[Objective] To address the delayed response of urban river networks to sluice and pump control rules, existing real-time control rules should be optimized to mitigate the backwater effect on drainage networks during storm events, thereby reducing flood risks. [Methods] First, a flood model was established using InfoWorks ICM to identify backwater-affected drainage outlets under different design storm events, followed by a quantitative analysis of surface inundation responses under both existing conditions and maximum drainage capacity. Then, a two-layer clustering model integrating AGNES and K-Medoids algorithms was established to determine river network control points based on the characteristics of backwater-affected drainage outlets. Finally, using these control points as control references, real-time control rules were optimized, and the performance of the proposed method was evaluated through observed storm events. A bidirectional tidal-influenced area in Cangshan District, Fuzhou City, was selected as a case study. [Results] The result showed that 23.73% of drainage outlets experienced backwater, and three river network control points were determined. Under the Super Typhoon Soudelor storm event, the optimized rules reduced the water head at river cross-sections by 3.51%, decreased the number of overflowing stormwater inlets by 1.53%, and lowered the surface inundation area and depth by 6.18% and 9.25%, respectively, compared to the original rules. [Conclusion] Identifying backwater-affected drainage outlets helps preliminarily locate flood-prone areas, and analyzing surface inundation responses provides a reliable basis for determining river network control points and optimizing real-time control rules. The comparative simulation of observed storm events verifies the effectiveness and advantages of the optimized rules in reducing river cross-section water head. Furthermore, it shows that updating sluice and pump control references is crucial for enhancing the responsiveness of urban river networks and mitigating flood risks. The proposed method provides a practical reference for optimizing river network operations and improving urban flood management.

[Objective] Under the “dual carbon” goals in China, the accurate prediction of influent water quality in wastewater treatment plants is crucial for energy conservation, emission reduction, and energy consumption reduction. [Methods] To address the insufficient accuracy of traditional influent water quality prediction method(such as artificial neural networks, recurrent neural networks, and long short-term memory networks) in handling the randomness and nonlinearity of wastewater water quality characteristics, a prediction model based on convolutional attention temporal neural network(CAT-NN) was proposed. The model integrated multi-scale information fusion and a hybrid attention mechanism, along with a temporal decoding module, to effectively capture the long-term trends and short-term abrupt changes in wastewater water quality indicators. [Results] Through the predictive analysis of four typical water quality indicators—COD, NH₃-N, TN, and TP—of influent water data from a wastewater treatment plant in Yan'an City, Shaanxi Province, the CAT-NN model demonstrated excellent prediction perfor-mance, with a root mean square error(RMSE) of 4.50% and a mean absolute error(MAE) of 5.00%. Compared to traditional models(such as ANN, LSTM, and gated recurrent units(GRU)), the RMSE and MAE improved by over 16.13% and 20.00%, respectively. [Conclusion] The result indicate that the CAT-NN model achieves higher accuracy and stronger robustness in predicting influent water quality in wastewater treatment plants. The model not only provides strong support for the precise control and efficient operation of wastewater treatment plants, but also serves as a key technological solution for achieving energy conservation and emission reduction goals.

[Objective] The efficient execution of emergency evacuation operations is crucial for protecting the lives and property of local residents when a flood occurs. Due to the sudden nature of breach floods and their rapid progression, it is necessary to investigate the impact of flood evolution on the evacuation process. [Methods] The breach flood evacuation process and evolution process of the Tuanzhou embankment in Huarong County were taken as the research object. The Dijkstra algorithm was used to identify emergency evacuation paths for villages within Tuanzhou embankment. The breach flood inundation process, calculated by the ANUGA model, was combined to analyze the impact of flood evolution on the emergency evacuation process. [Results] The simulated water levels from the ANUGA model align closely with the observed water levels, with a Nash efficiency coefficient of 0.97, indicating the model's high accuracy in simulating the flood evolution process following the embankment breach in Tuanzhou embankment. The evacuation route lengths for the main villages in Tuanzhou embankment ranged from 4 to 11 km, with the total evacuation time being exceeded 60 minutes for all routes, and the longest evacuation time being 80.3 minutes. The evacuation routes for villages in the northern part of Tuanzhou embankment were long, resulting in extended travel times. For villages in the central and southern parts, where the population was mainly concentrated near the 055 township road, the vehicle density was higher when the 055 township road was used as the evacuation route, which result ed in reduced road travel speed and increased travel time. Due to the breach being located in the northern part of Tuanzhou embankment, emergency evacuation routes for villages in the central and northern regions were affected by flooding within 2 hours of the embankment breach, while evacuation routes for southern villages began to be inundated approximately 3 hours after the breach. When a 1 hour early warning was issued, all residents in Tuanzhou embankment could be safely evacuated. However, when the early warning was issued 0.5 hours in advance or later, the flood resulted in residents in the northern villages being unable to evacuate successfully. [Conclusion] If a breach occurs at the northern embankment, the villages in the northern part of Tuanzhou embankment will face a higher flood risk, highlighting the urgent need for planning and constructing a safety zone in the northern area of Tuanzhou embankment. The emergency evacuation plans for embankment breach floods in the villages need to be reasonably planned to reduce the decrease in traffic efficiency caused by vehicle congestion and to improve the regional emergency response capability. At the same time, efforts should be made to strengthen the maintenance and inspection of Tuanzhou embankment, as well as to improve disaster perception and early warning capabilities. The findings provide valuable references for flood control and disaster reduction planning, as well as for emergency evacuation of residents in the Tuanzhou embankment.

[Objective] Carbon sequestration, as a key indicator for assessing the carbon cycle and storage capacity of ecosystems, is of great significance for mitigating climate change. [Methods] Based on Net Primary Productivity(NPP) data from the Moderate Resolution Imaging Spectroradiometer(MODIS) from 2012 to 2022, the Sen + Mann-Kendall trend analysis and Hurst index were used to quantitatively analyze the characteristics and future trends of carbon sequestration in Jinan City. Additionally, the relationship between carbon sequestration capacity and ecological patterns of typical ecosystems was investigated through landscape pattern index evaluation and SPSS correlation analysis. [Results] The result showed that:(1) In 2022, the total carbon sequestration in Jinan City reached 1.72×10⁹ kg, with cropland contributing the largest amount of carbon sequestration and forest land showing the highest carbon sequestration capacity.(2) From 2012 to 2022, the total carbon sequestration in Jinan increased by 7.5%, with 83.8% of the regions showing an upward trend in carbon storage, and 83.7% of the regions were expected to continue improving in the future.(3) A significant negative correlation was observed between total carbon sequestration and patch density in the study area. Cropland and grassland showed no significant correlation with landscape pattern indices, while forest land was significantly correlated with landscape percentage, landscape shape indices, and maximum patch indices.(4) Influenced by landscape type changes, the carbon sequestration capacity of stable areas was significantly higher than that of disturbed areas. [Conclusion] Jinan City should strengthen the rational planning of ecological spaces, establish a robust ecological network, and optimize and stabilize landscape patterns, thereby laying the foundation for a sustainable urban ecosystem and achieving the “dual carbon” goals.

[Objective] This study aims to develop a drought index suitable for the actual conditions of Yunnan Province, [Objective]ly reveal drought variation patterns, and achieve effective drought monitoring. [Methods] The meteorological drought index(Standardized Precipitation-Evapotranspiration Index, SPEI) and the agricultural drought index(Standardized Soil Moisture Index, SSMI) were combined using the entropy weight method to develop a new comprehensive drought index. Various drought indices were evaluated and screened using method such as correlation analysis, root mean square error, and standard deviation to identify the most suitable drought index for Yunnan Province. Then, based on the most suitable drought index, [Methods]such as the run theory and Mann-Kendall trend test were used to thoroughly analyze the spatiotemporal variation characteristics of drought in Yunnan Province. [Results] The comprehensive drought index outperformed other drought indices in reflecting drought conditions, showing correlations of 64% and 60% with meteorological and agricultural drought indices, respectively. Additionally, it showed 94.11% consistency with statistical drought records. During the 2009—2010 winter-spring consecutive drought events, the drought evolution pattern captured by this method showed high consistency with actual drought process. In terms of time, the COI values at both monthly and seasonal scales across the province showed a fluctuating downward trend over the past 20 years, indicating increased drought frequency and severity. Seasonally, drought conditions were the most severe in spring, followed by winter, while summer and autumn showed relatively milder conditions. However, summer drought showed a persistent intensification trend at a rate of 0.034 per year. Spatially, the drought intensity and severity in Yunnan Province showed a concentric pattern, decreasing outward from the central Yunnan. Severe and extremely severe droughts were mainly concentrated in southwest and central Yunnan in spring and winter, while mild and moderate droughts occurred more frequently in summer and autumn. Trend analysis further showed a significant weakening trend(p<0.05) in drought severity during spring, autumn, and winter. Specifically, about 60% to 70% of areas in spring and autumn showed a significant decrease. In contrast, summer showed significant drought intensification. About 25.93% of areas showed a notable increasing trend(p<0.05), particularly in central and southern Yunnan. In winter, about 12.96% of the northern Yunnan exhibited a significant increase in drought severity. [Conclusion] The COI proves to be more suitable for Yunnan Province than other drought indices. Summer drought shows a distinct intensification trend, with central and southern Yunnan experiencing the most significant increases.

[Objective] Runoff exhibits characteristics of randomness, non-stationarity, temporal continuity, and spatial heterogeneity. This paper considers the spatiotemporal two-dimensional correlation characteristics of runoff and establishes a multi-station runoff sequence reconstruction model that can simulate various spatiotemporal scenarios of runoff. [Methods] This study optimally selected appropriate marginal distributions and Copula functions to establish the runoff correlations at the same station over different time periods, as well as across different stations at the same time period. Subsequently, the inverse transform sampling method from Monte Carlo simulations was used to randomly simulate multi-station runoff sequences. The method was applied to the Upper Yellow River, where correlation analysis and stochastic simulation of monthly runoff were conducted for the two control hydrological stations at Tangnaihai and Lanzhou. [Results] The results indicated that as the number of simulations increased, the consistency between the simulated and observed runoff series improved. When the number of simulations was 500, the maximum mean relative error(MRE) of monthly runoff at Tangnaihai and Lanzhou stations reached 2.07% and 3.28%, respectively. When the number of simulations reached 10,000, the MRE for all monthly runoff at both stations was lower than 0.34% and 0.37%, respectively. [Conclusion] The runoff series reconstruction model based on the Copula function and Monte Carlo method is applicable to more stations. It provides reliable data support for extending hydrological sequences in areas with sparse data, establishing operational rules for reservoir systems with hydraulic and electrical connections, and for formulating basin water resource allocation schemes under various spatiotemporal runoff scenarios.

[Objective] Considering the spatial heterogeneity of river basins and the transmission of multi-station runoff information between upstream and downstream is essential for improving runoff simulation accuracy in river basins. A coupled runoff simulation model based on the Soil and Water Assessment Tool(SWAT) and Tree-Structured Gated Recurrent Unit(TreeGRU) was established. [Methods] The SWAT model was employed to simulate the hydrological and physical processes in sub-basins to obtain outputs of key physical variables such as precipitation, evapotranspiration, and surface runoff. These variables, along with simulated runoff data from upstream hydrological stations, were used as inputs to establish the SWAT-TGRU coupled model. By incorporating a tree-structured framework, the model enabled the transmission of hydrological information from upstream to downstream, while fully accounting for the spatiotemporal relationships among hydrological stations in the river network. [Results] The SWAT-TGRU model improved the Nash-Sutcliffe Efficiency(NSE) at four hydrological stations of Tantou, Longmenzhen, Lushi, and Heishiguan by 49%, 11%, 13%, and 15%, respectively, in the Yiluo River Basin, compared to the SWAT model. [Conclusion] Compared with SWAT-GRU and SWAT-TLSTM models, the SWAT-TGRU model exhibits higher accuracy and stability in multi-station runoff simulations. It effectively overcomes the significant increase in model complexity that arises when non-treed-structured approaches are not utilized, providing an efficient and accurate method for multi-station runoff simulation in complex river basins.

[Objective] To further explore the relationship between extreme runoff and river basin precipitation variations in small and medium-sized rivers, and to improve the accuracy of flood disaster warning. [Methods] Taking the Qian River, a representative small and medium-sized river in the semi-arid regions of the Weihe River system in the Yellow River Basin, as an example, the flow and hourly precipitation data from 2010 to 2021 in the Qian River Basin were utilized. Based on the mean standard deviation classification method and the Topsis entropy weight method, the spatiotemporal variations in the river flow were analyzed. Focusing on four extreme runoff events, the sensitivity and lag in the runoff's response to river basin precipitation were investigated. [Results] The result were as follows:(1) the flow in the Qian River Basin exhibited significant interannual variability, showing a trend of first decreasing and then increasing. Seasonal distribution was extremely uneven, with peak flow typically occurring in July, and the flow was mainly in dry or slightly dry states.(2) Based on four extreme runoff events, it was found that the flow was high, with a rapid onset and long flood peak duration. The runoff predominantly exhibited a unimodal pattern, although bimodal occurrences were also observed.(3) The distribution of river basin precipitation affecting extreme runoff in the Qian River was uneven, with strong precipitation concentrated in the upstream area at the junction of Longxian and Qianyang. This was characterized by sudden heavy rainfall, with 14 out of 22 stations reaching the short-duration heavy rainfall level, including two stations with precipitation exceeding 50 mm/h. In addition, continuous rainfall, even at low intensity, could lead to extreme runoff events due to cumulative precipitation.(4) The sensitivity and time lag of runoff responses to precipitation varied across stations. At 14 key stations, significant contributions to runoff were observed, with precipitation at Dongnan, Duyang, Longxian, and Wenshui stations stabilizing the flow variations after 3, 9, 15, and 19 hours, respectively. [Conclusion] The response relationship between runoff and river basin precipitation during extreme runoff events is revealed, which can provide decision-making support for the scientific and rational development and utilization of water resources, as well as flood and waterlogging disaster management.

[Objective] To address the problems of complex terrain and difficulty in traditional monitoring in alpine-gorge rivers, river morphological characteristics are clarified using remote sensing technology, providing a theoretical basis for runoff estimation in data-scarce areas. [Methods] Based on multi-source remote sensing data, river morphological characteristics were identified using an improved relative stability index, gradient, and sinuosity. Characteristics of runoff flux-stable river segments were analyzed based on confluence accumulation combined with geological types. The energy conversion frequency of the river was explored based on variations in channel gradients. The hydraulic geometry relationship between discharge and water surface width was verified and analyzed based on the principle of multi-station hydraulic geometry method.[Results]1) The average gradient of the upper reaches of the Jinsha River was 1.71‰, and the stability of river segments was regulated by geological types. The segments from Zhimen Da to Shengba Village(segment I) and from Wentuo Village to Shigu Town(segment III) were identified as stable, while the segment from Shengba Village to Wentuo Village(segment II) was identified as unstable.(2) Energy dissipation in river segments was controlled by geological type and channel gradient. Granite segments were characterized by erosion, while basalt and shale segments showed depositional tendencies.(3) The gradient of runoff flux-stable river segments at hydrological stations was significantly lower than the average gradient of their corresponding geological types, indicating better stability.(4) Hydraulic geometry analysis of the Benzilan river segment showed that the average water surface width at 500 m intervals had a power-law relationship with discharge, and the coefficient and exponent showed a logarithmic linear relationship. The exponent of the width regression equation was approximately equal to the slope of the logarithmic linear equation, which was beneficial for improving the accuracy of discharge estimation. [Conclusion] The stability and morphological characteristics of river segments are controlled by geological types and are closely related to energy dissipation characteristics. The identification of runoff flux-stable river segments can provide scientific support for discharge estimation and hydrological monitoring of alpine-gorge rivers.

[Objective] Lakes serve as indicators of climate change, with lake surface water temperature(LSWT) significantly influencing their physical-chemical processes and ecosystems. The spatial distribution characteristics of LSWT, referred to as lake temperature heterogeneity, are of great significance for understanding the spatial variability in lake responses to climate change. [Methods] The necessity of researching LSWT heterogeneity is first systematically elaborated. The data sources available for analyzing LSWT heterogeneity are then comprehensively reviewed. Furthermore, the mechanisms influencing LSWT heterogeneity are explored from three key dimensions: lake depth, climatic factors, and inflow rivers. Finally, an outlook on future research directions for LSWT heterogeneity is provided. [Results] Significant spatial variations in LSWT within lakes are identified, confirming the necessity of analyzing LSWT heterogeneity. Research on LSWT heterogeneity is currently conducted primarily through remote sensing data extraction and numerical modeling. Lake depth is found to regulate thermal stratification and heat capacity, leading to LSWT heterogeneity. The spatial variability of climatic factors above the lake is also demonstrated to significantly influence the distribution patterns of LSWT. Additionally, the temperature difference between inflow rivers and lake water is observed to cause localized anomalies of low or high temperatures, further intensifying LSWT heterogeneity. [Conclusion] Future research on LSWT heterogeneity is suggested to focus on quantifying the impact range of inflow rivers on LSWT and establishing quantitative relationships between influencing factors and LSWT heterogeneity. Through the analysis of LSWT heterogeneity characteristics, basin-scale hydrometeorological conditions can be inferred, providing scientific support for studying lake responses to regional climate change.

[Objective] The partial nitrification-anammox(PN/A) process, with its significant advantages in aeration energy savings and external carbon source input, closely aligns with the requirements of quality and efficiency improvement of wastewater treatment plants in the context of “dual-carbon” goals. In recent years, it has garnered increasing attention and applications in the treatment of high-ammonia-nitrogen wastewater. However, it still faces challenges such as limited applicability to various water qualities. To further improve the treatment performance of the PN/A process and expand its applicability, comprehensive review, analysis, and summary of existing research literature and engineering cases are conducted. [Methods] Using systematic analytical method, the reaction mechanisms, main functional microbial communities, and their interactions in the PN/A process are clarified. Based on this, the key factors influencing the treatment performance of the PN/A process, including temperature, dissolved oxygen, aeration intensity, and organic matter concentration, are systematically reviewed, and a detailed analysis of their influence patterns is conducted. Combined with a comparative analysis of reactor types used in the PN/A process, the applications of PN/A in different wastewater treatments are summarized. Furthermore, based on an in-depth analysis of current issues in the PN/A process, future development directions and improvement strategies are proposed. [Results] It is found that PN/A technology exhibits good adaptability and advantages in treating traditional high-ammonia-nitrogen wastewater through the analysis of the influencing factors, mechanisms, and current application status of the PN/A process. However, in the treatment of low-temperature and low-ammonia-nitrogen wastewater, the PN/A process still faces major challenges such as unstable NO^-₂-N supply and low growth activity of anaerobic ammonium-oxidizing bacteria(AnAOB), requiring further research. [Conclusion] Future research should combine process parameter optimization strategies with the development of new reactors, delving into method for treating high-ammonia-nitrogen wastewater and mainstream municipal wastewater nitrogen removal under low-temperature conditions. This aims to expand the applicability of the PN/A process in water quality treatment and provide references for broader engineering applications.

[Objective] The tailings dam failure accident, as a high-energy, low-frequency extreme event, poses a serious threat to the safety of people's lives and property in the downstream. To accurately assess the risk of dam failure, a risk assessment method based on monitoring data-level and decision-level fusion is proposed. [Methods] Based on the multi-source online monitoring data of the tailings dam and a four-level risk system framework, an adaptive weighted fusion algorithm(AWF) was used to achieve data-level fusion of monitoring projects such as displacement, minimum dry beach length, and infiltration line. To address the issue of conflicting evidence in D-S evidence theory, the cloud model was used to construct the basic probability assignment(BPA). The Wasserstein distance and an improved normalized projection method(iNP) were introduced to measure the degree of conflict in the evidence bodies and construct fusion weights, thereby achieving decision-level fusion of dam failure risk based on the improved D-S evidence theory. [Results] The case analysis result showed that the application of the proposed method for risk assessment of a tailings dam yielded consistent result with actual observations, both indicating “low risk”, with a support degree of 0.891 5 for the assessment result. [Conclusion] The result indicate that the risk assessment model based on multi-source data fusion has a higher support degree for the assessment result compared to existing typical improved method, offering more accurate and reliable risk assessment for tailings dams.

[Objective] The large-scale accumulation landslide induced by loading and rainfall effects located in Weicheng Town, Guiyang City, Guizhou Province, China. The landslide poses a threat to the safe operation of the hydropower and water conservancy projects downstream of the Maotiao River. It is crucial to reveal the developmental characteristics and genetic mechanisms of the landslide under the coupling effect of loading and rainfall. [Methods] A combination of geological surveys, field monitoring, drilling and numerical simulations was employed. These method were used to elucidate the material composition and developmental characteristics of the landslide. Additionally, the displacement field, shear band characteristics, effective stress state of the slip zone, and slope stability under natural conditions, loading, and the combined effects of loading and rainfall are analyzed. The primary triggering factors and genetic mechanisms of the landslide were systematically summarized. [Results] The results show that the landslide is in a stable state under natural conditions and a marginally stable state under loading conditions. However, under the combined effects of loading and rainfall, it transitions to an unstable state, exhibiting signs of overall deformation. Under the combined effects of loading and rainfall, the displacement field progressively increases, shear band characteristics become more pronounced, and the effective stress in the slip zone initially increases but subsequently decreases, leading to a continuous reduction in stability. [Conclusion] The failure mode of the landslide under the coupling effect of loading and rainfall is characterized by backward pushing and forward traction. The topography, geomorphology, and lithology of the strata constitute the geological conditions for the development of the landslide. Rear-edge loading serves as the preparatory condition, while intense rainfall acts as the primary triggering factor for the landslide. Our findings provide guidance for the prevention and control design of Weicheng landslide along Wu-Chang Expressway and offer reference for the prevention and control of accumulation landslides induced by loading and rainfall effects.

[Objective] The numerical simulation method is widely used in the study of landslide disaster mechanical evolution and plays an important role in the process of landslide control. To study the triggering mechanism of landslide, [Methods]reasonable model assumptions are made, boundary conditions and parameters are set accurately, and a two-dimensional dynamic numerical simulation evaluation method is established. The landslide of Zhangjiazhuang section of Lanzhou-Xin Railway is taken as a typical example. GeoSlope and ABAQUS software are used to analyze the characteristics of landslide main section, slip zone plastic development process, slip region distribution, displacement distribution, and incremental displacement before and after abrupt change, and the landslide mechanism is analyzed by two-dimensional limit equilibrium method. [Results] The result show that the confined water cannot affect the top of the sliding zone, and the reduction of the safety factor caused by the action of confined water on the top sliding surface is smaller than that of the hydrostatic pressure, while the effect of confined water on the bottom of the sliding zone is larger. The reduction of the safety factor caused by the action of confined water on the bottom sliding surface is larger than that of the hydrostatic pressure, and the safety factor is directly reduced by 0.26. [Conclusion] Following the application of confined water pressure, substantial alterations were observed in the Mises stress field adjacent to the sliding zone, with stress increments reaching up to 0.5 MPa.These changes indicated that the action of confined water pressure significantly modified the stress distribution within the landslide mass.Additionally, distinct displacement discontinuities were exhibited by the landslide body under the influence of confined water pressure.Notably, horizontal displacements at the slope crest increased rapidly when the reduction factor reached 1.05.These findings further confirmed the substantial impact of confined water pressure on the stability of the landslide body. Through the comprehensive method and analysis of numerical simulation combined with field investigation and test, the dynamic evolution law of landslide under complex conditions such as groundwater pressure is reasonably simulated, which provides a basis for the stability evaluation of the progressive failure process of slope and the visual dynamic demonstration of landslide.

[Objective] Loess is widely distributed in the northwestern regions of China and is characterized by its large pore structure and well-developed vertical joints. Under freeze-thaw cycles, these features make loess highly susceptible to frost heave, thaw settlement, and crack propagation, posing significant threats to the stability and durability of engineering projects in cold regions. To address these challenges, lignin and slag were used to improve the loess through a carbonation process. The freeze-thaw characteristics and microscopic mechanisms of the improved loess were investigated. [Methods] A one-dimensional freeze-thaw cycle model test was conducted to analyze the effects of freeze-thaw cycles systematically under open conditions on the temperature distribution, water migration, frost heave force, frost heave deformation, and mechanical properties of the improved loess. Additionally, scanning electron microscopy(SEM) and X-ray diffraction(XRD) were employed to examine changes in the microstructure and composition of the soil. [Results] The results demonstrated that the improved loess exhibited excellent thermal insulation properties, with temperatures at depths greater than 35 cm consistently remaining above 0℃, preventing freezing. Water migration was primarily confined to the upper 30 cm, and the water replenishment volume was lower than that of remolded loess. The frost heave force of the improved soil was concentrated within the 10 cm depth range, with a maximum frost heave deformation of 20 mm, which was 20% lower than that of remolded loess. Furthermore, the improved loess maintained a high dynamic stress level before and after freeze-thaw cycles. [Conclusion] The findings indicate that the improved loess exhibits superior frost resistance, along with high stiffness and deformation resistance, effectively mitigating structural degradation caused by cyclic loading. The synergistic improvement mechanism of lignin and slag operates on three levels: chemical reactions, physical filling, and structural enhancement. Lignin forms hydrogen bonds with soil particles through its carboxyl and hydroxyl groups, while multivalent ions released by slag complex with lignin to form a three-dimensional network structure within the soil. Additionally, carbonation of slag produces cementitious materials such as calcium carbonate, which fill soil pores, optimize the microstructure, and significantly enhance the soil's density and frost heave resistance. The freeze-thaw properties of loess soil, modified through lignin-slag synergistic carbonation, were systematically investigated. These findings establish fundamental theoretical and technical support for loess soil improvement in cold region engineering applications.

[Objective] Salt crystallization in saline soil absorbs water, leading to changes in unfrozen water content. To investigate the effect of sodium sulfate on the unfrozen water content in saline soils with higher salt content. [Methods] A systematic laboratory experiment was conducted to study the influence of factors such as temperature, initial water content, soil type, and salt content on the unfrozen water content. A model for unfrozen water under different salt content conditions was constructed based on the principle of mass conservation. [Results] The result showed that under the same water content conditions, the higher the salt content, the lower the unfrozen water content in saline soil when the temperature reached the freezing point. Under the same negative temperature conditions, the unfrozen water content in the freezing process was higher than in the melting process. Furthermore, a hysteresis was observed in the change in unfrozen water content with temperature during the freezing and thawing process. [Conclusion] The constructed model for predicting unfrozen water content considers the salt crystallization stage and the ice-salt eutectic stage and quantifies the water released by salt crystallization, making it more suitable for predicting the unfrozen water content in high-salt saline soils. This provides scientific support for agricultural development and engineering construction in the cold and arid regions of Northwest China.

[Objective] To solve the problems of cumbersome construction process, high cost and low drainage efficiency caused by the separation of slope drainage and reinforcement measures, [Methods]the vacuum drainage anti-slide pile(VDAP) which is a kind of support measure integrating vacuum drainage and anti-slide is designed. The model of gas unsteady seepage on slopes of the VDAP under evacuation is established. The change rule of vacuum degree in the slope caused by the VDAP and its influence on groundwater seepage under a fixed-head recharge boundary are investigated. The distribution rule of the vacuum degree in the slope under the action of vacuum drainage and the analytical solution of the groundwater seepage field in the slope are obtained. The finite element simulation software is used to establish the corresponding finite element model, and the differences between the theoretical and simulated values are compared. [Results] The results show that the theoretical analysis and the finite element calculation are in well agreement with each other, so the theoretical model can better describe the seepage characteristics of groundwater on the slope under the action of the VDAP. [Conclusion] The analysis of the influencing factors based on the theoretical solution showed that the influence range of the vacuum degree gradually expands with time, and the vacuum degree within the influence range is positively correlated with the vacuum degree in the VDAP. The increase of vacuum and pumping volume in the pile can improve the drainage performance of the VDAP. The drainage effect of the VDAP is more obvious for slopes with smaller head differences at the slope boundaries. The result of the study provide a theoretical basis for the future application of the VDAP in engineering.

[Objective] The rigid boundaries of the discrete element model for sand in triaxial tests have difficulty in reflecting the deformation and failure of the specimen. To simulate the flexible deformation of sand and the lateral confining rubber membrane and conduct an in-depth study on the micro-mechanical characteristics at the particle scale in the triaxial test of sandy soil, [Methods]the discrete-continuous coupling method was adopted. Based on the finite difference program FLAC^3D and the discrete element program PFC^3D, the deformable continuous membrane(Shell) element and the rigid discrete particle(Ball) element were used to simulate the rubber membrane and sand particles respectively, and a coupling model was established to deeply investigate the evolution laws of particle rolling and sliding as well as the distribution characteristics of normal and tangential contact forces during the shear failure process. [Results] The results show that, the coupling model exhibits a strain softening trend during the triaxial shearing process, and its stress-strain curve is similar to the real laboratory test result, well reproducing the deformation and failure process of the sand in the laboratory triaxial test. During loading, the average contact number of particles in the specimen gradually increases, and the microstructure tends to be stable. The shear deformation of the specimen is mainly caused by particle rolling, while the number of sliding particles increases during the failure softening stage. After compression, the normal contact force of the specimen particles shows significant anisotropy, the tangential contact force is evenly distributed, and the normal contact force plays a dominant role in bearing the deviator stress. [Conclusion] The discrete-continuous coupling model can effectively simulate the micro-mechanical behavior of sand in triaxial tests. The model takes into account the deviation of test conditions caused by the traditional coupling algorithm and solves the problem of difficultly accurately simulating test conditions in the traditional coupling algorithm by correcting the equilibrium conditions of discrete elements and the overall coupling system, achieving a more realistic and accurate characterization of the micro-mechanical characteristics of sand at the particle scale, providing a new perspective and a more solid theoretical support for in-depth understanding of the macro and micro mechanical behaviors of sand and related engineering applications.

[Objective] To predict the disaster scope of reservoir landslide-induced surges, the generation of initial maximum wave amplitude, and the propagation attenuation patterns accurately, thereby enhancing the prevention and control capabilities of surge disasters in mountainous river channels, [Methods]based on mountainous river channel characteristics, three-dimensional physical model experiments for block and granular landslide surges were designed. Through orthogonal experiments and multivariate nonlinear regression analysis, empirical formulas for the initial maximum wave amplitude in the sliding direction and upstream/downstream directions, as well as a propagation attenuation model, were developed. The model accuracy was validated using typical cases such as the Xintan landslide, Tangyanguang landslide, Qianjiangping landslide, and Gongjiafang landslide. [Results] The geometric characteristics of sliding bodies(relative thickness power exponent: 0.94) most significantly influenced the initial maximum wave amplitude of block landslides, while the Froude number(power exponent: 0.83) dominated granular landslide surges. The attenuation rate of maximum wave amplitude decreased exponentially with propagation distance, with the Froude number(power exponent: 0.34) playing a critical role. The model achieved a prediction error of <20% in low-speed scenarios(<30 m/s) and wide river channels, significantly outperforming traditional method, though errors increased to 29% in narrow channels. [Conclusion] The proposed model effectively predicts multidirectional initial surge characteristics, providing theoretical support for refined early warning of reservoir landslide surges in mountainous areas. Future work should integrate numerical simulations to optimize applicability in complex terrains.

[Objective] To investigate the strength softening and recovery mechanisms of silty clay under cyclic wetting-drying actions and clarify the impact mechanisms of multiple rainfall events on soil strength degradation and slope deformation, [Methods] The strength change characteristics of silty clay in the process of water-soaking and air-drying were investigated through the cyclic soaking and softening test, and the strength recovery law in the stage of air-drying was investigated; combined with the monitoring data of the rainfall and deformation of a slope of a clayey soil in Guangxi, the effect mechanism of multiple rainfalls on the response of slope deformation was verified; the dynamic prediction of slope stability was realized through the construction of a function model and the refinement of parameter assignment method. [Results] The result show that:(1) Silty clay exhibits significant cyclic wetting-induced softening effects. With increasing wetting-drying cycles, the initial cohesion decreases by over 79%, while the initial internal friction angle declines by more than 47%. The stabilization time for cohesion and internal friction angle during re-wetting shortens to 3.6%~10.9% of the original duration.(2) Strength recovery during drying displays a three-phase characteristic: in the initial phase(<1 d), cohesion and internal friction angle decrease slowly by 25.6% and 5.4%, respectively; during the intermediate phase(1~5 d), cohesion increases at 0.13 kPa/h and internal friction angle recovers at 0.08 kPa/h; in the late phase(>5 d), cohesion growth rate decelerates to 0.03 kPa/h while internal friction angle fully recovers to natural state.(3) Slope deformation response time follows an exponential decay pattern with rainfall frequency, showing 56% shorter lag time after the third rainfall compared to initial events, which strongly correlates with laboratory-observed strength degradation.(4) The proposed damage accumulation function model with dynamic parameter calibration predicts critical rainfall cycles(N=8±1) for slope instability, achieving less than 10% error compared to actual failure cases. [Conclusion] The research findings reveal the strength evolution mechanism of silty clay under cyclic wetting-drying processes and establishes a quantitative correlation model integrating rainfall frequency, strength degradation, and slope deformation. The dynamic prediction framework provides quantifiable theoretical criteria for emergency early-warning of rainfall-induced landslides, offering significant engineering value for disaster prevention systems in cohesive soil slopes.