Geotechnical Engineering Questions

Geotechnical engineering is a branch of civil engineering focused on analysing soil and rock properties to design foundations, slopes, and retaining structures. It ensures stability and safety in construction projects by studying subsurface conditions, addressing potential geohazards, and recommending appropriate earthworks and construction techniques.

It is the process in which the physical properties of the sites underlying soil or rock are assessed by types of ground testing, to provide information on the grounds physical properties to provide information for the design of foundation and recommendations to develop the site.

A geotechnical report advises you on the geological hazards and potential ground risks and constraints to develop your site, such as soft ground, slope stability, settlement risks, site excavations, liquefaction potential, etc. A geotechnical report is often required to support subdivision and building consent applications. The geotechnical report is also often a small cost of the overall development, and usually pays for itself in providing for an informed foundation design.

This is a hard question to answer, as each site is different and the scope of geotechnical services is tailored to reflect the site conditions and size of project. As a guide only, for a flat residential site, costs can range between $1000-$2000. For a steep residential site the costs can start from $2000 upwards. We recommend getting a number of quotes to compare.

The expiry date often stipulated by Councils in New Zealand is 10 years. On a geological time scale this is insignificant. However, the report may be outdated for other reasons:

• Firstly, engineering best practices, codes, and standards may have changed.
• If the site has undergone significant natural or man-made change within that period.
• A change of engineering consultancy, the new consultancy may not want to use third-party information for risk purposes.

This doesn't automatically mean the site investigation or geotechnical report has to be carried out again; a review and updated advice may be useful but should be assessed on a case-by-case basis.