Landslide Hazard Report_compressed

Specialists in transport geotechnics

   Table 4: Risk Level Implications

             Risk Level                                                        Example
                                                                             Implications
                                Unacceptable without treatment. Extensive detailed investigation and research, planning and
                                implementation of treatment options essential to reduce risk to Low; may be too expensive and not
         VH       Very High     practical. Work will likely cost more than the value of the property


         H          High        Unacceptable without treatment. Detailed investigation, planning and implementation of treatment options
                                required to reduce risk to Low. Work would cost a substantial sum in relation to the value of the property.

         M        Moderate      May be tolerated in certain circumstances (subject to regulator’s approval) but requires investigation,
                                planning and implementation of treatment options to reduce risk to Low.

         L          Low         Usually acceptable to regulators. Where treatment has been required to reduce the risk to this level,
                                ongoing maintenance is required.

         VL       Very Low      Acceptable. Manage by normal slope maintenance procedures.


Notes:

1. “Existing Slopes” in this context are slopes that are not part of a recognizable landslide and have demonstrated non-failure
performance over at least several seasons or events of extended adverse weather, usually being a period of at least 10 to 20 years.

2. “Existing Development” includes existing structures, and slopes that have been modified by cut and fill, that are not located on or
part of a recognizable landslide and have demonstrated non-failure performance over at least several seasons or events of extended
adverse weather, usually being a period of at least 10 to 20 years.

3. “New Constructed Slope” includes any change to existing slopes by cut or fill or changes to existing slopes by new stabilisation
works (including replacement of existing retaining walls or replacement of existing stabilisation measures, such as rock bolts or catch
fences).

4. “New Development” includes any new structure or change to an existing slope or structure. Where changes to an existing structure
or slope result in any cut or fill of less than 1.0m vertical height from the toe to the crest and this change does not increase the risk,
then the Existing Slope / Existing Structure criterion may be adopted. Where changes to an existing structure do not increase the
building footprint or do not result in an overall change in footing loads, then the Existing Development criterion may be adopted.

5. “Existing Landslides” have been considered likely to require remedial works and hence would become a New Constructed Slope
and require the lower risk. Even where remedial works are not required per se, it would be reasonable expectation of the public for a
known landslide to be assessed to the lower risk category as a matter of “public safety”.




2.2.2 Surface Characteristics of Landslides and Hazard Identification
The ability to recognise the presence of a landslide is dependent on a number of factors: fresh
landslides are generally easily recognisable providing they have distinct scarps and runouts, but
some landslides are more subtle in morphology – such as creep and lateral spread. Recognition
of these may be dependent on the experience of the geotechnical professional and the ability to
recognise the morphological context.
In general terms, weathering processes will tend to form fairly uniform hill slopes; the presence of
landslides will disrupt this uniformity and form (mainly) concave features, which may have
hummocky ground or talus slopes at the foot of the hill where the failed material has
accumulated.
The slope may also show benches, scars or scarps where the ground has been displaced,
changes in vegetation may be present in historical landslide areas, and this may take the form of
smaller trees in the form of regrowth, or a patch of different species through change in
subsurface conditions and opportunistic recolonization.




10 May 2022                                    CGC-SR-2022-011-R01-Rev01                                                             Page 6