Session 15 – 16 SHEET PILE STRUCTURES Course: S0484/Foundation Engineering Year: 2007 Version: 1/0.

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


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 )


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


245tan

245tan

2

2

p

a

K

K



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


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


245tan

245tan

2

2

p

a

K

K



a

a

KLLp

KLp

212

11

'..

..

3. Calculate L3

ap KK

pLLz

'2

3


4. determine L5 from the following curve (L1 and L2 are known)


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


'

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


StrutsGeneral Procedures:1. Draw the pressure envelope for the 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


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.


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


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

Session 15 – 16 SHEET PILE STRUCTURES Course: S0484/Foundation Engineering Year: 2007 Version: 1/0.

Documents

sheet pile structurestopic

sheet pile structurescourse

l1 l2l1

center of pressure

pressure envelopelimitations

pressure diagram

l2 l2 l5

apparent pressure envelopes