Hydraulic pressure accelerates ice growth in the stratum

Abstract

Engineering geological investigations indicate that confined water exists in the stratum during the warm season in permafrost regions and in underground engineering employing artificial ground freezing (AGF) to isolate groundwater, causing significant upward deformation of the stratum and frost damage to engineering structures. However, limited studies have explored the effect and mechanism of hydraulic pressure on ice growth during soil freezing upwards. Therefore, this study designs and conducts four groups of bottom-up freezing tests under various hydraulic pressures, and develops a model to investigate the mechanism of hydraulic pressure on ice growth, based on the theory that liquid water migrates towards the ice lens through an unfrozen water film. The experimental results, including thermal regime, frost heave, cryo-structure, and water redistribution are analyzed systematically, which show the frozen depth, frost heave increment, ice lens thickness, and the layered water content in the samples all increase with hydraulic pressure. The model is validated with experimental data, and the calculation results demonstrate that the ice growth rate increases with hydraulic pressure due to a higher pore water pressure (PWP) gradient in the unfrozen water film. Thus, the characteristics and mechanisms of ice growth in the stratum, accelerated by hydraulic pressure, are clarified. Finally, the applications and implications of this study to engineering geology are discussed, which contribute to a better understanding of ground ice formation in permafrost regions and frost damage prevention in underground engineering performing AGF.