GUIDE 01

What should you check before buying or developing land?

A section can look straightforward while its ground conditions make the proposed development more complex. An early geotechnical appraisal helps identify issues before you commit to a layout or construction budget.

Start with the records and the site

Useful information includes the LIM, Council property file, existing geotechnical reports, historical aerial photographs, terrain information and relevant Council hazard maps. A site walkover helps relate those records to actual slopes, drainage, ground features and existing structures.

Ask questions about your proposed project

• Is there evidence of previous filling, slips or ground movement?
• Could soft ground, groundwater or erosion affect the proposed building area?
• Will excavation or retaining walls affect neighbouring land or services?
• What further investigation is needed before design and costing?

An old report may still be useful, but it needs to be checked against the current proposal and any changes to the site.

References: Auckland Council CoP Chapter 2, §§2.3.1–2.3.2; Council guidance on regional landslide susceptibility maps [1, 2].

GUIDE 02

Why does your project need a ground investigation?

A ground investigation provides information for design and reduces uncertainty about what construction will encounter. Its scope should address the proposed building, earthworks and relevant hazards.

Different questions need different tools

Depending on the site, investigation may use hand-auger holes, machine-drilled boreholes, cone penetration testing (CPT), test pits, laboratory testing and groundwater monitoring. No single method answers every ground-related question.

Shallow testing may be appropriate for some simple projects. Deeper investigation may be needed to assess soft layers, liquefaction, piles or potential slip surfaces. The number and depth of investigation points should be selected for the site and proposal rather than offered as a universal package.

What should the findings tell you?

• What soil and rock conditions were encountered, and what remains uncertain?
• What foundation or earthworks options are appropriate?
• What construction constraints and further checks are needed?

Reference: Auckland Council CoP Chapter 2, §§2.3.2–2.3.3 [1].

GUIDE 03

Can you build on a sloping site?

Many sloping sites can be developed, but the slope and proposed works need to be assessed together. Excavating the bottom of a slope, adding fill or buildings above it, or changing drainage can alter stability.

A retaining wall is one part of the assessment

A wall must support the retained ground and its loads. The designer also needs to consider whether a larger mass of ground could move around or beneath the wall. A wall design alone does not establish that the whole hillside is stable.

Water and neighbouring slopes matter

Heavy rainfall and rising groundwater can reduce stability. Assessment may need to extend beyond the property boundary to consider slopes above and below the proposed works. Investigation and groundwater monitoring should reflect the potential failure mechanism.

Council's regional susceptibility maps are a screening tool. They indicate where landslides may be more likely, but do not determine the risk to an individual property or predict when a landslide will occur.

References: Auckland Council CoP Chapter 2, §§2.5.7, 2.6.8–2.6.9; Council landslide explanations and map guidance [1–3].

GUIDE 04

Soft soil, expansive clay and liquefaction: what is the difference?

These ground conditions can all affect foundations, but they involve different mechanisms. A foundation solution needs to address the conditions actually present.

Soft or compressible soil

Ground can compress under buildings or new fill. Peat and organic soils can undergo substantial settlement over time. Uneven settlement can distort a building and affect services. Investigation helps establish the thickness and behaviour of the layers involved.

Expansive clay

Some clay-rich soils shrink as they dry and swell as they become wetter. These seasonal movements can damage unsuitable foundations. Drainage, leaking pipes, trees and changes in landscaping can influence moisture conditions around the building.

Liquefaction and lateral spreading

During earthquake shaking, susceptible saturated soils can lose strength. Consequences may include settlement and horizontal movement towards a riverbank or other free face. Loose, wet sandy or silty deposits warrant particular attention. Flat land is not automatically free from this hazard.

Regional maps help identify where further assessment may be needed. Site-specific investigation, potentially including CPT or boreholes, provides information for the actual proposal.

References: Auckland Council CoP Chapter 2, §§2.5.1.1, 2.5.2, 2.5.4; Auckland liquefaction assessment; NZGS expansive-soil research [1, 4, 5].

GUIDE 05

What makes fill suitable for building?

Ground that looks firm at the surface may still contain loose fill, buried waste or weak layers. Uncontrolled fill has been placed without adequate engineering controls and should not be assumed suitable for foundations.

Engineered fill involves a controlled process

The design and specification establish suitable materials, preparation of the underlying ground, placement methods, moisture requirements and compaction criteria. Inspection and testing during construction provide evidence of how the fill was built.

Plan the checks before work starts

• Confirm approved drawings, specifications and applicable consent conditions.
• Arrange inspection of the prepared formation before covering it with fill.
• Agree testing requirements, inspection hold points and who keeps the records.
• Plan erosion, sediment and drainage controls.
• Notify the engineer if unexpected ground or unsuitable material is encountered.

A roller pass or an isolated test is not a substitute for the specified construction-control process.

Reference: Auckland Council CoP Chapter 2, §§2.5.13, 2.6.10, 2.8.2, 2.8.6 [1].

GUIDE 06

What is a GCR, and when is a PS4 needed?

A Geotechnical Completion Report (GCR) records relevant completed geotechnical work, supporting inspections and tests, and the resulting ground conditions and development limitations.

Why do the construction records matter?

The completion assessment relies on evidence collected while the works are visible. Missing inspections, test results or as-built information can make it difficult to demonstrate compliance after the work has been covered.

A GCR and a PS4 have different roles

A GCR documents the geotechnical outcome. A PS4 is a producer statement for construction review within its stated scope. Whether a PS4 is needed depends on the consented work and applicable requirements; it is not automatically interchangeable with a GCR.

Subdivision close-out and building-consent close-out may require different documents. Agree the deliverables with the project team and Council early, rather than waiting until the end of construction.

Reference: Auckland Council CoP Chapter 2, §2.9, especially Table 4 and §2.9.11 [1].

AUCKLAND GROUND-RISK CHECKLIST

Which geohazards should be considered in Auckland?

The following highlights ground hazards relevant to geotechnical assessment and design, drawing on Chapter 2, §2.5. Not every hazard occurs at every property. Groundwater and proposed construction can influence several of these hazards.

Broader natural hazards

Auckland also faces volcanic activity and tsunami. Flooding, overland flow and coastal inundation are related natural hazards requiring appropriate assessment, but they are not the same as a geotechnical stability assessment. Refer to Auckland Emergency Management and relevant Council mapping for these topics [6].

Sources and scope

1. Auckland Council: Code of Practice for Land Development and Subdivision, Chapter 2, Earthworks and Geotechnical, Version 2.0, May 2023. These guides summarise and adapt selected topics; they are not Council publications or endorsements. Source licensed CC BY 4.0; licence. Changes include plain-English rewriting, selection and client-oriented examples.
2. Auckland Council: Understanding Auckland's regional landslide susceptibility maps, 25 August 2026.
3. Auckland Council: Piha / Karekare geotechnical update.
4. Auckland Council: Auckland liquefaction assessment and liquefaction vulnerability maps, TR2021/19.
5. Teal & Rogers, NZGS: Identifying and classifying expansive soils in New Zealand. Used for general soil behaviour, not as a statement of current compliance rules.
6. Auckland Emergency Management: Natural hazards.

Chapter 2 sets minimum standards for relevant Council assets and provides guidance for other geotechnical and land-development work. It does not replace the Building Act, Building Code, Auckland Unitary Plan or project-specific consent conditions. Current requirements should be checked for each proposal. These guides do not prescribe universal investigation depths, foundation types, testing frequencies or consent outcomes.