Being told your site has poor ground can quickly raise concerns about cost, risk and whether your project is even viable. Phrases like soil improvement or soil modification techniques are often mentioned early, but they’re rarely explained clearly.
In reality, soil improvement is a well-established part of ground engineering. Rather than avoiding weak ground altogether, engineers can often improve the soil so it behaves more predictably and can safely support construction. In the right conditions, this can reduce risk and, in some cases, avoid deeper or more complex foundation solutions.
This guide explains what soil improvement is, why it’s used, the main methods available, and when soil improvement is the right approach or when piling may be more appropriate. The aim is to help you understand your options and make informed decisions with confidence.
What is soil improvement in construction?
In construction terms, soil improvement involves treating the ground to:
- Increase bearing capacity
- Reduce settlement
- Make soil behaviour more predictable
This work is carried out before foundations are installed, providing a more reliable base for the structure.
Soil improvement isn’t a foundation type. It doesn’t replace foundations or piling. Instead, it improves how the ground behaves so suitable foundation solutions can be used.
What problems does soil improvement address?
Soil improvement is typically used where:
- The ground is too soft or loose to support loads safely
- There’s a risk of excessive settlement over time
- Soil conditions vary across the site
- Removing and replacing soil would be impractical
By improving ground performance, engineers can often reduce construction risk and improve long-term stability.
What Are the Methods of Improving Soil?
1. Deep compaction of soil
This is a method that uses severe impact, vibration, and blasting to densify cohesive soil deposits in-situ. It involves the transformation of a loose cohesionless soil structure into a dense one so that it can support a bigger weight load.
Best suited to:
- Sand and gravel
- Shallow improvement needs
- Open sites with good access
It’s less effective in cohesive clays or where weak soils extend deeper.
2. Grouting and injection
Grouting is one of the methods for controlling groundwater during civil engineering projects. It is the injection of pumpable materials into a soil or rock formation to modify its physical qualities. This method is appropriate when soil permeability would place a high demand on pumping or where subsurface conditions would make drilling wells economically inefficient.
Alternatively, chemical grouting is also possible – this is a method of permeating pore spaces in granular soils with low viscosity, non-particulate grout that hardens to form a cemented mass.
3. Pre-compression
Pre-compression is a ground improvement technique in which the ground is compressed under pressure before the structural load is placed or finished. Pre-loading comprises adding and removing earth, water, or another dead load comparable in weight to the ultimate load before construction, achieving ground pre-compression.
4. Soil improvement with additives
Using admixtures such as lime, cement, and a cohesive-non-swelling (CNS) layer, any one or more of the soil qualities can be modified to increase soil strength and minimise shrink-swell characteristics.
5. Thermostatic soil improvement
There are two approaches for improving the soil with thermal processes, either by heating or cooling the soil. Removing heat from the soil and freezing its pore water is a potent approach for making the ground impermeable and more resilient for unconsolidated materials.
Alternatively, using heat to force out free pore water and, at higher degrees, water adsorbed on particle surfaces makes a strong, lasting material, such as bricks or mud construction blocks.
6. Consolidation
Reinforced soil reinforcement is a technique that uses technologies including reinforced soil, soil nailing, root or micro-piles, slope dowels, and embankment piles to enhance the stiffness and strength of the soil.
7. Importance of drainage
The risk of liquefaction can be lowered by improving the soil\’s drainage capacity. The build-up of excess pore water pressure will be decreased if porewater within the soil can drain easily.
Installation of drains made of gravel, sand, or synthetic materials is one method of drainage. In contrast to gravel or sand drains, which are typically laid vertically, synthetic wick drains can be positioned at various angles.
Limitations of Soil Improvement
Soil improvement can be effective, but it isn’t suitable for every site.
When soil improvement may not be enough
Soil improvement may not be appropriate where:
- Weak soils extend to significant depth
- Ground conditions are highly variable
- Structural loads are high
- Settlement tolerances are very tight
In these cases, improving near-surface soils may not provide the long-term stability required.
Soil Improvement vs Piling
A key decision is whether soil improvement is enough or whether piling provides a better solution.
- Soil improvement treats the existing ground so it performs better
- Piling bypasses weak soil and transfers load to deeper bearing strata
Piling is often the better option where weak soils extend deeper or where long-term settlement risk must be minimised.
You can learn more about piling options on our piling solutions page.
Why it’s important
There are many reasons why it is important to use correct solid improvement methods in the right circumstances, such as the previously mentioned stability in foundation construction, but there are many other reasons to invest time and thought into soil improvement before construction.
Soils capture and store carbon, lowering greenhouse gas emissions (GHG) in the atmosphere, and hence aid in the fight against and adaptation to climate change. Additionally, water can infiltrate into resilient soils, screening pollutants and preventing them from seeping into groundwater.
Ultimately, ensuring that your soil is secure and safe from liquefaction is a fundamentally important factor when starting any project.
Get in touch with our team of expert piling contractors to discuss your requirements and find the best soil improvement method for your project.