Faculty of Engineering
Civil Engineering Department
Building Construction I
Third Stage- First Semester
L8:RETAINGIN WALLS
Lecturer: Abdulqadir Bayz Hammad Amin
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Retaining wall
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When a desired change in ground elevation
exceeds the angle of repose of the soil, a
retaining wall becomes necessary to hold that
the mass of earth on the uphill side of the
grade change.
■
A retaining wall must be designed and
constructed to resist lateral pressure of the
soil being retained. This active pressure
increases proportionally from zero at the
upper grade level to a maximum value at the
lowest depth of the wall. The total pressure or
thrust may be assumed be acting through the
centroid of the triangular distribution pattern,
one-third above the base of the wall.
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Retaining walls
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RETAINING WALLS
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Retaining
wall
T= 0.286 * SH2/2
T= Total pressure or thrust
S= weight of retained soil;
100 pcf (1600 kg/m3)
W= composite weight of wall
acting through centroid of
the section
R= resultant of T and W
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• Retaining Walls ~ the major function
of any retaining wall is to act
as an earth-retaining structure for the
whole or part of its height
on one face, the other being exposed
to
the
elements.
Most small height retaining walls are
built entirely of brickwork or a
combination of brick facing and
blockwork or mass concrete backing.
To reduce hydrostatic pressure on the
wall
from
ground
water an adequate drainage system in
the
form
of
weep
holes
should be used. Alternatively subsoil
drainage behind the wall could
be employed.
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Retaining Walls up to 1m High (2)
Small Height Retaining Walls ~ retaining walls must be
stable and the usual rule of thumb for small height brick
retaining walls is for the height to lie between two and four
times the wall thickness.
Stability can be checked by applying the middle third rule †
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Medium Height Retaining Walls
Retaining Walls up to 6„000
high ~ these can be
classified as medium height
retaining walls and have the
primary function of retaining
soils at an angle in excess of
the soil's natural angle of
repose. Walls within this
height range are designed to
provide
the
necessary
resistance by either their
own mass or by the
principles of leverage.
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Medium Height Retaining Walls
Earth Pressures ~ these can
take one of two forms, namely:
1 . Active Earth Pressures †
these are those pressures
which tend to move the wall at
all times and consist of the
wedge of earth retained plus
any hydrostatic pressure. The
latter can be reduced by
including a subsoil drainage
system behind and/or through
the wall.
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Medium Height Retaining Walls
Earth Pressures ~ these can
take one of two forms, namely:
2. Passive Earth Pressures ~
these are a reaction of an equal
and opposite force to any
imposed pressure thus giving
stability by resisting movement..
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Medium Height Retaining Walls
Mass Retaining Walls ~ these walls
rely mainly on their own mass to
overcome the tendency to slide
forward. Mass retaining walls are not
generally considered to be economic
over a height of 1„800 when
constructed of brick or concrete and
1„000 high in the case of natural
stonework. Any mass retaining wall
can be faced with another material
but generally any applied facing will
not increase the strength of the wall
and is therefore only used for
aesthetic reasons.
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Medium Height Retaining Walls
Cantilever Retaining Walls ~ these
are constructed of reinforced
concrete with an economic height
range of 1„200 to 6„000. They
work on the principles of leverage
where the stem is designed as a
cantilever fixed at the base and
base is designed as a cantilever
fixed at the stem. Several formats
are possible and in most cases a
beam is placed below the base to
increase the total passive
resistance to sliding. Facing
materials can be used in a similar
manner to that.
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Cantilever Retaining Walls
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Thank you for your Attention
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