Design of Cantilevered Design of Cantilevered Retaining Walls Retaining Walls CE A433 – RC Design CE A433 – RC Design T. Bart Quimby, P.E., T. Bart Quimby, P.E., Ph.D. Ph.D. Spring 2009 Spring 2009
IntroductionA cantilever retaining wall is a system of
cantilever slabs (i.e. beams) that retain soil.The key is to draw
the appropriate FBDs so that you can determine the internal
forces.
Cantilever Retaining WallShear KeyToeStemHeel
Forces ACTING ON the WallWallFootingShear KeySoil on ToeSoil on
HeelActive Lateral Soil Pressure
ReactionsPassive Lateral Soil PressureVertical
ReactionFrictionACTUAL FRICTION is not the same as FRICTION
CAPACITY!
Computing Soil Bearing StressResolve applied forces into a
concentric vertical force and moment on the contact area.Ix =
bL3/12A = bLc = L/2smax = P/A + Mc/Ixsmin = P/A Mc/IxPM
SlidingDriving ForceResisting CapacityVslide = Driving Force =
DemandVresist = sum(Resisting Forces) = CapacityFS = Vresist /
VslideDesign for FS > 1.5Friction CAPACITY = m NNot Actual
Friction Reaction
Stem DiagramsFBDShearMomentDemandCapacityDemandCapacityMake stem
thick enough for shearSelect Steel to provide flexural capacityAdd
T&S Steel
ToeShearMomentDesign ShearDesign MomentVu can be calculated a
distance d from face of wall since there is a compressive reaction
with the wall.Mu is computed at the face of the wall.Flexural Steel
extends a development length into the heel and should develop
within the length of the toe.Add T&S Steel
HeelShearMomentDesign ShearDesign MomentVu must be calculated at
the face of wall since there is a tensile reaction with the wall.Mu
is computed at the face of the wall.Flexural Steel extends a
development length into the toe and should develop within the
length of the heel.Add T&S Steel
The Design ProcessSelect the overall dimensions (height,
embedment, footing length and position, and estimated footing &
wall thicknesses) based on stability (sliding and overturning) and
soil strength (max/min bearing pressures) using service level
loads.Check slab (wall and footing) thicknesses using shear
criteria and factored loads. Adjust thicknesses as necessary,
rechecking stability and soil strength of the values change.Select
the flexural steel for the three cantilever slab elements using
factored loads.Select the temperature and shrinkage steel for wall
and footing.Draw the resulting wall cross section (to scale!)
