220328 - Edwards Street - Slope Stability Assessment

Bev Jenner Const.                                                                                         22073-001-Rev0
C/- Westera Partners                                                                                       25 March 2022

Table 2: Details of Qualitative Risk Assessment for Property (AGS 2007)
                                                               Assessed
 Hazard                           Likelihood   Consequence       Risk     Comments


                                                                          Given the moderate natural gradients through the
                                                                          proposed building area (≤9° whereas limit of
                                                                          equilibrium for stability for loose sands typically
                                                                          ≥30°), lack of groundwater, it is considered Unlikely
 1: Failure through loose soils
                                   Unlikely      Medium             Low   that a landslip would develop in these materials,
above the foundation depth.
                                                                          subject to implementation of the recommendations
                                                                          in Section 4. Given a potential Medium impact from
                                                                          such instability the resultant risk would be Low as
                                                                          per AGS 2007.



                                                                          The likelihood of a deep failure through the medium
                                                                          dense (or denser) natural sands below the proposed
 2: Deep failure through the                                              foundation depth is assessed as Rare due to the
medium dense (or denser)                                                  strength of the materials, lack of precedence of such
                                    Rare          Major             Low
natural soils below the                                                   movements locally and no signs of any existing deep
foundation depth.                                                         seated slope instability. Although the consequence of
                                                                          such a failure would be Major, the resultant risk would
                                                                          be Low as per AGS 2007.




The potential impacts on slope stability of the development components have been assessed, and the
measures recommended below in Section 4 have been designed to mitigate those impacts.


4.0        RECOMMENDATIONS
General recommendations to help maintain the stability of the site are given in the document Some
Guidelines for Hillside Construction, which is attached.

4.1       Site Layout and Development Limitations
The planned extents of the proposed development shown in Text Figure 2 are acceptable from a slope
stability viewpoint. Should any revisions be made to the proposed extent of the development, Tectonic must
review these prior to construction to assess if there are any impacts on slope stability.

To achieve a Low Risk of instability, the following is recommended:

          All retaining walls exceeding 1 m high and/or subject to surcharge loads must be engineer designed
           and certified, which must include an assessment of global and internal stability.
          Any proposed fill exceeding 1 m must be fully supported by an engineer designed and certified
           retaining structure, unless assessed and approved by a suitably qualified and experienced
           geotechnical RPEQ.
          Deepened, piled footings will be required with design and construction of footings to be undertaken
           in accordance with Section 4.3.

No specific earthworks details were available at the time of reporting; however, based on existing site
conditions and the proposed development it is anticipated that bulk cutting of up to about 3 m depth would be
required to reach the design floor level for the basement. The swimming pool would require cut of about
1.5 m depth. Filling is expected to the corners of the block either side of the entrance, of about 1 m to
2 m height, to form landscaped gardens and exterior stairs.

Should proposed cuts/fills exceed these quantities, Tectonic must assess the impacts on slope stability
before construction.




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