Evaluation of strength characteristics of artificial permafrost based on electrical resistivity

Artificial ground freezing (AGF) is widely applied in complex geotechnical environments; however, in situ evaluation of frozen soil strength remains limited. This study employs a self-developed embedded four-electrode system to investigate the strength and electrical properties of water-rich silty clay from the Yangtze River floodplain. Results indicate that unconfined compressive strength (UCS) increases with decreasing temperature in a "slow-sharp-slow" pattern and rises with dry density. A critical water content of 22% produces peak strength, beyond which frost-heave cracking reduces strength, while near-saturation (~ 30%) promotes the formation of an ice skeleton that partially restores it. Resistivity exhibits stepwise growth with decreasing temperature, primarily due to free water freezing and increased tortuosity, with sharper conductivity losses at higher water contents. A conduction shift occurs at a critical dry density, transitioning from pore water dominated to bound water and soil matrix dominated pathways. Resistivity follows a power-law relationship with saturation, controlled by bound water freezing and frost-induced deformation. Both UCS and deformation modulus correlate strongly and linearly with resistivity. A resistivity-based model is proposed to link strength with microstructural and moisture changes. Brunauer-Emmett-Teller (BET) and Scanning Electron Microscopy (SEM) analyses reveal that higher water content enlarges pores, while freeze-thaw cycles transform flaky aggregates into honeycomb structures and convert micropores into macropores, highlighting the coupled influence of phase transitions and pore evolution on strength. These findings enhance understanding of the frozen soil-resistivity coupling mechanism and provide a basis for accurate strength evaluation using resistivity.