Reference Document - Geotechnical Investigation Report - DBW24/0090 & RAP24/0025

                Rebecca Stead                                                                                     20248-001-Rev0
                                                                                                                3 September 2020

                4.5     Drainage
                Surface diversion drainage (e.g. grassed or landscaped swales or diversion mounds) should be constructed
                on the upslope (western) side of the residence to intercept any surface runoff and direct it away from the
                residence. Adequate site drainage must be installed to ensure that stormwater runoff is directed away from
                house walls, footings, batters and retaining walls.
                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 retaining walls in order to prevent the development of
                hydrostatic pressure (e.g. slotted ‘aggi’ pipe wrapped in filter ‘sock’ placed in gravel backfill).

                All collected surface water, roof water, and overflow from the any tanks/pools should be directed by pipes or
                surface lined channels (with erosion protection) to the Council stormwater system or to the north-eastern
                corner of the property. A rock fill weir must be constructed at the drainage discharge point.
                Subsurface disposal of stormwater (i.e. infiltration pits) must not be undertaken.



                5.0       CONCLUSION
                It is assessed that there would be a Low Risk to the proposed extensions 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




                Scott Davis BEng CPEng RPEQ 16439                          Ashley Davey BEng (Geological) RPEQ 8159
                Senior Geotechnical Engineer                                      Principal Geotechnical Engineer

                Attachments: Borehole Reports and Explanatory Notes
                             Qualitative Terminology for Use in Assessing Risk to Property
                             Some Guidelines for Hillside Construction
                             Limitations




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Document Set ID: 23080488
Version: 1, Version Date: 27/06/2024