Addendum Report - Slope stability assessment - 400 Cooroy Mountain Rd, Cooroy

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Project DMS                                                                                    17385-002-Rev0
                                                                                               19 January 2022

An experienced engineering geologist completed a site-walkover assessment on 13 January 2022, in order
to make an appraisal of the current site conditions in the location of the pool deck. A two tier masonry
block retaining wall (~2.5 m total retained height) was present along the western and south-western edges
of the proposed deck area; with an irregularly shaped concrete pool shell to the south-east.

From the base of the wall and pool shell exposures some more recently tipped fill was noted, left inclined at
around 25° (Ref. Text Figure 2 below). Below this, exposures of residual soils were noted to the east of the
pool shell. The tipped fill was estimated to be in the order of about 0.5 m to 1 m depth over the slope. The
overall natural ground slope in this area was estimated at around 14°. Measurements of slope angles were
taken on site using a hand-held inclinometer.




Text Figure 2: View looking west over area of proposed deck showing tipped fill
In our previous investigation report (Ref. 17385-001-Rev0, dated 27 November 2017), test pits TP2 and
TPS were located to the south-eastern part of the new pool deck. These encountered stiff to very stiff,
residual sandy clay soils to depths of between 0.4 m and 0.7 m BGL, with highly weathered rhyolite below
to excavation refusal depths of between 1.2 m and 1.3 m BGL (depths at the time of the original
investigation fieldwork, 9 November 2017).

We understand that the pool deck is a structurally separate element from the adjacent retaining walls and
pool shell, and that being the case, we would recommend that all footings for the proposed pool deck are
taken through any recently placed fill, and residual soils, to be founded a minimum of 0.3 m into very low
strength (or stronger) weathered rock. It is understood that steel reinforced concrete bored piles are
proposed for the footing construction, which is considered suitable from a slope stability viewpoint. Footings
so founded could be designed using a maximum allowable end bearing pressure of 1 MPa. If the tipped fill
described above is to be left in place it should be trimmed no steeper than 1 V:2.5H (or flatter) and
protected from erosion with vegetation.

The risk assessment for the new pool deck has been carried out according to the AGS 2007 Practice Note
Guidelines for Landslide Risk Management. Based on the extents of the pool deck shown in Text Figure 1 ,
and that the footings are constructed as above, it is our assessment that a Low Risk of landslide could be
achieved, and that the assessment given in Table 3 of our previous report remains valid to the proposed new
pool deck construction. Considerations in our previous investigation report regarding other geotechnical
matters (such as siting of the deck, earthworks and drainage); would also be critical in maintaining a Low
Risk of slope instability.




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Project DMS                                                                              17385-002-Rev0
                                                                                         19 January 2022

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

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

TECTONIC GEOTECHNICAL PTY LTD




 Robert Gibb BSc (Hons)                                  Scott Davis BEng CPEng RPEQ 16439
 Engineering Geologist                                   Senior Geotechnical Engineer


Attachments: Limitations




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                                        geotechnical & environmental engineers




                                                 LIMITATIONS


This document has been prepared for the purpose outlined in Tectonic’s proposal and no responsibility is
accepted for the use of this document, in whole or in part, for any other purpose.

The scope of Tectonic’s Services are as described in Tectonic’s proposal, and are subject to restrictions
and limitations. Tectonic did not perform a complete assessment of all possible conditions or
circumstances that may exist at the site referenced in the report. If a service is not expressly indicated, do
not assume it has been provided. If a matter is not addressed, do not assume that any determination has
been made by Tectonic in regards to it.

Conditions may exist which were undetectable given that economic and time constraints limit the practical
extent of geotechnical investigation. Variations in conditions may occur between investigation locations,
and there may be special conditions pertaining to the site which have not been revealed by the
investigation and which have not therefore been taken into account in the document. Where variations exist
on site, additional studies and actions may be required.

Tectonic’s opinions are based upon information that existed at the time that the work was performed. The
passage of time, man-made or natural events, may alter the site conditions. It is understood that the
Services undertaken allowed Tectonic to form an opinion of the actual conditions of the site at the time the
site was visited and cannot be used to assess the effect of any subsequent changes in the quality of the
site, or its surroundings, or any laws or regulations.

Any assessments made in the preparation of this document are based on the conditions indicated from
published sources and the findings of the investigation described. Actual subsurface conditions may differ
from those indicated in the document (e.g. between boreholes or test pits). No warranty is included, either
express or implied, that the actual conditions will conform exactly to the assessments contained in this
document.

Where data supplied by the client or other external sources, including previous site investigation data, have
been used, it has been assumed that the information is correct unless otherwise stated. No responsibility is
accepted by Tectonic for incomplete or inaccurate data supplied by others.

This document is provided for the sole use by the Client and its professional advisers. No responsibility
whatsoever for the contents of this document will be accepted to any person other than the Client. Any use
which a third party makes of this document, or any reliance on or decisions to be made based on it, is the
responsibility of such third parties. Tectonic accepts no responsibility for damages, if any, suffered by any
third party as a result of decisions made or actions based on this document.




Rev 1 (March 2016)