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:

φσπ tan' KdlP vu =

K = K0 if the concrete grout is placed under pressure Lower limit of K is Rankine Ka In Clay:

au dlcP π=

ca = adhesion ≈ uc32

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) γh/cu > 4 γh/cu < 4

≥ 0.3 γH

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

211 2 φγ

Ks = K for sand layer (≈ 1) n' = a coefficient of progressive failure, 0.5 ~1.0, average 0.75. Case (b)

( )K++= 22111 HCHCH

Cav

( )K++= 22111 HHHav γγγ

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

maxsAM =

At level B 8

))(( 221

maxsBBM +

=

At level C 8

))(( 221

maxsCCM +

=

At level D 8

))(( 2

maxsDM =

Stability of Open Cut Bottom Heaving of a Cut in Clay

2.17.5

1

1 ≥−

=HCHB

BCFS

u

u

γ

5.1'"2.0114.5

≥+

+⎟⎠⎞

⎜⎝⎛ +

=qH

BHC

LBC

FS

uu

γ

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

ii

FS

Uplifting of a Cut in Inter-Layer

2.1)( 1

1 ≥Δ+

=ww

sat

HHH

FSγ

γ

Depth of Penetration

5.1≥−

=saa

pp

MlPlP

FS

H1

Uf = H1+ΔHw

Impervious

lp Pp Pa

la

Global Stability of Anchored Sheet Pile

5.1≥=o

r

MM

FS