How Ground Conditions Influence Aggregate Choice
When planning a groundwork project, aggregate selection is often seen as a simple supply decision. In reality, the performance of any aggregate is closely linked to the conditions beneath it. Two sites may appear identical at first glance, yet behave very differently once excavation begins.
Ground conditions play a significant role in how aggregates perform over time, particularly in relation to drainage, stability, load-bearing capability, and long-term durability. Understanding these conditions before selecting materials is a key part of achieving a reliable result.
Why Ground Conditions Matter
Groundworks rarely fail because of a single issue. More often, problems arise when material choice does not suit the underlying ground. Factors such as moisture retention, soil makeup, historical land use, and natural drainage all influence how an aggregate behaves once placed and compacted.
Selecting the right aggregate is therefore less about choosing a standard material, and more about matching that material to what is happening beneath the surface.
Clay Ground and Poorly Draining Soils
Clay-heavy ground is common across many parts of the South East and is known for retaining water and expanding in wet conditions. This can present challenges when installing sub-bases, access roads, and foundations.
In these conditions, aggregate choice must account for:
Reduced natural drainage
Potential ground movement
Risk of soft spots during installation
Using aggregates that provide stability while working alongside suitable separation layers and drainage solutions can help manage these risks. Correct compaction and staged installation are particularly important on clay-based sites to prevent future settlement.
Free-Draining Ground: Chalk and Sandy Soils
Chalk and sandy ground often drains well but brings its own set of considerations. While water disperses quickly, finer particles can migrate into the ground, reducing support over time if not managed correctly.
On these sites, aggregate selection focuses on:
Maintaining structure and load distribution
Preventing material loss into the subgrade
Supporting surfaces subjected to traffic or load
Even on well-draining ground, inappropriate aggregate choice can lead to uneven compaction or reduced long-term performance.
Made Ground and Previously Developed Sites
Sites with a history of previous development often contain made ground, which can vary significantly across short distances. This material may include a mix of soils, demolition remnants, and inconsistent fill.
In these situations:
Ground conditions can change rapidly across a site
Bearing capacity may be unpredictable
Aggregate consistency becomes more important
Selecting aggregates that perform reliably under variable conditions helps reduce risk, particularly on projects where unknowns are only revealed during excavation.
Sloping and Uneven Sites
Sites with changes in level or sloping ground require additional consideration. Aggregates on these sites must contribute to stability as well as providing a suitable working platform.
Key considerations include:
Preventing sideways movement
Supporting retaining features
Managing surface water runoff
Aggregate choice forms part of a wider approach that includes compaction methods, drainage planning, and layering techniques.
Areas with High Water Tables or Drainage Requirements
Ground conditions influenced by high water tables or poor natural drainage require a coordinated approach. Aggregate selection here often works in tandem with drainage systems to control water movement and maintain stability.
In these cases, it is not solely about the aggregate used, but how it integrates into a broader groundworks and drainage design.
Domestic vs Commercial Ground Conditions
Domestic projects such as driveways and extensions often have different tolerances compared to commercial or industrial works. While both require careful aggregate selection, commercial sites typically place greater emphasis on load-bearing performance and durability.
Recognising these differences ensures that aggregate choices align with the intended use of the site.
Assessment Comes Before Aggregate Selection
No two sites behave exactly the same, which is why ground assessment is a vital first step in any groundwork project. Visual inspection alone rarely provides enough information. Experience, site knowledge, and understanding local ground conditions all play a role in recommending the correct materials.
Aggregate choice should be the result of informed assessment, not assumption.
Getting the Groundwork Right from the Start
Aggregate selection is not an isolated decision; it forms part of the wider groundworks process. When ground conditions are properly understood, materials can be chosen with confidence, resulting in better performance, fewer delays, and reduced long-term issues.
At Kernahans, our approach to aggregates reflects our wider groundworks experience — practical, considered, and grounded in what works on site.
