Field monitoring of roller vibration during compaction of subgrade soil

A field investigation was carried out with an instrumented vibratory roller compactor to explore the relationship between vibration characteristics and underlying soil properties, namely soil stiffness. The roller was outfitted with instrumentation to monitor drum and frame acceleration, as well as eccentric excitation force. Multiple consecutive passes were performed over six test beds on an active earthwork construction site to capture changes in roller vibration during compaction. Using lumped parameter vibration theory, soil stiffness was extracted from the roller data (drum and frame acceleration and drum phase lag). Both drum acceleration and drum phase lag were found to be very sensitive to changes in underlying soil stiffness. The drum-soil natural frequency of the coupled roller-soil system varied considerably and increased with compaction-induced soil stiffening. Phase lag always decreased with increasing soil stiffness, whereas drum acceleration trends depended on whether the excitation frequency was less than or greater than resonance. Roller-determined soil stiffness was found to be a function of the eccentric force, and heterogeneity in moisture, lift thickness, and underlying stiffness has a considerable affect on roller vibration behavior. When used as a proof roller, the instrumented roller identified soft areas in the embankment that were not identified by a static proof roll test.