Development Reports

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Geotechnical Reports

A geotechnical report investigates the ground conditions of a development site to help determine how the soil, rock and groundwater may affect the proposed building or works.

The investigation is generally carried out by a geotechnical engineer. Depending on the scope of the project, it may involve boreholes, test pits, field testing, laboratory testing and an assessment of the site's geology and subsurface conditions.

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Depending on the project, a geotechnical report can provide information about soil types, depth to rock, groundwater, site stability and potential impacts on surrounding structures. The findings can then inform the design of foundations, retaining structures, excavations and other structural elements.

You may also encounter terms such as geotechnical investigation, geotechnical assessment, soil report, geotech report or geotechnical engineering report. These terms can overlap, but the scope of the investigation can vary significantly. The appropriate report should be determined by the project, the site and any requirements imposed by the relevant authority.

When this may be required

A geotechnical report is not required for every development. Whether one is needed depends on the proposed works, site conditions, engineering requirements and any requirements imposed by the relevant consent authority.

A report may be required or recommended where:

  • Excavation is proposed.
  • Foundations need to be designed for the site's particular soil or rock conditions.
  • The development includes basements, retaining walls or other substantial below-ground works.
  • Construction or excavation could affect adjoining properties or structures.
  • The site has constraints such as steep slopes or potentially unstable ground.
  • Groundwater conditions may affect excavation, foundations or the proposed development.
  • A structural or civil engineer requires subsurface information to complete the design.
  • A development application, development consent or other approval requirement specifically calls for geotechnical information.

City of Sydney, for example, requires a geotechnical report where excavation is proposed and notes that one may be required for developments that could affect surrounding properties, involve excavation close to boundaries or below-ground structures, or are located on constrained sites such as steep slopes.

The NSW Planning Portal also explains that a geotechnical report may be needed to support the soil component of an engineering report and can help an engineer design structural components based on the site's subsurface conditions.

Not sure which reports apply to your project? See our Development Application Reports Guide.

What does a geotechnical report investigate?

The scope of a geotechnical investigation depends on the site and proposed development. Depending on the project, it may examine:

  • Soil and rock conditions beneath the site.
  • Depth to rock and the characteristics of different ground layers.
  • Groundwater conditions.
  • Ground stability.
  • Conditions relevant to foundation design.
  • Excavation and slope stability.
  • Potential settlement or ground movement.
  • The possible effect of excavation or construction on adjoining structures.
  • Measures that may be required to manage identified geotechnical risks.

City of Sydney's development application guidance states that a geotechnical report may need to outline ground conditions including soil type, depth to rock and groundwater levels, assess the stability of the site and surrounding structures, and identify measures to manage adverse impacts.

For some specialised or higher-risk developments, the investigation can be significantly more detailed. NSW Planning's Development Referrals Guide, for example, sets out extensive geotechnical requirements for certain developments near rail infrastructure, including borehole information, geotechnical design parameters, groundwater assessment and consideration of excavation and vibration impacts.

Who typically prepares a geotechnical report?

A geotechnical report is generally prepared by a suitably qualified geotechnical engineer or geotechnical engineering consultancy.

The precise qualification requirements can depend on the development and the authority requesting the report.

  • City of Sydney specifies that a geotechnical report submitted for relevant development applications should be prepared by a suitably qualified geotechnical engineer.
  • Where your development consent, council or another authority specifies particular qualifications, registrations or certification requirements, check those requirements before engaging a consultant.

What to consider when choosing a geotechnical consultant

Before requesting a quote, first determine what type and level of investigation your project requires. A relatively straightforward residential site investigation can have a very different scope from a deep-basement, multi-storey or infrastructure project.

It is worth checking:

  • Whether the consultant has experience with developments of a similar type and scale.
  • What site investigation is included in the proposed scope.
  • Whether boreholes, test pits or other field investigations are required.
  • Whether laboratory testing is required and included.
  • Whether groundwater conditions need to be investigated.
  • Whether the report will provide the information required by your structural or civil engineer.
  • Whether excavation, retaining structures, slopes or neighbouring buildings require particular consideration.
  • Whether your council, certifier or consent conditions specify particular report requirements or professional qualifications.
  • The expected turnaround time and whether further investigation may be required as the project develops.

If the report is being commissioned for a development application, provide the consultant with relevant architectural drawings, surveys and any council or consent requirements so the scope can be tailored to the proposed works.

Related terms and services

Depending on the project or consultant, you may encounter terms including:

  • Geotechnical investigation
  • Geotechnical assessment
  • Geotech report
  • Soil investigation
  • Soil testing
  • Site classification
  • Borehole investigation
  • Ground investigation
  • Foundation investigation
  • Geotechnical engineering report

These services can overlap but are not necessarily interchangeable. A soil test or site classification undertaken for one purpose may not provide the level of investigation required for a complex excavation, basement development or development application.

Frequently asked questions

What is a geotechnical report?

A geotechnical report assesses the ground beneath a development site and explains how its soil, rock and groundwater conditions may affect proposed construction.

It is generally based on site investigation, testing and engineering analysis and can provide information relevant to foundations, excavation, retaining structures and other aspects of the project.

Is a geotechnical report required for a development application?

Not always.

Requirements depend on the proposed development, site conditions and the requirements of the relevant consent authority.

Some councils require geotechnical information for particular types of development. City of Sydney, for example, requires a geotechnical report where excavation is proposed and identifies other circumstances in which detailed geotechnical information may be needed.

Always check the development application requirements for your particular site and project before commissioning a report.

What is the difference between a soil test and a geotechnical report?

The terms are sometimes used loosely, but they can refer to different levels or purposes of investigation.

A soil test or site classification may provide information required for a relatively straightforward residential foundation design, while a broader geotechnical investigation can consider soil and rock profiles, groundwater, excavation stability, surrounding structures and other site-specific engineering issues.

The appropriate scope depends on what the project engineer, council, certifier or other relevant authority requires.

Who prepares a geotechnical report?

Geotechnical reports are generally prepared by suitably qualified geotechnical engineers or specialist geotechnical engineering consultancies.

Where the report is required for an approval, check whether the relevant authority specifies particular professional qualifications.

Does a geotechnical report involve drilling?

Often, but not necessarily in every case.

Depending on the site and purpose of the investigation, fieldwork may include boreholes, test pits, sampling and other investigation or testing methods. The appropriate methodology and investigation depth should be determined by the geotechnical professional based on the proposed development and site conditions.

When should I obtain a geotechnical report?

Where a geotechnical report is required as part of a development application, it may need to be completed before the application can be properly assessed.

Even where it is not required at DA stage, geotechnical information may be needed before structural or foundation design can be completed.

The NSW Planning Portal notes that geotechnical information can help an engineer design structural components based on the site's subsurface conditions.

NSW guidance and sources

Requirements differ between states, councils and individual developments. For NSW projects, useful primary guidance includes:

  • NSW Planning Portal — Common site assessment reports

    Explains the role of geotechnical reports in investigating subsurface conditions and supporting engineering and structural design. NSW Planning Portal

  • City of Sydney — Development application document requirements

    Provides detailed guidance on when a geotechnical report may be required, who should prepare it and the information it may need to contain. City of Sydney

  • NSW Planning — Development Referrals Guide

    Provides examples of more extensive geotechnical requirements that can apply to specialised developments, including development near rail infrastructure. NSW Planning