Due to the significant decrease in strength of loess after encountering water, loess landslides induced by rainfall are very catastrophic and widely distributed in the Chinese Loess Plateau. On September 17, 2011, a catastrophic loess landslide induced by rainfall occurred in Baqiao district, Xi'an, Shaanxi Province, China, resulting in 32 casualties and bringing great fear to the local residents. This landslide event was characterized by three individual landslides. Field investigations, geological exploration and model experiments were conducted to reveal its initiation and movement mechanisms. The results show that 1) Multiple groups of fissures in the ring-cut adits were found at a location 3 m inward from the slope surface. The minimum opening width of these fissures is 0.5 cm, and the maximum is 4 cm. The fissures develop nearly vertically and have good extensibility and connectivity. 2) the whole process of rainfall-induced landslides can be divided into 3 stages: rainfall infiltration and weight increase; crack expansion and slope deformation; slope collapse and creep deformation. 3) The volumetric water content, pore water pressure and vertical stress variation of the soil in our model all increase first and then decrease. Specifically, these three parameters increase slowly during the pretest and stabilization periods and increase fast shortly before the landslide occurrence. The volumetric water content of the soil on the side containing joints increases faster, verifying that the joints act as preferential channels that accelerate rainwater infiltration. The results of the study provide an important scientific foundation for future research on rainfall-induced loess landslides and their deep-seated mechanisms, and fill the gaps in research related to large-scale physical modeling experiments.

In order to master the creep deformation law of colluvial slope and the stress deformation characteristics of tunnel lining structure under rainfall, the response physical model test of seepage and stress deformation characteristics of tunnel slope parallel system is carried out by using earth pressure cells, strain gauges, dial indicators and hygrometers. The test results indicate that rainfall infiltration depth decreases with increasing slope height and distance from the slope surface. The existence of the tunnel will affect the seepage path of rainwater, accelerating infiltration and increasing peak moisture content on the slope above the tunnel, while decelerating infiltration and reducing peak moisture content on the slope below the tunnel. The slope deformation is positively correlated with the change rate of water content. Slope deformation is concentrated during rapid water content increase, with vertical displacements at the slope top, middle, and foot accounting for 89.6%, 96.4%, and 98.9% of the total, respectively. The earth pressure increment at the tunnel top due to slope deformation correlates positively with the tunnel's buried depth in the accumulation body, with an average increase of 24% per 15 cm. The earth pressure increment at the bedrock end is approximately 2.4 times that at the entrance end, while the increment at the tunnel bottom is smaller than that at the top. The tunnel exhibits the following stress and deformation characteristics: compression at the top, tension at the bottom, overall sinking, local downward bending with the central position as the inflection point, and abrupt strain changes at the bedrock-accumulation layer junction due to shear stress. These characteristics resemble the stress mode of a beam structure with one end hinged and one end anchored. It is recommended to incorporate anti-seepage measures such as sprayed concrete, shallow grouting, or slope ecological protection on the upper slope of the tunnel during the design and construction of similar tunnels. Reinforcement treatment should be implemented in the tunnel entrance area, the middle with significant deformation, and the rock-soil junction.

Occurrence of loess landslide has been more frequent due to the drastic global climate change, rapid expansion of human disturbances and continuous intensification of engineering activities. The activation and evolution mechanisms of the loess landslides under the rainfall are yet to be studied. In this paper, with reference to the Yangpoyao slope with seepage fissures under rainfall, an adjustable-angle landslide model test system is developed, integrating the rainfall simulation system, the measurement system and the data acquisition system, and the deformation development of the model, the rainfall infiltration, the change of water content and the destructive process of the model are monitored by the monitoring technology of multi-means and multi-methods throughout the course of the disaster. A distributed fibre-optic sensor system with the characteristics of continuity and high precision is used to monitor the temperature and strain within the slope model. The deformation evolution mechanism of fissured loess slopes under rainfall was elucidated through the observation of experimental phenomena and the analysis of the internal strain values of the soil, as measured by fibre optic sensors. The experimental results show that the collapse process of loess slopes can be categorised into three types, i.e. sinkhole collapse, block collapse and gully collapse, and that the deformation and damage patterns of the loess landslide model are mainly caused by shallow soil movement induced by erosion. Through the comparative analysis of the model test and the photographs of the field investigation, it is further demonstrated that the damage pattern shown in the physical model test is basically consistent with the slope condition of the real Yangpoyao slope, which provides a new theoretical reference for natural disaster prediction and management of loess slopes and landslides.

Fine grains migration is a primary cause of landslides and debris flows. This study investigates the effect of fine-grain migration on slope failure through flume experiments, focusing on the spatiotemporal characteristics and mechanisms of slope stability. A series of artificial rainfall flume experiments with varying rainfall intensities and slopes were conducted using soil samples collected from Wei Jia Gully. The experiments monitored pore-water pressure, grain migration, and failure sequences. Grain-size distribution parameters (mu and Dc) were analyzed to understand the migration path and accumulation of fine grains. The experiments reveal that fine-grain migration significantly alters soil structure, leading to random blockage and interconnection of internal pore channels. These changes result in fluctuating pore-water pressure distributions and uneven fine-grain accumulation, critical factors in slope stability. Slope failures occur randomly and intermittently, influenced by fine-grain content in runoff and resulting pore-water pressure variations. This study highlights that fine-grain migration plays a vital role in slope stability, with significant implications for predicting and mitigating slope failures. The stochastic nature of fine-grain migration and its impact on soil properties should be incorporated into predictive models to enhance their accuracy and reliability.

Understanding the rainfall-triggering mechanisms influencing loess landslides and developing targeted prevention and control strategies are critical challenges in engineering. This study focused on a representative landslide-prone area in Huxian County, Xi'an, China, and field experiments involving artificial rainfall simulations were conducted. Utilizing the annual rainfall statistics for Huxian County, three distinct rainfall scenarios-light, moderate, and heavy-were established. The aim was to explore the correlation between internal pore water pressure and temporal and depth-related changes during the postrainfall stage. At the same time, reflective patches were placed on the slope and total stations were used to monitor the impact of different rainfall intensities on slope displacement. Based on the field data, a three-dimensional simulation validation was executed using Surfer software. Our findings suggest that increasing rainfall intensity directly correlates with higher internal pore water pressure. As the rainfall persisted, the daily amplitude of pore water pressure initially surged before moderating, ultimately exhibiting a logarithmic trend with depth. The effective influence depths of the daily amplitude of pore water pressure during light, moderate, and heavy rainfall stages were found to be 1.6, 2.2, and 5.0 m, respectively. Following cessation of the rainfall, the surface pore water pressure underwent substantial change, and the daily amplitude rapidly declined before stabilizing. Slope displacement consistently increased from the summit to the base throughout the rainfall stages, with the base being most susceptible to sliding instability. The maximum displacement at the foot of the slope was in Columns 3-5, with a maximum displacement value of 1,158 mm. Proximity to the slope's base correlated with greater gravitational and downward forces. Specific maximum displacement values were recorded at different locations along the slope, revealing the most significant changes along the slope's centerline. This work will contribute to the effective management and landslide prevention of loess slopes.