Abstract: Artificial ground freezing (AGF) is widely applied in geotechnical engineering under complex site conditions. However, in situ methods for evaluating the strength of frozen soil are still insufficiently developed. This study employs a self-developed embedded four-electrode system to investigate the strength and electrical properties of water-rich silty clay collected from the Yangtze River floodplain. Results show that unconfined compressive strength (UCS) increases as temperature decreases, following a “slow rise–sharp increase–slow rise” pattern, and also increases with dry density. A critical water content of 22% produces the peak strength. Beyond this threshold, frost-heave-induced cracking reduces the strength. Under near-saturated conditions, the formation of an ice-skeleton structure partially restores the strength. Resistivity increases in stages as temperature decreases, primarily because of free-water freezing and increased pore tortuosity. At higher water contents, conductivity diminishes more sharply. A transition in the conduction mechanism occurs at a critical dry density, with conduction shifting from pore-water dominance to bound-water and soil-matrix dominance. A power-law relationship is observed between saturation and resistivity, and the freezing of bound water together with frost deformation further enhances this sensitivity. Unconfined compressive strength and deformation modulus are strongly linearly correlated, and both increase with resistivity. A resistivity-based predictive model is established to link macroscopic strength to microstructural evolution and moisture variation, thereby explaining the model dispersion and predictive accuracy from a microscopic perspective. Brunnauer-Emmett-Teller (BET) and Scanning electron microscope (SEM) analyses reveal that increasing water content enlarges the pore structure. In addition, freeze–thaw cycles transform soil aggregates from flaky to honeycomb-like forms and promote the development of micropores into continuous macropores. These microstructural changes illustrate the damage process and demonstrate how the coupling between water–ice phase transitions and pore evolution influences soil strength. This study enhances understanding of the multi-parameter coupling between frozen soil properties and resistivity, thereby supporting the development of accurate resistivity-based evaluation models for artificially frozen ground.

Key words: artificial permafrost resistivity, four-phase electrode method, unconfined compressive strength, electrical prediction model, microscopic damage mechanisms