Effects of ultralow temperature and water saturation on the mechanical properties of sandstone

The surrounding rocks are subjected to ultralow temperatures in applications like liquid nitrogen fracturing, underground storage of liquefied natural gas and polar constructions etc. The mechanical properties of sandstone with different saturations under freezing temperature and after one ultralow temperature freeze–thaw cycle test conditions were investigated in this study. The uniaxial compressive strength (UCS) of both dry and saturated samples increases with the decrease in temperature except at − 90 °C under freezing temperature test conditions, while the UCS of saturated samples is lower than that of dry samples after one ultralow temperature freeze–thaw cycle due to the water softening effects and the damage induced during the water–ice phase transition. The failure patterns of dry samples are more complex than those of saturated samples under freezing temperature, which is also indicated in the lower brittleness index for the saturated samples. The ice cohesion effect and its creep deformation increase the plastic deformation, while decreasing the Young’s modulus of saturated samples under freezing temperature. In addition, the ice net formed in the connected pores significantly increases the sample tensile strength and makes its failure less severe. The UCS, Young’s modulus and brittleness index decrease with saturation under − 120 °C, while the tensile strength increases with saturation. Porosity reduction measured by computerized tomography for the saturated samples after one freeze–thaw cycle is largest at − 120 °C compared with those at − 60 °C and − 180 °C, which is certified by the pore filling shown in scanning electron microscope images.