Sheet Pile Structures

Depending on the way the retaining structure is built and analyzed, it can be divided

into three categories:

1. Cantilever Sheet Pile

2. Anchored Sheet Pile

3. Braced Sheet Pile

Cantilever Sheet Pile

Case 1 (Sheet Pile Penetrating Sandy Soils)

A few key points that define the lateral earth pressure in Figure 8.7:

1. Point A to Point D (p1): Active earth pressure on the right hand side.

2. Point D to Point H (p3): (Passive earth pressure on the left hand side) - (Active

earth pressure on the right hand side).

3. Point G (p4): (Passive earth pressure on the right hand side) - (Active earth

pressure on the left hand side).

4. Point E (L3): Can be determined from equation derived in 2.

5. Point F (L5): To be determined.

Unknowns: D and L5

Equations: 0 xF

0 BM

The actual depth of penetration is increased by 20%~30% for construction.

To calculate maximum bending moment:

1. Determine point of zero shear force: let P (area of ACDE) = Shaded area E-F”

2. Moment can be determined at the section of zero shear force.

Case 2 (Sheet Pile Penetrating Clay)

A few key points that define the lateral earth pressure in Figure 8.7:

1. Point A to Point D (p1): Active earth pressure on the right hand side.

2. Point F to Point I (p6): (Passive earth pressure on the left hand side) - (Active earth

pressure on the right hand side).

3. Point G (p7) : (Passive earth pressure on the right hand side) - (Active earth

pressure on the left hand side).

4. Point E (L3): Can be determined from equation derived in 2.

5. Point G (L4): To be determined

Unknowns: D and L4

Equations: 0 xF

0 BM

To calculate maximum bending moment:

1. Determine point of zero shear force

2. Moment can be determined at the section of zero shear force.

Anchored Sheet Pile The two basic methods of designing anchored sheet pile walls are (a) the free earth

support method and (b) the fixed earth support method.

Dfree earth < Dfixed earth

Case 1. (Free earth support method for penetration of sandy soil)

Unknowns: D and T

Equations: 0 xF

0 oM

The actual depth of penetration is increased by 30%~40% for construction.

Anchors

Ultimate Resistance of Tiebacks

In Sand:

tan' KdlP vu

K = K0 if the concrete grout is placed under pressure

Lower limit of K is Rankine Ka

In Clay:

au dlcP

ca = adhesion ≈ uc3

2

Factor of Safety = 1.5-2.0 may be used over ultimate resistance to obtain the

allowable resistance offered by each tieback.

Braced Cut To avoid considerable settlement or bearing capacity failure of nearby structure.

To prevent water seepage into excavation Pressure Envelop for Braced Cut Design

The struts limit lateral wall movement, Ka not mobilized, P > Pa by 10% ~15%.

After observation of several braced cuts, Peck (1969) suggested using design pressure

envelops (apparent pressure envelop)

h/cu > 4 h/cu < 4

0.3 H

Limitations:

1. Pa may depend on construction sequence.

2. They apply when H about 6 m.

3. G.W.T. below the bottom of excavation

4. Sand is drained (uw =0)

5. Clay is undrained (uw not considered)

Cuts in Layered Soil

Case (a)

ucssssav CnHHK

HC 'tan

2

11 2

Ks = K for sand layer ( 1)

n' = a coefficient of progressive failure, 0.5 ~1.0, average 0.75.

Case (b)

2211

1HCHC

HCav

2211

1HH

Hav

Braced Cut Design

Strut

The strut force can be determined from (b) above.

Sheet Pile

Maximum moment on sheet pile can be determined from (b) above.

Wales

Treated as continuous horizontal members if they are spliced properly.

Or conservatively treated as though they are pinned at the struts.

At level A 8

))(( 2

max

sAM

At level B 8

))(( 221

max

sBBM

At level C 8

))(( 221

max

sCCM

At level D 8

))(( 2

max

sDM

Stability of Open Cut

Bottom Heaving of a Cut in Clay

2.17.5

1

1

HCHB

BCFS

u

u

5.1'

"2.0114.5

qH

B

HC

L

BC

FS

uu

B’ = T if T B/ 2 ; B’ = B/ 2 if T > B/ 2 ;

B” = 2 B’

Chang (2000)

Terzaghi (1943)

Piping of a Cut in Sand

5.1)max(

exit

cr

i

iFS

Uplifting of a Cut in Inter-Layer

2.1)( 1

1

ww

sat

HH

HFS

Depth of Penetration

5.1

saa

pp

MlP

lPFS

H1

Uf = H1+Hw

Impervious

lp Pp Pa

la

Global Stability of Anchored Sheet Pile

5.1o

r

M

MFS