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Stability of Sheet Pile Walls
HES3150 Geotechnical Engineering
Typically, sheet pile walls are cantilevered, anchored or braced.
Cantilevered Anchored Braced
Common forms of failure are: (i) rotation of wall, (ii) forward movement of wall, (iii) failure of piles (sheet piles) due to bending, and (iv) failure of anchors or bracing.
Failure of Cantilevered Sheet Pile Wall by Rotation
HES3150 Geotechnical Engineering
To calculate the minimum embedment depth of a cantilevered sheet pile wall, we first need to determine where the “point of rotation” is located.
Therefore, we need a simple model:
Active
Passive
Passive
Note: Wall depends on passive pressure for stabilityAssumed point of rotation
Actual Case (net)
Wall is assumed to rotate about some point producing active and passive pressures as shown on the right.
Failure of Cantilevered Sheet Pile Wall by Rotation – Simple Model
HES3150 Geotechnical Engineering
This can be further simplified to:
Hint: You can sum moments about different points to obtain equations, then solve to find the location of rotation.
Point of rotation
H
d
Active
Passive
Passive
Does this active pressure zone exist ?
Failure of Cantilevered Sheet Pile Wall by Rotation – Simple Model
HES3150 Geotechnical Engineering
Therefore,
H
d
Pactive
Ppassive
2/3 (H+d)
2d/3 P2 , which represents the sum of passive pressure below the point of rotation. This is not correct. However, by rule of thumb, we can assume this to simplify our calculations as long as we increase the final embedment depth by about 20%.
FS
Point of rotation
dHP aa 2
1 dHdHK soila 2
1 2
2
1dHK soila
And, dP pp 2
1ddK soilp
2
1 2
2
1dK soilp
Approximate Method for Calculating Embedment Depth of Sheet Pile Walls
HES3150 Geotechnical Engineering
Then summing the moments about the point of rotation to solve for d (Since H should be known),
H
d
Pactive
Ppassive
2/3 (H+d)
2d/3 P2 , which represents the sum of passive pressure below the point of rotation. This is not correct. However, by rule of thumb, we can assume this to simplify our calculations as long as we increase the final embedment depth by about 20%.
FS
Point of rotation
0033 2
Pd
FS
PdHP pa
M rotation point = 0 +
This simplifies to: 3
3
d
dHFS
K
K
a
p Now solve for d – then add 20%
Failure of Anchored Sheet Piling
HES3150 Geotechnical Engineering
To reduce sheet pile wall driving depth, or if the wall is too high, sheet piles maybe anchored near the top. Thus, the force produced by the anchor supplements the lost passive force
Assuming no passive failure to the toe occurs, we can simplify the lateral soil pressures.
or
Anchor Point
ActiveActive
PassivePassive failure at toe ?
Deflected Shapes
Anchored Sheet Piling – Simplified Lateral Earth Pressures
HES3150 Geotechnical Engineering
H
d
a
Point of rotation
Total passive force, Pp
Total active force, Pa
FS
Anchor Force
Knowing, 2
2
1dHKP soilaa and 2
2
1dKP soilpp
M anchor = 0 + 03
2
3
2
daH
FS
PadHP p
a
Then F horizontal = 0 a
p PFS
P ForceAnchor Should provide the required anchor force.
And solving for d.
