# Design of Cantilevered Retaining Walls

Document Sample

```					Design of Cantilevered
Retaining Walls

CE A433 – RC Design
T. Bart Quimby, P.E., Ph.D.
Spring 2009
Introduction

   A 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 Wall

Stem

Toe     Heel

Shear Key
Forces ACTING ON the Wall

Soil
on     Active
Heel   Lateral
Wall
Soil
Pressure

Soil on Toe

Footing

Shear Key
Reactions

Passive                    ACTUAL FRICTION
Lateral Soil               is not the same as
Pressure                  FRICTION CAPACITY!

Friction

Vertical
Reaction
Computing Soil Bearing Stress
   Resolve applied forces
into a concentric
vertical force and
moment on the contact
area.
   Ix = bL3/12
   A = bL
P
c = L/2

M
   smax = P/A + Mc/Ix
   smin = P/A – Mc/Ix
Sliding
Vslide = Driving Force
= Demand

Vresist = sum(Resisting
Forces) = Capacity                                         Driving
Force

FS = Vresist / Vslide    Resisting
Capacity

Design for
FS > 1.5

Friction CAPACITY = m N
Not Actual Friction Reaction
Overturning
MOT = Driving Force*arm
= Demand                    Resisting
Forces
MROT = sum(Resisting                    Driving
Moments) = Capacity                     Force

FS = MROT / MOT

Design for
FS > 2.0

Point of
Rotation
Draw FBDs

Stem

Toe
Heel
Stem Diagrams
Shear                   Moment
FBD

Make
stem
thick

Capacity
enough
for shear

Capacity
T&S
Steel

Select Steel to provide flexural capacity

Vu can be
calculated a                           Flexural Steel
extends a
distance ‘d’ from                      development
face of wall since                    length into the
heel and should
there is a                            develop within
compressive                            the length of
the toe.
reaction with the
wall.
Design Shear
Shear
Mu is computed at
the face of the      Design Moment
wall.
Moment
Heel

Vu must be
calculated at the
face of wall since
Flexural Steel
there is a tensile      extends a
reaction with the     development
length into the
wall.                toe and should
develop within
the length of
the heel.

Design Shear
Mu is computed at       Shear
the face of the
wall.
Design Moment
Moment
The Design Process
   Select 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
   Check slab (wall and footing) thicknesses using shear criteria
rechecking stability and soil strength of the values change.
   Select the flexural steel for the three cantilever slab