ALL ABOUT THE GEO TECH
1. Why does the Council want a geotechnical report?
The Environmental & Planning Assessment Act (NSW Government, 1979) requires a Consent Authority to consider a list of relevant matters when dealing with a development application; this normally includes whether a site is exposed to a hazard such as flood or landslip. To this end, most Local Councils [or Consent Authorities] in NSW now have an Environmental Planning Instrument which incorporates 'hazard maps' for bushfire, flood and landslip and these form the basis for a Council to request an appropriate report from qualified professional persons.
However, as the hazard maps usually only ‘identify’ the various hazards of an area to establish the criteria for the additional studies needed before approving the development, most Councils have a policy to request a geotechnical report for all site development proposals that the Council believes may be subject to geotechnical issues.
In short therefore, a Local Council wants you to submit a geotechnical report for your development in order that:
The Council can impose any special ‘conditions of consent’ [from a geotechnical point of view] on the development.
The Council has no responsibility, or liability for any geotechnical issues on the site.
Any responsibility / liability for a site’s geotechnical issues is transferred to the geotechnical engineer who advises on the site, and writes / submits the report to the Council.
2. Why do I need a geotechnical report?
You need a geotechnical report & the associated advice to help you:
• protect yourself and your most major investment against a site’s geotechnical hazards;
• minimise the risk of damage and / or major failure to the proposed development.
SCE also consider that a well thought-out geotechnical report is really an ‘investment’ in the long term security of the property.
If appropriate geotechnical advice is not obtained, and a problem occurs at your site / development as a consequence of geotechnical hazards / issues [e.g. slope instability, rock falls, excavation collapse, etc.],
then the biggest loser will always be the client / you because:
You will suffer considerable emotional and financial problems when you seek to obtain redress for the damage or failure.
2. Even if you recover all of your costs and the damage is repaired, it is most unlikely you will recover any recompense for your emotional & similar losses; you will also have undergone a very unpleasant experience.
SCE are also aware of a number of instances where ‘general’ civil / structural engineers have offered advice that extended to geotechnical issues with either:
• resultant serious problems for their clients; or
• greatly increased construction costs.
In short, SCE believe that you pay for good geotechnical advice whether you get it or not. In other words, a failure to obtain good geotechnical advice often leads to very considerable other costs [e.g. increased construction costs, costly building / structure repairs, etc.].
3. What information is needed in a geotechnical report to satisfy a Council?
It is firstly noted that a geotechnical report for a Council can vary enormously in scope and extent. Secondly, as the report for a Council has the purpose of transferring liability from the Council to the engineer who writes the report, the Council is usually not too concerned about the accuracy of the report content. A Council simply wants to shift liability for geotechnical issues from themselves to someone else.
Thus, a geotechnical report that would satisfy many Councils would be prepared by a suitably experienced geotechnical engineer and comprise a report text that includes:
1. A description of the site and its existing geotechnical hazards / risks.
2. Details of the site substrata [or sub-surface conditions], relevant geological information comments on groundwater seepage.
3. A risk assessment in accordance with the Australian Geomechanics Society [AGS] guidelines.
a) The risk assessment process normally requires a site plan and cross section to illustrate the development and the related site hazards.
b) A link to the AGS website where the guidelines are presented in full is provided here. AGS link.
4. Recommendations on the treatment of any identified hazards and design parameters & data for the construction of the development.