Appendix H - Slope Stability Assessment

Brett Hage                                                                                                    22328-001-Rev0
                                                                                                           14 September 2022

Immediately off Black Mountain Range Road to the west of proposed Lot 2, a road embankment was present
being <1 m height and inclined at about 25°. Natural ground below this sloped down at between 10° and 18°,
with the cut behind the earthworks pad in the Lot 2 building area being about 25° to 30°.
The earthworks pad was about 5 m to 6 m width, with the borehole drilling information indicating < 1 m height
of fill had been placed on the downslope side. This was battered at about 32°, with some evidence of rilling
(about 100 mm depth) over the face noted.
Natural ground below the proposed building area was sloping at between 13° and 15°, down to the east.
Below the centre of the proposed Lot 2 building area a very gently defined, rounded spur was present, with
the head of a larger (dry) gully present further to the north/north-east. The gully head was sloping at about
20°. To the south-east of the rounded spur, an intermediate drainage line proliferated. Some filling appeared
to have taken place across the top of this historically (possibly for horticultural purposes), leaving a number
of ‘benches’ with an overall slope of about 30° (the benches were about 2.5 m to 3 m wide, with the face of
fill at about 35° to 40°). At the base of the historic fill terraces, lusher ground was noted, with seepage
observed.
Despite the above, no irregular surface features were observed which would indicate wider scale global
slope instability (e.g. ‘hummocky’ ground, tension cracks).



                                         Broad gully head developing north-
                                         east of proposed Lot 2 building area
                                                                                             Overall existing lot boundary




                                                                                  Main drainage lie
                             Intermediate drainage line;
                             seepage at head




Text Figure 5: Image showing ground surface contours (courtesy Noosa Council [NC] Interactive Maps)

Text Figures 6 and 7 below and overleaf illustrate the site conditions at the time of our inspection.


                                                                 Drill rig at borehole BH1




Text Figure 6: View looking south over building area on proposed Lot 2




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