Compaction: The importance of what lies beneath the surface

Ground preparation is one of the most critical and often underestimated stages of any construction project. When compaction is poorly managed, the consequences can emerge much later through settlement, cracking, structural instability and costly rework.

Compaction plays an important role in all excavation and earthworks projects, forming the foundation for long-term structural performance. While the process of increasing soil density by reducing void space may appear straightforward, compaction failures are often difficult to detect until late in a project, when remediation becomes significantly more expensive and disruptive.

One of the biggest challenges in achieving effective compaction is the unpredictability of environmental conditions. Factors such as rainfall, humidity and temperature directly influence soil behaviour and can dramatically affect compaction outcomes on site.

Fluctuations in moisture content are one of the leading issues that can dramatically compromise compaction results. Even small fluctuations in moisture content can compromise soil stability.

The mechanics of shrink-swell soils

Insufficient moisture can lead to soil shrinkage, increasing the likelihood of:

• Sudden foundation heave and settlement, which occurs as soil expands during rewetting as they exert upward forces on both surface and subsurface structures. This compromises the integrity of building foundations, roads and telecommunication lines
• General surface distortion, as soil can suffer cracks and undulations, leading to safety hazards and high maintenance costs

On the other hand, swelling is when soil increases in volume as it absorbs water. Clay is the main culprit here, though swelling can also be influenced by soil density and water absorption levels.

Swelling can result in:

• Reduced shear strength: Moisture decreases the friction between soil particles, in turn affecting the soil’s ability to resist sliding or deformation under stress
• Increased compressibility: Soil with high moisture content is more prone to settling or subsiding under load

When soil shrinks or swells, it also has decreased bearing capacity. These conditions can lead to differential settlement, where parts of a structure’s foundation settle unevenly due to inconsistent ground conditions or load distribution.

How to mitigate the impact of shrink-swell soils

Managing shrink-swell soils requires proper planning, material selection and ground treatment methods. Common mitigation strategies include:

• Lime stabilisation: A widely used method to modify pH levels, to improve mineral balance and structure
• Cement stabilisation: Mixing soil with cement and water to strengthen the soil’s physical properties
• Geosynthetics: The engineered application of synthetic materials to address specific geotechnical challenges
• Incorporation of organic matter: Composts, manure and crop residues to encourage stable aggregates and decrease volume change

Why compaction is a critical lever for protecting project value

As construction standards continue to evolve, contractors are under increasing pressure to deliver compliant, well-documented ground works, including compaction outcomes. Aligning with work health and safety (WH&S) standards aren’t just a box-ticking exercise; this is what protects Australia’s infrastructure from potential failure and costly rework.

National safety regulators such as Safe Work Australia and the New Zealand Safety and Health Council (NZSHC) enforce strict WH&S requirements that contractors must follow on excavation, earthworks and compaction, ensuring ground conditions are made safe prior to any critical infrastructure being built. Failing to comply with these requirements can lead to serious safety risks and financial repercussions.

Compliance with work health and safety (WH&S) requirements is more than a regulatory obligation. It plays a critical role in reducing project risk, protecting workers and ensuring long-term infrastructure performance. Poor compaction can lead not only to structural failure, but also to costly remediation, project delays and reputational damage.

How Kennards Hire helps

Whether you’re clearing, digging, rolling or relocating earth, we offer a comprehensive range of earthmoving and compaction equipment to support projects of all sizes.

Designed to perform in real site conditions, our equipment helps contractors manage one of construction’s most overlooked risks: poor ground preparation. With reliable machinery that complies with state and national regulations, you can focus on maintaining productivity, safety and long-term project performance.

Our team of dedicated experts can help you select the right heavy-duty equipment for your project requirements. From planning through to completion, we work alongside you to provide practical advice and support.

Explore our comprehensive earthmoving and compaction range: