Against the backdrop of global warming, the increasing spatiotemporal variability in precipitation patterns has intensified the frequency and risk of dry-wet abrupt alternation (DWAA) events in semi-arid regions. This study investigates the Hailar River Basin in northern China (1980-2019) and develops the Soil Moisture Concentration Index (SMCI) using daily soil moisture (SM) data simulated by the VIC hydrological model. A high-resolution temporal framework is introduced to detect DWAA events and evaluate the impact of precipitation pattern variations on dry-wet transitions in the basin. The results indicate: (1) Annual precipitation in the basin has significantly increased (0.47 mm y(-1) in the south, P < 0.05), while precipitation intensity follows a gradient pattern, increasing in the upstream (3.65 mm d1 y1) and decreasing in the downstream (-2.34 mm y(-1)). Additionally, the number of dry days and short-duration, high-intensity precipitation events has risen; (2) Soil moisture (SM) data simulated by the VIC model effectively capture DWAA events, showing significantly higher | SMCI| values downstream than upstream (P < 0.05) and indicating more intense dry-wet transitions in the downstream region. Furthermore, 78 % of the area exhibits an increasing trend in |SMCI|(1980-2019), with dry-to-wet transition events occurring more frequently than wet-to-dry events. For instance, in 2013, the maximum coverage area reached 48 % in a single day; (3) The random forest model highlights the spatial heterogeneity of DWAA driving factors: upstream water yield is the dominant factor, whereas downstream variations are closely associated with precipitation intensity (R-2 = 0.76) and the frequency of heavy rainfall days. Permafrost degradation and land use changes further heighten hydrological sensitivity in the downstream region. This study offers a transferable methodological framework for understanding extreme hydrological events and reveals that the driving mechanisms of DWAA are spatially heterogeneous, shifting from being dominated by terrestrial factors in the headwaters to meteorological factors downstream-a finding with significant implications for water resource management in other large, heterogeneous semi-arid basins.

Suprapermafrost groundwater (SPG) plays a critical role in hydrological and ecological functioning of permafrost regions, yet its spatiotemporal dynamics and controlling mechanisms remain poorly understood on the Qinghai-Tibet Plateau (QTP). Here, we integrated in situ observations, geophysical surveys, and machine learning (ML) models (including XGBoost, LightGBM, and RandomForest) to investigate the seasonal variation, drivers, and projections of SPG dynamics in alpine meadow (AM) and alpine wet meadow (AWM) ecosystems. Results showed that SPG tables ranged from -1.1 to -0.1 m in AM and from -1.3 to -0.2 m in AWM during the warm season. SPG fluctuations were primarily driven by thaw depth (TD) and rainfall infiltration and exhibited similar seasonal patterns across both ecosystems. A greater TD was associated with a deeper SPG table, as deeper thawing expanded the unsaturated zone and enhanced vertical drainage, indicating an exponential relationship between TD and SPG table position, and a linear relationship with aquifer thickness. In contrast, rainfall infiltration increased shallow soil moisture and elevated SPG tables, with responses influenced by rainfall intensity, duration, and infiltration pathways. Spatial heterogeneity in SPG distribution was further shaped by vegetation structure and microtopographic variation. Furthermore, ML models projected that mean summer SPG table depths in the 2090s would increase by 0.06 m under SSP126 and 0.64 m under SSP585 in AWM ecosystems, and by 0.37 m under SSP126 and 0.87 m under SSP585 in AM ecosystems. These findings provide new insights into how climate warming affects hydrological processes in permafrost regions of the QTP.

The existence of rock weathering products has an important effect on the infiltration of water in the soil. Understanding the mechanism of water infiltration in a mixed soil and weathered rock debris medium is highly important for soil science and hydrology. The purpose of this study is to explore the effects of mudstone hydrolysis on water infiltration in the soil under different mixing ratios (0-70 %) of weathered mudstone contents. Soil column experiments and numerical modelling were used to study the processes of hydrolysis of weathered mudstone and water infiltration in the mixed medium. The results revealed that water immersion can cause the dense mudstone surface to fall off, thus forming pores, and that the amount of these pores first increase but then decrease over time. The disintegration of post-hydrolysis mudstone debris occurs mainly among particles ranging from 2-2000 mu m, predominantly transforming sand particles into finer fractions. Increasing the mudstone content in the soil from 0 % to 50 % enhances the infiltration rate and cumulative infiltration volume. However, when the mudstone content exceeds 50 %, these parameters decrease. The mudstone weathering products promote water infiltration in the soil within a certain range of mudstone contents, but as the ratio of weathered products increases, excessive amounts of mudstone hinder the movement of water in the soil. The identified transformation phenomenon suggests that the infiltration capacity of mixed soil will not scale linearly with mudstone content. The findings enable some mitigation strategies of geologic hazards based on the hydrological stability in heterogeneous environments.

Post-grouting pile technology has gained extensive application in collapsible loess regions through the injection of slurry to compress and consolidate the soil at the pile base, thereby forming an enlarged base that enhances the foundation's bearing capacity and reduces settlement. Despite the prevalent unsaturated state of loess in most scenarios, the conventional design methodologies for piles in collapsible loess predominantly rely on saturated soil mechanics principles. The infiltration of water can significantly deteriorate the mechanical properties of loess due to the reduction in matric suction and the occurrence of collapsible deformation, leading to a substantial degradation in the bearing behavior of piles. To explore the variations in load transfer mechanisms of post-grouting piles in collapsible loess under conditions of intense precipitation, a comprehensive large-scale model test was conducted. The findings revealed that the post-grouting technique effectively mitigates the adverse effects of negative pile shaft friction in saturated zones on the pile's bearing behavior. Furthermore, the failure criteria for piles may shift from the shear failure of the base soil to excessive pile settlement. By incorporating principles of unsaturated soil mechanics, modified load transfer curves were developed to describe the mobilization of both pile shaft friction and base resistance. These curves facilitate the extension of the traditional load transfer method to post-grouting piles in collapsible soils under extreme weather conditions. The proposed revised load transfer method is characterized by its simplicity, requiring only a few soil indices and mechanical properties, making it highly applicable in engineering practice.

Extreme rainfall causes the collapse of rammed earth city walls. Understanding the depth of rainwater infiltration and the distribution of internal moisture content is crucial for analyzing the impact of rainfall on the safety and stability of these walls. This study focuses on the rammed earth city wall at the Mall site in Zhengzhou. Based on Richards' equation, the water motion equation of rammed earth wall is deduced and established. The change of moisture content of rammed earth wall and the development of wetting front under rainfall condition are studied. The stability of the rammed earth city wall under rainfall infiltration is analyzed by finite element methods. The results show that the water motion equation can effectively describe the moisture distribution inside the rammed earth city wall during rainfall. As the rainfall continues, the wetting front deepens, and the depth of the saturated zone increases. Just below the wetting front, the moisture content decreases rapidly and eventually returns to its initial value. the water motion equation provides a theoretical basis for analyzing water-related damage in rammed earth walls. Factors such as the initial soil moisture content, rainfall duration, and rainfall intensity significantly influence the distribution of the wetting front and moisture content. The saturation of the upper soil layers reduces the shear strength of the shallow soil, leading to a decrease in the safety factor, which can result in shallow landslides and collapse of the rammed earth wall. The research results can provide theoretical support for the analysis of water infiltration law of rammed earth city walls under rainfall conditions, and provide reference for revealing the instability mechanism of rammed earth city walls induced by rainfall. (c) 2025 Elsevier Masson SAS. All rights are reserved, including those for text and data mining, AI training, and similar technologies.

PurposeThis study aims to investigate the effects of root exudates on the aggregate stability and permeability of loess and to further reveal the mechanisms of vegetation in preventing and controlling soil erosion beyond mechanical effects.Materials and methodsWetting tests were conducted to investigate how loess aggregate stability varies with curing time and root exudate concentration; and infiltration tests were carried out to examine the influence of root exudates on the infiltration characteristics of loess with varying degrees of compaction.Results and discussionThe results showed that the stability of loess aggregates significantly increased due to the application of root exudates. Curing could enhance the stabilizing effects of root exudates on loess aggregates; however, there existed a critical curing duration. The application of root exudates reduced the stable infiltration rate and hydraulic conductivity of loess. However, untreated specimens under lower degrees of compaction exhibited lower stable infiltration rate and hydraulic conductivity due to local structural damage. The stable infiltration rate of both treated and untreated specimens decreased with curing time.ConclusionsThe effects of root exudates can be attributed to their ability to function as stabilizing agents and promote aggregation, due to their high adsorption capacities and negatively charged groups on their surfaces. On the other hand, the presence of root exudates can significantly enhance the soil microbial activity, the microorganisms and their hyphae further strengthen the soil structure, fill pores and increase the soil hydrophobicity, thereby improving the aggregate stability while reducing the soil permeability.

Current studies on soil tortuosity models typically assume a single particle size, neglecting the impact of particle gradation and spatial arrangement on pore channels and structures. To address this limitation, we develop a tortuosity model that incorporates multiple factors by assuming ellipsoidal particles and accounting for their arrangement and gradation. This model, combined with the Bingham fluid flow equation in porous media, elucidates the spherical penetration grouting mechanism of Bingham fluids, considering both tortuosity and time-varying viscosity. Using COMSOL Multiphysics, we simulate seepage to create a numerical program for Bingham fluid spherical seepage grouting that accounts for tortuosity and time-varying viscosity. Theoretical analysis and simulations validate our proposed tortuosity model and diffusion mechanisms. Additionally, we examine the sensitivity of the diffusion radius to Bingham grout rheology, grouting pressure, groundwater pressure, and grouting pipe radius. The research results demonstrate that the established tortuosity theoretical model is in excellent agreement with numerical simulations, with a maximum error of less than 3%. The spherical permeation grouting diffusion mechanism of Bingham fluid, which accounts for the tortuosity effect of porous media, more closely matches the experimental test values, achieving an average error of 10.13% and a minimum error of 3%. Grouting pressure and groundwater pressure are key factors, and their interaction with the grouting pipe radius has the strongest effect. These research findings provide valuable theoretical support for designing construction controls related to restoration projects involving porous medium earth-rock dams.

This study numerically evaluates the stability of RS walls with select, marginal, and fly ash backfills under rainfall infiltration. A transient seepage, global stability, and lateral deformation were analyzed considering different rainfall intensities. As infiltration flux increases from 10 mm/h (low rainfall) to 80 mm/h (very heavy rainfall), wall stability decreases significantly due to the excessive buildup and inadequate dissipation of pore water pressure. Pore water pressure increases considerably due to infiltration. Fly ash fill exhibits approximately 125% higher pore water pressure than select fill. To allow for the dissipation of pore water pressure, the effect of chimney drains of various thicknesses was analyzed on the stability of the RS wall. It was observed that the stability of the wall increased with increasing thickness of the chimney drain.

Rainwater infiltration will significantly increase the pore water pressure of shallow soil, thus reducing the stability of slope soil. In order to study the migration law of rainwater infiltration wetting front of vegetated slopes, the law of rainfall infiltration was analyzed by using the data of in field monitoring test of slopes. Meanwhile, a vegetated slope infiltration model was established, and the changes in the pore pressure and saturation of the idealized root system on the slope under different rainfall were investigated and analyzed. We found that medium to heavy rainfall (>10 mm/d) can change the shallow water content of vegetated slopes, and light rainfall cannot change the water content; the change in water content of vegetated slopes is less than that of unvegetated slopes under long-duration rainfall, and more than that of unvegetated slopes under short duration rainfall; the change in water content of Ligustrum quihoui Carr. L. shrub slopes are smaller than that of Nerium oleander L. shrub slopes, which has a better effect of slope; under short duration rainfall, the permeability coefficient of root consolidation zone of the vegetated slope is large, the rainwater infiltration speed is fast and it is not easy to cause shallow landslides; with the increase of rainfall time, the plant root system provides a good pore channel, the depth of sudden change of pore pressure of vegetated slope is smaller than that of unvegetated slope. The results of this study provide a reference and analytical basis for vegetated slopes of road graben under rainfall.

The restraining effect of soilbags inhibits soil dilatancy, enhancing the strength and stiffness of the wrapped soil. As a permanent slope protection structure (SSPS), the application of counterpressure enhances stability by improving slope surface stiffness and limiting deformation. While reinforced slopes have been extensively studied, mechanistic investigations into the stability and failure processes of SSPS remain limited. This study numerically investigated the macro-meso mechanisms of SSPS instability using the discrete element method. Macroscopically, rainfall infiltration increases water absorption, resulting in longitudinal settlement, deformation, and eventual instability. With a friction coefficient of 0.5, the lower soilbags resist sliding forces until the front soilbags are damaged. Inadequate sufficient friction causes the front soilbags to be displaced outward, leading to structural collapse as the lower soilbags bear the additional load. Microscopically, geosynthetic wrapping restrains soil dilatancy, promoting tighter particle arrangements and secondary reinforcement through soilbag expansion. During instability, primary contact forces concentrate on longitudinal settlement, vertical back pressure, and downslope sliding, with force chain evolution revealing slip band formation. Soilbags facilitate coordinated particle deformation and stress distribution, transitioning from anisotropic to isotropic states as instability progresses. These findings enhance the understanding of SSPS instability mechanisms, providing guidance for more reliable design and construction practices.