Development Application Part 2 of 2 Planning report Geotechnical report and plans MCU11/0168 & OPW11/0257

1   GeoConsulting, Report 115988, July I1                                                                           Page 6
    Lot 34 Marcus Dues Court, Marcus Beach


    reach a balance between the progressive weathering of the rocks and the removal of the weathered
    debris by water erosion, landslides then occur only rarely and usually only on the steepest scarps. Such
    a balance exists even in geologically sensitive situations such as basalts regions, although it may be
    relatively more delicate.         Landslides activity has increased in many areas of Southeast Queensland
    within the last century because clearing of forests have disrupted the delicate balance in geologically
    sensitive situations.


    Landslides can be mobilised by both natural causes or by human activity. Natural causes may include:-
              *     Saturation of slope material from rainfall or seepage
              ♦     Undercutting of scarps and banks by erosion
               ♦    Gradual weathering and subsequent decrease in the internal strength properties of materials
               ♦    Vibrations caused by earthquakes


    Human activity may include: -
               ♦    Slope modification by earthwork activities (cutting and/or filling)
               ♦     Disruption to natural drainage characteristics
               ♦     Leaking pipes, pools, dams and tanks
               ♦     Inappropriate stormwater discharge
               ♦     Removal of vegetation


    In general, high intensity rainfall events combined with some form of human activity is by far the most
    common trigger of landslides in Australia.


    4.3        Classification of Landslides
    Landslide classification is based on the Vames (1978) system which has two terms. The first term
    describes the material type and the second term describes the type of movement. Table 4 shows how
    the two terms are combined to give the landslide type. Figure 1 gives schematics to illustrate the major
    types of landslide movement.


                                                Table 4 Landslide Classification

                                                                               "Type of Materials
                                                                                            Engineering Soils
          Type of movement
                                                    Bedrock                      Predominantly           Predominantly
                                                                                     Coarse                   Fine
                     Falls                          Rock Fall                        Debris Fall           Earth Fall

                    Topples                       Rock Topple                     Debris Topped           Earth Topple

                             Rotational
          Slid es                                  R oc k Slid e                    D e b ri s Slid e      E art h Slid e
                         Translational
                                                   Rock Flow                        Debris Flow           Earth Flow
                     Flows
                                                  (Deep cree)                       (Soil Creep)          (Soil Creep)
                              Complex (Combination of two or more principle types of movement)



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