Transcript

www.aarsleff.comNOM Oct 2015 1

DGF møde, 29.10.2015 i Øst, DTU, Kgs. Lyngby

Geoteknikerens hverdag

Multi anchored sheet pile wall in soft clay standing on rock

by

Kristoffer Lauridsen, COWI

Carsten S. Sørensen, COWI

Søren Juel Christensen, Aarsleff

Ole Møller, Aarsleff

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Multi anchored sheet pile wall in soft clay standing on rock

Scope

1. To compare design approaches (DAs) and partial coefficients

of the Nordic countries (on the agenda for NMGEC7 meeting

in Reykjavik on 21-22nd August 2015)

2. To evaluate different modelling and effect of prestress of

anchors

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Multi anchored sheet pile wall in soft clay standing on rock

Agenda

• ULS analysis with LEM

fixed support

elastic support without pre-stress

elastic support with pre-stress

• ULS analysis with FEM

with pre-stress

• SLS analysis with FEM

with pre-stress

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Multi anchored sheet pile wall in soft clay standing on rock

Comparison of DAs and partial coefficients

Parameters for LEM analysis

Fill: rough wall

/’ = 18/10 kN/m3

’ = 35

Soft clay: smooth wall

’ = 6 kN/m3

cu = 7 kN/m2 + 1,2 kN/m2 x z

= 0

Till: rough wall

/’ = 10 kN/m3

’ = 38

Hydrostatic water pressure

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Multi anchored sheet pile wall in soft clay standing on rock

Comparison of DAs and partial coefficients

NMGEC7 - meeting Reykjavik 2015 Encl. 1

Retaining wall ULS - LEM earth pressure calculation

DA3 DK NA, LC4

Parameter c' cu G Q

Partial coefficient 1,2 1,2 1,8 1,0 1,5

Id Soil level depth, z ' 'k 'd rough

[m] [m] [kN/m3] [ ] [ ] k K(k) Kp(k) Kc(k)

1 Fill 0,0 0,0 18 -35 -30,3 1,0 0,26 0,27 1,25

1 Fill -2,0 2,0 18 -35 -30,3 1,0 0,26 0,27 1,25

2 Soft clay -2,0 2,0 6 0 0,0 0,0 1,00 1,00 2,00

2 Soft clay -9,0 9,0 6 0 0,0 0,0 1,00 1,00 2,00

3 Till -9,0 9,0 10 -38 -33,1 1,0 0,23 0,24 1,17

3 Till -10,0 10,0 10 -38 -33,1 1,0 0,23 0,24 1,17

Soil parameters, M

Earth pressure coefficients

Actions, F

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Multi anchored sheet pile wall in soft clay standing on rock

Comparison of DAs and partial coefficients

NMGEC7 - meeting Reykjavik 2015

Retaining wall ULS - LEM earth pressure calculationC:\Users\nom\Desktop\NMGEC7\[Nordic LEM earth pressure.xlsx]DK DA3 LC4

DA3 DK NA, LC4

Parameter c' cu G Q surface load, pk = 10 kN/m2

Partial coefficient 1,2 1,2 1,8 1,0 1,5

Id Soil level depth, z ' 'k 'd c'k c'd cuk cud u s'vd pd ed ed + u

[m] [m] [kN/m3] [ ] [ ] [kN/m2] [kN/m2] [kN/m2] [kN/m2] [kN/m2] [kN/m2] [kN/m2] [kN/m2] [kN/m2]

1 Fill 0,0 0,0 18 -35 -30,3 0 0,0 0 0 15 4,05 4,05

1 Fill -2,0 2,0 18 -35 -30,3 0 0,0 0 0 36 15 13,52 13,52

2 Soft clay -2,0 2,0 6 0 0,0 0 0,0 7,0 3,9 0 36 15 43,22 43,22

2 Soft clay -9,0 9,0 6 0 0,0 0 0,0 15,4 8,6 70 78 15 75,89 145,89

3 Till -9,0 9,0 10 -38 -33,1 10 8,3 0 70 78 15 11,83 81,83

3 Till -10,0 10,0 10 -38 -33,1 10 8,3 0 80 88 15 14,14 94,14

Soil parameters, M Actions, F

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Multi anchored sheet pile wall in soft clay standing on rock

Comparison of DAs and partial coefficients

Total earth- and water pressure = 767 kN/m

by DK NA, LC 4

-10,0

-9,0

-8,0

-7,0

-6,0

-5,0

-4,0

-3,0

-2,0

-1,0

0,0

0 50 100 150 200

[kN/m2]

LEM earth + water pressure

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Multi anchored sheet pile wall in soft clay standing on rock

Structural analysis of wall … and anchors

• ULS analysis with LEM

fixed support

elastic support without pre-stress

elastic support with pre-stress

• AZ 50

I = 121.060 cm4/m, g = 253 kg/m2

Wel = 5015 cm3/m

Wpl = 5816 cm3/m

• AZ 19-700

I = 39.380 cm4/m, g = 114 kg/m2

Wel = 1870 cm3/m

Wpl = 2206 cm3/m

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Multi anchored sheet pile wall in soft clay standing on rock

Structural analysis of wall … and anchors

Spring constant of anchors: LL

EAN

L

LE

A

NE

s

per anchor per meter horizontal

Id Level c Ø0,62" A EA v L EA/L EA/L/c EA/L/c x cos(v)

Unit [m] [m] n [mm2] [kN] [ ] [m] [kN/mm] [kN/mm/m] [kN/mm/m]

Upper -1,0 3,5 6 900 189.000 45 12,73 14,85 4,24 3,00

Mid -3,5 3,5 6 900 189.000 45 9,19 20,56 5,87 4,15

Lower -7,0 2,4 7 1050 220.500 45 4,24 51,97 21,66 15,31

Note

c horizontal distance between anchors

n number of Ø0,62" strands, each with 150 mm2 cross sectional area

E = 210.000 N/mm2

v inclination to horizontal

L axial length from anchor point at sheet pile wall down to top of rock at level -10

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Multi anchored sheet pile wall in soft clay standing on rock

Structural analysis of wall … and anchors

Capacity of anchors and max. proof load Pp

axial per axial per horizontal

Id Level c Ø0,62" Nyk Nuk anchor meter per meter

Unit [m] [m] n [kN] [kN] [kN] [kN/m] [kN/m]

Upper -1,0 3,5 6 1494 1674 1339 383 271

Mid -3,5 3,5 6 1494 1674 1339 383 271

Lower -7,0 2,4 7 1743 1953 1562 651 460

Note

fyk 1660 MPa yield stress

fuk 1860 MPa tensile strength

Pp proof load ≤ min {0,8 fuk; 0,95 fyk) x A

Structural strength

Characteristic

Max possible Proof load Pp

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Multi anchored sheet pile wall in soft clay standing on rock

LEM: a) stiff support

-40

-35

-30

-25

-20

-15

-10

-5

0

5

10

0,0 1,0 2,0 3,0 4,0 5,0 6,0 7,0 8,0 9,0 10,0

mm Deflection

a) AZ50, stiff support

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Multi anchored sheet pile wall in soft clay standing on rock

LEM: a) stiff support

-150

-100

-50

0

50

100

150

200

250

300

350

0,0 1,0 2,0 3,0 4,0 5,0 6,0 7,0 8,0 9,0 10,0

kNm/m Bending moment

a) Stiff support

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Multi anchored sheet pile wall in soft clay standing on rock

LEM: b) elastic support, AZ50, no pre-stress

-40

-35

-30

-25

-20

-15

-10

-5

0

5

10

0,0 1,0 2,0 3,0 4,0 5,0 6,0 7,0 8,0 9,0 10,0

mm Deflection

a) AZ50, stiff support

b) AZ50 no PS

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Multi anchored sheet pile wall in soft clay standing on rock

LEM: b) elastic support, AZ50, no pre-stress

-150

-100

-50

0

50

100

150

200

250

300

350

0,0 1,0 2,0 3,0 4,0 5,0 6,0 7,0 8,0 9,0 10,0

kNm/m Bending moment

a) Stiff support

b) AZ50 no PS

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Multi anchored sheet pile wall in soft clay standing on rock

LEM: c1) Finish pre-stress, AZ50

-40

-35

-30

-25

-20

-15

-10

-5

0

5

10

0,0 1,0 2,0 3,0 4,0 5,0 6,0 7,0 8,0 9,0 10,0

mm Deflection

a) AZ50, stiff support

b) AZ50 no PS

c1) AZ50 Fin PS

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Multi anchored sheet pile wall in soft clay standing on rock

LEM: c1) Finish pre-stress, AZ50

-150

-100

-50

0

50

100

150

200

250

300

350

0,0 1,0 2,0 3,0 4,0 5,0 6,0 7,0 8,0 9,0 10,0

kNm/m Bending moment

a) Stiff support

b) AZ50 no PS

c1) AZ50 Fin PS

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Multi anchored sheet pile wall in soft clay standing on rock

LEM: c2) Finish pre-stress, AZ19-700

-40

-35

-30

-25

-20

-15

-10

-5

0

5

10

0,0 1,0 2,0 3,0 4,0 5,0 6,0 7,0 8,0 9,0 10,0

mm Deflection

a) AZ50, stiff support

b) AZ50 no PS

c1) AZ50 Fin PS

c2) AZ19 FIn PS

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Multi anchored sheet pile wall in soft clay standing on rock

LEM: c2) Finish pre-stress, AZ19-700

-150

-100

-50

0

50

100

150

200

250

300

350

0,0 1,0 2,0 3,0 4,0 5,0 6,0 7,0 8,0 9,0 10,0

kNm/m Bending moment

a) Stiff support

b) AZ50 no PS

c1) AZ50 Fin PS

c2) AZ19 FIn PS

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Multi anchored sheet pile wall in soft clay standing on rock

LEM: d) DK pre-stress, AZ19-700

-40

-35

-30

-25

-20

-15

-10

-5

0

5

10

0,0 1,0 2,0 3,0 4,0 5,0 6,0 7,0 8,0 9,0 10,0

mm Deflection

a) AZ50, stiff support

b) AZ50 no PS

c1) AZ50 Fin PS

c2) AZ19 FIn PS

d) AZ19 DK PS

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Multi anchored sheet pile wall in soft clay standing on rock

LEM: d) DK pre-stress, AZ19-700

-150

-100

-50

0

50

100

150

200

250

300

350

0,0 1,0 2,0 3,0 4,0 5,0 6,0 7,0 8,0 9,0 10,0

kNm/m Bending moment

a) Stiff support

b) AZ50 no PS

c1) AZ50 Fin PS

c2) AZ19 FIn PS

d) AZ19 DK PS

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Multi anchored sheet pile wall in soft clay standing on rock

LEM: Anchor loads, horizontal

Anchor / support A1 A2 A3 Rock bolt Total

Level -1,0 -3,5 -7,0 -10,0

Unit kN/m kN/m kN/m kN/m kN/m

a) stiff, FULS,d 17 206 422 123 768

b) AZ50, no PS, FULS,d 107 135 305 220 767

c1) AZ50, Fin PS, P0 81 101 162 344

c1) AZ50, Fin PS, FULS,d 99 145 308 215 767

c1) AZ50, Fin PS, FULS,d/P0 1,22 1,44 1,90

c2) AZ19, Fin PS, P0 81 101 162 344

c2) AZ19, Fin PS, FULS,d 76 149 369 174 768

c2) AZ19, Fin PS, FULS,d / P0 0,94 1,48 2,28

d) AZ19, DK PS, P0 60 100 100 260

d) AZ19, DK PS, FULS,d 71 165 350 182 768

d) AZ19, DK PS, FULS,d / P0 1,18 1,65 3,50

Max Pp (horizontal) 271 271 460

RGEO ,d = Max Pp / 1,3 = 208 208 354

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Multi anchored sheet pile wall in soft clay standing on rock

LEM: Anchor loads, horizontal

0 100 200 300 400 500

a) stiff, FULS,d

b) AZ50, no PS, FULS,d

c1) AZ50, Fin PS, FULS,d

c2) AZ19, Fin PS, FULS,d

d) AZ19, DK PS, FULS,d

kN/m

Final load on anchors and rock bolts

A1 (-1,0)

A2 (-3,5)

A3 (-7,0)

Rock bolts (-10,0)

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Multi anchored sheet pile wall in soft clay standing on rock

LEM: Anchor loads, axial + rock bolt

Anchor / support A1 A2 A3 Rock bolt

Level -1,0 -3,5 -7,0 -10,0

c-c (m) 3,5 3,5 2,4 1,0

Inclination, v ( ) 45,0 45,0 45,0 0,0

Unit kN kN kN kN

a) stiff, FULS,d 84 1020 1432 123

b) AZ50, no PS, FULS,d 530 668 1035 220

c1) AZ50, Fin PS, P0 401 500 550

c1) AZ50, Fin PS, FULS,d 490 718 1045 215

c1) AZ50, Fin PS, FULS,d/P0 1,22 1,44 1,90

c2) AZ19, Fin PS, P0 401 500 550

c2) AZ19, Fin PS, FULS,d 376 738 1252 174

c2) AZ19, Fin PS, FULS,d / P0 0,94 1,48 2,28

d) AZ19, DK PS, P0 297 495 339

d) AZ19, DK PS, FULS,d 351 817 1188 182

d) AZ19, DK PS, FULS,d / P0 1,18 1,65 3,50

Max Pp 1339 1339 1562

RGEO ,d = Max Pp / 1,3 = 1030 1030 1202

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Multi anchored sheet pile wall in soft clay standing on rock

LEM: Anchor loads, axial

0 200 400 600 800 1000 1200 1400 1600

a) stiff, FULS,d

b) AZ50, no PS, FULS,d

c1) AZ50, Fin PS, FULS,d

c2) AZ19, Fin PS, FULS,d

d) AZ19, DK PS, FULS,d

kN

Final load on anchors and rock bolts

A1 (-1,0)

A2 (-3,5)

A3 (-7,0)

Rock bolts (-10,0)

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Multi anchored sheet pile wall in soft clay standing on rock

LEM vs FEM

LEM: Limit Equilibrium Method

Influence of ration of stiffness between wall and anchors (no stiff support)

No soil-structure interaction, constant plastic earth pressure

FEM: Finite Element Method

compatibility between strains and stresses in the soil

elasto-plastic soil structure interaction

Plaxis vs. NovaPoint Geocalc? MC model?

modelling of rock bolt support

ULS with pre-stress? AZ50 vs. AZ19-700 ?

SLS with pre-stress? Final anchor loads (FServ;k vs. FULS;d c.f. new Ch. 8)

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Multi anchored sheet pile wall in soft clay standing on rock

FEM

The FEM model:

Finland uses NovaPoint Geocalc computer programme

)1(

1

' nk

n

a

va OCRmM

s

ss

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Multi anchored sheet pile wall in soft clay standing on rock

FEM

The FEM model:

In the Plaxis model a Mohr-coulomb material model was utilized, with a

depth(stress) depended stiffness and strength.

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Multi anchored sheet pile wall in soft clay standing on rock

FEM

The calculation phases:

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Multi anchored sheet pile wall in soft clay standing on rock

FEM

Modelling of the rock bolt:

Several approaches where tested:

best approach: to applied a fixity at the foot of the sheet pile wall

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Multi anchored sheet pile wall in soft clay standing on rock

FEM ULS

A1: 910kN/anchor

A2: N/A

A3: N/A

A1: 901kN/anchor

A2: 675kN/anchor

A3: N/A

A1: 861kN/anchor

A2: 598 kN/anchor

A3: 545 kN/anchor

Calculated ULS LK4 anchor forces:

c1) AZ50 with Finish prestress

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Multi anchored sheet pile wall in soft clay standing on rock

FEM ULS

Bending moment during excavation

-12

-10

-8

-6

-4

-2

0

-100 0 100 200 300 400 500 600 700

DEPT

H [

M]

BENDINGMOMENT

[KNM/M]

1. excav

2. excav

3. excav

Final excavation

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Multi anchored sheet pile wall in soft clay standing on rock

Comparison between LEM and FEM results

AZ 50 with Finish prestress, final stage

axial anchor loads

horizontal (shear) force on rock bolt

Pre-stress P0

LEM ULS FEM ULS FEM SLS

A1 401 400 400

A2 500 500 500

A3 550 550 550

Rockbolt 0 kN/m 0 kN/m 0 kN/m

Final Anchor Loads Pa

LEM ULS FEM ULS FEM SLS

A1 490 861 663

A2 718 598 620

A3 1045 545 562

Rockbolt 215 kN/m 433 kN/m 319 kN/m

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Multi anchored sheet pile wall in soft clay standing on rock

Comparison between LEM and FEM results

Bending moment at the final stage (AZ50 with Finish pre-stress)

-12

-10

-8

-6

-4

-2

00 100 200 300 400 500 600

Depth

[m

]

[kNm/m]

FEM ULS

LEM ULS

SLS FEM

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Multi anchored sheet pile wall in soft clay standing on rock

FEM

Deformations during excavation

-12

-10

-8

-6

-4

-2

00,00 0,01 0,02 0,03 0,04 0,05 0,06 0,07

Depth

[m

]

Displacement [m]

1. excav

2. excav

3. excav

Final excav

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Multi anchored sheet pile wall in soft clay standing on rock

Findings

• Big effect of pre-stress on deformation by LEM, not by FEM

• Effects of very soft clay, near failure during excavations by FEM

• Bending moments by FEM twice the moments by LEM

• Adverse tendency of anchor loads by LEM compared to FEM

Max at the bottom by LEM. Max at the top by FEM.

The reason for this is:

in spite of the relatively stiff (short) lower anchors, the effect of staged

construction by FEM and the wall rotating (~ rigid) around the foot (fixed by

the rock bolt) leads to bigger upper anchor loads and

the LEM is only carried out for the final stage with no superposed section

forces (pre bending) from previous stages.

• FEM: SLS anchor loads > ULS anchor loads for mid and lower anchors