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7/27/2019 Presentation Anchored Piles
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This document downloaded from
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ENCE 461
Foundation Analysis andDesign
Anchored Sheet Pile WallsOverview of Externally Stabilised Systems
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Anchored Sheet Pile Walls
Includes an anchor or tieback at or near the head
of the wall
More than one set of anchors or tiebacks can beused
Increases wall stability and enables taller walls tobe built and sustained
Almost a necessity with vinyl, aluminium andfibreglass sheet piles
Not exclusive to sheet piling; also used withother types of in situ wall systems
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Anchored Sheet Pile Walls
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Wales inSheetPile
Walls
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Inclination of Tiebacks
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Methods of Analysis forAnchored Walls
Free Earth Support Method
Assumes lower end of the pile incapable of producingnegative bending moments
Converts problem into a statically determinate one
Rowe’s Moment Reduction Method used to take in toaccount flexibility of sheeting
Fixed Earth Support Method (Equivalent BeamMethod)
Makes lower end is fixed like a cantilever beam
Beam on Elastic Foundation Method
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Free Earth
AnalysisofAnchored
Walls
Summation of moments about the anchor point(T) must equal zero
Factor of safety applied to passive (lower) force
triangle Reduced passive earth pressure coefficient (Coduto)
Direct factor of safety on the moment (SPW 911)
Anchor force equal to sum of other forces but inopposite direction
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Steps to Solve Problem Find location of Point O
Find magnitude, location of F1, z
1
Determine equation for magnitude, location of F2, z
2
Compute the location of point C by summing
moments about the tieback Compute tieback/anchor force using static equilibrium
Compute the maximum moment by finding the point
where the active force equals the tieback/anchor forceand computing the moment at that point
Reduce the moment for sheeting flexibility using
Rowe’s Moment Reduction Curves Compute tieback spacing and wale beam size
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Example of Anchored WallDesign
Given
Wall as shown, includingtieback location
Find
Required depth of wallbelow the dredge line
Tieback force and
spacing Size of H-beam for wale
Size of sheeting for
bending
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Pressure Diagram for Example
Net Pressure
Effective Stress
Active Pressure
Passive
Pressure
F1
T
F2
C
M T 0
T F 1F 2
K a0.295K p
F
3.39
1.5
2.26
O36.83'
O
L
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Computation of
Force F1
F1a
= (428)(12)/2 =
2568 lb/ft
zF1a
= 2*12/3 = 8'
F1b = (428+571)(4)/2 =1998 lb/ft
zF1b
= 8'+2.09'=10.09'
F1c
= (571+826)(14)/2
= 9779 lb/ft
zF1c
= 16’ + 7.42’ =
23.42’
F1d
= (826)(36.83-30)/2
= 2821 lb/ft z
1d= 30 + 6.83/3 =
32.28’
F1
= 2568 + 1998 +
9779 + 2821= 17,166lb/ft
z1
= ((2568)(8) +
(1998)(10.09) +(9779)(23.42) +
(2821)(32.28))/17166 =21.01’
zL
3q1q2q12 q2
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Compute Maximum Moment Maximum moment takes place where the shear
equals zero Zero shear takes place at the point below the tieback
where the active earth pressure force equals the
tieback force
Tieback force = 12160 lb/ft
Active earth pressures:
F1a
+ F1b
= 4566 lb/ft < 12160 lb/ft
F1a
+ F1b
+ F1c
= 14345 lb/ft > 12160 lb/ft
Since the zero shear point is between the “b” and “c” points,16 < z
V=0< 30; from interpolation, z
V=0= 27.27’
Compute
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ComputeMaximum
Moment Active earth pressure
z = 27.27’= 776 psf
F1c
’ = (27.27-16)(571+776)/2 = 7590 lb.
z1c
’ = 16 + (27.27-16)(571+(2)(776))/(3(571+776)) =
21.92’ F
1’ = 12160 lb/ft
z1’= ((2568)(8) + (1998)(10.09) + (7590)(21.92))/12160
= 17.02’
Maximum Momentz = 27.27’
= 12160(27.27 – 12) – 12160
(27.27-17.02) = 12160 (12 – 17.02) = - 61043 ft-lb/ft
zL
3q1
q2
q12 q2
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SPW
911
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Rowe’s Moment Reduction
Curves Used to take into consideration the flexibility of
the pile and its effect on relieving the actualbending moment the wall experiences
Different set of curves for clay and sand
Variables for Rowe’s Curves
Height of wall H = 30’ (above the dredge line)
Depth of embedment D = 45.92 – 30 = 15.92’ Modulus of Elasticity E = 29,000,000 psi
Moment of Inertia I = 250 in4 /ft (AZ 18, estimated frommaximum moment)
Following curves, M/Mmax
= 0.7, so M = 42,730 ft-lb/ft
AZ-13
Tieback
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Tiebackand
WaleDesign
S
B
e a m
w i t h U n i f o r m
P r e s s u r e T
a h
Can be considered either as a beam with rigid or flexible
supports
M maxT ah
S
10
Maximum walemoment:
S
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Tieback and Wale
Design Use 8’ spacing recommended in book
Tieback or anchor load = (12160 lb/ft)(8’) = 97820 lbper tieback anchor
Wale moment = (12160)(8)/10 = 97820/10 = 9782 ft-
lb
Using 36 ksi steel, would need a W 30 x 152 or W36 x182 beam
For this wall, probably need to either use multiplewales or decrease the spacing of the tiebacks
M maxT ah
S
10
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Tieback Angle
= 97820 lb.
= 20º
T A = 9 7 8 2 0 / c
o s 2 0 º = 1 0 4 0 9 8 l b .
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Anchor
Design
Anchor
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AnchorDesign
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Chart Solution
Chart for anchoredwall in homogeneous
granular soil:PBSSPDM, p. 56
Variables
Kp /K
a= 2.26/0.295 =
7.66
= 124 pcf = 12/30 = 0.4 (chart
for 0.25)
Results
Anchor Pull Ratio =
0.6
Moment Ratio = 0.15
Depth Ratio = 0.6
Anchor Pull = 19753lb/ft
Max. Moment =148,149 ft-lb/ft
Depth = 18’
Only valid if anchor is7.5’ below surface
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Soldier Beams
Externally
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ExternallyStabilised
Systems Massive Gravity Walls
Stone
Unreinforced Masonry
Unreinforced Concrete Rarely used today
Cantilever Gravity Walls
Reinforced; common today
Crib Walls
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Gravity Walls
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Crib Wall
Crib and Bin Walls
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Crib and Bin Walls
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Internally Stabilised Systems Reinforced Soils
Allow for walls in configurations where the wall itself could not support the earth
The earth behind such walls is Mechanically
Stabilised Earth (MSE)
Reinforcement can consist of steel strips, geogrids,wire mesh, etc.
Facing can consist of concrete panels or blocks,gabions, or other materials
In Situ Reinforcement
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Geogrid
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Geogrid
Reinforcement
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Gabion Walls
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Soil Nailing
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Questions