A resistivity-based study on the pressure melting of pore ice in frozen gravel soil

To investigate the presence of pressure melting during the compression of frozen gravel soil, we conducted unconfined compression tests and resistance tests on gravel soil samples with varying water (ice) contents and freezing temperatures. The unfrozen water content in saturated gravel soil samples was quantified using nuclear magnetic resonance (NMR) spectroscopy. The results indicate that: (1) During compression, the resistance of gravel soil initially decreased rapidly, subsequently slowing down, with only the dry sample exhibiting an increase in resistance post-peak stress. (2) In the rapid reduction stage, the resistance reduction rate of dry samples was lower compared to saturated frozen samples. Specifically, the resistance reduction rate of - 4 degree celsius saturated samples was 26.8%, which was fourfold that of dry samples at the same temperature. (3) As the freezing temperature decreased, the rate of resistance reduction initially increased and subsequently decreased during the rapid reduction stage. (4) Upon temperature reduction, the relative contents of both free water and capillary water underwent rapid declines, whereas the relative content of adsorbed water initially increased marginally before gradually decreasing. Analysis reveals that the compression of frozen gravel soil elicits a pressure melting effect, resulting in an increase in unfrozen water content within the high-stress regions of the sample during loading. This meltwater subsequently migrates through the unfrozen water film into the pore spaces of low-stress areas, where it re-freezes, altering the pore structure. Notably, the pressure melting effect is most pronounced within the temperature range of -2 degree celsius to -4 degree celsius .