Civil engineering projects must increasingly consider the effects of climate change and the reality that extreme weather events will be more common. This is particularly true for earthworks.
The effects of soil composition – particularly clay content – and slope angle are significant areas of study as engineers seek to achieve the optimum balance between land take, embodied carbon and long-term asset resilience.
The degree and uniformity of soil compaction is another critical performance factor in the construction of earthworks and their long-term stability. Put simply: are existing compaction testing methods the most appropriate ones for earthworks that will need to perform reliably in a more hostile environment?
Soil Compaction Testing Methods
Established techniques include spot testing using a Lightweight Deflectometer (LWD) or a nuclear density gauge. Although these accepted methods are recognised for producing reliable and repeatable results, they have limitations.
The first of these is that they are spot tests. Ultimate performance of the earthwork over many decades will be affected by the uniformity of compaction and the resulting mechanical properties.
They are also an additional process that interrupts production. Finally, nuclear density gauges involve handling potentially hazardous materials.
Is Continuous Compaction Control The Answer?
In the spirit of innovation that will be needed to address complex issues around asset resilience, Octavius initiated a project to evaluate Continuous Compaction Control (CCC) as an alternative to established spot-testing methodologies.
CCC involves running vibratory rollers over the compacted surface and measuring the feedback. This provides a real-time measurement of compaction across the entire surface. In theory it could be a more reliable method of ensuring that the entire earthwork structure conforms to site specifications.
The trial was conducted on the Binley Flyover Junction Scheme on the A46. The reinforced soil walls that form part of the structure for new slipways and a wider carriageway used Class 6i granular material for the soil blocks.
Our team set out to evaluate how closely CCC measurements correlated with the accepted industry standard methods.
What We Found
CCC results showed a reasonably strong correlation with nuclear density gauge readings (0.758). But the degrees of correlation with LWD and CBR readings were weak. The study also found that CCC measurements are significantly affected by the percentage of fine grained materials (below 0.063mm) and by the moisture content of the soil.
These results showed that CCC needs further investigation before it can be adopted as the primary method of compaction testing for earthworks structures with different compositions.
Studies are continuing to assess the applicability and limitations of the technique, as it has the potential to improve efficiency and provide a more comprehensive and homogeneous picture of a critical performance factor in earthworks resilience.
For more information, read the case study or contact hello@octavius.co.uk .
