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Session 15 – 16 SHEET PILE STRUCTURES
Course : S0484/Foundation Engineering
Year : 2007
Version : 1/0
SHEET PILE STRUCTURES
Topic:
• Anchored Sheet Pile
• Braced Cut
CALCULATION STEPSANCHORED SHEET PILE – FREE – SAND
CALCULATION STEPSANCHORED SHEET PILE – FREE – SAND
245tan
245tan
2
2
p
a
K
K
1. Determine the value of Ka and Kp
2. Calculate p1and p2 with L1 and L2 are known
a
a
KLLp
KLp
212
11
'..
..
3. Calculate L3
ap KK
pLLz
'2
3
4. Calculate P as a resultant of area ACDE
5. Determine the center of pressure for the area ACDE ( z )
CALCULATION STEPSANCHORED SHEET PILE – FREE – SAND
0
'
35,1 1321
32224
34
ap KK
lzLLLPLLlLL
Determination of penetration depth of sheet pile (D)
Dtheoretical = L3 + L4
Dactual = (1.3 – 1.4) Dtheoretical
Determination of anchor force
F = P – ½ [’(Kp – Ka)]L42
6. Calculate L4
CALCULATION STEPSANCHORED SHEET PILE – FREE – CLAY
CALCULATION STEPSANCHORED SHEET PILE – FREE – CLAY
245tan
245tan
2
2
p
a
K
K
1. Determine the value of Ka and Kp
2. Calculate p1and p2 with L1 and L2 are known
a
a
KLLp
KLp
212
11
'..
..
3. Calculate the resultant of the area ACDE (P1) and z1 (the center of pressure for the area ACDE)
In case of saturated soft clay with internal friction angle () = 0, we got
Ka = Kp = 1
CALCULATION STEPSANCHORED SHEET PILE – FREE – CLAY
216 '4 LLcp
Determination of penetration depth of sheet pile (D)
p6.D2 + 2.p6.D.(L1+L2-l1) – 2.P1.(L1+L2-l1-z1) = 0
Determination of anchor force
F = P1 – p6 . D
4. Calculate p6
CALCULATION STEPSANCHORED SHEET PILE – FIXED – SAND
J
CALCULATION STEPSANCHORED SHEET PILE – FIXED – SAND
245tan
245tan
2
2
p
a
K
K
1. Determine the value of Ka and Kp
2. Calculate p1and p2 with L1 and L2 are known
a
a
KLLp
KLp
212
11
'..
..
3. Calculate L3
ap KK
pLLz
'2
3
CALCULATION STEPSANCHORED SHEET PILE – FIXED – SAND
4. determine L5 from the following curve (L1 and L2 are known)
CALCULATION STEPSANCHORED SHEET PILE – FIXED – SAND
5. Calculate the span of the equivalent beam as l2 + L2 + L5 = L’
6. Calculate the total load of the span, W. This is the area of the pressure diagram between O’ and I
7. Calculate the maximum moment, Mmax, as WL’/8
CALCULATION STEPSANCHORED SHEET PILE – FIXED – SAND
'
1'L
P
'
'62.15 ap KK
PLD
'
1
LF
8. Calculate P’ by taking the moment about O’, or
9. Calculate D as
10. Calculate the anchor force per unit length, F, by taking the moment about I, or
(moment of area ACDJI about O’)
(moment of area ACDJI about I)
BRACED CUT
Type of Braced cut
BRACED CUT
Type of Braced cut
PRESSURE ENVELOPE
Cuts in Sandpa = 0.65HKa
Where:
= unit weight
H = height of the cut
Ka = Rankine active pressure coefficient
= tan2(45-/2)
PRESSURE ENVELOPE
• Cuts in Stiff Clay
pa = 0.2H to 0.4H
Which is applicable to the condition
4c
H
PRESSURE ENVELOPE
• Cuts in Stiff Clay
The pressure pa is the larger of
Which is applicable to the condition
Hp
or
H
cHp
a
a
3.0
41
Where:
= unit weight of clay
c = undrained cohesion (=0)
4c
H
PRESSURE ENVELOPE
Limitations:1. The pressure envelopes are sometimes referred to as
apparent pressure envelopes. The actual pressure distribution is a function of the construction sequence and the relative flexibility of the wall.
2. They apply to excavations having depths greater than about 20 ft (6m)
3. They are based on the assumption that the water table is below the bottom of the cut
4. Sand is assumed to be drained with zero pore water pressure
5. Clay is assumed to be undrained and pore water pressure is not considered
PRESSURE ENVELOPE
• Cuts in Layered Soil
csssav
usssssav
HHHH
qnHHHKH
c
.1
'..tan...2
1 2
Where:
H = total height of the cut
s = unit weight of sand
Hs = thickness of sand layer
Ks = a lateral earth pressure coefficient for the sand layer (1)
s = friction angle of sand
qu = unconfined compression strength of clay
n’ = a coefficient of progressive failure (ranging from 0.5 to 1.0; average value 0.75)
c = saturated unit weight of clay layer
PRESSURE ENVELOPE
• Cuts in Layered Soil
nnav
nnav
HHHHH
HcHcHcH
c
.......1
......1
332211
2211
Where:
c1, c2,…,cn = undrained cohesion in layers 1,2,..,n
H1, H2,…,Hn = thickness of layers 1, 2, …, n
1, 2, … n = unit weight of layers 1, 2, … , n
DESIGN OF VARIOUS COMPONENTS OF A BRACED CUT
Struts- Should have a minimum vertical spacing of about 9 ft
(2.75 m) or more.- Actually horizontal columns subject to bending- The load carrying capacity of columns depends on the
slenderness ratio.- The slenderness ratio can be reduced by providing
vertical and horizontal supports at intermediate points- For wide cuts, splicing the struts may be necessary.- For braced cuts in clayey soils, the depth of the first strut
below the ground surface should be less than the depth of tensile crack, zc
DESIGN OF VARIOUS COMPONENTS OF A BRACED CUT
StrutsGeneral Procedures:1. Draw the pressure envelope for the braced cut
DESIGN OF VARIOUS COMPONENTS OF A BRACED CUT
StrutsGeneral Procedures:2. Determine the reactions for the two simple cantilever
beams (top and bottom) and all the simple beams between. In the following figure, these reactions are A, B1, B2, C1, C2 and D
DESIGN OF VARIOUS COMPONENTS OF A BRACED CUT
StrutsGeneral Procedures:3. The strut loads may be calculated as follows:
PA = (A)(s)
PB = (B1+B2)(s)
PC = (C1+C2)(s)
PD = (D)(s)where:
PA, PB, PC, PD = loads to be taken by the individual struts at level A, B, C and D, respectively
A, B1, B2, C1, C2, D = reactions calculated in step 2s = horizontal spacing of the struts
4. Knowing the strut loads at each level and intermediate bracing conditions allows selection of the proper sections from the steel construction manual.
DESIGN OF VARIOUS COMPONENTS OF A BRACED CUT
Sheet PilesGeneral Procedures:1. Determine the maximum bending
moment2. Determine the maximum value of the
maximum bending moments (Mmax) obtained in step 1.
3. Obtain the required section modulus of the sheet piles
4. Choose the sheet pile having a section modulus greater than or equal to the required section modulus
materialpilesheettheofstressflexuralallowablewhere
MS
all
all
max
DESIGN OF VARIOUS COMPONENTS OF A BRACED CUT
Wales
all
MS
then
sDMAlevelAt
sCCMAlevelAt
sBBMBlevelAt
sAMAlevelAt
max
2
max
221
max
221
max
2
max
8,
8,
8,
8,
Where A, B1, B2, C1, C2, and D are the reactions under the struts per unit length of the wall
EXAMPLE
Refer to he braced cut shown in the following figure:
a. Draw the earth pressure envelope and determine the strut loads. (Note: the struts are spaced horizontally at 12 ft center to center)
b. Determine the sheet pile section
c. Determine the required section modulus of the wales at level A (all = 24 kip/in2)
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE