Anchorages and Retaining Structures

EUROCODES Background and Applications

EN1997-1: Anchora Anchorage ges s and Reta taining ining structure structures s

Brussels, 18-20 February 2008 – Dissemination of information workshop

EN 1997-1 Eu r o c o d e 7 Section 8 – Anchora Anchorage ges s Secti ction on 9 – Reta taini ining ng struct str ucture ures s

Bria Br ian n Simp Simpson son Arr u p Geo A Geott ec ech hnics

1

EN 1997-1 Geot ote ech chni nica call de desi sign gn – Gene nera rall Rul ule es 1 Gen er al 2 B as i s o f g eo t ec h n i c al d es i g n 3 Geo t ec h n i c al d at a 4 Sup upe erv rvis isio ion n of o f con c onst stru ruct ctio ion, n, mo moni nito tori ring ng and ma main inte tena nanc nce e 5 Fill ill,, de dewa wate terin ring, g, gr grou ound nd im impr prov ove eme ment nt and re rein info forc rce eme ment nt 6 Sp r ead f o u n d at i o n s 7 Pi l e f o u n d at i o n s 8 An A n c h o r ag ages es 9 Ret ai n i n g s t r u c t u r es 10 Hy d r au l i c f ai l u r e 11 Ov er al l st s t ab i l i t y 12 Em b an k m en t s BP111.5

A

BP112.6

di

BP124-T1.31

At J

BP106.9

EN 1997-1 Geot ote ech chni nica call de desi sign gn – Gene nera rall Rul ule es 1 Gen er al 2 B as i s o f g eo t ec h n i c al d es i g n 3 Geo t ec h n i c al d at a 4 Sup upe erv rvis isio ion n of o f con c onst stru ruct ctio ion, n, mo moni nito tori ring ng and ma main inte tena nanc nce e 5 Fill ill,, de dewa wate terin ring, g, gr grou ound nd im impr prov ove eme ment nt and re rein info forc rce eme ment nt 6 Sp r ead f o u n d at i o n s 7 Pi l e f o u n d at i o n s 8 An A n c h o r ag ages es 9 Ret ai n i n g s t r u c t u r es 10 Hy d r au l i c f ai l u r e 11 Ov er al l st s t ab i l i t y 12 Em b an k m en t s BP111.5

A

BP112.6

di

BP124-T1.31

At J

BP106.9

8

A n c h o r ag es BP124-F3.6

8.1

Gen er al

8.2

L i m i t s t at es

8.3

Des i g n s i t u at i o n s an d ac t i o n s

8.4

Des i g n an d c o n s t r u c t i o n c o n s i d er at i o n s

8.5

Ul t i m at e l i m i t st s t at e d es i g n

8.6

Ser v i c eab i l i t y li l i m i t st s t at e d es i g n

8.7

Su i t ab i l i t y t es t s

8.8

A c c ep t an c e t es t s

8.9

Su p er v i s i o n an d m o n i t o r i n g

8

Anchorages • Section depends on EN1537 - 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.

EN1537:1999

EN1537:1999 Execution of special geotechnical work - Ground anchors

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

Partial factors in anchor design

Partial factors in anchor design


EN1997-1: Anchorages and Retaining structures


EN 1997-1 Eurocode 7 Section 8 – Anchorages Section 9 – Retaining structures

Brian Simpson Arup Geotechnics

16




EN 1997-1 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

17






18

Genting Highlands

BP87.59

BP 106.30

BP111.22

BP112.43

BP119.43

BP124-F3.9

BP130.33

BP145a.8

Genting Highlands

BP87.60

BP 106.31

BP111.23

BP112.44

BP119.44

BP124-F3.10

BP130.34

BP145a.9

FOS > 1 for characteristic soil strengths BP87.61

BP119.45

BP124-F3.11

BP106.32

BP111.24

BP130.35

BP145a.10

- but not big enough

BP112.45

The slope and retaining wall are all part of the same problem. BP119.46

BP87.62

BP106.33

BP124-F3.12

BP130.36

BP111.25

BP112.46

BP145a.11

Structure and soil must be designed together - consistently.

ISGSR2007 - 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






24

EN 1997-1 Geotechnical design – General Rules 1 2 3 4 5 6 7 8 9 10 11 12

BP106.9

BP111.5

BP112.6

General Basis of geotechnical design Geotechnical data Supervision of construction, monitoring and maintenance Fill, dewatering, ground improvement and reinforcement Spread foundations Pile foundations Anchorages Retaining structures Hydraulic failure Overall stability Embankments

Appendices A to J

BP124-T1.31

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

9.2 Limit states

9.2 Limit states

9.3.2 Geometrical data

9.3.2 Geometrical data

100%

10 %

100%

10 %

9.4 Design and construction considerations

9.4 Design and construction considerations

9.4.2 Drainage systems

9.5 Determination of earth pressures

9.5 Determination of earth pressures

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

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.

Wall friction

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

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, 8 617-619. • Covers range of adverse wall friction. • Slightly more conservative than Caquot & Kerisel when φ and δ/φ large – but more correct?

Ka, Kp charts in Simpson & Driscoll

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

Kp(C&K) / Kp(EC7) %

9.7 Ultimate limit state design

9.7.2 Overall stability

9.7.3 Foundation failure of gravity walls

9.7.4 Rot ota at io ional nal f ai lu lurr e of emb embe edd dde ed wall walls s

9.7.5 Ver ti tical cal fail failur ure e of emb embe edd dde ed wall walls s

9.7.6 Str truc uctur tura al design of reta retain ining ing struc str uctur ture es

9.7.6 Structural design of retaining structures

9.7.7 Failure by pull-out of anchorages

9.8 Serviceability limit state design

9.8.2 Displacements






52

8m propped wall

BP87.71

BP111.33

BP112.49

8m propped wall - data BP112.50

BP119.50

BP78.26

BP111.34

BP124-F3.15

CASE: Unplanned overdig (m)

DA1 DA1 -1 -2 0.5 0.5

EC7 SLS 0

Dig level: Stage 1

-8.5

-2.5

-8.5

Stage 2

-8.0

Characteristic φ' ( )

24

24

24

γ (or M) on tan φ'

1

1.25

1

Design φ'

24

19.6

24

δ'/φ' active

1

1

1

δ'/φ' passive

1

1

1

0.34

0.42

0.34

1

1

1

Design K a

0.34

0.42

0.34

K p

4.0

2.9

4.0

1

1

1

4.0

2.9

4.0

K a Factor on K a

Factor on K p Design K Excd. side

8m propped wall - length and BM BP111.35

BP112.51

BP119.51

BP78.28

BP124-F3.16


DA1 DA1 -1 -2 0.5 0.5

EC7 SLS 0

Design φ'

24

19.6

24

Design K a

0.34

0.42

0.34

Design K p Excd. side Retd. side γQ

4.0

2.9

1

1.3

4.0 1.0 1

Computer program

STW STW

Data file Wall length (m)

PROP11

Max bending moment (kNm/m)

PROP1

15.1 17.9 * * 1097 1519

Factor on bending moment

1.35

1

ULS design bending moment (kNm/m)

1481 1519

F BCAP3A

17.8 ** -236 +682 1 -236 +682

Redistribution of earth pressure BP119.52

BP124-F3.17

BP87.75

BP111.36

BP112.52

Compare CIRIA 104

BP87.2

BP111.54

BP112.54

BP119.53

BP124-F3.18

10kPa (13kPa) 0

-8m (-8.5m)

φ′ = 24° (19.6°)

0 .

630kN/m 0 0 0 . 4 -

t n e m o m g n i d n e B : 7 0 2 0 1 2 8 2 : 1 1

0 0 0 . 8 -

1 t n e m e r c n I 3 n u R 3 t n e v E c 7 0 b e F 5 p a c b x

0 . 0 0 4

0 0 . 2 1 -

) m 0 0 0 5 . 0 = x ( e t a n i d r o o c y

0 0 . 6 1 -

0 . 0 0 2

0 .

0 . 0 0 2 -

0 . 0 0 4 -

0 . 0 0 6 -

Bending moment [kNm/m]

0 . 0 0 8 -

. 0 0 0 1 -

. 0 0 2 1 -

1 8 6 3 1 : 1 y 1 0 1 : 0 1 x 0 . e 0 l 2 - a c S

8m propped wall - length and BM BP111.38

BP112.55

BP119.54

BP124-F3.19

CIRIA Fs

CIRIA Fs

0

0

BS DA1 DA1 8002 -1 -2 0.5 0.5 0.5

Design φ'

16.5

24

20.4

24

Design K a

0.49

0.36

0.41

Design K p Excd. side Retd. side γQ

2.1

3.4

1

Computer program Data file Wall length (m)


Max bending moment (kNm/m) Factor on bending moment ULS design bending moment (kNm/m)

BP78.32

EC7 SLS 0

DA1 -1 0.5

DA1 -2 0.5

DA1 -2 0.5

DA1 -2 0.5

19.6

24

24

19.6

19.6

19.6

0.34

0.42

0.34

0.34

0.42

0.42

2.8

4.0

2.9

4.0

1

1

1

1.3

4.0 1.0 1

2.9 1.0 1.3

2.9 1.0 1.3

STW

STW

STW

STW

STW

FREW FREW FREW FREW

PROP4

PROP5

PROP1

BCAP3A BCAPBA BCAP1A BCAP4A XBCAP5

20.4 ** 1870 ##

14.1 ** 776

17.9 15.1 17.9 * * * 1488 1097 1519

17.8 ** -236 +682

17.8 ** -241 838

17.8 ** 1359

17.8 ** -308 1158

17.8 ** -229 1131

1.5

1.0?

1.35

1

1.35

1

1

1

-236 +682

-325 1131

1359

-308 1158

-229 1131

PR1B-03 PROP11

1

1164 1488? 1481 1519

1

1.3 SAFE

8m excavation - comparison of methods BP111.39

BP112.56

BP119.55

BP124-F3.20

35 30 25

Leng th (m)

20

BM/50

15

Prop F/50

10 5 0

4 0

2 0

W

7 W

7 E F

BP78.34

Redistribution of earth pressure BP119.56

BP124-F3.21

BP87.75

BP111.36

BP112.52

German practice for sheet pile design - EAB (1996) BP119.57

BP124-F3.22

BP87.39

BP111.37

BP112.53

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.

2m

SAFE Grundbau2

BP116.24

BP119.58

BP124-F3.24

q=80kPa

3.32m k

=35°

22.4

γ= 17 kN/m3

8m

/ = 2/3 (active) Ka = 0.224 30.5 15.3

= 20 kN/m3 ? Weissenbach, A, Hettler, A and Simpson, B (2003) Stability of excavations. In Geotechnical Engineering

Grundbau in STAWAL

BP119.59

BP124-F3.25

Bending Moment [kNm /m ] -60 0 .0 2.000

-40 0 .0

-2 0 0 .0

.0

.0 .0

2 00.0

4 00 .0

6 00 .0

199.3kN/m

[1 ]

-2.000

-4.000 R e d u c e d L e v e l [ m ]

-6.000

.0 -8.000

.0

-8.000

[2]

[2]

-10.00

T oe -10.59m

-12.00

-14.00

Shear Moment Wa ter Pres sure Ac tua l Pr ess ures

-24 0 .0 -16 0 .0 -24 0 .0 -16 0 .0 Scale x 1:128 y 1:128

-8 0 .0 0 -8 0 .0 0

.0 .0

8 0.0 0 8 0.0 0

1 60 .0 1 60 .0

2 40 .0 2 40 .0

Grundbau: DA1 and DA2

XBP119.60

BP124-F3.26

400 350 300

L=10.7

L=10.6

250 Penetration cm 200

BM

kNm/m

Strut force kN/m 150 100 50 0 Char

DA1-1

DA1-2

DA2






68

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

BP130.1

Example 5 – Cantilever Gravity Retaining Wall Surcharge 15kPa

• 20

6m 0.4m

Fill

Design situation -

o

• •

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. o The ground behind the wall slopes upwards at 20

Soil conditions -

0.75m

BP130.2

o

Sand beneath wall: c' k = 0, φ'k = 34 , γ = 19kN/m 3 o Fill behind wall: c'k = 0, φ'k = 38 , γ = 20kN/m 3

Actions - Characteristic surcharge behind wall 15kPa

Sand

B=?

•

Require -

Width of wall foundation, B Design shear force, S and bending m oment, M in the w all

Example 5

BP130.3

Surcharge 15kPa

20o

6m

Fill

20o

0.4m

Ka z 0.75m

Sand

B=?

Example 5

BP130.4

Surcharge 15kPa

20o

6m

Fill

20o

0.4m

Ka z 0.75m

Sand

B=?

Example 5 – Cantilever Gravity Retaining Wall Examp le 5 - Gravity wall 6.0 5.0

1 b

1

1=3

N N

N

m

2 N

4.0

H T D I 3.0 W E S 2.0 A B

3 N

1

3

1 N

1

N 2

2=N

2 b b

2 N

1 , 2 or 3 – EC7 DA1, DA2 or DA3 b – EC7 DA1 Comb 1 only

1.0

N – national method 0.0 0

0

1

1

1

2

2

C:\BX\BX-C\EC7\Dublin\ Dublin-results.xls

2

2

2

3

3

3

5

5

5

8

8 16 16 17

G

C

C

Contributor

C

C

C

C

C

BP130.5

Example 5 – Cantilever Gravity Retaining Wall •

Surcharge 15kPa

• 6m

Fill 0.4m

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. o The ground behind the wall slopes upwards at 20

Soil conditions -

-

•

B P 14 2A. 6 .1

Design situation -

20o

B P 1 3 0 2.

o

Sand beneath wall: c'k = 0, φ'k = 34 , γ = 19kN/m 3 o Fill behind wall: c'k = 0, φ'k = 38 , γ = 20kN/m 3

Actions - Characteristic surcharge behind wall 15kPa

0.75m

• Sand

B=?

Require -

Width of wall foundation, B Design shear force, S and bending mom ent, M in the wa ll

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).

Example 5 – Cantilever Gravity Retaining Wall

BP124.A6.12

Examp le 5 - Gravity w all 6.0 5.0

1 b

1

1=3

N N

N

m

N

2 N

4.0

3 N

1

H T D I 3.0 W E S 2.0 A B

3

1

1

N 2

2=N

2 b b

2 N

1.0 0.0 0

0

1

1

1

2

2

2

2

2

3

3

3

5

5

5

8

8

16 16 17

E

C

C

C

C

C

C

C


E

E{

F

Frep ; Xk /

M;

ad } = Ed

Rd = R{

F

Frep ; Xk /

M;

ad }/

R

BP130.5

Example 5 – Cantilever Gravity Retaining Wall Column no. Base width

1

2

3

4

5

3.75

3.75

3.75

3.75

3.75

Column no. 1

Column no. 2 Eccentricity (m)

0.57

0.57

0.57

0.79

0.79

Effective width B' (m)

2.61

2.61

2.61

2.17

2.17 Column no. 3

Vertical force kN/m

690

941

690

941

690

Horizontal force kN/m

207

285

285

285

285

0.30

0.30

0.41

See note

0.41

Inclination H/V

R (kN/m)

1392

1373

879

659

659

1

1.4

1.4

1.4

1.4

Rd (kN/m)

1392

981

628

471

471

Rd/Vd

2.02

1.04

0.91

0.50

0.68

γ(R)

Column no. 4

Column no. 5

BP130.5

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. Unfavourable (horizontal) force and resistance factored. Favourable (vertical) force not factored in deriving inclination or eccentricity, or for comparison with resistance.


BP124.A6.12

Examp le 5 - Gravity w all .

1200

m1000 / m N k

1

800

T N E 600 M O M 400 G N I D 200 N E B

1

1=3 b

N N 2

1

2=N N N

N

0

b b 1 2

3

2 0

0

1

1

1

2

2

2

2

2

3

3

3

5

5

5

8

8 16 16 17

G

C

C

C

C

C

C

C


BP124.A6.14

Exam pl e 5 - Gravity w all 300

.

2=N 1

250

m / N k 200 E C 150 R O F R 100 A E H 50 S

1

N

b b b

1

1 2

3

N N

N N

0

2 0

0

1

1

1

2

2

2

2

2

3

3

3

5

5

5

8

8 16 16 17

E

C

C

C

C

C

C

C


BP130.8

• Serviceability: – – – –

No criteria in the instructions Mainly ignored ½(Ka + K0) ? 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

Example 6 – Embedded sheet pile retaining wall •

10kPa

1.5m 3.0m

•

BP130.9

Design situation - Embedded sheet pile retaining wall for a 3m deep excavation with a 10kPa surcharge on the surface behind the w all 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 mom ent in the wall, M

Sand D= ?

Example 6 – Embedded sheet pile retaining wall •

10kPa

• 1.5m

Sand

Design situation - Embedded sheet pile retaining wall for a 3m deep excavation with a 10kPa surcharge on the surface behind the wall Soil conditions o 3 Sand: c'k = 0, φ'k = 37 , γ = 20kN/m

-

•

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

3.0m

BP130.9

D= ?

Additional specifications provided after the workshop: 1 The surcharge is a variable load. 2 The wall is a permanent structure.

Example 6 – Embedded sheet pile retaining wall • Huge range of results • Values of Kp ? •

C&K / EC7 / Coulomb ??

• What about overdig? • 2.4.7.1(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.

Kp(C&K) / Kp(EC7) %

BP130.14

Example 7 – Anchored sheet pile quay wall 10kPa

1.5m

Tie bar anchor

•

Design situation - Anchored sheet pile retaining wall for an 8m high quay using a horizontal tie bar anchor.

•

Soil conditions o - Gravelly sand - φ'k = 35 , γ = 18kN/m3 (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 - De th of wall embedment D

8,0m

GWL

Water 3.3m

Sand

3.0m

D=?

BP130.16

Example 7 – Anchored sheet pile quay wall 10kPa

•

Design situation - Anchored sheet pile retaining wall for an 8m high quay using a horizontal tie bar anchor.

•

Soil conditions o - Gravelly sand - φ'k = 35 , γ = 18kN/m3 3 (above water table) and 20kN/m (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 - De th of wall embedment D

1.5m

Tie bar anchor

8,0m

GWL

Water 3.3m

Sand

3.0m

D=?

BP130.16

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

Example 7 – Anchored sheet pile quay wall

BP130.23

Examp le 7 - B end ing m om ents . 600 m / m500 N k T 400 N E M300 O M200 G N I D 100 N E B 0

- not the end of the design 1

2

3 b

2 1

b

b

N

b N

1

1

3

3 3

3

1

3 2

b N

1 1 b

1*

N

N b

b

b

N

N c 1 N N b

N

N N

2 N N

0 0 0 0 0 0 0 A A 2 2 2 2 2 2 3 3 3 3 5 5 5 7 7 7 7 8 9 D 12121213141616 B C C C C C

N

1515151515

Eurocode 3, Part 5 BP87.78

BP130.26

Economies of up to 30% due to plastic design

The significance of yield in structural elements

BP114.32

BP116.50

BP130.27

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

BP130.28

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

BP130.37

BP87.114

As a cantilever, length would be about 14m. BP130.38

BP87.115

91

BP99.

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

BP130.39

BP87.116

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

BP99.

BP130.40

BP87.117





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 Ka and Kp 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 Kp for embedded Human error important – partly offset by safety factors

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Anchorages and Retaining Structures

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