A dynamic property index for compaction state assessment of highway subgrade with soil-shale mixtures: in-situ compaction tests

Intelligent Compaction (IC) technology assesses the continuous compaction quality of highway subgrades by monitoring the vibratory response of the roller drum. Existing models often fail to directly incorporate geomaterial properties, limiting their ability to characterize non-uniform states within complex mixed-fill materials. This study develops a dynamic constitutive model for soil-shale mixtures and proposes a calculation method for the Dynamic Property Index (DPI) to quantify structural damage and subgrade deterioration under dynamic loading. Twelve sets of in-situ subgrade compaction tests were conducted across varying operational parameters for validation. Results indicate that the Compaction Meter Value (CMV) correlates positively with the number of rolling passes and vibration intensity, whereas roller speed and loose lift thickness exert minimal influence. DPI effectively quantifies local subgrade states, with its standard deviation serving as a robust indicator of geomaterial uniformity and degradation. While CMV exhibits greater stability and provides a clearer representation of the overall compaction degree, DPI is more sensitive to localized damage, making it suitable for identifying over-compaction or local weak spots. Integrating CMV and DPI enables more comprehensive and intelligent continuous quality control in practical subgrade compaction.