Using continuous compaction control systems within an earthwork compaction specification framework

Cacciola, Daniel
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University of Delaware
The objective of the study presented in this thesis is to investigate the use of continuous compaction control (CCC) systems within an earthwork compaction specification framework. For this purpose, the Delaware Department of Transportation (DelDOT) funded a field study to construct a small-scale soil embankment, utilizing CCC technology simultaneously with conventional in situ compaction verification test methods during the construction process. The material that was used to build the embankment classified as poorly-graded sand with silt. The CCC roller measured machine drive power (MDP) values, compaction meter values (CMV), and corresponding global positioning system (GPS) location values. For conventional in situ compaction verification, numerous density-based quality assurance test methods (e.g., Nuclear Density Gauge and Sand Cone) and modulus-based test methods (e.g., Lightweight Deflectometer and GeoGauge) were performed. A holistic analysis of the data collected from the field study was performed to assess the use of CCC systems in an earthwork compaction specification framework. The first goal of this study was to examine the possibility of using data recorded by CCC systems to monitor and control the thickness of compacted soil lifts during earthwork operations. During the field study, the compaction roller utilized a real-time kinematic global positioning system (RTK-GPS) to determine the three dimensional location of the compactor in real-time. Data collected from the field study was then used to demonstrate how GPS measurements recorded by CCC equipment could be used for field monitoring of lift thickness. The use of simple and sophisticated geospatial interpolation techniques were examined for interpolating measured field elevation data onto a uniform grid for lift thickness evaluation. The approach that is presented can be used to build spatial maps of compacted soil lift thickness, which are a useful decision-making tool for field inspectors. The second goal of this study was to perform statistical regression analyses to compare the results of the in situ spot testing methods with the two CCC measurements (MDP and CMV) that were recorded during the compaction process. In order to accurately compare the in situ spot testing measurements and CCC measurements, Nearest Neighbor, Inverse Distance Weighting, and Ordinary Kriging interpolation techniques were utilized to predict CCC measurements at the corresponding in situ spot test locations. In general, regression analyses performed using the CCC predictions from the Ordinary Kriging method showed slightly higher correlations, however, the difference did not appear significant enough to outweigh the complex nature of this geospatial interpolation technique. Univariate regression analysis was performed first for point-by-point comparisons of the data and then on a data set which comprised of average values for each lift and pass. The point-by-point comparisons yielded weak correlations, while the comparison of the average value data sets showed much stronger correlations; this finding agrees well with observations that have been reported by other researchers. As other researchers have also reported that moisture content can drastically affect the compaction process and resulting density of soil, additional analyses using a multivariate regression technique were performed, which introduced the use of in situ measured moisture content as an independent variable. The results from these regression correlations showed generally much stronger correlation between the in situ test measurements and the CCC measurements for both the point-by-point and average data sets. This observation provided confirmation of the influence of moisture content on the in situ test measurements and the CCC measurements. The final goal of the study was to evaluate the use of CCC technology within an earthwork compaction specification framework. To accomplish this goal, implementation of existing CCC compaction verification acceptance criteria using the data collected from the aforementioned field study was performed. The acceptance criteria that were assessed include: spot testing of roller measured weakest areas, limiting percentage change in roller measured values, and comparison of roller measured values to in situ measured values. Each of the three acceptance criteria show potential for implementation into an earthwork specification; however, since the spot testing of roller measured weakest areas method still utilizes conventional in situ methods, it shows the most promise for immediate adoption and transition into CCC technology.