What Goes Into a Geotechnical Report? A Step-by-Step Guide for Auckland Property Owners

By Deane Consultancy — 5/03/2026

Planning a build in Auckland? Whether it's a new home, a retaining wall, or a commercial development, one of the first things your engineer or council will ask for is a geotechnical report. But what actually goes into one — and why does it matter?

At Deane Consultancy, we've prepared thousands of geotech reports across the Auckland region. Here's a plain-English walkthrough of our process, so you know exactly what to expect.

Why You Need a Geotech Report

Auckland sits on a patchwork of volcanic soils, clay, sandstone, and fill material — sometimes all on the same site. Without understanding what's beneath the surface, you're guessing at foundation design. That's a risk no one should take.

A geotechnical investigation gives your structural engineer the hard data they need to design foundations that actually work for your specific site. It's also a requirement under NZS 3604 and the Building Code for most residential and commercial projects.

Skipping this step — or cutting corners — can lead to: - Foundation settlement or cracking - Retaining wall failures - Council consent delays - Costly redesigns mid-build

Our Process: What Happens on Site and in the Lab

1. Desktop Study Before we set foot on your property, we review existing geological maps, council records, and any previous reports for the area. This gives us a head start on what to expect underground and helps us plan the fieldwork efficiently.

2. Site Walk and Assessment Our engineers visit the site to assess the terrain, slopes, drainage patterns, vegetation, and any signs of ground movement. We're looking for clues — things like leaning fences, cracked paths, or saturated ground that tell a story about what's happening below.

3. Drilling and Sampling This is where the real data comes from. We use hand augers, Scala penetrometers, or machine-drilled boreholes depending on the site. Soil samples are collected at various depths to build a detailed picture of the ground profile.

For most residential sites in Auckland, we'll drill to between 3 and 6 metres. Larger or more complex sites may require deeper investigation.

4. Laboratory Testing Samples go to an accredited lab for testing. Common tests include: - Moisture content - Atterberg limits (plasticity) - Particle size distribution - Unconfined compressive strength - Chemical testing (for sulphate or organic content where relevant)

These results tell us how the soil will behave under load, how it drains, and whether it's likely to shrink or swell.

5. Engineering Analysis Our geotechnical engineers interpret all the data — field observations, drill logs, and lab results — to assess bearing capacity, settlement risk, slope stability, and groundwater conditions. This is where experience matters. Numbers alone don't design foundations; understanding local conditions does.

6. The Report The final geotech report includes: - Site description and geological setting - Borehole logs and test results - Bearing capacity recommendations - Foundation type and depth recommendations - Earthworks and compaction specifications - Retaining wall and slope recommendations (where applicable) - Groundwater and drainage considerations

This document goes to your structural engineer, architect, and council as part of your building consent application.

A Note on Compaction

If your site requires earthworks — cut and fill, re-levelling, or building platforms — compaction testing is critical. Poorly compacted fill is one of the most common causes of foundation problems in Auckland.

We specify compaction requirements in the report and can also provide compaction testing during construction to make sure the earthworks meet the standard before you pour concrete.

How Long Does It Take?

For a standard residential site, the turnaround from site visit to completed report is typically 5 to 10 working days, depending on lab testing requirements. We'll always give you a realistic timeline upfront.

Why Work With Deane Consultancy?

We're a small, specialist team based on Auckland's North Shore. That means you get direct access to the engineers who actually do the work — not a call centre. We know Auckland's ground conditions because we work in them every day, from the volcanic clays of the isthmus to the Waitemata sandstone of the North Shore and the variable fills of new subdivisions.

Our reports are clear, practical, and designed to give your project team exactly what they need — nothing more, nothing less.

Need a geotech report for your Auckland project? Get in touch with our team to discuss your site and get a quote.

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