Attachment C - Soil Survey Report · MCU18/0013

Project No. 1-20119                                                                                                        Page | 9
March, 2018
Ref: 1-20119, 2018-03-02, BR VER 2
Sam Hopper – Slope Stability Assessment and Geotechnical Report - Proposed Residence, 24 Arakon Crescent, Sunshine Beach




4.0 HAZARD IDENTIFICATION

    4.1 General Discussion On Stability Assessment
The stability of a site is usually controlled by a number of factors:-

          The existing and proposed ground surface angles.
          The properties and nature of the subsurface profile, existing and proposed.
          Existing and future loadings of the site including the construction of structures and any
           earthworks proposed.
          The groundwater regime of the site.

Once the above factors have been evaluated and/or estimated, a geotechnical model is
developed to establish the possible site slope stability hazards. Based on the geotechnical
failure model, the potential of a failure eventuating either in the short or long term is assessed
and the site categorised accordingly.

Instability is usually associated with seepage. Near surface groundwater particularly at the toe
of slopes affects the slopes stability by:-

          Reducing the in situ strength of the material.
          Increasing pore pressures within the slope.
          Lowering the effective “weight” of the toe material.

    4.2 Typical Hazards
The rate of landslide movement varies from extremely slow (millimetres to centimetres per year)
to sudden and extremely rapid (metres per second) as with rock fall or debris flow. Sudden and
rapid events are the most dangerous because of the lack of warning and the high speed
resulting in an increased force of impact.

Typically landslides may be classified into the following main types (Refer Figure G1 Appendix
G):-
     Translational Slides: where failure occurs on a planar surface or surfaces, usually
       natural defects in the material such as fissures, joints or bedding. Material within the
       slide can remain relatively undisturbed.
          Creep Slides: where failure occurs as a gradual downslope progression of slope
           material (often extremely slow rates). The slide area may appear relatively undisturbed
           and identification of the slide is often reliant on surface features.
          Rotational Slides: where failure occurs through the material substance commonly on a
           concave surface. Material within the slide is considerably disturbed.
          Topple: where failure occurs from the end over end motion of rocks down a slope. Often
           resulting from closely spaced sub-vertical jointed rock outcrops.
          Falls: where movement is by free-falling or rolling of fragments on steep slopes with
           outcrops of closely jointed rock.
          Flows: where, after failure along a planar or concave surface, the material is
           transformed into a viscous fluid consisting of soil and rock particles suspended in water.
          Complex: where there is a combination of one or more of the above mechanisms.