Sheet Pile Walls - · PDF file · 2012-12-16determine forces acting on SPW. ... Anchored Sheet Pile Walls Faculty of Engineering Cairo University Sheet Pile Walls Design: Cohesionless

Sheet Pile WallsSheet Pile Walls

By

Dr. Ashraf Kamal Hussein

Professor of Geotechnical Engineering and Foundations

Faculty of Engineering - Cairo University

2012

1. Introduction1. Introduction

- Same purpose as retaining walls.

Faculty of Engineering

Cairo University

Sheet Pile Walls

- Commonly used as:

● Temporary structures to facilitate excavation and dewatering of limited

area.

● Water front structures.

2. Types of Sheet Pile Walls2. Types of Sheet Pile Walls

● Cantilever


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Sheet Pile Walls

● Anchored

● Strutted

Cantilever SPW Anchored SPW Strutted SPW



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Sheet Pile Walls

Materials:

● Timber: (shallow excavations)

● Precast reinforced concrete

● Steel



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Sheet Pile Walls

- Steel SPW is the most common type since:

● it resists high driving stresses.

● it is of relatively light weight.

● it can be reused several times.

● it is more durable.

● it is easy to increase its length by welding or bolting.

Typical Shapes:

3. Cantilever Sheet Pile Walls3. Cantilever Sheet Pile Walls


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Sheet Pile Walls

Stability:

- from passive resistance.

t

H

Excavation Height:

- H < 7 m

Design Steps:

● determine forces acting on SPW.

● determine penetration depth (t).

● determine Mmax and section modulus.



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Sheet Pile Walls

Design:

- Forces

- Simplification

t

H

Ea

Ep

OC

M

t

H

Ea

Ep

EpEa

O



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Sheet Pile Walls

Design: Cohesionless Soils

- Penetration Depth

- ∑Mo = 0

neglect ∆M � Ea ya – Ep yp = 0

� get D

� t = 1.2D

H

t

Ea

Ep

O C

∆∆∆∆M

γγγγ

φφφφ

D



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Sheet Pile Walls


- Maximum Moment

- Mmax @ pt of zero shear (n)

� Eay = Epy

� get y

� M at pt (n) = Mmax

Sec. Modulus: Z = Mmax/σy

H

t

Eay

Epy

n

γγγγ

φφφφ

y Mmax



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Sheet Pile Walls


- Penetration Depth

- at distance u: zero pressure

� eau = epu

γ Ka (H + u) = γ Kp u � get u

- epn = γ x (Kp – Ka)

- ∑Mo = 0

neglect ∆M � ∑Ea ya – Ep yp = 0

� get x

� t = 1.2(u + x)

Net Earth Pressure

H

t

Ea1

Ep

O C

∆∆∆∆M

γγγγ

φφφφ

u

x

epn

O

Ea2



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Sheet Pile Walls


- Maximum Moment


� ∑Ea = Epy

� get y



Net Earth Pressure

nMmax

H

t

Ea1

Epy

O

γγγγ

φφφφ

y

epn

Ea2



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Sheet Pile Walls


- Effect of GWT

H

t

Ea

Ep

O C

∆∆∆∆M

γγγγ

φφφφ

D

Ew1

GWT

Ew2

GWT



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Sheet Pile Walls

Design: Cohesive Soils

- ea = γ H – 2cu

- epn = 4cu – γ H

H

t

Ea

Ep

O O

γγγγcu

D

ea

zo

epnLimiting Height:

- HL < (4cu – q)/γ

Short Term Analysis �� cu, φφφφ = 0

4. Anchored Sheet Pile Walls4. Anchored Sheet Pile Walls


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Sheet Pile Walls

Stability:

- from passive resistance and

tension in anchor rods.

Effect of Anchors:

● reduces lateral deflection.

● reduces penetration depth.

● reduces bending moments.

t

H

Methods of Design:

● free earth support.

● fixed earth support.



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Sheet Pile Walls

t

H

Mmax

Free

t

H

Mmax

Fixed

Conditions of Free and Fixed Earth Support



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Sheet Pile Walls

Conditions of Free and Fixed Earth Support

- Soil type

- Penetration depth

- Section

Free

compressible soil (loose sand, clay)

relatively short

relatively stiff

Fixed

strong soil (φ > 32o)

greater depth

flexible



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Sheet Pile Walls

t

H

Design Steps:

● determine forces acting on SPW.

● determine penetration depth (t).

● determine forces in anchor rod.

● determine Mmax and section modulus.

● design anchor rod and anchor plate.



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Sheet Pile Walls


1- Forces

Free Earth Support:

Net Earth Pressure

H

t

Ea1

Ep O

γγγγ

φφφφ

u

x

epn

a

Ea2

H

t

Ea

Ep

a γγγγ

φφφφ



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Sheet Pile Walls


2- Penetration Depth

Free Earth Support:

H

t

Ea

Ep

a γγγγ

φφφφ

- ∑Ma = 0 � Ea ya – Ep yp = 0

� get D

� t = D



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Sheet Pile Walls



Free Earth Support:

Net Earth Pressure

H

t

Ea1

Ep O

γγγγ

φφφφ

u

x

epn

a

Ea2

- ∑Ma = 0 � ∑Ea ya – Ep yp = 0

� get x

� t = u + x

Net Earth Pressure



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Sheet Pile Walls


3- Force in Tie Rod

Free Earth Support:

- ∑X = 0 � A = Ea – Ep t/m

force in each tie rod:

T = A.S ton

as S = spacing between rods (2 to 4 m)

H

t

Ea

Ep

a γγγγ

φφφφ

A



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Sheet Pile Walls


4- Maximum Moment

Free Earth Support:


(n) lies above L.G.L.

� A = Eay � get y



n

A

t

H

Mmax

yEay



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Sheet Pile Walls


1- Forces

Fixed Earth Support:

H

t

Ea

Ep

Ep

Ea

OC

Ea

Ep

∆∆∆∆M

Net Earth Pressure

Ep

OC

Ea1

∆∆∆∆M

Ea2



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Sheet Pile Walls


1- Forces


Mmax

N

H

tu

x

OC

Ea2

Ep

∆∆∆∆M

Ea1

b

Assumptions:

● Point of zero B.M. (N) is point of zero loading (b).

● Virtual hinge is at point of zero loading (b).



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Sheet Pile Walls




- For upper beam:

at distance u: zero pressure

� eau = epu

γ Ka (H + u) = γ Kp u � get u

∑Ma = 0

� ∑Ea ya – R( H + u – d) = 0 � get R

- For lower beam:

for equilibrium with Ep

� reaction at O should be 2R

�3R = Ep = γ x2 (Kp– Ka)/2 � get x

� t = u + 1.2x

x

Oepn

Ep

b R

2R

R

H

uEa2

Ea1

b

Aa

d



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Sheet Pile Walls



H

uR

Ea2

Ea1

b

Aa

3- Force in Tie Rod

- For upper beam:

∑X = 0 � A = ∑Ea – R t/m

force in each tie rod:

T = A.S ton

as S = spacing between rods (2 to 4 m)



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Sheet Pile Walls



4- Maximum Moment

- For upper beam:


(n) lies above L.G.L.

� A = Eay � get y



H

uR

Ea2

Eay

b

Aa

Mmax

y

n



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Sheet Pile Walls


5- Design of Wales

- Transfer horizontal reaction from S.P.W. to

tie rods.

M = A.S2/10

Two channels:

Sec. Modulus: Z = Mmax/2σy



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Sheet Pile Walls


6- Design of Anchor Rod

- Area of rod:

area = T / σy

as T = A.S

area = π d2/4

A



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Sheet Pile Walls


7- Design of Anchor Plate

- Continuous Plate:

t2 < t1/3

KFS

K

2

tA a

p21

appossib )−(γ

==Ε−Ε=

as FS = 1.5

For equilibrium � d = 2/3 t1 � t1 = 1.5 d

Aexist < Apossib if not increase d

ep

t2

ea

t1d

A



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Sheet Pile Walls



- Continuous Plate:

for small anchor forces

KFS

K d

A

KFS

K de

a

p

exist

a

p

d

)−(γ

=Β

)−(γ=

plate of thickness t as t

6

12

t

2

t

yM

t.m/m8

M

23y

max

=Μ

=Μ

=Ι

=σ

ΒΑ=

ed ea

Bd

A



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Sheet Pile Walls



- Isolated Plate:

KFS

K d

T.L

a

p)−(γ

=Βed ea

Bd

T



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Sheet Pile Walls


8- Length of Anchor Rod

- Zone I � active zone � dangerous

t

H

45+φ/2

45–φ/2

φ

(I)(II)

(III)

(IV)

- Zone II � transition zone � capacity reduced

- Zone III � transition zone � capacity reduced

- Zone IV � passive zone � full capacity

5. Strutted Sheet Pile Walls5. Strutted Sheet Pile Walls


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Sheet Pile Walls

Types:

● Soldier Beams:

- Soldier beams: vertical steel or

timber beams driven into

ground before excavation.

- Laggings: horizontal timber

planks are placed between

soldier beams as excavation

proceeds.

- Wales and Struts: horizontal

steel beams are installed when

excavation reaches desired

depth.



Cairo University

Sheet Pile Walls

Types:

● Sheet Piles:

- Sheet piles: (steel, concrete, or

timber) driven into ground

before excavation.

- Wales and Struts: inserted

immediately after excavation

reaches desired depth.



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Sheet Pile Walls

Types:

- timber lagging, steel

wales, and timber



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Sheet Pile Walls

Lateral Earth Pressure:

- Braced cut shows different type of

wall yielding where deformation of

wall gradually increases with depth.

Retaining WallStrutted SPW

- Deformation depends on:

● type of soil.

● depth of excavation.

● workmanship.

● strutting configuration.

● construction sequence.

● relative flexibility of wall.



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Sheet Pile Walls


- at top � very little wall yielding �

close to at rest E.P.

- at bottom �larger yielding � much

lower than Rankine active E.P.

Retaining WallStrutted SPW

� Distribution of E.P. in strutted SPW varies substantially

compared to the linear distribution in R.W.

� E.P. distribution cannot be predicted from theory.

- Field measurements show that E.P. does not follow same laws

(Rankine or Coulomb).

� Apparent E.P. Envelopes



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Sheet Pile Walls


Cohesionless Soils:

ea = 0.8 (γ H + q) Ka

as Ka = Rankine active E.P. coefficient

In case of GWT:

- take hydrostatic water pressure (triangular distribution), E.P. with γγγγsub

Loose: φφφφ < 32o

H

0.2H

0.8H

ea ew

� Ea = 1.44 Ea(Rankine)

as Ea(Rankine) = γ H2Ka/2



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Sheet Pile Walls


Cohesionless Soils:

ea = 0.8 (γ H + q) Ka

as Ka = Rankine active E.P. coefficient

In case of GWT:

- take hydrostatic water pressure (triangular distribution), E.P. with γγγγsub

Dense:

ew

� Ea = 1.28 Ea(Rankine)

as Ea(Rankine) = γ H2Ka/2

H

0.2H

0.6H

0.2Hea



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Sheet Pile Walls


Cohesive Soils:

ea = (γ H + q) – m (4cu)

m depends on soil below F.L.

m = 1.0 if stiff layer below F.L.

m = 0.4 if no stiff layer below F.L.

Soft to Medium Stiff Clay:

Ns = γ Η / γ Η / γ Η / γ Η / cu > 4

H

0.25H

0.75H

ea




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Sheet Pile Walls


Cohesive Soils:

ea = α (γ H + q)

α: 0.2 to 0.4 for long construction period.

Stiff Clay:

Ns = γ Η / γ Η / γ Η / γ Η / cu < 4


H

0.25H

0.5H

ea

0.25H



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Sheet Pile Walls


Cohesive Soils:

- when several clay layers are encountered in the cut:

cu(avg) = (cu1 H1 + cu2 H2 + cu3 H3 + …) / H

γ(avg) = (γ1 H1 + γ2 H2 + γ3 H3 + …) / H

Multiple layers




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Sheet Pile Walls

Design of Struts:

H

ea

- min vertical spacing of 2.75 m.

- subjected to compression forces � buckling

� provide vertical & horizontal supports at

intermediate points

- depth of 1st strut < depth of tension crack zo = 2cu/γ



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Sheet Pile Walls

Design of Struts:

- TA = A.S

- TB = (B1 + B2) S

- TC = (C1 + C2) S

- TD = D.S

as S = spacing between struts

Forces in StrutsA

B1

C1

D

B2

C2

A

ea

B

C

D

H

- Assume intermediate hinges at

struts (B) and (C)



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Sheet Pile Walls

Design of Sheet Pile:

- for each beam, determine maximum moment.

- determine absolute Mmax.

- Sec. Modulus: Z = Mmax/σy.

A

B1

C1

D

B2

C2

A

ea

B

C

D

H



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Sheet Pile Walls

Design of Wales:

- Continuous horizontal beams.

- Mmax = A.S2/10.

- Sec. Modulus: Z = Mmax/σy.

A

B1

C1

D

B2

C2

A

ea

B

C

D

H



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Sheet Pile Walls

Base Stability:

Cohesive Soils:

as cu = undrained strength below base

Nc = bearing capacity factor (see chart)

Deep Excavation: Η / Β Η / Β Η / Β Η / Β > 1


51 qH

NcFS cu .≥

+γ=



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Sheet Pile Walls

Base Stability:

Cohesive Soils:

Shallow Excavation: Η / Β Η / Β Η / Β Η / Β < 1


51

70

cqH

NcFS

u

cu .≥

Β.

Η−+γ

=

as cu = undrained strength below base

Nc = bearing capacity factor (see chart)

if depth to firm layer D < 0.7 B take D instead of 0.7 B

- load = 0.7B (γ H + q) – cu H

- resistance = 0.7B (cu Nc)

D



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Sheet Pile Walls

Base Stability:

Cohesive Soils:




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Sheet Pile Walls

Base Stability:

Cohesive Soils:

If FS < 1.5

�� Sheet pile should be driven deeper


51 t2c

qH

NcFS

a

cu .≥

Β−+γ

=

as ca = soil adhesion = α cu

α = 0.35 to 1.0 (soft)

H

t



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Sheet Pile Walls

Base Stability:

Cohesionless Soils:

w

subcrit

exit

crit

i as

2 i

iFS

γ

γ=

≥=

iexit from flow analysis or see chart

- Base heave due to B.C. failure is not critical.

- Base heave is more critical due to upward seepage.

If FS against piping < 2

�1-Sheet pile should be driven

deeper to limit iexit



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Sheet Pile Walls

Base Stability:

Cohesionless Soils:

iexit from chart



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Sheet Pile Walls

Base Stability:

Cohesionless Soils:

2- Cutoff penetrates into

impermeable layer

11 h

ddFS

ww

22 11 .≥γ

γ+γ=

H

t

Clay

d1

d2γ2

γ1

Sand

Sand

GWT

hw

γwhw



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Sheet Pile Walls

Base Stability:

Cohesionless Soils:

3- Cutoff by means of grout plug

11 h

dFS

ww

1 .≥γ

γ=

SandH

td γ1

GWT

hw

γwhw

� get d = depth of grout plug



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Sheet Pile Walls

Settlement adjacent to Strutted Excavation

depends on:

- wall height.

- soil type below bottom of cut.

- elapsed time between excavation and placement of

wales and struts.

- stiffness of wall.

- lateral yielding will cause ground surface to settle.

- sheet pile is driven to a certain depth below bottom

of excavation to reduce lateral yielding of wall (δh).



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Sheet Pile Walls


- Lateral yield (δh) induces ground settlement (δv).

- Prediction of ground settlement in various types of

soil (see Figure).

δv(max) = 0.5 � 1.0 δh(max)



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Sheet Pile Walls


For Cohesionless Soils:

δh(max) = 0.2% H

if bracings are installed as soon as support levels are reached.

Means of Reducing Movements:

- unsupported depth of wall between supports can be decreased by using more levels of

bracings.

- top braces should be placed as high as possible

- vertical spacing of 2.5 m between strut levels is minimum with 4 to 5 m being max.

- unsupported depth of wall can be reduced by use of soil berms.

- if stiff layer lies below clay layer, wall should be embedded in the stiff layer. This will

greatly reduce lateral yield.

Documents

Sheet Pile Walls - · PDF file · 2012-12-16determine forces acting on SPW. ... Anchored Sheet Pile Walls Faculty of Engineering Cairo University Sheet Pile Walls Design: Cohesionless