Response to Information Request - MCU12/0184

Geotechnical and Slope Stability Investigation




      .   Fill batter slopes should not exceed 1V:3H. All surface water should be diverted away from the
          fill batters with engineered drainage paths.

      .   Where fill is placed over side slopes of the ridges, the subgrade slopes should be cut to from a
          series of horizontal terraces to ensure that the fill is bonded to the subgrade.


          Retaining structures exceeding 0.9 metre in height must be designed by a professional
          engineer in accordance with AS4678-2002 "Earth Retaining Structures". The design should be
          adequately designed for earth pressures, surcharges and elevated ground water conditions and
          fully account for sloped backfill and retained ground. The adopted design should also include
          conservatively sized drainage and regularly scheduled maintenance measures.

      .   Control of surface water flows is important for slope stability control. Well designed and

          engineered surface water controls should be used to reduce the infiltration potential of the site
          during and following rainfall. To divert runoff away from footing system, cut and fill batters and
          retaining walls, the use of appropriate self-flushing spoon drains is recommended.

      .
          Discharge from rainwater tanks, roof water and runoff collection systems must be controlled
          and discharged as diffuse flow at least 10 metres down slope of any footing, batter and

          retaining wall.

      .   Reference should be made by building designers and landscape designers to "Good Hillside
          Practice" as published by The Australian Geomechanics Society in 2007 along with Australian

          Geoguide LR8 (Construction Practice) a copy of which is attached in Appendix F. Appendix F
          also provides GeoGuides on Slope Management and Maintenance from the Australian
          Geomechanics Society. Coffey recommends adherence to these guidelines which should be
          read in conjunction with this report.


7.9         Impact Assessment
The construction of seven large sheds as described in this report has been assessed to have a low risk

assuming the recommendations of this report are implemented.

This risk level may be considered acceptable to the designers and owners. However, any opportunities
to reduce the risk should be sought and undertaken if reasonable and practicable. This risk
assessment has been based on the assumption that the proposed structure will be designed by a

competent engineer in consideration of the guidance set out in the GeoGuides in Appendix F. This
level of risk is not likely to adversely affect the stability of the site or the adjacent lots provided the
recommendations outlined in this report are adopted. There are no specific requirements for the design
of the driveway, sewer or service connections other than the recommendations set out in this report.

On the basis of our assessment, the building envelope shown in the MWA drawings of the proposed
structures is considered to provide a stable building platform for the proposed construction. Access and
services to the building envelope can also be provided without significant risk. As the site is relatively

steep, the recommendations of this report and the guidance provided in the Geoguides in Appendix F
should be adopted. These represent standard good engineering practice for building on slopes.

It is noted that, providing the recommendations of this report are adopted in the design and construction
of the residence within the defined building envelope and associated access and service connections, a
FOS against landslip failure has been assessed to be greater than 1.5.




Coffey Geotechnics                                                                                             7
GEOTKPAR01945AAJA
23rd April 2013