Att 3 - Landslide Risk Assessment

                                                                                      Job No: 23-458
                                                                                              Page 5

2.0 LANDSLIDE RISK ASSESSMENT / METHODOLOGY

Based on the information provided by the Client, our methodology in addressing the geotechnical brief
included the following:

    •   A geotechnical site walkover for landslide risk assessment of the existing site slopes, fill
        conditions, and proposed earthworks;
    •   Review of the survey data for the site;
    •   Review of proposed development plans;
    •   Review of the Engineering Drawings;
    •   Review of the previous geotechnical report by AW Geotechnics; and
    •   Review of AS3798 – Guidelines on Earthworks for Commercial and Residential Developments;
No Level 1 certification report has been provided for the onsite fill. Hence, the fill is considered to be
uncontrolled until it is proven otherwise.
A suitably qualified and experienced geotechnical engineer undertook the detailed site walkover on
October 17, 2023.
Onsite drilling was not part of this slope stability risk assessment because a previous investigation report
for the site was made available to Qualtest for review.

2.1 Geotechnical Issues

Based on the site conditions, issues of geotechnical relevance are the following:

    •   The overall site slopes of approximately 15o, and the presence of localised site slopes of up to
        30o generally falling to the east;
    •   The low bearing capacity of the site as identified in the AW geotechnics report;
    •   The planned removal of the existing building;
    •   The risk of failure of the existing unsupported cut and fill batters, as well as existing retaining
        structures around the site;
    •   The potential and consequences of failure of the proposed new structures on the site, including
        cut-to-fill batters, retaining structures and footing systems.

2.2 Landslide Assessment Criteria and Methodology

With a view to managing risks to life and property associated with natural disasters such as landslides,
etc., posed to occupants in a development, it is Council's requirement that the susceptibility of such
developments to natural disasters should be addressed. The following criteria are considered as part of
Council's Operational Work condition for approving a Site:

    •   That the landslide risk susceptibility of a site should be deemed to be 'low' in accordance with
        'Landslide Risk Management' Australian Geomechanics Journal Vol. 43, No. 1 March 2007.
    •   Part B of the Council's requirement indicates that where the average grade of a finished lot
        surface exceeds 15%, the site must be certified by a geotechnical professional as having a 'low
        risk' in relation to landslide.
The methodology adopted for the landslide risk assessment at this site was to the requirement of
Australian Geomechanics (AGS) Landslide Risk Management guidelines as contained in the Australian
Geomechanics Journal Vol. 42 No. 1, March 2007. Due to the broad scope of the AGS journal, it does
not specifically cover small-sized developments. The work of Hargreaves and Kidd (2012), which is in
line with AGS Vol. 42, No. 1 2007, has conceptualised landslide risk management in a way that is
amenable to small-sized developments and has been adopted for this assessment.

This study by Hargreaves and Kidd (2012) provides an evaluation of the level of site hazards in relation
to landsliding. The hazard rating is based on a five-level system and classified into Very Low, Low,
Moderate, High, and Very High categories.

The implications of this hazard rating classification are indicated in Table 1.
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                                                                          399 Sunrise Road, Tinbeerwah