presentation anchored piles

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ENCE 461

Foundation Analysis andDesign

Anchored Sheet Pile WallsOverview of Externally Stabilised Systems



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



Anchored Sheet Pile Walls



Wales inSheetPile

Walls



Inclination of Tiebacks



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



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



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



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



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



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



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



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



SPW

911



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



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



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



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 .



Anchor

Design

Anchor



AnchorDesign



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



Soldier Beams

Externally



ExternallyStabilised

Systems Massive Gravity Walls

Stone

Unreinforced Masonry

Unreinforced Concrete Rarely used today

Cantilever Gravity Walls

Reinforced; common today

Crib Walls



Gravity Walls



Crib Wall

Crib and Bin Walls



Crib and Bin Walls



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



Geogrid



Geogrid

Reinforcement



Gabion Walls



Soil Nailing



Questions

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