Earthworks Testing & Certification

Orogen carries out in-situ density testing using nuclear densometers, Clegg impact hammer testing, and visual assessment of fill material. We can also arrange laboratory testing (Proctor compaction tests, CBR tests, grading analyses) through accredited testing laboratories where the specification requires it.

Compaction testing verifies that fill has been placed and compacted to the density required by the geotechnical specification. Without testing, there is no objective evidence that the fill meets the required standard. Consent conditions and NZS4431 requirements make testing mandatory for most residential and commercial earthworks.

A compaction test measures the density of compacted fill relative to the maximum density achievable in the laboratory. It is carried out on each compacted layer of fill at specified intervals. A passing result is required before the next layer can be placed. Failing results trigger remediation and retesting.

Consent conditions and council inspection hold points require evidence of compaction compliance before earthworks can proceed. Orogen's testing records form part of the geotechnical completion report that supports engineering certification and council sign-off.

Failing test results require remediation before further fill placement. This typically means removing or re-compacting the non-compliant material and re-testing. Orogen advises on what is needed and re-tests once remediation is complete. We document the failure, the remediation, and the passing retest result.

On large projects, Orogen sets up a systematic testing regime with defined test locations and frequencies, and maintains a testing record database. Regular reporting keeps the client and contractor informed of compliance status. We flag areas where testing results are marginal so risks are managed proactively.

NZS4431 is the New Zealand Standard for the Code of Practice for Earthfill for Residential Development. It sets out the requirements for the design, placement, and testing of fill used as a foundation for residential buildings. Compliance with NZS4431 is typically required by councils as a condition of subdivision consent on sites with significant earthworks.

NZS4431 applies when residential buildings are to be founded on engineered fill. This includes most greenfield and cut-and-fill residential developments where the finished platform levels differ significantly from the existing ground levels. Council consent conditions and building consent requirements typically specify NZS4431 compliance.

NZS4431 requires the earthworks to be designed by a geotechnical engineer, fill to be sourced from approved material, placement to be in controlled layers, compaction to be tested at specified intervals, and the completed earthworks to be certified by a Chartered Professional Engineer. Orogen manages all of these requirements as part of our earthworks service.

NZS4431 requires in-situ density testing of each compacted fill layer at specified test frequencies (typically one test per 500 square metres or per 200 cubic metres). Test results must show that the compacted density meets the specified percentage of the maximum dry density determined by laboratory Proctor testing.

At completion of the earthworks, Orogen prepares a geotechnical completion report summarising the fill sources, placement records, compaction test results, and any departures from the design. This report is signed by a Chartered Professional Engineer and submitted to the council as evidence of NZS4431 compliance.

Non-compliant fill must be removed or remediated before the next layer can be placed. Orogen advises on what action is required and re-tests after remediation. A clear record of the non-compliance, the remediation, and the passing retest is maintained in the project file.

NZS3604 is the New Zealand Standard for light timber-framed buildings. It includes foundation design tables that apply when the ground conditions are classified as 'Good Ground.' A Good Ground determination is an assessment by a qualified geotechnical engineer or engineering geologist that the site meets the NZS3604 criteria, allowing the building to use the standard's simplified foundation designs.

A Good Ground determination is required when a building consent application relies on NZS3604 foundation designs and the ground conditions are not obviously compliant from visual inspection alone. Councils often require a written determination from a qualified engineer before accepting that NZS3604 foundations are appropriate.

We review the site's geotechnical history, council hazard maps, any available borehole or test pit data, and carry out a site visit. We assess the bearing capacity, stability, and settlement potential of the ground and confirm whether it meets the NZS3604 criteria or whether a site-specific geotechnical investigation is needed.

A Good Ground determination confirms that the site meets the NZS3604 standard conditions, allowing standard foundation designs to be used. A site-specific geotechnical report is a more comprehensive investigation required for sites with unusual ground conditions, high loading, or where NZS3604 foundations are not appropriate. Sites that do not qualify as Good Ground need a site-specific report.

Most Good Ground determinations are completed within three to five working days. If we need to carry out test pits or arrange laboratory testing, the timeframe is longer. We will advise on the scope and timeframe when you contact us with the site details.

If the site does not qualify as Good Ground, the building cannot use NZS3604 foundation tables without modification. A site-specific geotechnical investigation will be required to determine appropriate foundation design parameters. Orogen will tell you clearly what is needed and can manage the geotechnical investigation if required.