Requirements for geotechnical reports

The purpose and applicability of this information sheet is to:

Development on steep and/or potentially unstable land may be adversely affected by:

Inappropriate development on steep and/or potentially unstable land may have significant risks for property and human safety on the site, and in areas above and downslope of the site. To ensure such risks are avoided or minimised, the Planning Scheme require Geotechnical Reports to be prepared where development may affect or be affected by land instability.

 

Expertise required in preparing a geotechnical report

The preparation of a geotechnical report requires specialised skills. Geotechnical reports prepared by an appropriately qualified and experienced Geotechnical Engineer (Registered Professional Engineer of Queensland (RPEQ)) – will only be accepted by Council. It is highly desirable that the person has local experience with steep and unstable areas, and demonstrable general experience with steep and unstable land. The Geotechnical Engineer must hold and maintain professional indemnity insurance for any one occurrence of at least $2 million and have Geotechnical Investigations listed as an activity on the policy.

 

Requirements of a geotechnical report

Geotechnical Reports must be addressed to Toowoomba Regional Council and clearly state that the report is for the use and reliance upon by Council and must not contain any limiting clauses in this regard. A Geotechnical Report must document:

The extent and detail of investigation will depend upon the particular site characteristics and the nature of the development being proposed. Council will require each report to demonstrate a scope and depth of investigation appropriate to the specific proposal. The extent of the work carried out is to be determined by the Geotechnical Engineer, provided the investigation concludes that the site, house, retaining wall or other features under assessment have a stability risk acceptable to Council, as described here:

The preferred format of the Geotechnical Report is outlined in the table below.

1.  Introduction

1.1 Details of development

1.2 Site location and description (including survey coordinates/coordinate system)

1.3 Method and Scope of Investigations

1.4 Qualifications of Responsible Individual(s) and/or Company

2.  Description of Existing Conditions

2.1 Geology (local and regional)

2.2 Topography

2.3 Groundwater

2.4 Surface drainage

2.5 Vegetation

2.6 Buildings, Other Structures etc.

3.  Assessment of Land Stability

3.1 Existing Conditions

3.2 Geotechnical Constraints to Development

4.  Description of Proposed Development

4.1 Site Layout

4.2 Proposed Development Components

4.3 Potential Geotechnical Effects

5.  Assessment of Development Impacts

5.1 Site Layout

5.2 Roadworks, Driveways and other Pavements

5.3 Earthworks (Excavation, Materials Usage)

5.4 Footings

5.5 Surface Drainage

5.6 Wastewater (Treatment and Disposal)

5.7 Underground Services

5.8 Overall Effect of Development on Stability

6.  Measures Recommended to Mitigate Impacts

7.  Summary and Conclusions

8.  Site Plans

Appendix - Field and Laboratory Test Results

 

Previous geotechnical reports

Where a Geotechnical Report has already been provided as support documentation to Council for previous development applications over the site (e.g. reconfiguring a lot or material change of use), these documents must be clearly referenced in the report. The reference should state the report was prepared as support documentation for the subsequent application (e.g. operational work or building work). Support documentation must be made available to Council and should be current and relevant to the proposed development i.e. not for an alternate form of development on the same site.

This Information Sheet outlines matters to be addressed in a geotechnical report, on the basis that such support documentation (earlier Geotechnical Report) is not available. In the event Geotechnical Reports and certifications for the previous applications are available, items already covered in these earlier reports/certifications may be referenced and covered in less detail.

 

Investigation of existing conditions

The Geotechnical Report must include an investigation of existing site conditions. This should include an assessment of the existing stability of the site and details of geotechnical constraints on building and/or other development works on the site. The investigation of existing conditions is to include descriptions of:

Field investigations and tests using methods such as excavators, drill rigs and/or seismic techniques will be required, particularly to assess the following factors:

The results of all field and laboratory tests must be included in the geotechnical reports, including the location and level (including datum) of field investigations such as boreholes and trench pits.

 

Conclusions

The Geotechnical Report must include conclusions about the overall suitability of the land for the proposed development. These are to include clear statements on whether:

all existing/proposed lots are presently stable;

all lots, and associated completed buildings (e.g. detached house) and infrastructure, will have an acceptable stability risk if constructed in accordance with the geotechnical recommendations - that is, a loss of life risk no greater than 1 x 10⁻⁵ per annum, and no more than a “Low” risk to residential property in accordance with AGS 2007 Guidelines ; and

any conditions need to be placed on the development of lot/s to maintain an acceptable risk of long term stability i.e. a factor of safety against slope failure of at least 1.5.

 

Recommendations

The Geotechnical Report must include recommendations that outline the following:

The recommendations must also provide guidance on appropriate measures required to make the site suitable for the proposed development, including:

 

Required certifications by geotechnical engineer

Formal certifications by a Geotechnical Engineer will be relied upon by Council to make judgements on the suitability of developing land for residential purposes and on approving stages of developments.

Certifications must be prepared by a Geotechnical Engineer (RPEQ), be addressed to Toowoomba Regional Council and be in the form of an engineering design certificate which includes a description of project components covered by the certification, the basis of certification, reference documents, any exclusions and details and signature of the RPEQ.

Additional certifications may be required by Council for the following circumstances:

Reconfiguring a lot

With the development application

Certification that:

Operational work

With the development application

Certification that:

Building Work/Planning Scheme Works

With the development application

Certification that:

 

Further information

For further specific information on Geotechnical Report requirements, please contact Council’s Development Services – Engineering Section on 131 872 or visit your nearest Customer Service Centre.

 

Related document

INFO 045 Requirements for geotechnical reports information sheet 

 

Disclaimer

The information contained in this sheet is a guide only.

This information has been prepared by Toowoomba Regional Council to help people gain an understanding of the Toowoomba Regional Planning Scheme. Please consult the Toowoomba Regional Planning Scheme for detailed information including maps (zones, local plans, overlays and priority infrastructure plan), provisions and policies. The content of this information sheet is not intended to replace the provisions of the Toowoomba Regional Planning Scheme

Last Updated: Friday, 06 September 2019 14:24