New Zealand map Davis Ogilvie – Engineering, Surveying and Planning

Geotechnical Engineering

Geotechnical engineering investigates ground conditions to determine appropriate soil or rock properties to use in the design and foundations of structures. It also involves the assessment of existing or potential natural hazards (such as erosion, falling debris, subsidence, inundation and slippage) in relation to the effects of developing land.

Our Geotechnical Engineers assess sites to ensure that geohazards are appropriately identified and managed, and mitigation measures are given to meet your objectives.

Please contact our experienced geotechnical engineers/ engineering geologists below for further information.

Our areas of Geotechnical expertise include:

  • Geomorphological mapping
  • Geotechnical investigations
  • Coordinating specialist geotechnical testing and the associated soil analyses
  • Liquefaction and lateral spreading assessments
  • Detailed assessment for TC1, TC2, TC3 and hillside sites
  • Earth dam and irrigation system design
  • Slope stability analysis
  • Rockfall protection systems
  • Rock and earth anchor design
  • Foundation design for residential and commercial projects
  • Earthworks construction monitoring
  • Geotechnical peer review

Geotechnical engineering FAQs

Why do you need a Geotechnical Engineer?

To ensure geological conditions are identified and examined, geotechnical information is concisely collected and assessed to ensure all parties understand potential hazards and the extent of necessary solutions before work begins.

What will we need from you to carry out your geotechnical investigation?

If you are able to provide any building plans, previous/subdivision geotechnical reports and fill certificates before we visit your site, it will assist with our investigations.

Why do I need a geotechnical report?

You need a geotechnical report to enable your builder or architect to appropriately assess the cost of constructing your foundations, as part of your building consent and, if needed, to enable a structural engineer to design your foundations.

Even if you have been provided with the council required overall geotechnical report for your subdivision, you will still require a site specific geotechnical report relating to the site you have purchased.  This is because ground conditions often vary over short distances and testing is required in the specific location of your proposed building.

How is a geotechnical investigation carried out?

A geotechnical investigation will involve our geotechnical team being onsite to undertake shallow hand testing beneath the ground surface and to supervise any external contractors, such as service clearance, an excavator or drill rig.

It is likely that there will be some machinery noise associated with the investigation. Any material excavated during the investigation will be reinstated, as close as possible, to how it was before testing began.

What are the benefits of a geotechnical investigation?

The aim of a geotechnical investigation is to determine the ground conditions so that your foundations, or other proposed construction can be appropriately designed, ensuring that they are suitable for the specific ground conditions of your site during their design life.

What type of geotechnical investigation and report do I need?

The level of geotechnical investigation, analysis and reporting will depend on what is known about the ground conditions on your site. Factors such as the Technical Category (TC) or liquefaction potential, historic use of the land, location relative to natural hazards and slope of the land will influence the type of investigation required.

The nature of your development also affects the scale of the investigation. For example, if you want to subdivide or build a multi-storey building more investigation will be needed than building a standard residential home. In most cases an investigation on land classified as TC 3 will involve deep testing, while investigations on TC 1 or TC 2 require only shallow testing methods.

If you are unsure of what services you need for your site, please contact our geotechnical team and we can help you determine the extent of testing required.

What type of geotechnical inspection do I need when my foundation has been excavated during the construction process?

You will need a subgrade inspection (inspection and testing of the unearthed soil, also known as cut or excavation inspection)to confirm that the ground conditions are as expected from the geotechnical investigation and that the designed foundations are therefore suitable.

What type of geotechnical report do I need when I am purchasing a property?

We can provide a Pre-Purchase assessment to help you identify the risks associated with the ground conditions, on a property you may be interested in purchasing. This can be a desk study only, if the information is publicly available or with the current property owner’s permission we can undertake testing on the site. Please note that if the likely location of the dwelling on the property is known at the time of our testing and does not change during the design process, then our report may also be suitable for building consent. Please contact us before the due diligence period begins to discuss the timeframe for the assessment.

What type of geotechnical investigation do I need if I am going to subdivide my property?

For subdivision consent you will require a Detailed Geotechnical Investigation (DGI).  This involves deep investigation such as test pits, boreholes and/or CPTs and an assessment of Section 106 of the Resource Management Act (1991) including a Statement of Suitability for Subdivision, in reference to natural hazards.

The amount of testing depends on the size of your property and the number of lots it is being subdivided into. You can contact our geotechnical team to discuss your plans for subdivision and we will then provide you with an appropriate scope of work for your development.

 

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Contact

Christchurch

Bjorn Raasch

Senior Engineering Geologist
027 700 7533 bjorn@do.nz
Christchurch

Joanna Lea Petheram

Senior Engineering Geologist
021 352 213 joanna@do.nz
Christchurch

Ben Parry

Senior Engineering Geologist
027 3311 555 benp@do.nz
Christchurch

Elliot Duke

Director, Chartered Professional Engineer
021 352 297 elliot@do.nz
Greymouth

Joe Turner

Engineering Manager
021 836 112 joet@do.nz