (knm/m) 1870 ## Factor on bending moment ? ULS design bending moment (knm/m) ? * Computed ** Assumed ## Not used in design

BP111.39 BP112.56 BP119.55 BP124-F3.20 BP78.

30 25 20 15 10 Length (m) BM/50 Prop F/50 5

61 BP BP BP BP124-F3.20 BP m excavation - comparison of methods Length (m) BM/50 Prop F/ CIRIA 104 BS8002 EC7-STW FREW EC7- EC7- SAFE

62 BP BP124-F3.21 BP BP Redistribution of earth pressure BP87.75

63 BP BP124-F3.22 BP BP German practice for sheet pile design - EAB (1996) BP

64 Weissenbach, A, Hettler, A and Simpson, B (2003). Stability of excavations. In Geotechnical Engineering Handbook, Vol 3: Elements and Structures (Ed U Smoltczyk). Ernst & Sohn / Wiley. 64

65 BP BP124-F3.24 2m SAFE Grundbau2 BP q=80kpa φ k =35 γ= 17 kn/m 3 δ/φ = 2/3 (active) K a = γ = 20 kn/m m 8m Weissenbach, A, Hettler, A and Simpson, B (2003) Stability of excavations. In Geotechnical Engineering Handbook, Vol 3: Elements and Structures (Ed U Smoltczyk). Ernst & Sohn / Wiley.? 65

66 BP124-F3.25 Grundbau in STAWAL BP Bending Moment [knm/m] [1] kN/m Reduced Level [m] [2] [2] Toe m Shear Moment Water Pressure Actual Pressures Scale x 1:128 y 1:128 Pressure [kpa] Shear Force [kn/m] 66

67 BP124-F3.26 Grundbau: DA1 and DA2 XBP L=10.7 L=10.6 Penetration cm BM knm/m Strut force kn/m Char DA1-1 DA1-2 DA2 C:\bx\Grundbau\Prague\[grundbau.xls] 67

68 EUROCODES Background and Applications EN1997-1: Anchorages and Retaining structures Brussels, February 2008 Dissemination of information workshop 68 EN Eurocode 7 Section 9 Retaining structures Fundamentals Design Approaches Main points in the code text Examples: Comparisons with previous (UK) practice Comparison between Design Approaches Lessons from the Dublin Workshop

69 BP130.1 Eurocode 7 Workshop Dublin, 31 March to 1 April 2005 Organised by European Technical Committee 10 Technical Committee 23 of ISSMGE GeoTechNet Working Party 2 Retaining Wall Examples 5 to 7 69

70 BP130.2 Example 5 Cantilever Gravity Retaining Wall 6m 0.75m Surcharge 15kPa 20 o Fill 0.4m Sand B =? Design situation - 6m high cantilever gravity retaining wall, - Wall and base thicknesses 0.40m. - Groundwater level is at depth below the base of the wall. - The wall is embedded 0.75m below ground level in front of the wall. - The ground behind the wall slopes upwards at 20 o Soil conditions - Sand beneath wall: c' k = 0, φ' k = 34 o, γ = 19kN/m 3 - Fill behind wall: c' k = 0, φ' k = 38 o, γ = 20kN/m 3 Actions - Characteristic surcharge behind wall 15kPa Require - Width of wall foundation, B - Design shear force, S and bending moment, M in the wall 70

71 BP130.3 Example 5 Surcharge 15kPa 20 o 6m 0.4m Fill 20 o K a γz 0.75m Sand B =? 71

72 BP130.4 Example 5 Surcharge 15kPa 20 o 6m 0.4m Fill 20 o K a γz 0.75m Sand B =? 72

73 BP130.5 Example 5 Cantilever Gravity Retaining Wall Example 5 - Gravity wall BASE WIDTH m b 1=3 N N N N N 1 3 N N 1 2 2=N 2 b b 2 N 1, 2 or 3 EC7 DA1, DA2 or DA3 b EC7 DA1 Comb 1 only N national method G C C C C C C C C:\BX\BX-C\EC7\Dublin\[Dublin-results.xls] Contributor 73

74 BP124.A6.11 Example 5 Cantilever Gravity Retaining Wall BP m 0.75m Surcharge 15kPa 20 o Fill 0.4m Sand B =? Design situation - 6m high cantilever gravity retaining wall, - Wall and base thicknesses 0.40m. - Groundwater level is at depth below the base of the wall. - The wall is embedded 0.75m below ground level in front of the wall. - The ground behind the wall slopes upwards at 20 o Soil conditions - Sand beneath wall: c' k = 0, φ' k = 34 o, γ = 19kN/m 3 - Fill behind wall: c' k = 0, φ' k = 38 o, γ = 20kN/m 3 Actions - Characteristic surcharge behind wall 15kPa Require - Width of wall foundation, B - Design shear force, S and bending moment, M in the wall Additional specifications provided after the workshop: 1 The characteristic value of the angle of sliding resistance on the interface between wall and concrete under the base should be taken as 30º. 2 The weight density of concrete should be taken as 25 kn/m3. 3 The bearing capacity should be evaluated using to the EC7 Annex D approach. 4 The surcharge is a variable load. 5 It should be assumed that the surcharge might extend up to the wall (ie for calculating bending moments in the wall), or might stop behind the heel of the wall, not surcharging the heel (ie for calculating stability). 74

75 BP124.A6.12 Example 5 Cantilever Gravity Retaining Wall Example 5 - Gravity wall 6.0 BASE WIDTH m b 1=3 2 N N 1 N 1 N N N N N 2 2=N b b E C C C C C C C C:\BX\BX-C\EC7\Dublin\[Dublin-results (version 1).xls] 23-Jun-05 00:02 75

76 BP130.5 Example 5 Cantilever Gravity Retaining Wall γ E E{γ F F rep ; X k /γ M ; a d } = E d R d = R{γ F F rep ; X k /γ M ; a d }/γ R 76

77 BP130.5 Example 5 Cantilever Gravity Retaining Wall Column no Base width Eccentricity (m) Effective width B' (m) Vertical force kn/m Horizontal force kn/m Inclination H/V See note 0.41 Column no. 1 Column no. 2 Column no. 3 Column no. 4 Characteristic values of all parameters. Characteristic eccentricity and inclination; forces and resistance factored. Characteristic eccentricity; unfavourable (horizontal) force and resistance factored. Favourable (vertical) force not factored in deriving inclination or for comparison with resistance. Unfavourable (horizontal) force and resistance factored. Favourable (vertical) force not factored in deriving inclination or eccentricity, but factored for comparison with resistance. R (kn/m) γ(r) Rd (kn/m) Rd/Vd Column no. 5 Unfavourable (horizontal) force and resistance factored. Favourable (vertical) force not factored in deriving inclination or eccentricity, or for comparison with resistance. 77

78 BP124.A6.12 Example 5 Cantilever Gravity Retaining Wall Example 5 - Gravity wall BENDING MOMENT knm/m =3 1 b 2 1 N 1 N N G C C C C C C C N N 2 2=N b b C:\BX\BX-C\EC7\Dublin\[Dublin-results.xls] 27-Jun-05 21:43 78

79 BP124.A6.14 Example 5 Cantilever Gravity Retaining Wall Example 5 - Gravity wall 300 2=N SHEAR FORCE kn/m b 1 N 1 N N N N b b E C C C C C C C 2 C:\BX\BX-C\EC7\Dublin\[Dublin-results (version 1).xls] 23-Jun-05 00:02 79

80 BP130.8 Example 5 Cantilever Gravity Retaining Wall Serviceability: No criteria in the instructions Mainly ignored ½(K a + K 0 )? Middle third? Very large range of results Importance of sequence of calculation and factoring this is the main difference between the design approaches for this problem Factors of safety must allow for errors and misunderstanding 80

81 Example 6 Embedded sheet pile retaining wall BP130.9 Sand 10kPa 1.5m 3.0m D=? Design situation - Embedded sheet pile retaining wall for a 3m deep excavation with a 10kPa surcharge on the surface behind the wall Soil conditions - Sand: c' k = 0, φ' k = 37 o, γ = 20kN/m 3 Actions - Characteristic surcharge behind wall 10kPa - Groundwater level at depth of 1.5m below ground surface behind wall and at the ground surface in front of wall Require - Depth of wall embedment, D - Design bending moment in the wall, M 81

82 Example 6 Embedded sheet pile retaining wall BP130.9 Sand 10kPa 1.5m 3.0m Design situation - Embedded sheet pile retaining wall for a 3m deep excavation with a 10kPa surcharge on the surface behind the wall Soil conditions - Sand: c' k = 0, φ' k = 37 o, γ = 20kN/m 3 Actions - Characteristic surcharge behind wall 10kPa - Groundwater level at depth of 1.5m below ground surface behind wall and at the ground surface in front of wall Require - Depth of wall embedment, D - Design bending moment in the wall, M D=? Additional specifications provided after the workshop: 1 The surcharge is a variable load. 2 The wall is a permanent structure. 82

83 Example 6 Embedded sheet pile retaining wall BP Huge range of results Values of Kp? Kp(C&K) / Kp(EC7) % C&K / EC7 / Coulomb?? What about overdig? (5) Less severe values than those recommended in Annex A may be used for temporary structures or transient design situations, where the likely consequences justify it. 83

84 BP Example 7 Anchored sheet pile quay wall 10kPa 1.5m Tie bar anchor GWL 3.3m Sand 8,0m Water 3.0m D =? Design situation - Anchored sheet pile retaining wall for an 8m high quay using a horizontal tie bar anchor. Soil conditions - Gravelly sand - φ' k = 35 o, γ = 18kN/m 3 (above water table) and 20kN/m 3 (below water table) Actions - Characteristic surcharge behind wall 10kPa - 3m depth of water in front of the wall and a tidal lag of 0.3m between the water in front of the wall and the water in the ground behind the wall. Require - Depth of wall embedment, D 84

85 BP Example 7 Anchored sheet pile quay wall 10kPa 1.5m Tie bar anchor GWL 3.3m Sand 8,0m Water 3.0m D =? Design situation - Anchored sheet pile retaining wall for an 8m high quay using a horizontal tie bar anchor. Soil conditions - Gravelly sand - φ' k = 35 o, γ = 18kN/m 3 (above water table) and 20kN/m 3 (below water table) Actions - Characteristic surcharge behind wall 10kPa - 3m depth of water in front of the wall and a tidal lag of 0.3m between the water in front of the wall and the water in the ground behind the wall. Require - Depth of wall embedment, D Additional specifications provided after the workshop: 1 The surcharge is a variable load. 2 The wall is a permanent structure. 3 The length of the wall is to be the minimum allowable. 85

86 BP Example 7 Anchored sheet pile quay wall BENDING MOMENT knm/m Example 7 - Bending moments - not the end of the design b b b b N N b 1 1 N N b 1* N N N N b b N b 2 N N N c 1 N N N b A A D B C C C C C C:\BX\BX-C\EC7\Dublin\[Dublin-results (version 1).xls] 23-Jun-05 00:14 86

87 Eurocode 3, Part 5 BP87.78 BP Economies of up to 30% due to plastic design 87

88 BP BP The significance of yield in structural elements BP

89 BP Example 7 Anchored sheet pile quay wall Large range of results SSI important Optimise: length, BM, anchor force? Design doesn t end at the bending moment Nobody considered SLS 89

90 BP99.90 BP The wall must be 12m long. What tie force is required? BP

91 BP As a cantilever, length would be about 14m. BP BP

92 BP99.92 BP BP DA1 Comb 2 gives a tie force of 75kN 92

93 BP BP But characteristic calculation gives zero tie force, for 12m length. BP

94 EUROCODES Background and Applications EN1997-1: Anchorages and Retaining structures Brussels, February 2008 Dissemination of information workshop 94 EN Eurocode 7 Section 9 Retaining structures Fundamentals Design Approaches Slopes and walls all one problem Design Approaches matter! Main points in the code text Good basic check lists Values of K a and K p Overdig Not enough attention to SLS (by users, at least) Examples: Results broadly similar to existing practice DAs: big effect on gravity walls; small effect on embedded Lessons from the Dublin Workshop Very wide range of results Effect of DAs for gravity walls and K p for embedded Human error important partly offset by safety factors Need to work with EC3-5

95 EUROCODES Background and Applications EN1997-1: Anchorages and Retaining structures Brussels, February 2008 Dissemination of information workshop 95 EN Eurocode 7 Section 8 Anchorages Section 9 Retaining structures Brian Simpson Arup Geotechnics

Approaches to ULS design The merits of Design Approach 1 in Eurocode 7

ISGSR2007 First International Symposium on Geotechnical Safety & Risk Oct. 18~19, 2007 Shanghai Tongji University, China Approaches to ULS design The merits of Design Approach 1 in Eurocode 7 B. Simpson