220328 - Edwards Street - Slope Stability Assessment

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

4.5    Drainage
Surface diversion drainage should be constructed above the crest of any new cut or fill embankment (e.g.
grassed or landscaped swales or diversion mounds). Adequate site drainage must be installed to ensure
that stormwater runoff is directed away from building walls and footings (including overflow form the
proposed pools affecting the main dual occupancy buildings).
Although unlikely, if groundwater seepage is encountered during excavations, Tectonic must be notified to
assess the impact on stability.

Subsurface drainage must be installed behind any retaining walls (e.g. slotted ‘aggi’ pipe wrapped in filter
‘sock’ placed in gravel backfill). Depending on matters such as the extent of drainage installed and site-
specific groundwater conditions, the designer must make an assessment of hydrostatic pressure to be
accounted for in the design of the retaining structure. It is assumed that the pool floors will include a
hydrostatic pressure relief valve. The outlet pipe from this valve must be taken to ‘daylight’ at the ground
surface.
All excess stormwater collected around the site (including overflow from rainwater tanks and pool) should be
directed by pipes or lined channels to discharge into the existing stormwater infrastructure along Edwards
Street. Subsurface disposal of stormwater must not be undertaken.



5.0     CONCLUSION
It is assessed that there would be a Low Risk to the proposed residence from slope instability subject to
implementation of the recommendations given in this report.


6.0     LIMITATIONS
Your attention is drawn to the document Limitations, which is attached to this letter report.

Please contact the undersigned should you wish to discuss any of the above matters.

Yours faithfully

TECTONIC GEOTECHNICAL PTY LTD




Robert Gibb BSc (Hons)                                     Ashley Davey RPEQ 8159
Engineering Geologist                                      Principal Geotechnical Engineer


Attachments: Qualitative Terminology for Use in Assessing Risk to Property
             Some Guidelines for Hillside Construction
             Limitations




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