为研究孔隙水压力实时作用下冻结饱水砂岩的力学特性,开展了4个地应力梯度下砂岩常温(20℃)和负温(-5℃)、有孔隙水压力和无孔隙水压力条件下的三轴压缩力学特性研究,并对冻结前后砂岩试样进行微观扫描电镜测试。结果表明:低温冻结可以强化砂岩试样的三轴抗压强度,冻结后形成的孔隙冰可以隔绝孔隙水的流动;孔隙水压力在常温和负温情况下均会弱化砂岩三轴抗压强度,且在常温状态下更为显著;随着地应力的增大,常温情况下孔隙水压力对砂岩试样三轴抗压强度的弱化作用逐渐变强,负温情况下则相反;有孔隙水压力冻结的砂岩弹性模量普遍低于同地应力条件下无孔隙水压力冻结砂岩试样,且弹性模量随着地应力的增大先增长然后逐渐衰弱;砂岩试样在常温条件下加载破坏面多为平滑的剪切破坏,冻结之后破坏面多呈“S”状;有孔隙水压作用的砂岩试样微观结构中有更多的冻结散落颗粒和碎屑,冻结条件下更为显著。

To study the mechanical properties of frozen saturated sandstone under real-time action of pore water pressure, the triaxial mechanical properties of sandstone are analyzed under four different in- situ stress levels at both room temperature (20 ℃) and sub-zero temperatures (-5 ℃), considering var- iations with and without pore water pressure. And the microscopic scanning electron microscope test was carried out on the sandstone samples before and after freezing. The results show that low temperature freezing can enhance the triaxial compressive strength of sandstone samples, and the pore ice formed af- ter freezing can restrict the flow of pore water. The pore water pressure weakens the triaxial compressive strength of sandstone at room temperature and sub-zero temperature, with a more pronounced effect ob- served at room temperature. With the increase of in-situ stress, the weakening effect of pore water pres- sure on the triaxial compressive strength of sandstone samples becomes stronger at room temperature, and vice versa at negative temperature. The elastic modulus of sandstone frozen with pore water pressure is generally lower than that of sandstone frozen without pore water pressure under the same ground stress condition, and the elastic modulus increases first and then gradually and decreases with the increase ofground stress. The loading failure surface of sandstone samples at room temperature is mostly smooth shear failure, and the failure surface is mostly ‘S’ after freezing. There are more frozen scattered parti- cles and debris in the microstructure of sandstone samples with pore water pressure, especially under freezing condition.