不同干湿循环路径下Q_(2)原状黄土强度与微观结构演化试验

Experimental Research on Strength and Microstructure Evolution of Q_(2)Undisturbed Loess Under Different Wetting-drying Cycle Paths

为探明不同干湿循环路径对Q_(2)原状黄土宏观强度和微观结构的影响,考虑地下黄土赋存环境,开展了3种干湿循环路径下的三轴剪切试验、核磁共振测试和扫描电镜试验,分析了Q_(2)原状黄土强度、微观孔隙分布和土颗粒结构的演化规律与特征,并结合矿物成分变化探讨了相互之间的影响关系。研究结果表明:不同干湿循环路径下,宏观参数-黏聚力与微观参数-孔隙分布、孔隙和土颗粒平均直径均表现出不同程度的劣化效应,参数衰减趋势完全一致,即干湿循环幅度越大,上限含水率越高,衰减越严重,劣化效应越明显。宏观参数-内摩擦角与微观参数-孔隙和土颗粒结构演化特征相似,即内摩擦角小幅波动,孔隙与土颗粒的形态、结构复杂度和排列有序性基本稳定。考虑干湿循环幅度、上限含水率和循环次数3种参数,构建了微观孔隙劣化特征函数,解释了不同干湿循环路径下的孔隙劣化特征,揭示了Q_(2)原状黄土微观孔隙损伤劣化两阶段发展规律,即波动式损伤积累上升阶段和损伤劣化稳定阶段。相关研究成果可为不同循环路径下的原状黄土宏微观劣化认知提供有益参考。

This paper aimed to investigate the influence of different wetting-drying cycle paths on the macro strength and microstructure of Q_(2)undisturbed loess.Considering the environment of buried loess,the triaxial shear,nuclear magnetic resonance and scanning electron microscope were carried out under three wetting-drying cycle paths respectively.The strength and microstructure of Q_(2)undisturbed loess,combined with the change of mineral composition,were analysed.The relationship between the strength and microstructure was discussed.Results indicate that:the macroscopic parameter-cohesion and the microscopic parameters-pore distribution,average diameter of pore and soil particles have different degrees of degradation under different cycle paths,and the trend of parameters attenuation is completely consistent,that is,the larger the range of wetting-drying cycle and the higher the upper limit water content,the more serious the parameters attenuation and the more obvious the degradation effect.The evolution characteristics of internal friction angle,pores and soil particles structure are similar,that is,the internal friction angle fluctuates slightly,and the morphology,structural complexity and arrangement order of pores and soil particles are basically stable.Considering the wetting-drying amplitude,the upper limit water content and the number of cycles,the characteristic function of micro pore degradation was constructed to explain the degradation characteristics of pore.The two-stage development law of pore deterioration was also revealed,namely,the rising stage of wave-like damage accumulation and the stable stage of damage.These related results can provide useful guidance for understanding the macro and micro degradation of undisturbed loess under different wetting-drying cycles.