Landslide Hazard Report_compressed

                          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,
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
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
                                                                                           Figure 4 - Poorly built masonry wall
the soil "wall" from erosion and give it a finished appearance.
Most reinforced soil walls are proprietary products. Construction should
be carried out strictly in accordance with the manufacturer's instructions.
Inspection and maintenance should be the same as for formed concrete
and concrete block walls. If unusual materials such as timber, or used
tyres, are used as a facing it should be checked to see that it is not rotting,
or perishing.
OTHER WALLS
Cantilevered and anchored walls (Figure 6) - rely on earth pressure on
the low side, rather than self-weight, to provided the restoring force and
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
excess of 3 m height normally require at least one row of permanent
ground anchors.
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
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
                                                                                      Figure 6 - Typical cantilevered or
GeoGuide LR4 under the heading "Rock bolts and rock anchors".
                                                                                                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