Appendix F - Geo-Environmental Investigation Report · RAL24/0003

                               PROPOSED SUBDIVISION
                               41 TALLOWWOOD PLACE, BLACK MOUNTAIN

The proposed new development area is located on a moderately sloping, relatively linear and planar shaped
part of the ridge flank, with gradients typically in the order of about 15° to 17°, steepening downslope up to
about 20°.
To the south of the proposed new building area, the ground surface had been altered by previous cut and fill
earthworks presumably during the construction of Tallowwood Place. The roadside fill embankments were
estimated to range up to about 1.5 m high, and were typically battered between 30° and 35°; however,
crestline slumping was observed in parts resulting in steeper sections. An apparent track was observed
cutting across the roadside fill embankment down to the proposed new building area. It appeared that cut/fill
earthworks less than 1 m depth/height had been undertaken to form the track; however, due to the long
grass visual appraisal was difficult.



   Apparent Track




                                                                          Rock Fill Embankment




Text Figure 6: Views of roadside fill embankments

A drainage line intersected the ridge flanks between the existing residence and proposed new building area.
The roadside embankment across the head of this drainage line comprised imported rock fill, being about
3 m high, and battered between about 25° and 30°. Rock spalls extended from the toe of the rock fill batter
to the southern property boundary, with a level track about 5 m wide traversing the head of the drainage line.
It was estimated that about 2 m of fill had been placed over the drainage line.

Based on the above observations, it appeared that a section of Tallowwood Place about 40 m to the south-
west of the existing residence had been impacted by a previous landslide. It appears that the area was
remediated using rock fill; however, no design details were available. A review of higher resolution aerial
imagery from Nearmap and Qimagery suggests that the rock fill embankment has been in place since 2006;
however, due to the low resolution of earlier images it cannot be confirmed prior to this.

A stormwater pit was observed at the crest of the rock fill embankment; however, there was no obvious
evidence of an outlet below the toe of the batter. Text Figures 7 and 8 overleaf illustrate this area at the time
of the investigation.




22 May 2023
Report No. 23099-001-Rev0                               5