Water level fluctuations in the reservoir deteriorate soils and rocks on the bank landslides by dryingwetting (D-W) cycles, which results in a significant decrease in mechanical properties. A comprehensive understanding of deterioration mechanism of sliding-zone soils is of great significance for interpreting the deformation behavior of landslides. However, quantitative investigation on the deterioration characteristics of soils considering the structural evolution under D-W cycles is still limited. Here, we carry out a series of laboratory tests to characterize the multi-scale deterioration of sliding-zone soils and reveal the mechanism of shear strength decay under D-W cycles. Firstly, we describe the micropores into five grades by scanning electron microscope and observe a critical change in porosity after the first three cycles. We categorize the mesoscale cracks into five classes using digital photography and observe a stepwise increase in crack area ratio. Secondly, we propose a shear strength decay model based on fractal theory which is verified by the results of consolidated undrained triaxial tests. Cohesion and friction angle of sliding-zone soils are found to show different decay patterns resulting from the staged evolution of structure. Then, structural deterioration processes including cementation destruction, pores expansion, aggregations decomposition, and clusters assembly are considered to occur to decay the shear strength differently. Finally, a three-stage deterioration mechanism associated with four structural deterioration processes is revealed, which helps to better interpret the intrinsic mechanism of shear strength decay. These findings provide the theoretical basis for the further accurate evaluation of reservoir landslides stability under water level fluctuations. (c) 2025 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/ 4.0/).

The thixotropy of lime-modified loess is a key engineering problem in large-scale mountain levelling and urban construction on the Loess Plateau in China. We analyse the thixotropic factors and establish thixotropic models of modified loess at macroscales and microscales to interpret the evolution of the thixotropic mechanism of lime-modified loess. A custom-made volume-preserving thixotropic instrument is used to eliminate the influence of consolidation deformation on thixotropy and simulate soil consolidation in the field. Consolidated undrained triaxial tests, nuclear magnetic resonance analysis, and electron microscopy are used to investigate the thixotropy of soils with different thixotropic periods (0 days, 7 days, 14 days, 21 days, 42 days, 84 days, 126 days, and 168 days). The results show that the failure strength increases and the growth rate decreases with the thixotropic period length. The failure strength increases rapidly in the early thixotropic stage; the inflexion point occurs at 21 days, and stabilisation is observed at about 42 days. The internal friction angle and cohesive force increase over time, the cohesive force increased more obviously, which was 2.94 times of the initial thixotropic period, the increase in internal friction angle is within 4 degrees. The pore distribution is more uniform at the microscopic level, and large and small pores are transformed into medium pores over time. As the thixotropic period increases, the amount of cementitious material generated in the modified loess and the cementation degree increase, and the number of surface pits and large pores on the particles substantially decreases, resulting in numerous flower-shaped and grid structures. The thixotropic mechanism of modified loess consists of pore homogenisation, gravitational repulsion between particles, and cementation caused by the lime reaction.

Due to climatic factors and rapid urbanization, the soil in the Loess Plateau, China, experiences the coupled effects of dry-wet cycles and chemical contamination. Understanding the mechanical behavior and corresponding microstructural evolution of contaminated loess subjected to dry-wet cycles is essential to elucidate the soil degradation mechanism. Therefore, direct shear and consolidation tests were performed to investigate the variations in mechanical properties of compacted loess contaminated with acetic acid, sodium hydroxide, and sodium sulfate during dry-wet cycles. The mechanical response mechanisms were investigated using zeta potential, mineral chemical composition, and scanning electron microscopy (SEM) tests. The results indicate that the mechanical deterioration of sodium hydroxide- contaminated loess during dry-wet cycles decreases with increasing contaminant concentration, which is mainly attributed to the thickening of the electrical double layer (EDL) by Na & thorn; and the precipitation of calcite, as well as the formation of colloidal flocs induced by OH-, thus inhibiting the development of large pores during the dry-wet process. In contrast, the attenuation of mechanical properties of both acetic acid- and sodium sulfate-contaminated loess becomes more severe with increasing contaminant concentration, with the latter being more particularly significant. This is primarily due to the reduction of the EDL thickness and the erosion of cement in the acidic environment, which facilitates the connectivity of pores during dry-wet cycles. Furthermore, the salt expansion generated by the drying process of saline loess further intensifies the structural disturbance. Consequently, the mechanical performance of compacted loess is sensitive to both pollutant type and concentration, exhibiting different response patterns in the dry-wet cycling condition.

Loess has a unique structure that makes it susceptible to liquefaction during intense seismic activity. Liquefaction is closely linked to microstructural changes due to hydraulic coupling. This study examined the threedimensional microstructure evolution of loess in various liquefaction states using dynamic triaxial tests and high-precision micrometer CT scanning. As the ratio of pore water pressure (Rwp) increases, the size of loess particles tends to decrease while the roundness is inclined to increase. Moreover, the morphology and orientation of particles remain relatively stable under such circumstances. In addition, increasing Rwp will decrease the number of macropores, increase the number of mesopores and fine-pores, and decrease the size of throats and channel length, with which petite throats and pores become more prominent. Consequently, liquefaction gradually opens closed pores, enhances soil connectivity, and divides large pores to increase small to mediumsized pores, improving pore distribution uniformity. Liquefaction induces the pore shape coefficient to decrease, the number of slim pores to increase, and irregular and circular pores to decrease. These findings provide a scientific foundation for preventing and evaluating loess liquefaction disasters and shed light on the microscopic mechanisms of loess liquefaction.