Temperature- and stress-dependent electrical responses of frozen soils

Abstract

Characterisation of freezing conditions (i.e. temperature and unfrozen water content) and stress states (e.g. stress level and specific volume) is critical to evaluate the thermo-hydro-mechanical properties of frozen soils. This study aims to utilise frozen soils’ electrical responses to characterise mechanical properties and interpret the associated frost heave phenomenon and compression characteristics. Frozen soils were prepared by freezing sand and bentonite at various temperatures (i.e. −5, −10, −20 °C), in which the electrical conductivity and frost heave were monitored. A modified oedometer was thereafter utilised to conduct compression tests on frozen soils. Results showed that electrical responses were highly sensitive to soil temperature variations during freezing: electrical conductivity decreasing by 2–5 orders of magnitude in response to the temperature drop of 15–40 °C. Soil freezing characteristic curves were associated with freezing point depression phenomena, as reflected in correlations between electrical conductivity and unfrozen water content. Frozen soils exhibited sensitive electrical responses to stress changes along the loading path (e.g. electrical conductivity increased by 2–4 orders of magnitude due to stress increase from 1 to 2500 kPa); while no significant stress-dependent electrical responses were observed during unloading, likely due to the loss of electric contacts. Moreover, the preconsolidation pressure of the frozen bentonite increased by 10–60 times compared to the unfrozen bentonite because of the ice invasion mechanism. This study investigates thermomechanical couplings in frozen soils and highlights the potential applicability of electrical conductivity for monitoring thermal and stress states of frozen soils in cold regions.