Response to Information Request - MCU12/0184

                         AUSTRALIAN GEOGUIDE LR6 (RETAINING WALLS)




Old Masonry walls (Figure 4)         -

                                         Many old masonry retaining walls have
not been built in accordance with modern          design standards and often
have a low "factor of safety" (GeoGuide LR1).          They may therefore be
close to failure and a minor change in their condition, or loading, could
initiate collapse. You need to take particular care with such structures
and seek professional advice sooner rather than later. Although masonry
walls sometimes deflect significantly over long periods of time collapse,                                                         No drainage medium
                                                                                                                                  behind wall
when it occurs, is usually sudden and can be catastrophic. Familiarity
with a particular situation can instil a false sense of confidence.

Reinforced soil walls (Figure 5)           -
                                               are   made of compacted select fill in      t,l
which layers of reinforcement are buried to form a "reinforced soil zone".
The reinforcement is all important, because it holds the soil "wall"
together. Reinforcement may be steel strip, or mesh, or a variety of
geosynthetic ("plastic") products. The facing panels are there to protect
the soil "wall" from erosion and give it a finished appearance.                                  Figure 4 Poorly built masonry wall
                                                                                                               -




Most reinforced soil walls are proprietary products.                Construction should
be carried out strictly in accordance with the manufacturer’s instructions.                              Reinforced
                                                                                                          soil zone
                                                                                                                           I
Inspection and maintenance should be the same as for formed concrete
and concrete block walls.        If unusual materials such as timber, or used
                                                                                                                               Drainage layer
tyres, are used as a facing it should be checked to see that it is not rotting,
or perishing.                                                                                                                     Compacted fill of specified
                                                                                                                                  Quality and density
OTHER WALLS
                                                                                                                                   Drainage pipes
Cantilevered and anchored walls (Figure 6)       rely on earth pressure on
                                                          -




                                                                                                                                   Facing panels (concrete,
the low side, rather than self-weight, to provided the restoring force and                                                         blockwork, timber poles,
                                                                                                                                   used lyres etc.)
an adequate factor of safety. These walls may comprise:


. a line of touching bored piers (contiguous bored pile wall) or

.
  sprayed concrete panels between bored piers (shotcrete wall) or
. horizontal timber or concrete
                                 planks spanning between upright timber                    Figure 5 Typical reinforced soil wall
                                                                                                           -




  or steel soldier piles or

. steel sheet piles.

Depending on the form of construction and ground conditions, walls in
                                                                                                                                    Ground anchor
excess of 3 m height normally require at least one row of permanent
ground anchors.                                                                                                            I        (not required for
                                                                                                                                    cantilevered wall)
                                                                                                                           ....
                                                                                                                           .’
INSPECTION

All walls should be inspected at least once a year, looking for tilting and
other signs of deterioration. Concrete walls should be inspected for
                                                                                          -:::::.::::-;::::.:~~:y~./       _        Retaining wall

cracking and rust stains as for formed concrete gravity walls. Contiguous
bored pile walls can have gaps between the piles      look for loss of soil
                                                                -




from behind which can become a major difficulty if it is not corrected.
Timber walls should be inspected for rot, as for timber crib walls. Steel
sheet piles should be inspected for signs of rusting. In addition, you
should make sure that ground anchors are maintained as described in
                                                                                                               """’~
                                                                                                                                           --_j
GeoGuide LR4 under the heading "Rock bolts and rock anchors".
                                                                                                      Figure 6 Typical cantilevered or
                                                                                                                       -




                                                                                                                       anchored wall
One of the most important issues for walls is that their internal drainage systems are operational. Frequently verify that
internal drainage pipes and surface interception drains around the wall are not blocked nor have become inoperative.

More information relevant to your particular situation may be found in other Australian GeoGuides:



         GeoGuide LR1     -
                              Introduction                                       GeoGuide LR7     -
                                                                                                      Landslide Risk
         GeoGuide LR2     -
                              Landslides                                         GeoGuide LR8     -
                                                                                                      Hillside Construction
         GeoGuide LR3     -
                              Landslides in Soil                                 GeoGuide LR9     -
                                                                                                      Effluent & Surface Water Disposal
         GeoGuide LR4     -
                              Landslides in Rock                                 GeoGuide LR10    -
                                                                                                      Coastal Landslides
         GeoGuide LR5     -
                              Water & Drainage                                   GeoGuide LR11    -
                                                                                                      Record Keeping

The Australian GeoGuides       (LR series) are a set of publications intended for property owners; local councils; planning authorities;
developers; insurers; lawyers and, in fact, anyone who lives with, or has an interest in, a natural or engineered slope, a cutting, or an
excavation. They are intended to help you understand why slopes and retaining structures can be a hazard and what can be done with
appropriate professional advice and local council approval (if required) to remove, reduce, or minimise the risk they represent. The
GeoGuides have been prepared by the Australian Geomechanics Society, a specialist technical society within Engineers Australia, the
national peak body for all engineering disciplines in Australia, whose members are professional geotechnical engineers and engineering
geologists with a particular interest in ground engineering. The GeoGuides have been funded under the Australian governments’ National
Disaster Mitigation Program.




                               Australian Geomechanics Vol 42 No 1 March 2007                                                              171