Analysis of intelligent compaction field data on layered soil

Abstract

Intelligent compaction (IC) procedures have been gaining popularity as a way to measure mechanistic soil material properties (e.g. stiffness) during the compaction process for earthwork projects. IC procedures involve the interpretation of roller measured soil stiffness from vibratory roller drum accelerations and offer an advantage over current spot testing methods, as IC provides real-time continuous feedback during the compaction process and 100% test coverage of the earthwork site. The objective of this study is to provide the first detailed analysis of IC field data from vibratory roller compaction of layered soil systems. The interpretation of roller measured soil stiffness is currently ambiguous for two main reasons: (1) IC vibratory rollers provide a composite measure of soil stiffness in layered earthwork situations and (2) roller measured soil stiffness from edge mounted (EM) accelerometers can vary significantly due to rocking motion of the drum. To investigate these issues, left and right EM acceleration data from a vibratory roller are used to compute a composite roller measured soil stiffness at the center of gravity (CG) of the drum. CG soil stiffness, which is not subject to the variations associated with drum rocking, are used to evaluate data from two field sites with multiple 15 - 30 cm thick base/subbase/subgrade lifts to investigate their sensitivities to variable lift materials and thicknesses. CG soil stiffness increases with the addition of subbase and base lifts, showing sensitivity to changes in soil materials. CG soil stiffness also increases with the addition of multiple base lifts, showing sensitivity to an increase in the overall thickness of the base material. CG soil stiffness is not sensitive to small variations in the subbase and base lift thicknesses, showing CG soil stiffness is sensitive to the addition of 15 - 30 cm thick subbase and base lifts but not the small variations in lift thickness associated with each of these lifts.