Effects of ice content on compression characteristics of frozen sandstone by in-situ NMR technology

Abstract

In cold regions, the freezing of pore water in rock affects the mechanical behavior of the rock. This paper studied the ice content of frozen sandstone at different temperatures and its effects on the mechanical properties of sandstone. First, the progressive freezing treatment (from 25.0 to − 30.0 °C) and in-situ nuclear magnetic resonance test were conducted to study the evolution of the ice content of sandstone with temperature. This evolution was quantitatively described by the frozen ratio defined as the percentage of the mass of ice and the total mass of water. Then, the mechanical properties of frozen sandstone at different temperatures (25.0 °C, 0.0 °C, − 5.0 °C, − 10.0 °C, − 20.0 °C and − 30.0 °C, respectively) were tested, such as P-wave velocity, uniaxial compressive strength (UCS), peak strain and elastic modulus. Finally, the effects of the frozen ratio on these properties were discussed. The results show that the pore water in sandstone shows three stages as the temperature decreases: stable liquid (from 25.0 to 0.0 °C), sharp phase transition (from 0.0 to − 2.5 °C) and slow phase transition (from − 2.5 to − 30.0 °C). Especially, the capillary and bulk water in sandstone is almost completely frozen in the sharp phase transition stage. As the temperature decreases, the frozen ratio first remains constant, then increases rapidly and finally increases slowly. Moreover, as the frozen ratio increases, the P-wave velocity, UCS and peak strain increase while the elastic modulus decreases. Interestingly, the compressive failure mode of sandstone changes from brittle to ductile as the frozen ratio increases.