Wei Liu

To reveal the mechanism of rainfall- and irrigation-induced landslides in loess slopes within cold regions, a series of tests on loess samples subjected to different permeability durations were conducted, and the effects of rainfall on several performance indicators, including the permeability coefficient, composition, microstructure, soil–water characteristic curve, and the shear strength of the loess, were investigated. The results show that the permeability coefficient of the loess decreased by 68% after permeability testing. With increased permeability duration, there is a marked decrease in total dissolved solids, sand particles, and clay particles, contrasted with an increase in silt particles. This dynamic alters the original soil structure and impacts the soil–water characteristic curve of the loess. Additionally, rainwater infiltration heightens the effective saturation of the loess, in turn diminishing the shear strength of the loess as effective saturation increases. This reduction in shear strength is further intensified with extended infiltration time (or rainfall duration). A landslide is triggered once the shear strength diminishes to the level of the geostatic stress of the loess slope, and the influence of the rainfall-induced loss of soil shear strength should be taken into account during slope stability analysis. This study enhances the understanding of the initiation mechanisms of rainfall-induced landslides in loess slopes.

To reveal the landslide mechanism of the loess slope induced by rainfall, we carried out a series of tests for loess under different permeability durations, and studied the influences of rainfall on the permeability coefficient, the soil water characteristic curve, the components, the microstructure, and the shear strength of the loess. Test results show that the total dissolved solids, the sand particles, and the clay particles will decrease, but the silt particles will increase with the permeability duration, it changes the soil original structure and influences the soil water characteristic curve of the loess. And more than 68% permeability coefficients will loss after permeability test. The infiltrated rainwater will increase the effective saturation of the soil, and the shear strength of the soil will decrease with the increasing of effective saturation. The shear strength further decreases with the infiltration time (or rainfall duration). The landslide will initial once the shear strength reduces to the geostatic stress of the soil slope. The shear strength loss of the soils induced by rainfall should be considered during slope stability analysis. This study can help to understand the initiation of loess landslide induced by rainfall.

黄土因其遇水产生湿陷变形而对工程构筑物的安全性造成严重威胁.强震区黄土遭遇先期地震后其内部结构将发生变化，结构演变与黄土初始含水量密切相关.先期地震对黄土的结构性破坏引起宏观力学特征变化，为揭示强震区黄土结构演变与力学响应的内在机制，基于动三轴对黄土试样预先施加不同PGA（peak ground acceleration）条件下动荷载进行预震处理，模拟强震区先期地震对黄土的扰动，后进行固结不排水试验，分析抗剪强度指标与地震荷载及初始含水量的关联性.试验结果表明，初始含水率为2%时，预先施加地震动荷载的黄土试样与未预先施加动荷载的试样相比，其峰值强度出现了明显降低，且随着预先施加动荷载PGA的增加，峰值强度降幅增加.孔隙水压力随应变的不断增加趋于平缓，有效轴向应力和有效围压随应变的不断增加而持续减小，最终趋于平缓；初始含水量增加至12%，预震处理后的黄土试样强度增大.通过绘制应力路径关系曲线，确定了强震区黄土失稳的临界失稳线，对于同一黄土试样，PGA增加后引起黄土失稳线不断下移，表明黄土中的应力状态随地震动荷载的增加而发生变化.初始含水量为12%时，预震后的黄土试样剪切强度增大，表明含水量增加后，前期地震荷载开始破坏黄土初始结构性，导致试样密度增大，产生强度增加效应.

In China, engineers have worked to create additional usable land for building construction by flattening the ridges of hills and filling in the adjacent valleys. China’s Loess Plateau comprises a type of soil (loess) with a large pore structure that can collapse and become unstable when exposed to groundwater. Conventional valley fill materials include remolded loess or remolded loess treated with cement, lime, gypsum, or other stabilizing additives. These stabilizers are often detrimental to the surrounding environment. Moreover, loess treated with conventional stabilizers exhibits excessive brittleness, which is not suitable for building foundations. Adequate stability of the building foundations in the filled valleys is required to ensure public safety. In this study, we tested 50 remolded loess samples treated with a lignin polymer compound to determine its potential as a valley fill material. Triaxial tests, scanning electron microscopy (SEM), and X-ray diffraction (XRD) were used to study the mechanical characteristics of each sample, determine the effects of the lignin treatment on the loess, and identify the microscopic mechanism affecting shear stress in the lignin-treated loess. The corresponding development of excess pore pressure and volumetric responses under monotonic triaxial testing were also considered. Based on this study’s results, the optimum lignin content in the treated loess samples was 4%; lignin contents exceeding 4% decreased axial stress and increased dilation after saturation. The shear strength and strain-hardening phenomenon of the lignin-treated loess samples increased as the lignin content increased, while the excess pore water pressure decreased. Microscopically, the addition of lignin increased cohesion in the loess samples, while slightly contributing to the internal friction angle. The use of lignin as a stabilizing additive for valley fill material shows potential for controlling building foundation deformation by increasing soil strength and minimizing environmental impacts by maintaining the soil pH and limiting pollutant production.

Transparent porous media combined with digital image processing technology can be used to quantify the saturation of local fluids. In this regard, the calibration relationship between the pixel intensity of the image and the saturation of the wetting liquid is the crucial premise for whether this technique can be promoted and applied, and it is also a bottleneck that limits whether this technique can be rapidly and extensively developed. However, owing to gravity‐driven effects, wetting liquid in a residual state usually exhibits an irregular boundary caused by the phenomenon of saturation overshoot, which makes it very difficult to use the previous overflow method to obtain the data pair of saturation‐pixel intensity accurately. To this end, we have made some improvements to the specific testing method for wetting liquid saturation in the residual state and proposed a local centrifugal sampling method, which considerably improved the accuracy of this method. The results show that the relationship between the pixel intensity and saturation of the transparent soil obtained through this method is generally consistent with the regularity of the previous calibration method but shows better correlation. The results of this study will drive further potential application of transparent soil in the flow of partially saturated porous media.

The soil water characteristic curve (SWCC) describes the relationship between matric suction and moisture of soil, the testing process of which is time-consuming. The test time of particle size distribution (PSD), in contrast, is relatively short. Thus, it is quite important to establish a proper model for PSD to forecast SWCC. This paper analyzed PSD of 25 groups of loess by way of laser diffraction technique (LD) and sieve-settlement method. Works were carried out on fitting analysis on PSD with Logarithmic model, Fredlund model, Jaky model, and Gompertz model. Statistical method was used to explain the fitting performance. Meanwhile, an empirical model was put forward. Compared to the four models, the empirical model has fewer parameters, simple model form, and smaller fluctuations of parameters. Results of LD showed higher clay content but lower silt content. It is suggested that Fredlund model or the empirical model be adopted to forecast SWCC of Malan loess.