Ganju, E., Prezzi, M., Salgado, R., Siddiki, N. Z., & Sommer, K. (2015). QA/QC of subgrade and embankment construction: Technology replacement and updated procedures (Joint Transportation Research Program Publication No. FHWA/IN/JTRP-2015/01). West Lafayette, IN: Purdue University. http://dx.doi.org/10.5703/1288284315521
The Dynamic Cone Penetrometer (DCP) is a device that is used for the estimation of in situ compaction quality of constructed subgrades and embankments. It is a relatively inexpensive, light-weight and easy to use device that measures the dynamic penetration resistance of the compacted soil, from which an estimate of soil strength and stiffness characteristics can be made. Owing to its ease of use, many DOTs in the U.S. have employed the DCP in their compaction quality control procedures, and over the past few decades, extensive research has been carried out on the development of correlations between the results of the DCP test and the results of strength and stiffness tests performed on compacted soils (e.g., California bearing ratio, and resilient modulus)
The objectives of this research are to refine DCP-based quality assurance and quality control correlations for compaction quality control developed by previous research studies carried out at Purdue for the Indiana Department of Transportation, especially focusing on i) grouping of the soils based on their mechanical response to the DCP loading, and ii) limiting the in situ moisture range of the soils used for development of correlations within -2% of the optimum moisture content of the tested soil. The factors outlined above are studied, and in particular, soil grouping is examined critically. The AASHTO (‘A-based’) classification employed previously for classification of soils is replaced by a new classification criteria specifically developed for the DCP test. Soils are grouped into one of the two categories of coarse-grained or fine-grained soils on the basis of the size of the dominant particle in the soil. The criteria developed for the classification of soil into one of these two categories is based on index properties of the soil, such as the standard Proctor maximum dry density, optimum moisture content, plasticity index (PI) and fines content (percentage passing0.075 mm sieve size).
For the purpose of refinement of the QA/QC correlations, extensive field and laboratory tests (more than 750 DCP tests) were carried out on soils found in Indiana to add to the existing database of DCP test results. The database was then statistically analyzed for extraction of the representative DCP test value (number of DCP blows required for a specific depth of penetration into the compacted soil) for different types of soil.
Results show that the DCP test results for fine-grained soils have a good correlation with the PI, which is indicative of the clay content of the soil, while the DCP test results for coarse-grained soils have good correlations with the optimum moisture content of the soil, which is indicative of the targeted in situ density of the soil. Furthermore, a statistical analysis of the distribution of DCP blow counts in the field revealed that the mean of a minimum of 7 closely spaced tests is required to get a representative blow count of the compacted soil at a given location. More targeted testing is needed to assess the frequency of DCP testing required for larger areas.
dynamic cone penetrometer, compaction quality control, moisture content, variability, coarse-grained soils, fine-grained soils
Joint Transportation Research Program
Indiana Department of Transportation
West Lafayette, Indiana
Date of this Version