Octavius recently carried out a study to evaluate whether Continuous Compaction Control (CCC) could be applied to highways earthworks construction. In particular to assess whether the method could deliver comprehensive quality control and specification compliance data regarding soil compaction.
Issue
Soil compaction improves the strength and stability of earthworks by increasing the shear strength of the soil to limit future settlement and reduce permeability. Current compaction testing methodologies rely on spot testing using a Lightweight Deflectometer (LWD) or a nuclear density gauge.
CCC monitors feedback from a vibratory roller as it passes over the compacted soil. This feeds real-time compaction data to roller drivers to ensure each area undergoes a sufficient number of roller passes to achieve a uniform level of compaction.
In theory, CCC offers more efficient and homogeneous control over the level of compaction, ensuring that all areas are compacted according to site specifications. However, to be an acceptable method CCC would need to demonstrate that the results have a high degree of correlation with industry-accepted test methods.
The Study
Octavius tested the CCC approach 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. This material is commonly used in embankments and as backfill for concrete structures.
CCC measurements were compared with LWD and nuclear density gauge readings as well as the California Bearing Ratio (CBR). Calculating the ‘r’ value – a statistical method that indicates the degree of correlation between two variables – would ideally give a result close to 1 with each of the industry-accepted methods. This would be the highest degree of correlation, with -1 being the lowest.
Results and Recommendations
- CCC results showed a reasonably strong correlation with nuclear density gauge readings (0.758).
- The degrees of correlation with LWD and CBR readings were weak. This may be partly because the 6i material is not greatly affected by the falling 10KG weight used by the LWD test.
- CCC measurements are significantly affected by the percentage of fine grained materials (below 0.063mm) and by the moisture content of the soil.
- Where soils contain less than 15% of fine grained material there is a good correlation between CCC measurements and compaction unless the moisture content is high. It’s likely that a soil surface softened by heavy rain deforms under the force of the CCC roller vibrations to render the results unreliable.
- For a valid result the roller drum must maintain full contact with the surface, which should also be homogeneous.
Effective innovation is a process and further testing is being planned to validate the applicability of CCC for 6i and other materials.
For more information contact hello@octavius.co.uk
