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The large-scale accumulation of coal gangue not only occupies land resources but also poses serious environmental risks, while offering opportunities for resource recovery through mine land reclamation. This study investigates how soil cover thickness regulates rainfall infiltration in coal gangue backfill systems through laboratory testing of hydraulic parameters, field infiltration monitoring, and HYDRUS-based numerical simulations. Results show that a 50 cm soil interlayer effectively delays infiltration and reduces moisture at the soil–gangue interface by approximately 40%, achieving a balance between hydraulic barrier performance and cost efficiency. Increasing the soil cover thickness to 70–100 cm further improves water retention capacity but results in reduced economic benefits. For long-term rainfall conditions, a layered configuration consisting of alternating coal gangue and soil layers, capped with a 1 m surface layer, moderated moisture transfer and limited deep percolation, maintaining stable hydrological behavior throughout the simulation period. Multi-objective optimization using the NSGA-II algorithm identified a total cover thickness of 50–60 cm as the optimal configuration, reducing leachate generation by about 90%, controlling heavy-metal migration risk below 3%, and maintaining unit costs within 120–150 CNY m −2 . These findings provide a quantitative and practical basis for designing sustainable soil cover systems that integrate solid waste utilization with environmental protection across different climatic regions.

The susceptibility mapping of rainfall-induced landslides is an effective tool for predicting and locating disaster-prone zones at the regional scale. One of the most important parts of landslide susceptibility models is the hydrological model. In this context, the present study considers three pore water pressure (PWP) profiles with surface runoff to estimate the spatiotemporal variation of wetting front depth (WFD) during rainfall episodes. To reasonably simulate the inherent uncertainty and variability involved in the hydrogeomechanical properties of the surficial soil layers at the regional scale, probabilistic analysis based on the recursive first-order reliability method (FORM) is employed to calculate the probability of slope failure. The regional time-dependent landslide susceptibility mapping is realised using a newly developed model called Physically-based probabilistic modelling of Rainfall Landslides using Simplified Transient Infiltration Model (PRL-STIM). The proposed model is applied in a representative area that suffered extensive rainfall-induced landslides in July 2013 (Niangniangba Town, Gansu Province, China). The results indicate that the PRL-STIM model achieved a satisfactory prediction accuracy of 75% AUC compared to existing models like transient rainfall infiltration and grid-based regional slope-stability model (72%) and the probabilistic analysis results based on the first-order second moment method (74%). It also performed well in predicting the spatial distribution of shallow landslides, with a success rate of 81.6%. Regarding the model efficiency, the completion of a raster file for calculating the landslide probabilities of the study area (including 711,051 cells) requires only 17.1 s. It is thus hoped that the proposed calculation framework of PRL-STIM that considers various uncertainties (e.g., nonlinearity of the physical model, non-normal probability distributions, random variable cross correlations, etc.) in geotechnical parameters is better suited for landslide susceptibility mapping at the regional scale, where only limited historical event data is available.

Baseflow is an important component of river or streamflow. It plays a vital role in water utilization and management. An improved Eckhardt recursive digital filter (IERDF) is proposed in this study. The key filter parameter and maximum baseflow index (BFI max ) were estimated using the minimum smoothing method to improve baseflow estimation accuracy. The generally considered BFI max of 0.80, 0.50 and 0.25 according to the drainage basin’s predominant geological characteristics often leads to significant errors in the regions that have complex subsurface and hydrologic conditions. The IERDF improved baseflow estimation accuracy by avoiding arbitrary parameter values. The proposed method was applied for baseflow separation in the upstream of Yitong River, a tributary of the Second Songhua River, and its performance was evaluated by comparing the results obtained using isotope-tracer data. The performance of IERDF was also compared with nine baseflow separation techniques belonging to filter, BFI and HYSEP methods. The IERDF was also applied for baseflow separation and calculation of rainfall infiltration recharge coefficient at different locations along the Second Songhua River’s mainstream for the period 2000–2016. The results showed that the minimum smoothing method significantly improved BFI max estimation accuracy. The baseflow process line obtained using IEDRF method was consistent with that obtained using isotope 18 O. The IERDF estimated baseflow also showed stability and reliability when applied in the mainstream of the Second Songhua River. The BFI alone in the river showed an increase from the upstream to the downstream. The proportion of baseflow to total flow showed a decrease with time. The intra-annual variability of BFI was different at different locations of the river due to varying climatic conditions and subsurface characteristics. The highest BFI was observed at the middle reaches of the river in summer due to a water surplus from power generation. The research provided valuable information on baseflow characteristics and runoff mode determination, which can be used for water resources assessment and optimization of economic activity distribution in the region.

In the present study, stability analysis of an unsaturated homogenous pond ash slope subjected to rainfall using the limit equilibrium method based n Bishop and Morgenstern-Price methods under steady-state seepage and transient seepage conditions was carried out. Seepage and stability analyses were carried out using SEEP/W and SLOPE/W models, respectively. The factor of safety (FoS) in the case of the unsaturated pond ash slope was observed to be higher than the saturated slope. The effect of slope geometry, rainfall intensity, anisotropy in permeability, and provision of drains on slope stability were investigated. It is observed that with an increase in rainfall infiltration, there was a tendency of surficial failure when the rate of infiltration is higher than the saturated permeability in the unsaturated pond ash slope. The study assumes importance related to the stability of slopes constructed with coal ash in the context of ever-growing requirements of electricity in the country, slope failures due to extreme weather events associated with climate change, and the requirement of sustainable alternatives, theories, and technologies to tackle the coal ash waste produced.

Rainfall infiltration is a key hydrological process influencing agriculture, pollutant transport, and flood modeling. Accurate prediction of rainfall losses, defined as rainfall that does not contribute to surface runoff is critical in rainfall‐runoff models. Rainfall–runoff models are typically calibrated using historical data to estimate loss parameters, which often deviate from physically realistic infiltration behavior as they compensate for other sources of error and uncertainty in the model. This study addresses this gap by investigating infiltration losses based on physical attributes under controlled rainfall conditions. Seventy‐five sites in southeastern Queensland, Australia, were subjected to rainfall of approximately 60 mm/hr for 1‐hr, allowing detailed analysis of infiltration responses. Key predictors of infiltration included grass cover, leaf litter, soil organic carbon, and bulk density, while slope had minimal predictive power. Findings indicate that, during short, high‐intensity rainfall events, initial losses were relatively low, with runoff beginning within 10–30 min, while continuing loss rates exceeded expectations within the first hour. Multiple Linear Regression (MLR) techniques were used to develop prediction equations for several loss models, including lumped loss, initial loss–continuing loss, and Horton infiltration. These equations explained approximately 60% of the variance between observed and predicted losses. The equations provide a practical tool for estimating infiltration losses in ungauged catchments. The prediction equations are suitable for 1‐hr, 60 mm/hr intensity rainfall events, with limited applicability to longer, low‐intensity rainfall. The results offer insights for improving flash flood predictions, particularly in ungauged catchments experiencing intense, short‐duration storms.

This study addresses the unclear water transport patterns in reconstructed layered soils in the arid and semi-arid climate zones of northwestern China by utilizing the Hydrus-3D model to simulate the rainfall infiltration process. Simulation experiments were designed to investigate different configurations of layered soils, with changes in soil moisture profiles monitored throughout. The water transport characteristics of these soils were comprehensively analyzed from four perspectives: soil moisture, water potential, water flux, and lateral flow within the soil. In order to further explore the influence of interlayer properties on shallow soil moisture dynamics, scenario simulations and global sensitivity analysis were conducted based on optimized models. The results demonstrated that interlayers significantly influence soil water distribution and transport patterns. During the rainy season, soil water content and lateral flow decreased with increasing soil depth, whereas these values increased during the dry season, suggesting that deeper soil layers exhibit strong water storage capacities. Both loess and sandy interlayers impeded water infiltration, albeit through different mechanisms. The loess interlayer retained water due to its low permeability, while the sandy interlayer caused water retention in the overlying clay soil as a result of its low matric potential. Based on the simulation outcomes, it is recommended that a 10 cm thick loess interlayer at a depth of 40 cm in sandy soil enhances upper soil moisture availability for vegetation, whereas a 10 cm thick sandy interlayer at the same depth in loess soil improves soil permeability. This study not only advances understanding of the impact of loess infill on soil moisture dynamics in sandy soil regions but also provides critical guidance for soil reconstruction practices in northwestern China, where sandy soils and loess are predominant.

Rainfall is a primary coefficient of slope instability. To study patterns of slope failure mode and key index threshold values of slope instability under varying rainfall intensities, real-time data from in-situ monitoring tests of an engineering slope were utilized. This data facilitated the analysis of the temporal and spatial responses of a rainfall infiltration slope. Four field tests were conducted under four different rainfall intensities, namely 75mm/h, 125mm/h, 150mm/h, and 175mm/h, to study the progressive failure characteristics of the granite residual soil slope. These characteristics were studied based on water-time and displacement-time curves, and the rainfall duration and threshold for slope instability were proposed. The result revealed that the granite residual soil slope undergoes progressive failure under rainfall conditions, which can be categorized into four modes: “shallow local sliding”,“shallow global sliding and collapse”, “deep local sliding”, and“deep global sliding”. It takes 25 ~ 135min for the shallow sliding failure characteristics from significant deformation to instability, while the deep sliding only lasts for 18 ~ 20min. A significant correlation was observed between soil moisture content and slope instability. Instability symptoms such as cracking and peristaltic deformation begin to appear when the soil moisture content in the shallow layer of the slope increases to 42 ~ 45%. When the soil moisture content escalates to 47 ~ 50%, the slope begins to disintegrate, leading to rapid landslides and collapses.

Many sandy soil slopes easily deform during or immediately after rainfall infiltration, which causes soil erosion. A novel double polymer used as a chemical sand-fixing agent (DPCM) based on water-soluble polymers of carboxymethyl cellulose and polyacrylamide was studied in this paper. The resistance to water erosion of sandy soil slopes with a DPCM stabilization layer has been studied by the physical modelling of rainfall. Nine laboratory rainfall erosion tests were carried out to establish a mathematical model to calculate the soil loss on sandy soil slopes. The experimental treatments included DPCM to sand mass ratios of 0:0, 1:2 and 1:3, slope gradients of 30°, 40° and 50°, rainfall intensities of 150, 200 and 250 mm/h, and elapsed times of 10, 20 and 30 min. The results showed that the average water erosion moduli in a mixture of DPCM and sandy soil with mass ratios of 1:2 and 1:3 were 5.71 g/m2/min and 3.13 g/m2/min, respectively, which were significantly lower than the average water erosion modulus of 14.28 g/m2/min on the bare slope. The water erosion modulus of the slope treated by DPCM was 60–78% lower than that of the untreated slope, and the infiltration rate and total runoff yield from the covered plots were 42.9–53.6% and 56.1–80.2% lower than those from the controls, respectively. The sensitivities of the DPCM to the sand mass ratio, rainfall intensity, slope gradient, and elapsed time to infiltration and water erosion were 1.26, 0.70, 0.53, and 0.32 and 11.15, 1.72, 1.48, and 0.73, respectively. Finally, combined with rainfall simulation testing results, an erosion calculation model on sandy soil slopes composed of rainfall, infiltration rate and slope characteristics was obtained. A comparison analysis between data collected in testing and calculated by the model showed an ideal effect in the calculation method, with a relative error of less than 15% in estimating erosion on sandy soil slopes. Experimental data showed that DPCM could effectively improve the stability and resistance to water erosion on sandy soil slopes, and these results could be verified in the practical application of sandy soil slope reinforcement.

This paper presents the results of centrifuge tests on rainfall-induced instabilities in variably saturated slopes. The roles of rainfall intensity and initial conditions, such as slope angle, porosity and degree of saturation of the soil, in the failure initiation and postfailure kinematics are considered. The failure patterns, infiltration profile and deformation at prefailure and postfailure stages are characterized. The results indicate that rainfall-induced slope failures usually follow one of the following two failure modes, i.e. slide-to-flow and flowslide failure modes. The former pattern is characterized by soil mass flow after initial failure along a continuous shear surface, while the latter is more relevant to the rapid increase in the saturation at the slope surface, resulting in surface erosion channels followed by the acceleration of the soil mass. The flowslide failure pattern usually gives rise to several superficial shear surfaces and longer run-out distances. The rainfall intensity and profiles of the degree of saturation play the key roles in initiating the slope failure at the prefailure stage and subsequently in mobilizing the soil mass at the postfailure stage. Our test data, together with the data from the literature, are presented in two threshold curves to define the critical condition of slope failure under rainfall infiltration.

In order to study the effect of the rainfall infiltration on water migration in compacted loess, a model device was developed for testing water migration in the soil under rainfall conditions. In this study, the volumetric water content and resistivity of soil were introduced into the model test device. This model test device was applied to the study of water migration characteristics in compacted loess under different rainfall conditions. The results show that the resistivity decreases with the increase of the volumetric water content at the same depth of the loess column. In this way, the characteristics of the water migration can also be reflected from the change of the resistivity. There is an intimate relationship between the resistivity and volumetric water content, dry density. The volumetric water content and dry density are normalized by saturation of loess, arriving the equation of saturation against the resistivity. The characteristics of rainfall infiltration in compacted loess show a particular pattern, which demonstrates that, with the increase of dry density of the loess column, the rainfall infiltration line present “Y”, “D” and “Λ” shape distribution respectively, under light rain, heavy rain and rainstorm.