Study of Laboratory Compaction System Variance Using an Automatic Proctor Calibration Device

This paper describes the development of a portable dynamic energy calibrator (PDEC) for mechanical Proctor compaction machines along with an analysis of system variance on a silty sand’s (A-2-4) dry unit weights. The PDEC measures a rammer’s kinetic energy delivered to the sample and the compressive energy retained in the sample. The monitoring system uses a photoelectric gate and impact force sensor attached to the machine. When the rammer mass is included, the system’s impedance can be calculated. Next, 30 Florida Department of Transportation (FDOT)-approved machines throughout the state were tested, and summary statistics (i.e., mean, standard deviation, and so on) of the kinetic and compressive energies of the machines were found. Scatter plots of hammer kinetic energy along with sample energies allowed for identification of poorly functioning machines (e.g., low-impact energies or variations in mold support). Finally, a series of blind modified compaction tests were performed on A-2-4 soil at six labs at dry and wet of optimum. A regression analysis of the mean and variance of dry unit weight as a function of moisture content, kinetic energy, and sample energy was undertaken. Approximately 50% of the measured dry unit weight variance was associated with variance of kinetic energy, sample energy, or sample moisture. The other 50% of the variance was attributed to operator influence (i.e., sample preparation, lift thicknesses, moisture determination, and so on), which was not measured in this study.