干湿循环效应下玄武岩纤维加筋黄土三轴剪切力学行为研究

Triaxial shear behavior of basalt fiber reinforced loess under drying-wetting cycles

通过干湿循环效应下的数字图像三轴剪切试验、CT扫描试验及扫描电镜SEM(scanning electron microscopy)试验,研究了玄武岩纤维加筋黄土干湿循环过程的三轴剪切力学行为及微细观结构演化机制。结果表明:随干湿循环次数增加,纤维含量较高试样的三轴剪切鼓胀破坏形态转变为剪切带破坏;干湿循环早期阶段,剪切破坏形态随纤维含量增加,由剪切带破坏转变为鼓胀破坏。干湿循环作用和纤维含量对应力-应变曲线的类型及特征无明显影响,均表现为应变硬化型。破坏偏应力随干湿循环次数增加而逐渐减小,但衰减速率逐渐减小;破坏偏应力随纤维含量增大先增加而后减小,呈抛物线变化特征,存在一个最佳纤维含量为0.6%。CT数均值ME值呈现与破坏偏应力相似的变化规律。干湿循环作用下筋-土界面产生一定的开裂和松弛现象,弱化了纤维的加筋效应,但与素黄土相比,纤维加筋黄土的微观结构表现出显著的整体稳定性。构建了干湿循环效应下玄武岩纤维加筋黄土的宏细观损伤变量,其表现出一致的变化规律。

In this paper,the digital image based triaxial shear,CT scanning and SEM tests were employed to investigate triaxial shear behavior and microstructure evolution of basalt fiber reinforced loess under drying-wetting action.The results show that the shear failure morphology of soil samples with relatively higher basalt fiber content changes from overall bulging to shear band failure with increasing drying-wetting cycles,while it exhibits the opposite variation with increasing fiber content at the early stage of drying-wetting process.Drying-wetting cycles and fiber content have no obvious effect on the type of stress-strain curves,which present strain hardening behavior.The deviator stress at failure decreases with the increasing number of drying-wetting cycles;however,the attenuation rate gradually decreases.The deviator stress at failure shows a parabolic variation with increasing fiber content and the optimal fiber content is 0.6%.A similar trend is observed between the ME value of CT scanning and the deviator stress at failure.Drying-wetting action induces cracking and loosening around the soil-fiber interface,thus weakening the fiber reinforcement effect.However,compared with unreinforced loess,fiber reinforced loess demonstrates strong stability in its microstructure.The macroscopic and microscopic damage variables reflecting the drying-wetting induced deterioration of loess samples were finally established,which shows consistent trend.