geotech report · 132003.220660.5

5.2.4 Geotechnical Constraints to Development
Based on the contents of Sections 5.1 and 5.2, we consider that there are geotechnical constraints to the
proposed development with regards to existing slope instability. However, we note that the excavations
required to achieve design surface levels may extend below the existing building footings and temporary
batter slopes will not, in most cases, be achievable. Consequently, appropriate care will need to be exercised
when completing the excavations and providing support for both the cut faces in sands and the existing
footings. Further advice is provided in the following sections of this report.

Provided the proposed development is designed and constructed using the advice presented in Section 6, we
consider that following construction, the levels of risk to life and property will remain at “Acceptable” levels.


6     COMMENTS AND RECOMMENDATIONS

6.1    Site Layout and Development Details
As noted in Section 2 above, the proposed additions to the north and north-east of the house and the
proposed lift area will require excavations to a maximum depth of approximately 1.5m adjacent to the
northern side of the house. In addition, a new grass covered area will be constructed immediately to the east
of the existing house with the eastern (downslope) side of the grass covered area supported by concrete
block retaining wall (maximum height about 1m).



6.2    Site Classification
Due to the presence of ‘uncontrolled’ fill and noting the low bearing capacity of the near surface soils, the
site classification is Class P in accordance with AS2870-2011. The standard designs in AS2870-2011 are not
applicable to the proposed alterations and additions and so the design of the footing system must therefore
be carried out using engineering principles.



6.3    Demolition and Excavation

6.3.1 Dilapidation Survey
We forewarn that Unitywater may require a dilapidation survey report be completed on the sewer main that
extends north-south through the site and below a portion of the proposed walkway connecting the addition
and the lift access. Unitywater should be asked to confirm that the report, if required, presents a fair record
of existing conditions as the report may assist the client in defending themselves from unfair damage claims.



6.3.2 Demolition and Excavation Methods
The excavation recommendations provided below should be complemented by reference to the current Safe
Work Australia Code of Practice ‘Excavation Work’.



32032URrpt                                         11