Response to Information Request - MCU12/0184

Geotechnical and Slope Stability Investigation




Table 1: Summary of Risk Assessment


                                                                 ASSESSED RISK               ASSESSED RISK WITH
                                                      "   rn"    m, "I                        I!!!!   "’

,
                        HAZARD                                  WITHOUT DESIGN                             DESIGN
    ,

                                                                RECOMMENDATION               RECOMMENDATIONS


1: Shallow failure in the footing zone of the
                                                                           Low                              Low
future structure


2: Deep failure through the weathered rock
                                                                           Low                              Low
below the future structure


3: Failure of engineered retaining structures or
                                                                         Moderate                           Low
cut and fill batters on the site.




7.8          Special Requirements for Construction and Site Drainage with Respect
             to Slope Stability

Given the slope of the site and the proposed works on the site, consideration should be given to the
results of the risk assessment when planning the proposed subdivision. It is important to recognise that
a low to moderate landslide risk has been assessed for this                property, and that the future design should
aim to reduce this risk wherever possible. The following recommendations are made in relation to the
construction of a residence within the proposed building envelope, and with respect to making

provisions for the site slope stability conditions.

It is recommended:

        .   The footings for the proposed sheds should be designed using a strip or pad footing founded in

            very stiff residual soils or siltstone.

        .   The founding conditions must be inspected by a suitably qualified geotechnical engineer or

            engineering geologist during construction.

        .   Footing excavations should not be left open for prolonged periods to avoid exposure of the
            founding soils to the elements, and to prevent deterioration of in-situ strength.

        .
            Any cut or fill batters constructed on the site should be benched to no greater than 1.2 metres
            at an average slope not exceeding 1V:1.5H.


For works associated with the construction of the proposed structures or for providing access or service
connections elsewhere on the site, the following recommendations are made:

        .   Permanent cut batter slopes should not exceed an average slope of 1V:2H. All surface water
            should be diverted away from the top of the batter slope via engineered drainage paths.

            Regular maintenance of slopes will be required to preserve their condition.

        .   All fill should be placed under a Level 1 overview in accordance of the requirements of AS3798-
            2007 "Guidelines on Earthworks for Commercial and Residential Developments" and certified

            by a geotechnical inspection and testing authority.




Coffey Geotechnics                                                                                                   6
GEOTKPAR01945AA1A
23rd April 2013