sheet pile structures
TRANSCRIPT
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