What is Soil Compaction in Construction?
Soil compaction is a crucial process in construction to stabilise base materials, ensuring the longevity of projects such as building foundations, roads, airports, railway embankments, bridges and more. In fact, it’s estimated that 80% of all structural failures are due to soil movement, highlighting the importance of soil compaction. Aside from reducing soil settlement, proper soil compaction decreases erosion and flooding as well by improving water drainage.
This article delves into the role of compaction, including best practices and use cases, as well as introducing the common equipment involved and why they’re the foundation of every construction project.
What is soil compaction?
Soil compaction is the process of compressing soil particles to stabilise the ground in preparation for construction and reduce the risk of erosion. When done correctly, compacted soil will boast greater density, enhancing the load-bearing capacity and reducing water seepage and swelling.
While compaction methods vary depending on the soil type (e.g. clay versus sand) and conditions (e.g. moisture content and slope), the core principle remains the same: eliminating voids between loose particles to strengthen the soil.
For example, as clay holds moisture well and can shrink and expand well, it requires heavy compaction and optimal moisture control. Silt is similar in that it can retain water which can cause poor compaction. As such, you’ll need to reduce the moisture gradually before compaction.
On the other hand, sand drains quickly. With the help of vibratory rollers, it can easily be compacted.
Generally, 95 percent compaction is regarded as the benchmark for proper compaction. However, for roads, pavements, and commercial building sites that require a higher degree of soil stability, this benchmark is typically higher. To measure the soil density, contractors use the Standard or Modified Proctor tests. As part of their quality control methods, they can also use equipment like penetrometers that use a rod to evaluate soil density quickly.
Why is soil compaction needed in construction?
Soil compaction is used in civil construction for the following reasons:
Improve load-bearing capacity
Compaction significantly increases the soil’s ability to support heavier loads. This is crucial for projects such as building foundations, road construction, and dam creation.
Reduces soil settlement and shrinkage
Compaction minimises soil volume changes caused by shrinking or swelling. Advanced systems like the Völkel intelligent compaction system can help achieve this with absolute precision.
Controls permeability
Compacted soil helps control water drainage, minimising. As such, it also offers environmental benefits as it can prevent soil erosion, reduce dust and air pollution, and decrease the risk of flooding and erosion.
Essentially, compaction is crucial for the safety and longevity of construction work, greatly reducing the cost of ongoing repairs and maintenance. Roads, foundations, and pavements will last longer and maintain their value better.
In fact, the cost of improper soil compaction might already be felt during the construction phase. Construction projects involving issues with the soil structure can experience more delays and less efficient use of materials as more concrete/asphalt might need to be used.
Need a hand with compaction equipment servicing and maintenance? We’ve got you covered.
How does soil compaction work?
Effective soil compaction in construction takes several factors into account
These include:
- The type of soil
- The soil’s moisture content
- The machinery used
- Budgets and lead time for the rest of the project.
Steps and best practices in soil compaction
Soil assessment
The first, and probably most important step, is conducting a thorough soil assessment. You want to understand the physical properties of the soil, such as grain size distribution, shape, and specific gravity. These factors all strongly influence how well the soil will compact.
Optimum moisture content
The soil’s moisture content also plays a significant role. The ‘Proctor Test’ or ‘Modified Proctor Test’ are typically performed to identify the ideal moisture content for maximum density when compacted. Achieving this optimum moisture level ensures that the soil compacts effectively, limiting water infiltration and ground expansion.
As such, after you’ve assessed the soil and started preparing it by removing debris, vegetation, large rocks, and organic matter, moisture conditioning will be your next task.
Layered compaction
Rather than compacting the entire volume of soil in one go, it’s advisable to carry out the compaction in layers. These layers usually range in thickness from 15-60cm. This approach ensures compaction is thorough and uniform throughout the soil mass, thereby enhancing the structural integrity.
Use of appropriate equipment
Next, you want to select the right machinery for the job. Different soil types and construction projects require varying compaction equipment. Whether it’s a vibratory roller for road construction or a plate compactor for building foundations, suitable equipment ensures effective compaction.
Even once you’ve settled on the type of roller best suited to the soil, other factors like site access may come into play. For example, if your site has limited space, you’ll likely need to choose a roller small and manoeuvrable enough to get in and out safely.
Need a hand finding the right equipment? Read our blog on choosing the right compaction roller.
Soil compaction testing and quality assurance
After you’ve completed the compaction process with the right compaction machinery, you still need to conduct field density tests and ensure the overall quality.
Soil compaction methods and machinery Field density testing is crucial because it helps to verify whether the soil compaction in real-world conditions achieves the required percentage of maximum dry density.
That said, field tests don’t replace laboratory testing methods like the Standard Proctor or Modified Proctor tests. These tests help to define the target values against which field results are compared. Without these benchmarks, your field data won’t have a reliable reference point.
In fact, in the construction industry, contracts and regulations typically require that you document your testing results and which corrective actions that were taken, if needed. Aside from satisfying regulatory requirements, this crucial step also protects contractors from liability in the event of a dispute.
Soil compaction equipment and methods
Soil compaction is employed in a wide array of civil construction projects, from road construction and building foundations to railway embankments, earth dams, and airport runways. Each application may require different compaction methods and machinery.
Road construction
Vibratory rollers, also known as drum rollers, are commonly used for road construction. Their vibrating mechanism enhances the compaction force, making them ideal for compacting granular soils over large areas.
Building foundations
Plate compactors are often used for compacting the soil around building foundations. Suitable for cohesive soils, they apply force through a vibrating plate to eliminate air pockets and rearrange soil particles.
Trenches and confined spaces
For smaller, hard-to-reach areas such as trenches, rammers are ideal. These tools deliver high-impact compaction and are most effective on cohesive soil types.
Large-scale projects
Tamping rollers or padfoot compactors are often the go-to choices for more expansive projects like airport runway construction or land reclamation. They offer high compaction performance and are capable of compacting a wide variety of soil types.
Need a refresher on soil compaction methods for your next project? Check out our Simple Guide to Compaction.
Traditional vs modern compaction technologies
Traditional compaction technologies widely use the number of rolling passes to ensure the right degree of compaction is achieved. Modern compaction technologies like the Völkel intelligent compaction system builds on this. The system can be fitted to any compaction roller and combines all the solutions for compaction measurement and documentation into a central system. Operators will have more information, giving them a complete view of compaction levels across each pass of the project.
Considerations and maintenance tips for soil compaction equipment
When it comes to soil compaction equipment, the project requirements, frequency of use, and budget will determine whether it will make more sense to buy or rent compaction equipment. For a one-off construction project or seasonal jobs, renting is ideal. On the other hand, if you’ll be using compaction equipment frequently, the ownership route will be more cost-effective over time compared to repeated rentals.
A rental company will also typically handle servicing and maintenance. As it’s an expensive piece of equipment and issues can lead to costly downtime or jeopardise safety, this is another big benefit that can influence your choice.
Alternatively, if you plan to buy compact equipment, the following essential maintenance tips will help to extend its life:
- Check for loose bolts, worn belts, fluid leaks, and cracks in the frame each time before use
- After each use, remove dirt, mud, and any other accumulated debris
- Regularly check and replace engine oil, hydraulic fluids, and fuel filters
- Inspect filters and spark plugs frequently and replace according to the manufacturer’s guidelines (or when clogged)
- Adhere to the manufacturer’s recommended maintenance schedule
Soil compaction for residential construction
Typically, in residential construction, lighter equipment like oscillating smooth drum rollers and plate compactors is used to ensure the soil can support the structure’s weight effectively. This process is crucial, especially for single-family homes, townhouses, or low-rise apartment buildings.
The goal is to minimise water infiltration and ground expansion to reduce the risk of structural problems such as sinking or tilting over time. A well-compacted residential site also helps prevent water pooling and soil erosion in gardens and driveways.
In terms of residential foundations, 95-98% on the Standard Proctor test is the right level of compaction. It will offer enough support for residential structures without complicating excavation for utilities.
If an existing residential property has cracks in foundation slabs, basement walls, or brickwork, or doors or windows that no longer open smoothly, it could be a sign of poor soil compaction. Exterior issues like uneven or sinking driveways and walkways and drainage problems could also point to issues with soil compaction.
While homeowners might be tempted to go the DIY route over professional soil compaction for their residential project, there’s a steep learning curve to achieve even, consistent compaction. You’ll need to have knowledge of the different types of soil, moisture levels, and know how to operate the equipment. As such, it’s best limited to garden paths or landscaping beds.
On the other hand, construction professionals know how to test soil moisture and achieve the right soil density level. While it will involve a higher cost because of labour and service fees, you’ll prevent costly repairs down the line.
Soil compaction for commercial construction
Commercial construction involves larger scale projects such as skyscrapers, industrial complexes, and shopping malls with heavier loads. This requires more robust machinery like vibratory rollers, padfoot compactors, double-drum rollers and multi-tyre rollers.
The compaction process needs to be even more rigorous to accommodate the additional stresses and strains that commercial buildings bring. For example, carparks and loading areas require soil that can bear the weight of numerous vehicles without deforming.
Soil compaction challenges and solutions
Achieving the right level of compaction isn’t always straightforward. This is especially true in Australia, where contractors often need to face challenging soil profiles and adverse weather conditions.
As Australia boasts such a vast landscape, there’s no one-size-fits-all solution. From clay to sand to rocky terrains, contractors often need to work with various types of problematic soils. For example, clay-based soils offer restricted drainage, while rocky soils’ inconsistent density can cause impediments.
Aside from the obvious impact that weather can have on your timeline, it can also impact the behaviour of the soil. If there’s a spell of heavy rain, the soil will become oversaturated, making compaction impossible until it dries. On the other hand, drought can turn clay into rock-like conditions.
For contractors who’ll be working primarily in urban areas, there’s the added challenge of accessibility. Construction sites like residential backyards offer limited maneuverability, which means that traditional compaction equipment might be impractical.
Innovation in soil stabilisation techniques improves project outcomes and helps to address many of these challenges. For example, Conplant offers a wide range of compaction equipment for various soil types and settings. Then, by retrofitting the Völkel intelligent compaction and navigation equipment to the roller needed for the project, contractors will gain access to verified results to ensure quality standards and reporting requirements are met.
Key takeaways
Whether you’re laying the foundation for a small home or a large-scale industrial complex, soil compaction is an essential process in construction. It lays the groundwork — quite literally — for the stability, longevity, and overall success of a building project. As such, the impact compaction will have on the final result should never be underestimated.
At its core, soil compaction serves to stabilise and strengthen base materials, enhancing its ability to bear loads and minimise water-related damage. While the process can be intricate, involving varying methods and machinery, the core principles remain universal.
The key to successful soil compaction lies in understanding the specific soil characteristics, using the correct compaction equipment, and adhering to the best practices of the compaction process.
At Conplant, we’re committed to helping you understand these complexities with no-nonsense advice, while providing Australia’s largest fleet of compaction rollers to choose from.
Make your next project a success from the ground up. Give us a call on 1300 166 166 or get a free online quote now.
Frequently Asked Questions
Soil compaction occurs when soil particles are pressed together. Proper soil compaction is important because it directly affects how soil performs in both construction and agriculture. Achieving the right level of compaction ensures stability for everything from a plant’s roots to a pavement to a heavy structure. It also helps control water movement and drainage.
It’s used in many construction projects to increase the density of the soil and reduce its ability to hold water and air. This way, a stable base for foundations, buildings, and roads is created.
In construction, poorly compacted soil can lead to foundation failure, issues with soil settlement, and increase erosion risk. It also reduces the soil strength and the ground may be unable to support structures or heavy equipment like vehicles.
If the soil has been compacted too much, it can cause drainage issues as water won’t be able to move through the soil which can lead to flooding or erosion. It can also make excavation and utility installation difficult as it will be harder to dig through the soil layers.
