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

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Detailed Geotechnical Investigation

Site inspection, including an assessment of site geohazards. Shallow and deep geotechnical testing to assess ground conditions for TC3 and commercial buildings. Detailed reporting including soil logs and a site plan.

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A detailed geotechnical investigation is required for MBIE TC3 Blue and commercial buildings. The investigation and report are needed by local authorities, architects and structural engineers to confirm requirements for complex TC3 and commercial sites and include:

• Site inspection, including an assessment of site geohazards
• Shallow and deep geotechnical testing to assess ground conditions
• Detailed reporting including soil logs and a site plan

The geotechnical assessment will typically comprise of:

• Shallow Ground Testing: Combination of 3.0 m deep hand augers, Dynamic Cone Penetrometers (DCP) and handheld shear vane testing
• Deep Ground Testing: where ground conditions allow, testing will typically comprise a Cone Penetration Test (CPT) to at least 15m below ground level.
• The Shallow and Deep Geotechnical Testing will be interpreted and presented within a report which will cover the following:
o A review of the historical aerial photographs of the site, if available
o Appraisal of data available on the New Zealand Geotechnical Database, and geological cross sections, if required
o The consistency and density of the soils underlying the site
o The expected performance of the site in future significant seismic events, including analysis of the liquefaction hazard, settlement potential and lateral spreading risk
o Recommendations regarding appropriate foundation and/or ground improvement, including soil parameters to be used in designs
o Identification of any geological issues, or areas of concern, that may require additional ground investigation

Please Note:
This price is for a detailed geotechnical investigation within Christchurch City, Selwyn District or Waimakariri District.

If there are any unforeseen conditions that need further investigation, that will incur additional costs, these will be discussed with you to decide on how you wish to proceed. Additional work may include further geological investigations such as mechanical excavation, borehole drilling, laboratory testing of soils and an external peer review. Any additional works and costs agreed will be invoiced following conclusion of the work.

Depending on our current workloads and commitments, and also dependant on sub-contractor availability, the shallow and deep field work will commence within two to three weeks of confirmation from you and the report issued three to five weeks after. In total there is an approximately a five to eight weeks turnaround, dependant on the size and complexity of the project.

Foundation Subgrade Inspection

An FSI is typically used by contractors and builders to confirm ground conditions at the time of construction. We will issue a Site Inspection Record (no site plans or soil logging).

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An inspection of the foundation excavation is made to confirm removal of topsoil and any other unsuitable material from the entire footprint of the proposed dwelling, followed by Dynamic Cone Penetrometer (DCP) and/or shear vane testing, to confirm ultimate bearing capacity of the subgrade.

A Site Inspection Record will be given to you, your structural engineer or builder.

Please Note:
This price is for a foundation subgrade inspection within Christchurch City, Selwyn District or Waimakariri District.

If a Producer Statement (PS4) Construction Review is needed there will be an additional $500 fee, which will be invoiced separately. The PS4 can be used to partially fulfil the code of compliance required by the local regional authority for the foundation subgrade bearing capacity.

If the site excavations are not adequately prepared at the time of our initial inspection, or if the subgrade conditions differ from those inferred to exist, or if any unexpected suspect soils are encountered additional inspections will be needed. These are charged at a rate of $80 – $150 per hour.

We require at least 24 hours’ notice for construction observations and testing. The PS4, and accompanied results, will be issued as soon as practicably possible after completion of all inspections and following a review by a Chartered Professional Engineer (CMEngNZ, CPEng or PEngGeol).

If there are any unforeseen conditions that need further investigation, that will incur additional costs, these will be discussed with you to decide on how you wish to proceed. Any additional works agreed to will be invoiced following the conclusion of work.

Hillside Geotechnical Investigation

Site inspection, including a preliminary assessment of site stability and geohazards. Shallow geotechnical testing to assess ground conditions. Preliminary reporting including soil logs and a site plan.

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A hillside geotechnical investigation and report are needed by local authorities, architects and structural engineers to confirm foundation and retaining wall design requirements and will include:

• Site inspection, including a preliminary assessment of site stability and geohazards
• Shallow geotechnical testing to assess ground conditions
• Preliminary reporting including soil logs and a site plan

The geotechnical assessment will typically comprise a combination of 3.0 m deep hand augers, Dynamic Cone Penetrometers (DCP) and handheld shear vane testing, followed by a preliminary geotechnical report outlining our findings and recommendations.

The geotechnical report will include, but not be limited to the following:
• Underlying ground conditions
• Foundation recommendations
• Assessment of Section 6 of the MBIE Guidance ‘Hillsides and Retaining Walls,’ are required by the local authority to grant consent
• Any geological issues that may require additional investigation

Please Note:
This price is for a hillside geotechnical investigation within Christchurch City, Selwyn District or Waimakariri District.

If there are any unforeseen conditions that need further investigation, that will incur additional costs, these will be discussed with you to decide on how you wish to proceed. Any additional works agreed to will be invoiced following the conclusion of work.

Depending on our current workloads and commitments, typically the shallow field work would commence within one to two weeks of confirmation from you and the report issued two to three weeks thereafter. In total there is an approximately three to five-week turnaround time for shallow geotechnical investigation and reporting.

Shallow Geotechnical Investigation

Shallow geotechnical testing to assess ground conditions in MBIE TC1 and TC2 areas. Short report including soil logs and a site plan. Typically needed by local authorities, architects and structural engineers, to confirm the foundation design requirements.

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A shallow geotechnical investigation is required for buildings of up to 200m² plan area, in MBIE TC1 Grey and TC2 Yellow. These investigations and reports include:

• Site inspection and shallow geotechnical testing to assess ground conditions
• Preliminary reporting including soil logs and a site plan

The geotechnical assessment will typically comprise a combination of 3.0 m deep hand auger, Dynamic Cone Penetrometer (DCP) and handheld shear vane testing, followed by a preliminary geotechnical report outlining our findings and recommendations.

The geotechnical report will include, but not be limited to the following:
• Commentary on the underlying Technical Category, MBIE or underlying subdivision report
• Underlying ground conditions
• Foundation recommendations
• Any geological issues that may require additional investigation

Please Note:
This price is for a shallow geotechnical investigation within Christchurch City, Selwyn District or Waimakariri District.

If there are any unforeseen conditions that need further investigation, that will incur additional costs, these will be discussed with you to decide on how you wish to proceed. Any additional works agreed to will be invoiced following the conclusion of work.

Depending on our current workloads and commitments, the shallow field work will commence within one to two weeks of confirmation from you and the report issued two to three weeks after. In total there is an approximately three to five-week turnaround time for shallow geotechnical investigation and reporting from time of booking.

Geotechnical engineering FAQ’S

Why you need a Geotechnical Engineer

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

What we need from you for the 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.

What are the benefits of a geotechnical investigation?

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

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.

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-store 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 2 require only shallow testing methods.

If you are unsure of what services you needyour site, please contact our Geotechnical Department 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 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.

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 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 subdivisions, 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 department 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 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

Mark Gray

Engineering Geologist
021 649 806 markg@do.nz