Development Application Part 2 of 2 - Plans 7 Banksia Avenue Noosa Heads · OPW10/2120

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                                                                                   Job No. DE101061




5.0       SLOPE STABILITY

At the time of the walkover survey, the site displayed no evidence of existing or recent past
slope instability involving large scale or small scale movements of significant quantities of soil or
rock in a short duration event such as a slip or landslide.

There were no signs of instability, such as uneven or hummocky ground or leaning trees. Minor
creep movement of the surficial very loose and loose sands to depths of up to 0.3m is expected
after heavy rainfall but is not anticipated to significantly impact on the proposed development.
There is no evidence of erosion or any other soil instability mechanism across the property.

Based on the Elevation Drawings provided in the DEC Consulting Engineers Report, cut to fill of
up to 1.5m is expected as part of the residential development. It is assumed that all earthworks,
including cuts and fills will be structurally engineered to the recommendations described in
Section 6.0 of this report. Due to the moderately sloping terrain, it is assessed that the most
likely mechanism of slope instability will be related to the very loose to loose natural sand within
the upper 0.3m soil profile, and natural surfaces exposed during the proposed cut or fill
earthworks.

This potential instability will be confined to slumping and erosion after rainfall events within
unvegetated fill or the loose natural sands to depths of up to 0.3m. The descriptor "Possible"
means that "the event could occur under adverse circumstances" and is considered appropriate
to describe the likelihood of a rainfall triggered slump, with an Annual Indicative Probability of
about 10'3. Slumping and erosion of fill and loose natural sands would likely cause limited
damage to part of the house structure and landscaping, with a descriptor of damage as "Minor"
to "Insignificant".

On this basis, the risk to property can be assessed as "Low to Moderate" if the minor earthworks
and other construction aspects are carried out in accordance with our recommendations. This
level of risk is acceptable as long as the guidelines in Section 6.0 are followed at all times.


6.0       GENERAL GUIDELINES FOR DEVELOPMENT

The following development guidelines, in conjunction with the attached Guidelines for Hillside
Construction, must be implemented to maintain a Tolerable level of risk for the residential
development:-

          All building and retaining wall footings must found in the medium dense natural sands at
          a minimum depth of 0.4m below the natural ground surface, or at least 0.4m below the
          surface of controlled fill, The supervision and certification of controlled filling platforms
          can be conducted by this office where required.

      •   Strip, pad, stiffened raft footings or bored or screw piles may be used for the residential
          footing design. It is recommended that a suitably qualified geotechnical professional be
          engaged during installation of footings to confirm a competent foundation base.

      •   No structural development is to found within any other material apart from the medium
          dense natural sands encountered at 0.3m to 0.5m below the natural ground surface, or
          controlled fill.

          Prior to any filling, all foundation slopes must be benched to provide a suitable key for
          the fill materials. Benches exceeding 0.5m in height must be battered to prevent batter
          collapse.




Ref: 14858B DEC Consulting Engineers Pty Ltd                           MORR/SON GEOTECHNIC