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Road Construction: Understanding the Value of Soil Stabilisation



From highways to local roads, soil stabilisation is a critical step in the construction process. Unstable or even weak soil can contribute to significant problems during road construction, resulting in damage to the road pavement and even its surrounding environments.

Improving soil properties with engineered or chemical materials helps to improve the performance characteristics of the soil, leading to increased tensile strength, resilience against cracking, and more.

But before we go further into the most common methods of enhancing soil stabilisation performance, let’s discuss the very basics of soil stabilisation, what soil stabilisation entails, and why it plays a significant role in road construction.

What is soil stabilisation?

Soil stabilisation, in terms of road construction, is the process of transforming a soil’s physical properties through the use of engineering techniques. The method of altering the physical properties of weak soil with a stabilising agent has been around since the Mesopotamians and the Romans.

Both civilisations found that by combining native soil with pulverised limestone or calcium, the load-carrying ability of roadways was much improved. Further still, it was discovered that a wearing surface (such as stone slabs) over these conditioned soil bases protected against the damaging effects of environmental forces.

The application of a wearing surface enabled the soil within its foundation to remain stable and capable of carrying heavier loads and increased traffic volumes.

Why is soil stabilisation important?

Since the days of the Romans, many improvements to soil stabilisation have been made. New equipment and technology ensure that even the most inferior quality soil in the most remote region in the world is able to become a strong impermeable medium.

Nowadays, poor quality soil no longer needs to be excavated and replaced with coarse aggregate. Advanced soil stabilisation agents can convert this poor quality soil in-situ, allowing the ground to possess more favourable engineering properties.

Soil stabilisation eliminates the need for a coarse aggregate substitution. By forgoing the traditional “dig and dump” method of substituting low-grade soil, even the most remote regions can realise safe and durable infrastructure, enhancing their economic viability.

Chemically engineered soil also displays increased compressive and tensile strength, improved resilience against fatigue and induced cracking, and water impermeability. This further saves on cost as roads can be built with a reduced pavement thickness.

Resilience to failure from external forces makes soil stabilisation ideal for any number of infrastructure applications from public highways to unsealed rural roads and construction projects that require a strong foundation.

In places like Australia, infrastructure and road transport frequently deal with extreme weather variables ranging from sweltering heat to sudden downpours. If such variables are not accounted for during the construction process, the shrink/swell potential of roads can be significantly harmful.

Pavement defects such as potholes and longitudinal cracks can quickly occur, limiting the stipulated design life of the construction material. Not only does this negatively affect the economic development of the region, but it can also contribute to a higher rate of road accidents.

By offering a superior soil base that provides greater resilience, a newly constructed pavement requires minimal remedial maintenance works. This minimises the impact of road closures and better safeguards against traffic accidents associated with poor road conditions.

Common methods to stabilise soil

There are two primary stabilisation methods used to improve the strength and stiffness characteristics of native soil. Below, we highlight both techniques as well as their intended effects on the overall properties of the soil in question.

Mechanical methods

One of the earliest mechanical stabilisation methods is soil compaction. The compaction process has been used since the age of the Romans, making it one of the most commonly used road construction practices to date.

Soil compaction is done via static force or vibratory force. This mechanically presses soil particles together, allowing for greater foundational strength to be realised. Compacted soil has improved load-bearing capacity and provides greater stability for road traffic.

Another physical process that remedies sub-standard soil is the addition of graded aggregate materials. The inclusion of additive materials such as cement helps to form a composite base material that contains more favourable engineering properties.

Soil reinforcement is also considered when the subgrade soil lacks the shearing and compressive strength necessary for road traffic activities. By adding geotextiles and engineered plastic mesh, soil strength is improved, soil erosion is better controlled, and soil migration is prevented.

Chemical methods

Chemical soil stabilisation makes use of chemical additives and binders like lime, bitumen, and other chemical compounds to alter the behaviour of soil when interacting with water. The modification of soil properties with chemical additives leads to improved strength and durability.

Of the common chemical components used to strengthen soil, slaked lime is most often used. This is because lime works effectively well with various soil grades, from medium-grained soil to fine-grained soil, to produce favourable characteristics.

As lime removes moisture, the soil becomes more compactable. Altering the effect of water on the soil results in increased soil density and greater stability.

Of course, lime is not without its drawbacks.

In environments where sulphur and organic materials are present, lime stabilisation becomes inhibited. Sulphate reacts with calcium-based stabilisers like lime. This induced reaction can cause very high swelling pressures, negatively impacting soil strength.

Polymer soil stabilisation is another favourable chemical technique that is quickly growing in popularity. As a high performing stabilisation agent, liquid polymer works by physically bonding with native, in situ soil, which consequently improves soil strength, resilience, and water impermeability.

The specially formulated liquid polymer also assists in the elimination of harmful airborne dust particles and waterproofing.

Conclusion

As there are various forms of soil stabilisers available on the market, careful consideration must be made to the site’s conditions to ensure that the right processes and techniques are applied. Several factors, such as soil type, environmental conditions, location, and construction expenses, must be considered before deploying any type of soil stabilisation strategy.

The most effective way to achieve a stable soil foundation that produces long-term benefits is by working with a team of experienced civil engineers and industry experts who can advise on the best stabilisation methods and options for your specific construction project.

AUTHOR BIO

Troy Adams is the Managing Director of Global Road Technology, an international engineering technology company in Australia that specialises in engineered solutions for dust suppression, erosion control, soil stabilisation and water management. A pioneering, socially conscious Australian entrepreneur, Troy is passionate about safer, healthier and more cost-effective solutions in the mining and infrastructure sectors and beyond.