渗透剪切作用下黄土的力学特征

黄土高原地区黄土在灌溉作用下,逐渐达到饱和状态,饱和中,陡坡类黄土坡体自重增加引起下滑力增加. 该过程持续进行后,坡体内部同时发生渗流和剪切过程,导致坡体的变形不断增大,直至破坏后形成滑坡. 本文选取黑方台4.29滑坡为研究对象,在现场调查的基础上,利用滑坡后壁原状黄土试样,基于三轴试验设置10组共60个原状样对饱和黄土的渗透剪切行为进行模拟. 试验中设置了0.5、0.1和0.05 mm·min^-1三个不同的加载速率对黄土试样进行剪切,为比较分析,对0.1 mm·min^-1剪切速率试样设置了0、1、2和5 m几个不同水头进行了试验. 试验结果表明:饱和黄土在渗流与剪切耦合作用下,表现出应变硬化特征,渗透作用明显降低了黄土的强度,尤其是黄土黏聚力降低,其降幅达5.24%~63.35%. 对已有强度指标拟合后获得黄土在渗透剪切工况下的强度修正公式.

Mechanical characteristics of loess under seepage shear

In the recent years, an increasing number of loess landslides were triggered due to extreme climate. The initiation of loess landslides was related to water, including surface water and groundwater, landform, geologic structure, and other factors. Both surface water and groundwater significantly affect loess landslides. Rainfall and irrigation provide plenty of water to loess, creating surface water and groundwater. Surface water flows on the surface of a loess, infiltrating into loess at the same time. The infiltration of surface water transforms loess from an unsaturated state to a saturated state in the loess plateau. The weight of slope mass increases due to the increase in water content of loess. Therefore, the loess slope mass bears shear force and seepage stress at the same time, and the deformation of loess gradually increases with time. More attention should be paid to seepage stress during the infiltration. The fabric inside loess is damaged because of shear force and seepage stress. The presence of seepage stress makes the failure mode different from the shear mode in loess. Eventually, a loess landslide forms as the deformation exceeds the bearing capacity. In this study, the 4.29 landslide in Heifangtai was selected for the purpose of research. Based on field investigation, 60 undisturbed samples from the backwall of landslide were used to conduct triaxial tests. To simulate the shear behavior of saturated loess under seepage shear, loading rates of 0.5, 0.1, and 0.05 mm·min-1 were used and the effect of loading rate on shear strength was identified. Moreover, water heads of 0, 1, 2, and 5 m were set to study the effect of water head on shear strength with loading rates of 0.1 mm·min-1. The stress-strain curve shows obvious strain hardening under seepage shear. Loading rate slightly affects the stress-strain relationship of loess during the seepage shear. In contrast, an increasing water head rapidly decreases the shear stress of loess. The cohesion of loess decreases by 5.24%-63.35% due to seepage shear. Further, the strength correction formula for a loess under the seepage shear condition is obtained by fitting the existing strength index. Fitting performance is evaluated following the fitting process. An empirical equation could be used in geotechnical engineering when seepage shear is considered.