Sheet Pile Walls - · PDF file · 2012-12-16determine forces acting on SPW. ......
Transcript of Sheet Pile Walls - · PDF file · 2012-12-16determine forces acting on SPW. ......
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
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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
Faculty of Engineering
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Sheet Pile Walls
● Anchored
● Strutted
Cantilever SPW Anchored SPW Strutted SPW
2. Types of Sheet Pile Walls2. Types of Sheet Pile Walls
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Sheet Pile Walls
Materials:
● Timber: (shallow excavations)
● Precast reinforced concrete
● Steel
2. Types of Sheet Pile Walls2. Types of Sheet Pile Walls
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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.
3. Cantilever Sheet Pile Walls3. Cantilever Sheet Pile Walls
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Sheet Pile Walls
Design:
- Forces
- Simplification
t
H
Ea
Ep
OC
M
t
H
Ea
Ep
EpEa
O
3. Cantilever Sheet Pile Walls3. Cantilever Sheet Pile Walls
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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
3. Cantilever Sheet Pile Walls3. Cantilever Sheet Pile Walls
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Sheet Pile Walls
Design: Cohesionless Soils
- 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
3. Cantilever Sheet Pile Walls3. Cantilever Sheet Pile Walls
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Sheet Pile Walls
Design: Cohesionless Soils
- 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
3. Cantilever Sheet Pile Walls3. Cantilever Sheet Pile Walls
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Sheet Pile Walls
Design: Cohesionless Soils
- Maximum Moment
- Mmax @ pt of zero shear (n)
� ∑Ea = Epy
� get y
� M at pt (n) = Mmax
Sec. Modulus: Z = Mmax/σy
Net Earth Pressure
nMmax
H
t
Ea1
Epy
O
γγγγ
φφφφ
y
epn
Ea2
3. Cantilever Sheet Pile Walls3. Cantilever Sheet Pile Walls
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Sheet Pile Walls
Design: Cohesionless Soils
- Effect of GWT
H
t
Ea
Ep
O C
∆∆∆∆M
γγγγ
φφφφ
D
Ew1
GWT
Ew2
GWT
3. Cantilever Sheet Pile Walls3. Cantilever Sheet Pile Walls
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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.
4. Anchored Sheet Pile Walls4. Anchored Sheet Pile Walls
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Sheet Pile Walls
t
H
Mmax
Free
t
H
Mmax
Fixed
Conditions of Free and Fixed Earth Support
4. Anchored Sheet Pile Walls4. Anchored Sheet Pile Walls
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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
4. Anchored Sheet Pile Walls4. Anchored Sheet Pile Walls
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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.
4. Anchored Sheet Pile Walls4. Anchored Sheet Pile Walls
Faculty of Engineering
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Sheet Pile Walls
Design: Cohesionless Soils
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
4. Anchored Sheet Pile Walls4. Anchored Sheet Pile Walls
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Sheet Pile Walls
Design: Cohesionless Soils
2- Penetration Depth
Free Earth Support:
H
t
Ea
Ep
a γγγγ
φφφφ
- ∑Ma = 0 � Ea ya – Ep yp = 0
� get D
� t = D
4. Anchored Sheet Pile Walls4. Anchored Sheet Pile Walls
Faculty of Engineering
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Sheet Pile Walls
Design: Cohesionless Soils
2- Penetration Depth
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
4. Anchored Sheet Pile Walls4. Anchored Sheet Pile Walls
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Sheet Pile Walls
Design: Cohesionless Soils
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
4. Anchored Sheet Pile Walls4. Anchored Sheet Pile Walls
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Sheet Pile Walls
Design: Cohesionless Soils
4- Maximum Moment
Free Earth Support:
- Mmax @ pt of zero shear (n)
(n) lies above L.G.L.
� A = Eay � get y
� M at pt (n) = Mmax
Sec. Modulus: Z = Mmax/σy
n
A
t
H
Mmax
yEay
4. Anchored Sheet Pile Walls4. Anchored Sheet Pile Walls
Faculty of Engineering
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Sheet Pile Walls
Design: Cohesionless Soils
1- Forces
Fixed Earth Support:
H
t
Ea
Ep
Ep
Ea
OC
Ea
Ep
∆∆∆∆M
Net Earth Pressure
Ep
OC
Ea1
∆∆∆∆M
Ea2
4. Anchored Sheet Pile Walls4. Anchored Sheet Pile Walls
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Sheet Pile Walls
Design: Cohesionless Soils
1- Forces
Fixed Earth Support:
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).
4. Anchored Sheet Pile Walls4. Anchored Sheet Pile Walls
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Sheet Pile Walls
Design: Cohesionless Soils
2- Penetration Depth
Fixed Earth Support:
- 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
4. Anchored Sheet Pile Walls4. Anchored Sheet Pile Walls
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Sheet Pile Walls
Design: Cohesionless Soils
Fixed Earth Support:
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)
4. Anchored Sheet Pile Walls4. Anchored Sheet Pile Walls
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Sheet Pile Walls
Design: Cohesionless Soils
Fixed Earth Support:
4- Maximum Moment
- For upper beam:
- Mmax @ pt of zero shear (n)
(n) lies above L.G.L.
� A = Eay � get y
� M at pt (n) = Mmax
Sec. Modulus: Z = Mmax/σy
H
uR
Ea2
Eay
b
Aa
Mmax
y
n
4. Anchored Sheet Pile Walls4. Anchored Sheet Pile Walls
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Sheet Pile Walls
Design: Cohesionless Soils
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
4. Anchored Sheet Pile Walls4. Anchored Sheet Pile Walls
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Sheet Pile Walls
Design: Cohesionless Soils
6- Design of Anchor Rod
- Area of rod:
area = T / σy
as T = A.S
area = π d2/4
A
4. Anchored Sheet Pile Walls4. Anchored Sheet Pile Walls
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Sheet Pile Walls
Design: Cohesionless Soils
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
4. Anchored Sheet Pile Walls4. Anchored Sheet Pile Walls
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Sheet Pile Walls
Design: Cohesionless Soils
7- Design of Anchor Plate
- 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
4. Anchored Sheet Pile Walls4. Anchored Sheet Pile Walls
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Sheet Pile Walls
Design: Cohesionless Soils
7- Design of Anchor Plate
- Isolated Plate:
KFS
K d
T.L
a
p)−(γ
=Βed ea
Bd
T
4. Anchored Sheet Pile Walls4. Anchored Sheet Pile Walls
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Sheet Pile Walls
Design: Cohesionless Soils
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.
5. Strutted Sheet Pile Walls5. Strutted Sheet Pile Walls
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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.
5. Strutted Sheet Pile Walls5. Strutted Sheet Pile Walls
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Sheet Pile Walls
Types:
- timber lagging, steel
wales, and timber
5. Strutted Sheet Pile Walls5. Strutted Sheet Pile Walls
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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.
5. Strutted Sheet Pile Walls5. Strutted Sheet Pile Walls
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Sheet Pile Walls
Lateral Earth Pressure:
- 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
Lateral Earth Pressure:
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
5. Strutted Sheet Pile Walls5. Strutted Sheet Pile Walls
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Sheet Pile Walls
Lateral Earth Pressure:
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
5. Strutted Sheet Pile Walls5. Strutted Sheet Pile Walls
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Sheet Pile Walls
Lateral Earth Pressure:
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
Short Term Analysis ���� cu, φφφφ = 0
5. Strutted Sheet Pile Walls5. Strutted Sheet Pile Walls
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Sheet Pile Walls
Lateral Earth Pressure:
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
Short Term Analysis ���� cu, φφφφ = 0
H
0.25H
0.5H
ea
0.25H
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Sheet Pile Walls
Lateral Earth Pressure:
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
Short Term Analysis ���� cu, φφφφ = 0
5. Strutted Sheet Pile Walls5. Strutted Sheet Pile Walls
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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
5. Strutted Sheet Pile Walls5. Strutted Sheet Pile Walls
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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)
5. Strutted Sheet Pile Walls5. Strutted Sheet Pile Walls
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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
5. Strutted Sheet Pile Walls5. Strutted Sheet Pile Walls
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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
Short Term Analysis ���� cu, φφφφ = 0
51 qH
NcFS cu .≥
+γ=
5. Strutted Sheet Pile Walls5. Strutted Sheet Pile Walls
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Sheet Pile Walls
Base Stability:
Cohesive Soils:
Shallow Excavation: Η / Β Η / Β Η / Β Η / Β < 1
Short Term Analysis ���� cu, φφφφ = 0
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:
Short Term Analysis ���� cu, φφφφ = 0
5. Strutted Sheet Pile Walls5. Strutted Sheet Pile Walls
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Sheet Pile Walls
Base Stability:
Cohesive Soils:
If FS < 1.5
���� Sheet pile should be driven deeper
Short Term Analysis ���� cu, φφφφ = 0
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
5. Strutted Sheet Pile Walls5. Strutted Sheet Pile Walls
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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
Settlement adjacent to Strutted Excavation
- 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
Settlement adjacent to Strutted Excavation
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.