Rainfall has been recognized as a key factor in triggering landslides. However, it is not entirely clear why many landslides have been triggered by slight-to-moderate rainfall. The Mudui landslide that occurred in Sichuan Province, China, on June 22, 2020, exemplifies the evolution of landslides induced by seasonal rainfall, which can cause substantial damage to infrastructure. This landslide was a deep-seated debris slide with a volume of approximately 0.64 million m3. It occurred in colluvial deposits, which are heterogeneous soil-rock mixtures with high permeability that easily retain water. On the basis of detailed site investigations and various monitoring data-including interferometric synthetic-aperture radar (InSAR), ground-slope and subsurface-slope deformation monitoring, and hydrogeological monitoring-we investigated the landslide-triggering mechanism along with pre- and post-landslide kinematics and assessed the effects of remedial works. The results show that both the soil water content and the slope deformations have significant seasonal characteristics. The soil water content decreases during dry seasons and increases during rainy seasons. Correspondingly, the deformation rates increase with the onset of rainy seasons and decrease with the onset of dry seasons. The landslide area underwent progressive deformations linked to groundwater seepage, inducing a continuous deterioration of the soil body. Finally, prolonged rainfall triggered the landslide of the deteriorated soil mass. The results indicate that the adverse effects of long-term seasonal soil-water-content fluctuations need to be take into account in analyzing slope instabilities in colluvial deposits.

In this study, the evolution process of a landslide model under continuous rainfall conditions with a rainfall intensity of 30 mm/h is studied in depth based on an outdoor rainfall model test of a colluvial slope as the research material. The response law of pore water pressure and settlement amount is also obtained, and the influence of bedrock inclination angle on the development and deformation failure of the colluvial landslide is discussed. When the dip angle of the bedrock is 40 degrees, it is prone to sudden slip-type landslides, and the evolution process is as follows: tensile cracks appear at the trailing edge, and these cracks continue to increase, leading to overall sliding. When the bedrock dip angle is 30 degrees, traction landslides are prone to occur, and the evolution process is as follows: there is sliding at the foot of the slope, tensile cracks appear in the middle, sliding occurs in the middle, and tensile cracks appear in the upper part, leading to overall sliding. Before the landslide starts, the pore water pressure rises significantly. In the process of landslide evolution, the fine particles move to the foot of the slope with the rainwater, and the larger the angle of the slope, the greater the number of fine particles that accumulate at the foot of the slope, and the higher the elevation and the larger the scale of the trailing edge of the sliding body during sliding.

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.

Slope failures are a significant natural geohazard in hilly and mountainous regions, often resulting in loss of life and infrastructure damage. The Muketuri-Alem Ketema road in Ethiopia is particularly vulnerable to landslides due to colluvial deposits on steep slopes from the higher northeastern plots to the lower Jemma River valley. This study investigates the characteristics of colluvial soil and evaluates the stability of slopes prone to landslides. It combines geophysical data, penetrometer tests, laboratory analyses, Google Earth images, and detailed field visits to assess the soil and bedrock composition and structure. Numerical methods, including limit equilibrium (Bishop, Janbu, Spencer, and Morgenstern-Price methods) and finite element methods, were used to analyze slope sections under various saturation conditions and simulate different rainfall patterns. The results indicate that the Bishop, Morgenstern-Price, and Spencer methods produce similar safety factors with minimal differences (<0.3%), while the Janbu method shows more significant variation (1.5%-5.6%). Safety factor differences for sections A-A and B-B range from 5.26% to 9.86% and 3.5%-4.7%, respectively. Simulations reveal that short-term saturation significantly reduces the stability of the upper slope layer by 20%-46.76%, and long-term saturation decreases the entire slope by 26.81%-46.76% compared to dry conditions due to increased pore water pressure and self-weight. Long-term saturation effects, combined with dynamic loads, can further reduce colluvial soil stability by over 50% compared to a dry static state. The finite element method predicts larger failure zones than limit equilibrium methods, emphasizing the need for accurate predictions to characterize slope behavior during failure and inform stabilization decisions. This study provides crucial data for maintaining and planning the Muketuri-Alem Ketema Road, highlighting slope performance over time and the effectiveness of stabilization techniques.

Colluvial landslides develop in loose Quaternary deposits, with deformation generally being progressive and crack development dominant in the sliding mass surface layer. With the Tanjiawan landslide in the Three Gorges Reservoir (China) as a case study, field investigations, deformation monitoring, and groundwater level monitoring data were integrated to analyze the landslide deformation characteristics and elucidate the influence of cracks on its deformation. We used numerical simulations, including the finite element and discrete element methods, for investigating the progressive deformation mechanism of rainfall-triggered landslides in the accumulation layer and predicting the failure process. The results indicated that crack formation instigated a preferential seepage channel in the shallow layer of the sliding mass, rainfall infiltration along cracks generated water pressure, and the landslide gradually morphed from a stable into a step-like progressive deformation state. Preferential flow inside the cracks effectively elevated the groundwater level within the landslide, and either the number or depth of cracks significantly affected the groundwater seepage field, thereby influencing slide stability. Geological conditions controlled the deformation and failure processes of each landslide section. The uplifted bedrock on the right side blocked the sliding process of the rear sliding mass, and the middle and front sliding masses moved faster but the sliding distance was shorter. The deformation trend is deformation, crack formation, preferential flow occurrence, crack extension, and deformation. The ultimate cause of failure was a steep rise in groundwater level following short duration heavy rainfall or long duration light rainfall.

Landslides in colluvial soils under rainfall have been identified as a significant problem due to their loose, heterogeneous nature and low shear strength. Evaluation of the stability of colluvial slopes under rainfall conditions is challenging. This study investigated two landslide failure case studies of colluvial soils to understand the failure patterns using finite element (FE) and limit equilibrium (LE) slope stability analysis methods under unsaturated conditions. Transient seepage conditions due to rainfall infiltration and failure were analysed using hydromechanical models. Here, a FE fully coupled hydromechanical model and a sequential coupling of a FE hydrological and LE mechanical model were used to evaluate the failure of variably saturated slopes. Results from the case studies revealed that the failure occurred due to the rise in the groundwater table in both cases. It was evident that there can be significant disparities in the pore water pressure profiles with the fully coupled and sequentially coupled analysis. The dynamic capability of the two models can also affect the interplay between the hydrological and mechanical aspects. When the thickness of the colluvium layer is large, the failure could potentially occur as a deep-seated failure along the boundary of overburden and the bedrock surface due to the large driving force. However, when the thickness is small, failure can occur along the colluvium-weathered rock surface. The outcomes from the study will contribute to mitigate the uncertainty of failure prediction of landslides in colluvial soils.

This study establishes a foundational framework addressing challenges, implications, and potential remedies related to collapsible soils. Serving as a cornerstone for global exploration, it emphasizes the importance of understanding geological, structural, and mechanical characteristics for early identification and proactive mitigation. The study underscores the significance of preventing structural damages in regions prone to collapsible soils, discussing their diverse types and origins, structural composition, and mechanical behavior. A detailed exploration highlights their prevalence in semi-arid and arid regions, emphasizing distinct geological features associated with their occurrence.

The objective of this study is to assess the impact of utilizing a BW (Buttress wall) to control the deflection of a diaphragm wall in colluvial soil conditions in Vietnam. The physical and mechanical properties of the colluvial layers are evaluated using data closely monitored during a specific project, serving as validation for 3D numerical simulations utilizing the Hardening Soil Model. The analysis results closely match the field monitoring data, which has tested the accuracy of the simulation model. This forms the basis for further investigations into the dimensional parameters of BW walls, including length, thickness, and spacing between them. The results obtained from the parametric study demonstrate that altering the wall length and spacing between BW walls significantly limits the deflection of the diaphragm wall, while changes in thickness have a negligible effect. Through the 3D numerical simulations, a linear relationship between the maximum wall deflection and parameters such as wall length and spacing between BW walls has been established.

Fan-shaped landforms occur in all climatic regions on Earth. They have been extensively studied in many of these regions, but there are few studies on fans in periglacial, Arctic and Antarctic regions. Fans in such regions are exposed to many site-specific environmental conditions in addition to their geological and topographic setting: there can be continuous to discontinuous permafrost and snow avalanches and freeze-thaw cycles can be frequent. We study fans in the high-Arctic environment of Svalbard to (1) increase our fundamental knowledge on the morphology and morphometry of fans in periglacial environments, and (2) to identify the specific influence of periglacial conditions on fans in these environments. Snow avalanches have a large geomorphic effect on fans on Svalbard: the morphology of colluvial fans is mainly determined by frequent snow avalanches (e.g., flattened cross-profiles, exposed fine-grained talus on the proximal fan domain, debris horns and tails). As a result, there are only few fans with a rockfall-dominated morphology, in contrast to most other regions on Earth. Slush avalanches contribute significant amounts of sediment to the studied alluvial fans. The inactive surfaces of many alluvial fans are rapidly beveled and leveled by snow avalanches, solifluction and frost weathering. Additionally, periglacial reworking of the fan surface often modifies the original morphology of inactive fan surfaces, for example by the formation of ice-wedge polygons and hummocks. Permafrost lowers the precipitation threshold for debris-flow initiation, but limits debris-flow volumes. Global warming-induced permafrost degradation will likely increase debris-flow activity and -magnitude on fans in perigladal environments. Geomorphic activity on snow avalanche-dominated colluvial fans will probably increase due to future increases in precipitation, but depends locally on climate-induced changes in dominant wind direction. (c) 2015 Elsevier BM. All rights reserved.