Electromechanical Impedance Framework Based on Piezoelectric Smart Aggregates for Tracking the Evolution of Frozen Soil State and Pore-Ice Development

Abstract The continuous variations in stiffness and moisture conditions of seasonally frozen soil materials render the assessment of the state of geological infrastructure particularly intricate. This study presents an electromechanical impedance (EMI)-based framework that uses an embedded soil-based piezoelectric smart aggregate to monitor the evolution of the freezing state in frozen soil. A frozen-soil–piezoelectric coupling model was developed to interpret impedance responses under varying temperature, initial water content, freeze–thaw cycles, and unidirectional freezing. Results show that, above 0°C, the resonant response is governed mainly by temperature and unfrozen-soil stiffness, whereas below 0°C, freezing-induced stiffening dominates resonant-frequency shifts. Nuclear magnetic resonance measurements were used to calibrate the soil-freezing characteristic relationship, and the EMI response was then interpreted to estimate the evolution of pore ice in frozen soil. Under unidirectional freezing conditions, the estimated pore-ice content agreed well with the reference value, with a relative error of less than 6.7%. These results demonstrate the potential of embedded smart aggregates for continuous, nondestructive assessment of frozen subgrades and other cold-region geoinfrastructure.