Soil aggregate stability and pore structure are key indicators of soil degradation. Waves generated by the water-level fluctuations could severely deteriorate soil aggregates, which eventually induce soil erosion and several other environmental issues such as sedimentation and flooding. However, due to limited availability of the hydrological alteration data, there is a limited understanding of soil aggregates, intra-aggregate pore dynamics, and their relationships under periodically flooded soils. The present study has relied on long-term hydrological alteration data (2006-2020) to explore the impacts of inundation and exposure on soil aggregates and pore structure variations. Soil samples from increasing elevations (155, 160, 163, 166, 169, and 172 m) in the water-level fluctuation zone of the Three Gorges Reservoir were exposed to wet-shaking stress and determined soil structural parameters. The overall inundation and exposure ratio (OvI/E) gradually decreased from 1.87 in the lowest to 0.27 in the highest elevation, respectively. Predominant distribution of macropores was recorded in lower elevations, while micropores were widely distributed in the upper elevations. The mean weight diameter (MWD) was significantly lower in the lower (2.4-3.7 mm) compared to upper (5.3-6.0 mm) elevations. The increase in MWD has increased the proportion of micropores (PoN < 50 mu m), with R-2 = 0.59. This could suggest that the decrease in flooding intensity can create favorable conditions for plant roots growth. The strong flooding stress in lower elevations (i.e., higher values of the OvI/E) accelerated the disintegration of soil aggregates and considerably increased the formation of macropores due to slaking and cracking. The findings of the present study emphasize the need to restore degraded soils in periodically submerged environments by implementing vegetation restoration measures. This could enhance and sustain aggregate stability, which was also proved to increase functional pores under hydrological alterations.

With the continued development of water resources in Southwest China, fluctuations in water levels and rainfall have triggered numerous landslides. The potential hazards posed by these events have garnered considerable attention from the academic community, making it imperative to elucidate the landslide mechanisms under the combined influence of multiple factors. This study integrates laboratory tests and numerical simulations to explore the instability mechanisms of landslides under the combined effects of rainfall and fluctuating water levels, as well as to compare the impacts of different factors. Results indicate that the sensitivity of landslide deformation decreases as the number of water level fluctuations increases, exhibiting a gradually stabilizing tendency. However, the occurrence of a heavy rainfall event can reactivate previously stabilized landslides by increasing pore water pressure and establishing a positive feedback loop with rainfall infiltration. This process reduces boundary constraints at the toe of the slope, promotes the development of an overhanging surface, and ultimately leads to overall instability and landslide disaster. Under the same rainfall intensities, the presence of water level fluctuations prior to rainfall significantly shortens the time for the landslide to reach a critical state. The key mechanisms contributing to landslide failure include terrain modification, fine particle erosion, and outward water pressure, all of which generates substantial destabilizing forces. This research offers valuable insights for the monitoring, early warning, and risk mitigation of landslides that have already experienced some degree of deformation in hydropower reservoir areas.

Landslides commonly evolve from slow, progressive movements to sudden catastrophic failures, with saturation and displacement rates playing significant roles in this transition. In this paper, we investigate the influence of saturation, displacement rate, and normal stress on the residual shear strength and creep behaviour of shear-zone soils from a reactivated slow-moving landslide in the Three Gorges Reservoir Region, China. Results reveal a critical transition from rate-strengthening to rate-weakening behaviour with increasing displacement rates, significantly influenced by the degree of saturation. This transition governs the observed patterns of slow movement punctuated by periods of accelerated creep, highlighting the potential for exceeding critical displacement rates to trigger catastrophic failure. Furthermore, partially saturated soils exhibited higher residual strength and greater resistance to creep failure compared to nearly and fully saturated soils, underscoring the contribution of matric suction to shear strength.

Tensile cracks play a pivotal role in the formation and evolution of reservoir landslides. To investigate how tensile cracks affect the deformation and failure mechanism of reservoir landslides, a novel artificial tension cracking device based on magnetic suction was designed to establish a physical model of landslides and record the process of landslide deformation and damage by multifield monitoring. Two scenarios were analyzed: crack closure and crack development. The results indicate that under crack closure, secondary cracks still form, leading to retrogressive damage. In contrast, under crack development conditions, the failure mode changes to composite failure with overall displacement. The release of tensile stresses and compression of the rear soil are the main driving forces for this movement. Hydraulic erosion also plays a secondary role in changing landslide morphology. The results of multifield monitoring reveal the effects of tensile cracking on reservoir landslides from multiple perspectives and provide new insights into the mechanism of landslide tensile-shear coupled damage.

Human impact in the form of reservoir construction and river regulation downstream of reservoirs, is causing irreversible alterations to hillslope and river channel connectivity in river catchments. This disruption in the dynamic equilibrium of the river is attributed to sediment accumulation upstream of the reservoir's dam, limited sediment outflow from the reservoir, and increased downcutting downstream of the dam. Consequently, these alterations necessitate further human interference in natural environmental processes through the construction of various river engineering structures designed to reduce the intensity of downcutting. The purpose of the present study was to assess the impact of a small mountain reservoir and additional river regulation structures on the Wapienica River in southern Poland, focusing on the structural and functional connectivity of the river channel in terms of sediment transfer. This assessment was based on erosion and connectivity modeling, as well as field mapping. A high-resolution digital elevation model (HRDEM) was examined in the study along with survey data on suspended sediment accumulation sites along the river. The study utilized open-source tools, including SedInConnect for connectivity index (IC) calculation, and the Soil and Water Assessment Tool (SWAT) for ArcGIS software. It was found that the Wapienica reservoir permanently retains the floating material, making the likelihood of this material flowing out of the reservoir minimal. Within the reverse delta of the reservoir, the entire load of bottom material (sand) is also retained. Thicker bottom material (gravel, boulders) is deposited in the riverbed within the delta, leading to the shallowing of the bed upstream of the delta. These processes disrupt longitudinal connectivity. Six connectivity zones have been identified within the catchment. The first four are situated in the southern part of the catchment: strong connectivity, reduction, concrete channel, and damage area. The remaining two, situated in the northern part are: artificial channel and drainage channels. Each of the six zones is characterized by different sediments and river processes. It was demonstrated that a more detailed and more probably connectivity pattern for hillslopes and river channels may be obtained through the use of several tools and parameters at the same time (i.e., fieldwork, SWAT, IC).

Slip zone soil, a crucial factor in landslide stability, is essential for understanding the initiation mechanisms and stability assessment of reservoir bank landslides. This study investigates the strength characteristics of slop zone soil under drying-wetting (D-W) cycles to inform research on reservoir bank landslides. As an illustration of this phenomenon, the Shilongmen landslide in the Three Gorges Reservoir serves as a case study. Taking into account the impact of both D-W cycles and the overlying load on the soil. the strength characteristics of the slip zone soil are investigated. Experimental results show that slip zone soil exhibits strain softening during D-W cycles, becoming more pronounced with more cycles. D-W cycles cause deterioration in shear strength and cohesion of slip zone soil, especially in the first four cycles, while the internal friction angle remains largely unchanged. The compaction effect of the overlying load mitigates the deterioration caused by D-W cycles. The findings reveal the weakening pattern of mechanical strength in slip zone soil under combined effects of overlying load and D-W cycles, offering valuable insights for studying mechanical properties of slip zone soil in reservoir bank landslides.

Direct shear creep tests have scarcely been used for long-term creep behavior studies of landslides in the Three Gorges reservoir area. In this study, based on field investigations and monitoring of the Huangtupo Landslide, direct shear creep tests were performed on the sliding zone soil of Riverside Slump #1, and the creep characteristics of sliding zone soil after varying cycles of reservoir water level fluctuation were studied. Using the creep results, the Mohr-Coulomb parameters were obtained by numerical simulation, and the deformation pattern of the reservoir landslide was analyzed. The results show that the direct shear creep of sliding zone soil can mainly be divided into stages of attenuation creep and steady-state creep. Under the same shear stress, with the increase of loading-unloading cycles N, the soil's strain and shear strain rate in the sliding zone decreased accordingly, and the long-term strength gradually improved. As the shear stress increases, the shear strain rate increases and the creep of the soil in the sliding zone has an obvious time effect. Our numerical simulation results showed good agreement with both the landslide deformation monitoring data and direct shear testing data. The Burgers model is suitable for describing creep deformation of landslides under fluctuating reservoir water levels. Under high shear stress, the fitted curve showcased both attenuation and constant velocity characteristics. Numerical simulation and burger model can reflect the direct shear creep test characteristics well. These research findings can provide an important reference on the creep characteristics of landslides, potentially aiding geotechnical engineering applications.

Underground coal mining induces significant surface deformation and environmental damage, particularly in deeply buried mining areas with thin bedrock and thick alluvial layers. Based on the case study of the Zhaogu No.2 coal mine in Xinxiang City, Henan Province, China, this study employs a comprehensive research methodology, integrating field investigations, numerical simulations, and theoretical analyses, to explore the surface subsidence features at deeply buried mining areas with thin bedrock and thick alluvial layers, to reveal the effect of alluvial thickness on the surface subsidence characteristics. The findings indicate that the surface subsidence areas span 4.2 km2 with an advanced influence distance of 540 m. The rate of surface subsidence primarily depends on the panel's position and its advancing rate. Moreover, the thickness of the alluvial layer amplifies both the extent and magnitude of surface deformation. The displacement of overlying rock primarily exhibits a two-stage progression: the thin bedrock control stage and the alluvial control stage. In the thin bedrock control stage, surface subsidence initiates with relatively low subsidence values and amplitudes. Subsequently, in the alluvial control stage, surface subsidence accelerates, leading to a rapid increase in both subsidence values and amplitudes. These characteristics of rock formation displacement result in distinct phases of surface subsidence. Furthermore, the paper addresses the utilization of surface subsidence areas and proposes a method for calculating reservoir storage capacity in these areas. According to calculations, the storage capacity amounts to 1.05e7 m3. The research findings provide valuable insights into the surface subsidence laws in regions with similar geological conditions and practical implications for the management and utilization of subsided areas.

The strength of the sliding zone soil determines the stability of reservoir landslides. Fluctuations in water levels cause a change in the seepage field, which serves as both the external hydrogeological environment and the internal component of a landslide. Therefore, considering the strength changes of the sliding zone with seepage effects, they correspond with the actual hydrogeological circumstances. To investigate the shear behavior of sliding zone soil under various seepage pressures, 24 samples were conducted by a self-developed apparatus to observe the shear strength and measure the permeability coefficients at different deformation stages. After seepage-shear tests, the composition of clay minerals and microscopic structure on the shear surface were analyzed through X-ray and scanning electron microscope (SEM) to understand the coupling effects of seepage on strength. The results revealed that the sliding zone soil exhibited strain-hardening without seepage pressure. However, the introduction of seepage caused a significant reduction in shear strength, resulting in strain-softening characterized by a three-stage process. Long-term seepage action softened clay particles and transported broken particles into effective seepage channels, causing continuous damage to the interior structure and reducing the permeability coefficient. Increased seepage pressure decreased the peak strength by disrupting occlusal and frictional forces between sliding zone soil particles, which carried away more clay particles, contributing to an overhead structure in the soil that raised the permeability coefficient and decreased residual strength. The internal friction angle was less sensitive to variations in seepage pressure than cohesion. (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/).

We study CO2 injection into a saline aquifer intersected by a tectonic fault using a coupled modeling approach to evaluate potential geomechanical risks. The simulation approach integrates the reservoir and mechanical simulators through a data transfer algorithm. MUFITS simulates non-isothermal multiphase flow in the reservoir, while FLAC3D calculates its mechanical equilibrium state. We accurately describe the tectonic fault, which consists of damage and core zones, and derive novel analytical closure relations governing the permeability alteration in the fault zone. We estimate the permeability of the activated fracture network in the damage zone and calculate the permeability of the main crack in the fault core, which opens on asperities due to slip. The coupled model is applied to simulate CO2 injection into synthetic and realistic reservoirs. In the synthetic reservoir model, we examine the impact of formation depth and initial tectonic stresses on geomechanical risks. Pronounced tectonic stresses lead to inelastic deformations in the fault zone. Regardless of the magnitude of tectonic stress, slip along the fault plane occurs, and the main crack in the fault core opens on asperities, causing CO2 leakage out of the storage aquifer. In the realistic reservoir model, we demonstrate that sufficiently high bottomhole pressure induces plastic deformations in the near-wellbore zone, interpreted as rock fracturing, without slippage along the fault plane. We perform a sensitivity analysis of the coupled model, varying the mechanical and flow properties of the storage layers and fault zone to assess fault stability and associated geomechanical risks. (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 license (http://creativecommons.org/licenses/by/4.0/).