基于单轴压缩与扫描电镜试验的冻融红砂岩损伤特性研究

Research on damage characteristics of freeze-thawed red sandstone based on uniaxial compression and SEM experiments

为研究冻融循环作用对岩石力学性能及微观结构的影响,以饱和红砂岩试样为研究对象,进行了不同冻融循环次数(0、5、10、15、20、30次)的冻融循环试验。通过单轴压缩试验,分析红砂岩试样在冻融循环作用下的力学性能变化规律;通过扫描电镜(SEM)试验,并借助Image-Pro Plus图像分析软件,定量地表征不同冻融循环次数下损伤岩石微观孔隙结构变化;最后基于岩石的损伤理论定量分析冻融循环红砂岩的损伤劣化特性。结果表明:在整个冻融循环过程中,红砂岩试样的质量变化率呈现出先增加后减小的趋势;随着冻融循环次数的增加,其单轴抗压强度、弹性模量和泊松比均逐渐降低;在冻融循环作用下,红砂岩试样表面颗粒剥落且胶结程度降低,颗粒间孔隙逐渐增大,微裂纹萌发、扩容、连通;随着冻融循环次数的增加,孔隙结构愈发均匀,表现为分形维数随冻融循环次数的增加逐渐减小;试验中的红砂岩抗冻性较差,其抗冻系数和冻融损伤程度随冻融循环次数变化较为明显,两者均可通过指数函数进行拟合;该研究对于寒区工程建设中衡量砂岩宏微观特性具有一定的参考价值。

In order to study the effect of freeze-thaw cycles on mechanical properties and microstructure of rock,saturated red sandstone samples were taken as the research object,and freeze-thaw cycle experiments with different number of freeze-thaw cycles(0,5,10,15,20,30)were carried out.The variation of mechanical properties of red sandstone samples under freeze-thaw cycles was analyzed through uniaxial compression test.Through scanning electron microscopy(SEM)experiment,and with the help of Image-Pro Plus image analysis software,the changes of microscopic pore structure of damaged rock under different freezing and thawing cycles were quantitatively characterized.Finally,the damage degradation characteristics of freeze-thaw cycle red sandstone were quantitatively analyzed based on rock damage theory.The results show that the mass change rate of red sandstone samples increases first and then decreases during the whole freeze-thaw cycle.With the increase of freeze-thaw cycles,the uniaxial compressive strength,elastic modulus,and Poisson s ratio decrease gradually.Under the action of the freeze-thaw cycle,the particles on the surface of red sandstone sample are exfoliated and the degree of cementation is reduced.The pores between particles gradually increase,and the micro-cracks germinate,expand and connect.In addition,as the number of cycles increases,the pore structure becomes more uniform,showing that the fractal dimension decreases gradually with the increase of freeze-thaw cycles.The red sandstone in the test has poor frost resistance,and the frost resistance coefficient and freeze-thaw damage degree change significantly with the number of freeze-thaw cycles.Both can be fitted by the exponential function.This study has a certain reference value for measuring the macro and micro characteristics of sandstone in cold area engineering construction.