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Designing and building safely on Victoria’s expansive soils

What we did and why

The BPC supported research conducted by Adelaide University to explore how climate change may affect expansive soils across Victoria and the implications for residential buildings and underground infrastructure.

Expansive soils are widely distributed across Victoria. They are clay-rich soils that shrink when they dry and swell when they become wet. These movements can cause cracking and distortion in residential buildings and footing systems, and contribute to leaks, bursts and other failures in underground pipelines.

While expansive soils already affect many parts of Victoria, future climate conditions, including higher temperatures, longer dry periods and increased rainfall variability may intensify expansive soil movement in some regions.

To better understand the impacts, the research undertook a comprehensive state-wide assessment of expansive soil behaviour under current and projected future climate conditions.

The research combined soil reactivity data, climate projections, Thornthwaite Moisture Index, depth of seasonal suction change, characteristic ground movement, and historical infrastructure failure records and spatial mapping techniques to develop a climate-responsive framework for geotechnical design, risk assessment and residential footing design guidance.

The research was led by Dr Hoang Bao Khoi Nguyen and was supported by the BPC through a research grant awarded in 2024. The research also received in-kind support from Tonkin & Taylor and Zinfra, engineering and energy consultancies. The project was completed in 2026.

What we found

The research provides a state-wide, climate-responsive assessment of expansive soil behaviour across Victoria and demonstrates that climate change is likely to increase ground movement in many regions.

High-resolution maps were developed for current climate conditions and future climate scenarios for 2050 and 2090, showing:

  • Thornthwaite Moisture Index
  • depth of seasonal suction change
  • characteristic ground movement
  • projected trends in building damage risk.

Climate change is likely to increase ground movement

The research found that higher temperatures, more frequent dry periods and greater variability in rainfall are likely to intensify seasonal soil moisture fluctuations and increase ground movement across many regions of Victoria.

While only a relatively small proportion of suburbs and towns are projected to shift into higher soil reactivity classifications, the impacts on building performance and foundation design may still be significant for those areas.

Small changes in ground movement can have large design consequences

Even relatively modest increases in characteristic ground movement and depth of seasonal suction change can have substantial implications for residential footing design.

In some locations, relatively small changes in projected climate conditions were found to require deeper footing beams, reduced beam spacing, greater quantities of reinforcement and more robust footing systems to maintain performance over time.

These findings highlight the sensitivity of residential footing systems to climate-driven soil movement and demonstrate how small changes in climate can have significant implications for construction costs, material use and long-term durability.

Building damage is the primary risk for residential housing

For residential buildings, the primary consequence of increased expansive soil movement is serviceability-related building damage.

Potential impacts include:

  • cracking of walls and slabs
  • differential movement of foundations
  • distortion of building elements
  • uneven floor movement
  • reduced functionality and durability
  • increased maintenance requirements over the building's life.

The footing analysis indicates that future climate conditions may require more robust footing systems in some regions to maintain acceptable long-term performance.

Buried infrastructure is also vulnerable

Analysis of historical underground pipe failure records revealed a strong relationship between climate conditions, expansive soil behaviour and infrastructure performance.

Pipe failures were observed to increase during prolonged hot and dry periods when soil shrinkage is greatest. The findings indicate that climate-driven soil behaviour can contribute to pipe bursts, leaks, and cracking.

Future climate conditions may increase these risks in some regions, highlighting the importance of climate-informed infrastructure planning, maintenance and asset management.

What difference this made

The research provides a practical framework for incorporating climate change considerations into geotechnical engineering, residential construction and infrastructure planning.

By combining climate science, soil mechanics, spatial analysis and structural design, the research provides:

  • state-wide expansive soil risk mapping
  • evidence-based climate-responsive residential footing design guidance
  • improved understanding of infrastructure vulnerability
  • evidence to support climate-responsive planning and policy development
  • a practical tool to support climate-informed design decisions, and
  • a framework that can be updated as climate and soil datasets evolve.

The findings support more proactive planning and risk management for both residential buildings and buried infrastructure in reactive soil environments.

The research demonstrates that future climate conditions should be considered alongside traditional geotechnical assessments when planning and designing homes and infrastructure in Victoria.

The methodologies, datasets and tools developed through this project provide a strong foundation for improving resilience and can be updated as new climate projections and soil information become available.

Climate-resilient footing design guidance

The research developed practical footing design guidance for residential construction (see section 6.2 of the research report).

The guidance was developed using a representative single-storey articulated brick veneer house that reflects common residential construction practices in Victoria, and should be considered indicative guidance for typical residential housing rather than a universal design solution for all building types or site conditions

Victorian suburbs and towns were grouped into 42 geotechnical categories based on local values of characteristic ground movement and depth of seasonal suction change. Representative footing systems were then designed for each category using Code Oriented Raft Design (CORD) software.

This provides a practical framework for incorporating future climate considerations into residential footing design and improving housing resilience across Victoria.

Download the report

Read the full report: Guidelines to mitigate structural damage due to water content change in Victoria’s expansive soils.

    Related research

    This research complements other BPC-supported research that aims to reduce harms associated with moisture ingress, water damage and other risks that affect the safety, performance and durability of buildings, including:

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