Evaluation of Intelligent Compaction Technology Based on Correlations to Relative Density
Project ID: 3785
Principal Investigator: Robert Rinehart
Research Topic: Improving Geotechnical Infrastructure Reliability
Funded Fiscal Years: 2012
Keywords: compaction, density, earthwork, intelligent, soil
Intelligent compaction (IC), whereby earthwork (soil) compaction quality control/quality assurance (QC/QA) is accomplished by monitoring roller-compactor drum vibrations and relating them to soil properties via mathematical modeling, is an established technology in Europe and is gaining traction in the road construction industry in the U.S.. IC holds tremendous benefit for Reclamation as it has the potential to result in a higher quality and more uniform product.
The majority of IC research has been funded by the transportation industry. As pavement design is becoming increasingly mechanistic, the majority of IC research has focused on correlating IC-based measurements of soil properties (i.e., roller measured values [MVs]) to other in-situ, spot-test based measures of soil stiffness or modulus. The work that has been documented in the literature to correlate roller MVs to density has all been based on absolute density or relative level of compaction (i.e., percentage of maximum density). This work has shown correlations with density to be problematic as absolute density and relative compaction only change a few percent over the compaction process as soil is transformed from loose to dense. Correlating to such an insensitive parameter is difficult, and since these correlations form the underpinnings of IC, it has been difficult to implement IC based on traditional density criteria. However, within Reclamation, it is customary to use relative density instead of relative compaction for granular materials. Relative density is more sensitive and can change by more than 50 percent during compaction.
In order for Reclamation to realize the potential benefits of IC, it must be demonstrated that robust correlations exist between roller MVs and relative density. The proposed research is aimed at re-evaluating existing IC data in terms of relative density rather than absolute density or relative compaction to determine the quality of the potential regressions.
Need and Benefit
Implementation of IC technology into Reclamation earthwork construction holds several potential benefits. Direct benefits include:
1) 100 percent coverage: IC enables QA/QC with 100 percent coverage of the compacted area. Roller MV data (which form the basis for acceptance) exists whereever the roller has been operated. This is a substantial improvement in comparison to traditional spot testing, which covers much less than 1 percent of the compacted area. This allows for inspectors to hone in on problem areas quickly and effectively. It also results in a final product with much lower uncertainty and risk because 100 percent of it has been inspected.
2) Phase out nuclear gage: Implementing IC decreases dependence on the nuclear density gage, as the roller becomes the primary QC/QA tool. This is desirable for several reasons, including the cost associated with purchasing, maintaining and storing gages, as well as the training and licensing of operators. Further, there is more and more risk associated with storing nuclear material, and many agencies are looking for ways to phase out the use of the nuclear density gage for this reason.
3) Better documentation: IC technology provides GPS-position indexed QA data for the entire constructed area. This comprehensive electronic data can be stored long term and referenced in the event issues arise that require investigation into the as-built facility.
4) Test more materials: Materials such as pea gravel and rock fill are difficult and expensive to perform density testing on reliably. These materials are often used by Reclamation and have traditionally been controlled by a method specification rather than by rigorous density testing. IC is applicable to these materials however, and the same level of control can be applied to them as to any other granular material.
Another, more indirect benefit of IC also exists. The operator of the roller compactor is able to view the roller MV data in real time. These data are displayed on a screen onboard the roller and is color coded (i.e., green = good, red = bad) to give the operator immediate feedback regarding where more compactive effort is needed and where compaction is likely finished. This allows for more efficient and more uniform compaction operations. This is a great benefit not only to the contractor but also to Reclamation as it results in more efficient construction and a more uniform product.
All of these benefits, both direct and indirect, result in higher quality products. QA has been performed for the entire compacted area, and QA data can be easily stored for future reference. More uniform compaction operations are enabled, and the use of the nuclear density gage is decreased. Materials that were previously not tested and controlled by method specifications are now rigorously tested.
As discussed earlier, investigating the correlations between roller MVs and relative density has been identified as one of the next steps in Reclamation's implementation of IC technology. This research enables that important step to be taken.
The following documents were not reviewed. Statements made in these documents are those of the authors. The findings have not been verified.
Project Synopsis (final, PDF,
By Robert Rinehart
Report completed on May 27, 2014