损伤砂岩冻融循环后物理力学行为

Physical and mechanical behavior of damaged sandstone after freeze-thaw cycles

关键词:  损伤砂岩  冻融循环  单轴压缩  孔隙结构  分形维数

Key words:  damaged sandstone  freeze-thaw cycles  uniaxial compression  pore structure  fractal dimension

摘要:

为研究砂岩经历不同单轴应力水平损伤和冻融循环作用后的物理特征及力学行为演化规律,首先,给砂岩试样施加不同轴向应力水平,使试样内产生不同程度损伤；然后,对经过应力损伤后的砂岩试样进行冻融循环处理；最后,开展损伤砂岩冻融循环后单轴压缩试验。研究了应力损伤和冻融循环对砂岩变形特征的影响,分析了不同损伤程度砂岩单轴抗压强度和弹性模量演化规律,揭示了损伤砂岩冻融循环前后孔隙率、孔隙尺寸和孔隙结构分形维数演化机制。结果表明:冻融循环后,相同应力下试样的轴向变形显著增大；砂岩单轴压缩强度和弹性模量随损伤应力和冻融循环次数的增大均表现为逐渐减小；冻融循环前后,砂岩孔隙率随损伤应力的增大均逐渐增大,冻融循环后砂岩孔隙率明显大于冻融循环前砂岩孔隙率,且冻融循环前后砂岩孔隙率的差异随损伤应力的增大而增大；随等效半径的增大,冻融循环前的砂岩孔隙数量占比分为逐渐减小、先增大后减小和逐渐减小3个阶段,冻融循环后的砂岩孔隙数量占比逐渐减小,冻融循环后等效半径较大的孔隙占比增大；冻融循环后砂岩孔隙结构分形维数大于冻融循环前砂岩孔隙结构分形维数,冻融循环后试样孔隙结构比冻融循环前试样孔隙结构复杂；冻融循环前后,砂岩孔隙结构分形维数均随损伤应力的增大均逐渐增大,但冻融循环后砂岩孔隙结构分形维数增长幅度明显小于冻融循环前的砂岩。

Abstract:

To study the evolution of physical properties and mechanical behavior of sandstone under different uniaxial stress-induced damage conditions and freeze-thaw cycles, firstly, different axial stress levels were applied to sandstone samples to produce different damage degrees. Then, the stress-induced damaged sandstone samples were treated by freeze-thaw cycles. Finally, uniaxial compression tests were carried out on the damaged sandstone. The effects of damage inside the samples and freeze-thaw cycle on the deformation characteristics of sandstone were studied. The evolution laws of uniaxial compressive strength and elastic modulus of sandstone with different damage degrees were analyzed. The evolution mechanism of porosity, pore size, and pore structure fractal dimension before and after freeze-thaw cycle was revealed. The results show that the axial deformation of the samples increases significantly under the same stress after freeze-thaw cycles. The uniaxial compressive strength and elastic modulus of sandstone decrease gradually with the increase of damage stress and the number of freeze-thaw cycles. Before and after the freeze-thaw cycles, the porosity of sandstone increases gradually with the increase of damage stress, and the porosity of sandstone after the freeze-thaw cycle is obviously larger than that before the freeze-thaw cycles. The difference of sandstone porosity before and after the freeze-thaw cycles increases as the damage stress increases. With the increase of the equivalent radius, the proportion of sandstone pore number before the freeze-thaw cycle can be divided into three stages: gradually decreasing, first increasing and then decreasing, and gradually decreasing. After the freeze-thaw cycles, the proportion of sandstone pore number gradually decreases, and the proportion of pores with larger equivalent radius increases after the freeze-thaw cycle. The fractal dimension of sandstone pore structure after freeze-thaw cycles is larger than that before freeze-thaw cycles. The pore structure of sandstone samples after freeze-thaw cycle is more complex than that of sandstone samples before freeze-thaw cycle. Before and after the freeze-thaw cycles, the fractal dimension of sandstone pore structure increases gradually with the increase of damage stress, but the increase amplitude of the fractal dimension of sandstone pore structure after the freeze-thaw cycles is obviously smaller than that before the freeze-thaw cycle.