Geotechnical Engineering

In most cases, yes. Councils require a geotechnical report for new buildings, significant extensions, subdivisions, and retaining walls, particularly on sites with slopes, soft soils, or liquefaction risk. An early assessment can prevent costly surprises during the design and construction phases of a project. A Site Suitability Assessment (SSA) is often the first step to determine whether a full investigation is necessary.

A typical investigation follows these steps:

1. Desktop review: check existing reports, maps, and hazard data.

2. Site visit & testing: undertake boreholes, CPTs, test pits, or soakage tests.

3. Laboratory analysis: measure soil strength, moisture content, density or soil classification tests.

4. Engineering analysis: assess foundation capacity, slope stability, or liquefaction susceptibility analysis.

5. Reporting: produce a council-ready report with recommendations.

Timeframes are usually 2–3 weeks for residential sites, with larger or more complex projects taking longer. We’ll give you a realistic programme up front.

Your report will include:

• A clear description of the ground profile, including soil/rock layers and groundwater depth.

• Hazard screening for slope instability, liquefaction, and flooding risks.

• Foundation options with bearing capacities and settlement advice, ground improvement options (where needed).

• Geotechnical parameters for designing retaining wall and earthworks.

• Stormwater infiltration results, if tested.

The report is written to satisfy council requirements while giving the design team practical, actionable guidance to keep your project moving forward.

Costs for completing geotechnical reports largely depend on:

• The type of development (house, subdivision, commercial).

• Site complexity (presence of slopes, soft soils, liquefaction).

• Number and type of investigations required, reflecting the scale, complexity and cost of the development and variability of ground conditions.

• Local council and consent requirements.

Every project is tailored to the site-specific ground conditions. Our approach is to match the level of investigation to the development, ensuring the work is justifiable, cost-effective and risk appropriate.

We’ll run a quick desktop check and will outline the necessary scope and associated fees based on available information before proceeding.

Sometimes. If the report is recent, relevant, and already covers the same part of the site that is intended to be developed, it may still be valid. However, if the design has changed, the site has been altered, or council requirements have shifted, the report is likely to need updating. Consider any limitations that have been included to check the applicability of the existing report.

If in doubt, it’s always best to check before starting the decision-making process. We’ll review your existing information and let you know whether it is appropriate to be reused for your intended purpose.

In most cases, yes, there have been many different solutions developed to address challenging site conditions. The design and construction requirements adapt depending on the geotechnical hazards identified:

• Liquefaction/soft soils: use a raft foundation, ground improvement, or engineered fills to control settlement. A deep piled foundation option may be viable if site conditions allow. There are typically additional requirements for design and construction on such sites.

• Slopes/instability: adopting setback distances, drainage control, retaining/anchored solutions, and confirm post-improvement stability with analysis and testing.

• High groundwater/poor soakage: adjust stormwater strategy, consider waterproofing and subsoil drainage improvements.

We work closely with your structural and civil designers to balance safety, compliance, and cost, so you avoid over-engineering and surprises.

Doing the minimum testing may get you through consent, but it can leave gaps in understanding that create surprises during design or construction. On more complex or hazard-prone sites, investing in additional investigation can:

• Provide more accurate design parameters. This allows engineers to optimise foundation and retaining wall designs.

• Reduce unnecessary conservatism. More testing can lead to less assumptions and over-engineering, saving on construction materials and costs.

• Lower construction risk. There will be significantly fewer unexpected ground issues that cause delays or budget blowouts.

• Support long-term resilience. Better design and construction reducing the chance of settlement, slope movement, or stormwater failures.

• Strengthen consent outcomes. Comprehensive investigations give councils and insurers greater confidence in the design.

In short, more data upfront often means fewer problems later, especially where ground conditions are complex or hazards are significant.