Design of Rigid Retaining Walls

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Design of Rigid Retaining Walls

• Prof. Jie Han, Ph.D., PE
• University of Kansas

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Outline of Presentation

• Failure modes
• Stability design
• Structural design
• Drainage design

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Rigid Retaining Walls
Backfill
Cantilever Wall - backfill to help mobilize
stability
Gravity Wall - self-weight to stabilize the wall
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Failure Modes
?x
(b) Overturning
(c) Bearing
(a) Sliding
Crack or break
(e) Structural failure
(d) Deep seated failure
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Force Diagram
?
?
xs
Ws
Ws
Pa
PaV
H
xw
Ww
PaH
Ww
za
T
xr
Heel
Toe
N
B
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Factor of Safety against Sliding
Sliding resisting force
FSsliding
Sliding driving force
cb and ?b Cohesion and interface friction
angle between wall base and foundation soil
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Factor of Safety against Sliding
Required FS
FSsliding gt 1.5 if the passive earth pressure In
front of the wall is neglected
FSsliding gt 2.0 if the passive earth pressure In
front of the wall is included
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Factor of Safety against Overturning
Resisting moment about toe
FSoverturning
Driving moment about toe
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Factor of Safety against Overturning
Required FS
FSoverturning gt 1.5 if granular backfill is used
FSoverturning gt 2.0 if cohesive backfill is used
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Stability against Overturning (eccentricity)
Distance from the toe to the resultant vertical
force at the base
Eccentricity, e
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Factor of Safety against Bearing
Ultimate bearing capacity
FSbearing
Maximum contact pressure
Required FSbearing ? 3.0
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Factor of Safety against Deep-Seated Failure
Use slope stability methods to compute the
factor of safety against deep-seated failure
Required Fsdeep-seated ? 1.5
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Internal Stability (Structural Design)
q
Compute shear force, Vu and flexural moment, Mu
based on earth pressure distribution
Stem
?aH
Footing
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Internal Stability (Stem Shear Design)
Nominal shear capacity
(English units)
(SI units)
Design requirement
? 0.85
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Internal Stability (Stem flexural Design)
Required cross-sectional area of reinforcing steel
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Internal Stability (Stem-Footing Joint Design)
Joint shear capacity is based on sliding friction
with the normal force provided by the reinforcing
steel
Required steel area
? coefficient of friction 0.6
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Internal Stability (Footing Design)
Minimal required footing thickness, T, is
governed by the required development length of
the vertical steel from the stem
T ? ldh 70mm
ldh
T
70mm
12db
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Internal Stability (Footing Shear Flexural
Design)
Shear requirement
(SI units)
Flexural requirement
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Drainage behind Gravity Walls
Drainage blanket (coarse-grained soil)
Non-woven geotextile
Longitudinal drain
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Drainage behind Cantilever Walls
Gravel
Gravel
Weep hole
Perforated -pipe drain
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Drainage Design
Geotextile
h
Weep hole
Rate of flow into geotextile
q kh(Nf/Nd)
Rate of flow out of geotextile
q ki(t b) ?(ib)
? allowable transmissivity