Geotechnical Investigation Report

                                      PRACTICE NOTE GUIDELINES FOR LANDSLIDE RISK MANAGEMENT 2007
                                                              APPENDIX C: LANDSLIDE RISK ASSESSMENT
                                    QUALITATIVE TERMINOLOGY FOR USE IN ASSESSING RISK TO PROPERTY


   QUALITATIVE MEASURES OF LIKELIHOOD

Approximate Annual Probability
                                             Implied Indicative Landslide
                                                                                                                     Description                                           Descriptor               Level
Indicative          Notional                    Recurrence Interval
  Value             Boundary
   10-1                5x10-2
                                              10 years                           The event is expected to occur over the design life.                                ALMOST CERTAIN                   A
                                                                    20 years     The event will probably occur under adverse conditions over the
        -2
   10                                      100 years
                                                                                 design life.
                                                                                                                                                                     LIKELY                           B
                            -3
     -3               5x10                                       200 years
   10                                      1000 years                            The event could occur under adverse conditions over the design life.                POSSIBLE                         C
                      5x10-4                                     2000 years
                                                                                 The event might occur under very adverse circumstances over the
   10-4                                   10,000 years
                                                                                 design life.
                                                                                                                                                                     UNLIKELY                         D
     -5               5x10-5                                     20,000 years
   10                                                                            The event is conceivable but only under exceptional circumstances
                                         100,000 years                                                                                                               RARE                             E
                                                                                 over the design life.
     -6                5x10-6                                    200,000 years
   10                                   1,000,000 years                          The event is inconceivable or fanciful over the design life.                        BARELY CREDIBLE                  F
   Note:     (1)   The table should be used from left to right; use Approximate Annual Probability or Description to assign Descriptor, not vice versa.


   QUALITATIVE MEASURES OF CONSEQUENCES TO PROPERTY

  Approximate Cost of Damage
                                                                                               Description                                                                 Descriptor               Level
Indicative           Notional
  Value              Boundary
                                         Structure(s) completely destroyed and/or large scale damage requiring major engineering works for
   200%                                                                                                                                                             CATASTROPHIC                      1
                                         stabilisation. Could cause at least one adjacent property major consequence damage.
                     100%
                                         Extensive damage to most of structure, and/or extending beyond site boundaries requiring significant
   60%                                                                                                                                                              MAJOR                             2
                                         stabilisation works. Could cause at least one adjacent property medium consequence damage.
                       40%
                                         Moderate damage to some of structure, and/or significant part of site requiring large stabilisation works.
   20%                                                                                                                                                              MEDIUM                            3
                                         Could cause at least one adjacent property minor consequence damage.
                       10%
    5%                 1%                Limited damage to part of structure, and/or part of site requiring some reinstatement stabilisation works.                 MINOR                             4
                                         Little damage. (Note for high probability event (Almost Certain), this category may be subdivided at a
   0.5%                                                                                                                                                             INSIGNIFICANT                     5
                                         notional boundary of 0.1%. See Risk Matrix.)
   Notes:    (2)   The Approximate Cost of Damage is expressed as a percentage of market value, being the cost of the improved value of the unaffected property which includes the land plus the
                   unaffected structures.
             (3)   The Approximate Cost is to be an estimate of the direct cost of the damage, such as the cost of reinstatement of the damaged portion of the property (land plus structures), stabilisation
                   works required to render the site to tolerable risk level for the landslide which has occurred and professional design fees, and consequential costs such as legal fees, temporary
                   accommodation. It does not include additional stabilisation works to address other landslides which may affect the property.
             (4)   The table should be used from left to right; use Approximate Cost of Damage or Description to assign Descriptor, not vice versa


   91                                                          Australian Geomechanics Vol 42 No 1 March 2007