[Objective] Slope failure theory is the fundamental basis for safety assessments of earth-rock dams, embankments, and slope engineering projects. Most existing slope analysis methods focus on single processes and struggle to adequately characterize slope deformation, failure characteristics, and their evolution under the coupling of multiple processes such as loading, moisture variation, and rheological effects. Moreover, conventional failure analyses often rely on stress-based failure criteria, limiting their ability to analyze the slope failure process and to reveal the underlying failure mechanisms. Commonly used engineering methods, such as the limit equilibrium method, have difficulty properly accounting for the coupling mechanism between slope deformation and failure, and their instability criteria often rely heavily on empirical judgment. Therefore, there is an urgent need to reveal the deformation-failure coupling mechanism of slopes under multi-process conditions and to establish a mechanical model for progressive slope failure. [Methods] This study proposed a novel research approach of “integrated analysis of the deformation and failure process”, which used measurable deformation to quantitatively track and describe the failure process, in combination with multi-factor testing and multi-perspective analysis. To this end, centrifugal model testing and measurement techniques for slope multi-processes were developed. These techniques could effectively simulate various loads, environmental changes, and engineering scenarios, while enabling full-field, whole-process measurement of slope deformation. Based on experimental observations, the slope failure process was quantitatively determined, and the progressive failure characteristics of slopes, along with the influence of loading conditions, were investigated. Under various test conditions, the deformation-failure coupling mechanism of slopes and its influencing factors were revealed, and the applicability of this mechanism was discussed. By introducing a coupled macro-micro integrated model for load-water-time effects and the slope deformation-failure coupling mechanism, three major mechanical equations were formulated, and an integrated analysis method for slope deformation and stability was developed. New equipment, independently developed on a centrifugal model testing platform, was used to simulate various loads, environmental changes, and engineering scenarios. A high-quality image-based displacement measurement system for the centrifugal field was developed, achieving multi-factor coupling simulation and measurable deformation. [Results] Slope failure was progressive and its evolution primarily depended on loading conditions. Changes in factors such as loading, water, and time induced localization near the potential failure surface of the slope, forming a “localization zone” that comprehensively reflected the main characteristics of slope deformation-failure behavior. The evolution of this localization zone reflected the coupling mechanism between the slope deformation localization process and the failure surface formation process. The increasing degree of localization development led to local failure within the zone, which subsequently exacerbated the degree of localization in the surrounding slope. The potential failure surface could represent this localization zone and exhibited a displacement coordination rule. Regardless of whether it was before, during, or after slope failure, the relative horizontal displacement of the soil masses on either side of the potential failure surface was independent of their spatial position. [Conclusion] Practical applications were conducted on typical projects including reservoir slopes and mining slopes. Slope displacement monitoring data obtained by the Global Navigation Satellite System were used for parameter inversion analysis, and the optimized parameters were then applied to calculate the slope response. The predicted slope displacement shows consistency with the monitored slope displacement, verifying the effectiveness of the proposed method. Furthermore, a practical slope failure case was analyzed using the proposed method. The slope stability safety factor was calculated. The results show that the slope stability gradually decreases and ultimately reaches a value lower than 1.0, which indicates that slope failure has occurred. Further analysis shows that the predicted failure time is in good agreement with the actual failure time. The findings demonstrate that the integrated deformation-stability analysis method can uniformly calculate slope deformation and stability. It effectively computes the entire process of slope deformation from small strains to post-failure, as well as the evolution of the stability safety factor. This method addresses the challenge of scientifically predicting slope stability based on deformation monitoring.
[Objective] This study aims to scientifically recognize and evaluate the equilibrium of domestic, ecological, and production water use in Yangtze River Basin from the perspectives of water and soil spatial matching and differences in per capita water use. [Methods] The Gini coefficient and Lorenz asymmetry coefficient were used to analyze the disequilibrium of water use and its sources. Furthermore, the matching degree index was used to analyze the matching degree between water use, regional area, and population. [Results] The water usage per unit area in Yangtze River Basin was 92.7 mm, and the per capita water use was 1 194.0 L/d. Among these, production water use was the highest, followed by domestic water use, while ecological water replenishment was the lowest. Analysis based on water use per unit area and per capita water use showed that, overall, water use was higher in the eastern region, followed by the central region, and lower in the western region. Based on the administrative divisions, Yangtze River Basin was divided into 18 sub-regions according to provincial administrative boundaries. The Gini coefficients and Lorenz asymmetry coefficients for domestic, ecological, production, and total water use in Yangtze River Basin were calculated from the perspectives of water and soil spatial matching and differences in per capita water use. The Gini coefficients for the spatial distribution of domestic, ecological, production, and total water use in Yangtze River Basin were 0.42, 0.53, 0.51, and 0.49, respectively. The Gini coefficients for per capita water use were 0.10, 0.37, 0.25, and 0.21, respectively. Further analysis using matching degree index to evaluate the matching degree between water use, regional area, and population revealed that the matching degrees for domestic, ecological, production, and total water use with regional area were 0.83, 0.80, 0.81, and 0.81, respectively, and with population were 0.97, 0.90, 0.92, and 0.93, respectively. [Conclusion] Differences in water use are constrained by the inherent endowment of water resources, and the uneven spatial distribution of water resources directly leads to the disequilibrium in water use. The spatial distribution of domestic, ecological, production, and total water use in Yangtze River Basin exhibits disequilibrium, while per capita water use is relatively balanced, with a high degree of matching between water use, regional area, and population. Water resource management must balance “people-oriented” and “spatial equity” principles, coordinating domestic, ecological, and production water use through technological advancements and institutional innovations to reduce disparities in water use per unit area and per capita water use. The research findings can provide important support for the rational utilization of water resources and the realization of human-water harmony.
[Objective] This paper aims to reveal the hydrological evolution patterns of transboundary rivers on the western Yunnan Plateau (the Lancang River, Nu River, and Irrawaddy River) during 1956-2016, to quantify the spatial differentiation characteristics of changes in water resources in the three major river systems, and to establish a water quantity prediction method based on multi-scale periodic analysis. [Methods] Based on precipitation and runoff data of the three major river systems in Southwest China from 1956 to 2016, the Mann-Kendall trend test method was used to analyze the long-term variation trends of hydrological elements. The Morlet wavelet analysis method was applied to identify the multi-scale periodic characteristics of hydrological sequences, and the phase extrapolation method was employed to predict future water quantity variation trends. [Results] The water yield modulus of the study area reached 78.83×104 m3/km2; however, all three river systems exhibited significant decreasing trends. Among them, the attenuation rate of the Irrawaddy River (-0.175×108 m3/a) was significantly higher than that of the Lancang River (-0.024×108 m3/a). A dominant 24-year hydrological variation period was identified at the regional scale, and the year 2016 was located at the end of the low-frequency phase of this cycle. Combined with phase extrapolation, the results indicated that future water quantity may continue to remain relatively low. The Lancang River exhibited secondary periodic oscillations of 7-12 years, which differed from the single dominant periodic pattern observed in the Nu River and the Irrawaddy River, revealing the hydrological response heterogeneity of the Lancang River caused by its specific underlying surface conditions. Precipitation showed a significant correlation with water resources (R2>0.75); however, asynchronous characteristics were observed in the Lancang River due to its specific underlying surface conditions. [Conclusion] This study systematically quantifies the spatial differentiation characteristics of hydrological evolution in the Lancang River, Nu River, and Irrawaddy River systems, establishes a water quantity prediction method based on multi-scale periodic analysis, and further reveals the secondary periodic oscillation characteristics of the Lancang River and its differences from the Nu River and Irrawaddy River, providing new scientific evidence for transboundary river water resources management in Southwest China. The results indicate that water resources of transboundary rivers on the western Yunnan Plateau may show a persistently low trend in the future, highlighting the need to strengthen transboundary water resources coordination and to formulate adaptive water resources allocation strategies.
[Objective] This study aims to address the issues of uneven spatiotemporal distribution of water resources and the difficulty in developing integrated urban-rural water supply in mountainous cities. Based on the connotation of integrated urban-rural water supply and the characteristics of its different development modes, this study innovatively constructs a coupling coordination evaluation indicator system and a zoning model for integrated urban-rural water supply. Taking the typical mountainous city of Chongqing as a case study, water supply zoning patterns with distinct regional characteristics are identified, and differentiated development schemes for urban-rural water supply are proposed. [Methods] Eight indicators were selected from three dimensions—current status of rural water supply engineering systems, natural geographical conditions, and socio-economic development. An “engineering-natural-economic” coupling coordination evaluation indicator system for integrated urban-rural water supply was constructed, and the Delphi method was used to determine the indicator weights. Considering the mutual constraints and synergistic effects among the three subsystems, a coupling zoning model for integrated urban-rural water supply was constructed. [Results] (1) The coupling coordination degree of each district and county ranged from 0.245 to 0.877. The coupling coordination degree intervals for the urban pipeline extension mode, regional pipeline interconnection mode, regional integrated block mode, and single-village upgraded point mode were [0.8, 1], [0.75, 0.80), [0.60, 0.75), and (0, 0.60), respectively. (2) All eight districts and counties under the urban pipeline extension mode were located in the main metropolitan area. These areas had relatively flat terrain and high population density, which was conducive to the construction of large-scale water supply projects and pipeline networks. Eight districts and counties under the regional pipeline interconnection mode were mostly located in the main metropolitan area, with a small number in the Three Gorges Reservoir area of northeastern Chongqing. These areas had abundant but unevenly distributed water resources. Interconnection of regional main water supply pipelines could achieve regional water resource complementarity and pipeline network connectivity. Five districts and counties under the regional integrated block mode were distributed in the main metropolitan area and the Three Gorges Reservoir area of northeastern Chongqing. In northeastern Chongqing, small reservoirs and ponds served as the main water sources, and the scale of water supply projects was small but had integration potential. Integrating surrounding small water supply projects could enhance regional water supply security. Thirteen districts and counties under the single-village upgraded point mode were mainly located in the Three Gorges Reservoir area of northeastern Chongqing and the Wuling Mountain area of southeastern Chongqing. Due to the large terrain relief in mountainous areas, water supply projects were significantly constrained by terrain. Rural areas were remote with dispersed population, making it difficult for large-scale water supply to cover them. This mode was suitable for point-based water supply targeting individual villages. [Conclusion] (1) Four development modes suitable for integrated urban-rural water supply in Chongqing City are proposed, namely the urban pipeline extension mode, regional pipeline interconnection mode, regional integrated block mode, and single-village upgraded point mode. (2) According to the zoning results, the urban pipeline extension mode relies on its high urbanization rate to achieve full water supply coverage. The regional pipeline interconnection mode addresses elevation difference issues through interconnected pipeline networks, the regional integrated block mode forms intensive water supply units by integrating small water sources, and the single-village upgraded point mode solves drinking water problems in areas with complex terrain through decentralized water supply. The research findings provide technical support for the construction of integrated urban-rural water supply in Chongqing City and are of significant importance for ensuring regional water supply security and promoting the high-quality development of the Chengdu-Chongqing Twin-City Economic Circle.
[Objective] This study aims to develop a comprehensive diagnostic method for evaluating the water balance status across water resources, ecosystems, and socio-economic systems in the context of large-scale water management projects. The focus is on the potential water source areas of the West Route of South-to-North Water Diversion Project, analyzing the interactions between natural water balances, socio-economic demands, and ecological considerations. [Methods] The research centered on quantifying and assessing the coordination and sustainability of these systems in the West Route’s water source region from 2005 to 2020. An analytical framework based on the principles of water balance was constructed, incorporating four key components: natural water supply and demand, socio-economic water needs, ecological water consumption, and the competition between ecological and socio-economic systems within the river basin. This framework was used to quantify the water balance status by evaluating water availability, ecological functioning, and socio-economic demands over the study period. Statistical methods and multidimensional analysis were applied to calculate the coupling coordination degree, which measures the extent of coordination between water resource management, ecological protection, and socio-economic development. The study relied on regional hydrological records, socio-economic data, and ecological assessments to ensure robust and reliable results. [Results] From 2005 to 2020, the water balance of the West Route’s water source areas remained relatively stable. Importantly, the region maintained a steady equilibrium in water resources, with significant improvements in the coordination between water resources, socio-economic development, and ecological systems. The coupling coordination degree among these three systems showed a clear upward trend, reflecting the growing harmony between water management, ecological conservation, and socio-economic growth. The research highlighted that the ecological system within the water source areas effectively adapted to changes in water availability, demonstrating resilience in sustaining water use. Moreover, there was a substantial positive synergy between water resource management and ecological protection, which contributed to the stability and improvement of the regional water balance. Additionally, the study showed that the competition between ecological and socio-economic water demands became more balanced, shifting toward a more integrated approach. The region’s ecological protection strategies became better aligned with water resource management policies, resulting in improved sustainability in both ecological and economic terms. [Conclusion] The findings suggest that enhanced water use efficiency, combined with adaptive ecological protection measures, has played a pivotal role in achieving these positive trends. The study’s innovative approach—integrating natural water balance, socio-economic factors, and ecological needs—provides a comprehensive framework for evaluating the sustainability of water resources in large-scale inter-basin water diversion projects. The findings demonstrate that coupling water resource management with ecological protection is not only feasible but essential for ensuring the long-term sustainability of water source areas. In conclusion, this study underscores the importance of adopting an integrated approach to water resource management, one that recognizes the interdependencies between natural, economic, and ecological systems. The research highlights that coordinated water management, paired with adaptive ecological conservation strategies, is critical to achieving sustainable development and ensuring the resilience of water source areas in large-scale water transfer projects. Furthermore, the study suggests that such integrated management models can serve as a blueprint for other regions facing similar water resource and environmental challenges, ultimately supporting the global pursuit of water sustainability.
[Objective] The time series of reservoir water quality indices,especially dissolved oxygen content, exhibit strong nonlinearity,high complexity,and uncertainty,which lead to insufficient accuracy of single prediction models.This study aims to construct a high-precision hybrid prediction model that integrates time series decomposition,intelligent optimization,and residual correction,thereby significantly improving the prediction accuracy of dissolved oxygen (DO) content and providing reliable support for water environment management and pollution early warning. [Methods] The core procedures of the proposed hybrid prediction model are as follows. 1) Data decomposition and reconstruction. Singular spectrum analysis (SSA) was applied to decompose the dissolved oxygen time series, and the series was reconstructed into trend components, periodic components, and residual components to reduce sequence complexity and highlight features at different frequencies. 2) An improved dung beetle optimizer (IDBO) which integrates piecewise chaotic mapping and opposition-based learning strategies was designed to enhance population diversity and initialization quality. The improved IDBO was used to optimize key hyperparameters of the GRU network, including the number of hidden layer neurons and the initial learning rate. 3) Component prediction and residual correction. The GRU model optimized by IDBO was used to predict the trend component and periodic components separately. A residual series prediction difference correction method (DCM) was proposed. The residual component was first predicted using GRU, and the difference sequence between the predicted values and the observed values was calculated. Variational mode decomposition (VMD) was then applied to the difference sequence to fully extract high-frequency detail information. Each decomposed component was predicted using GRU and aggregated to obtain the predicted difference values. Finally, the predicted differences were compensated into the initial residual prediction to obtain the corrected residual prediction results. 4) Model integration and validation. The prediction results of the three components were aggregated to obtain the final DO prediction values. Measured dissolved oxygen data from Daheiting Reservoir in Tangshan, Hebei Province were used for experiments. The dataset contained 2352 records with a sampling interval of four hours. Root mean square error (RMSE), mean absolute error (MAE), mean relative error (MRE), and the coefficient of determination (R2) were used as evaluation metrics. The proposed model was compared with GRU, SSA-GRU, SSA-DBO-GRU, SSA-IDBO-GRU, and models reported in the literature such as LSTM and PSO-GRU. [Results] The proposed SSA-IDBO-GRU-DCM hybrid model achieved the best performance among all comparative models. The prediction errors were significantly reduced, with an RMSE of 0.580 2 mg/L, an MAE of 0.329 2 mg/L, an MRE of 0.0269, and an R2 of 0.918 8. Ablation experiments confirmed that the proposed IDBO improvement strategies effectively enhanced hyperparameter optimization accuracy. The residual difference correction method (DCM) significantly improved the prediction performance of the residual component and was the key factor contributing to the overall accuracy improvement. These results fully demonstrated the effectiveness and superiority of the “decomposition-optimization-correction” framework. [Conclusion] SSA effectively decouples the complex characteristics of water quality time series. IDBO efficiently and accurately optimizes GRU hyperparameters. The proposed VMD-GRU-based residual difference correction method (DCM) is the key innovation for improving overall prediction accuracy. The proposed model significantly improves the prediction accuracy of dissolved oxygen content and provides an efficient and reliable new approach for reservoir dissolved oxygen prediction. Future work can extend this framework to the prediction of other key water quality parameters such as ammonia nitrogen and total phosphorus, and further explore the integration of natural evolutionary strategies to improve computational efficiency and generalization ability.
[Objective] Microplastics are widely present in reservoirs across China, posing threats to water quality safety and the stability of reservoir ecological functions. Accurately assessing the current status of microplastic pollution in China’s reservoirs, analyzing their migration patterns and environmental behavior, and scientifically evaluating the associated ecological risks are essential prerequisites for implementing effective management and control measures. [Methods] This study systematically reviewed recent data on microplastic pollution in China’s reservoirs, summarized the impact of reservoir operation on microplastic transport behaviors, analyzed associated ecological and health risks, and proposed feasible prevention and control strategies based on current plastic restriction policies. [Results] 1) Research on microplastic pollution in China’s reservoirs primarily focused on the Yangtze River and its tributaries, followed by the Xiaolangdi Reservoir on the Yellow River, the Erdaozha Reservoir on the Haihe River, and the cascade reservoirs in the Shaying River Basin. 2) Field investigations revealed that the abundance of microplastics in the Jiayan Reservoir was relatively high, with water column microplastic abundance ranging from approximately 11 000 to 61 700 particles/m3 and sediment microplastic abundance ranging from 2 600 to 15 700 particles/kg. The Three Gorges Reservoir received considerable attention regarding its microplastic pollution status, with water column microplastic abundance ranging from 800 to 6 214 particles/m3 and sediment microplastic abundance ranging from 1 031 to 63 081 particles/kg. The Guanyinyan Reservoir on the Jinsha River and the cascade reservoirs in the middle and lower reaches of the Hanjiang River exhibited a relatively moderate level of microplastic abundance, while other reservoirs showed comparatively lower levels. 3) A diverse range of microplastic types was detected in reservoirs, predominantly smaller than 1 mm. Microplastic shapes included fibers, fragments, films, and microbeads. The primary polymer types identified were polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), polystyrene (PS), polyamide (PA), and polyvinyl chloride (PVC). 4) In terms of microplastic origin, secondary microplastics constituted the majority in reservoirs, mainly derived from plastic waste associated with daily life, fishing and shipping, agricultural irrigation, and tourism activities. The primary sources of microplastics in reservoirs were upstream areas and tributary inflows. Additionally, rainfall and agricultural irrigation facilitated the transport of land-based microplastics into reservoir waters via surface runoff, while atmospheric deposition contributed to the settling of microplastics from the air into reservoir water bodies. [Conclusion] Reservoirs in China are generally polluted by microplastics, and diverse microplastic types pose potential threats to the ecological environment. Reservoir operations significantly affect the environmental behavior and transport of microplastics through dam interception and changes in hydrological and hydrodynamic conditions, indirectly influencing the ecological and environmental effects of microplastics. Currently, effective prevention and control measures for microplastic pollution in reservoirs are insufficient and face significant challenges. We recommend to strengthen the monitoring of microplastic pollution in reservoirs and to develop prevention, control, and removal technologies to alleviate microplastic pollution in reservoirs and ensure the health of reservoir ecosystems.
[Objective] This study focuses on the practical demand for advanced nitrogen and phosphorus removal from the tail water of urban wastewater treatment plants. Aiming at the problem of low carbon-to-nitrogen ratios in urban wastewater treatment that result in unsatisfactory nitrogen removal efficiency, this study investigates the effects of different combinations of emergent plants and composite substrates on nitrogen and phosphorus removal from tail water through experiments. The application potential of natural manganese sand as a substrate is evaluated, providing theoretical and practical support for the optimization of constructed wetland technology and the resource utilization of manganese ore. [Methods] Three emergent plants, Acorus calamus L., Iris wilsonii C. H. Wright, and Scirpus validus Vahl were selected. Three experimental groups were established based on pairwise plant combinations, including Gp1 (Iris wilsonii C. H. Wright + Scirpus validus Vahl), Gp2 (Iris wilsonii C. H. Wright + Acorus calamus L.), and Gp3 (Scirpus validus Vahl + Acorus calamus L.). A composite substrate without plants was used as the blank control group (BC). The composite substrate consisted of natural manganese sand, zeolite, and ceramsite mixed at a ratio of 1∶3∶1. Constructed wetland systems were built using transparent polyethylene cylindrical columns with a height of 500 mm and a diameter of 160 mm to simulate the tail water treatment process of wastewater treatment plants. The experiment lasted for 70 days. During the experimental period, water quality indicators including total nitrogen, total phosphorus, ammonia nitrogen, and nitrate nitrogen were measured regularly. High-throughput sequencing was used to analyze the structure of microbial communities in plant root zones. [Results] All three plant combinations effectively removed nitrogen and phosphorus pollutants from the tail water, and the Gp3 group (Scirpus validus Vahl + Acorus calamus L.) showed the best performance. The total phosphorus removal rate reached 93.2%, the total nitrogen removal rate was 77.7%, the ammonia nitrogen removal rate was 91.7%, and the nitrate nitrogen removal rate was 70.6%. Pollutant concentrations in all experimental groups decreased rapidly during the first 30 days and then tended to stabilize, while the purification performance of the blank control group was significantly poorer. Microbial community analysis showed that the Gp3 group exhibited the highest microbial diversity and richness, with a Shannon index of 7.24 and unique OTUs accounting for 69.15%. The dominant phyla were Proteobacteria and Bacteroidetes, which together accounted for nearly 80%. Among them, Gammaproteobacteria played a key role in the denitrification process, and its relative abundance in the Gp3 group reached 29.2%, which was the highest among the three groups. [Conclusion] The synergistic effects of plant combinations and root-associated microbial communities in constructed wetlands are the key to efficient nitrogen and phosphorus removal, and the combination of Scirpus validus Vahl and Acorus calamus L.performs particularly well in advanced tail water treatment. The composite substrate containing manganese sand shows potential application value, while the specific mechanisms by which it promotes plant growth and microbial community formation still require further investigation. This study confirms the optimal purification performance of the Scirpus validus Vahl and Acorus calamus L. combination and the potential application value of manganese sand as a substrate, providing a reference for plant selection and targeted microbial cultivation in constructed wetlands for wastewater treatment plant tail water.
[Objective] As the core water source of the middle route of the South-to-North Water Transfer Project, the spatiotemporal distribution of water temperature in Danjiangkou Reservoir directly affects the aquatic ecological processes and water quality evolution within the reservoir area. This study aims to clarify the spatiotemporal distribution patterns of water temperature in Danjiangkou Reservoir through prototype observations across the entire reservoir, to identify thermal stratification types, and to reveal the factors influencing differences in thermal structure between the Danjiang Reservoir and the Hanjiang Reservoir, thereby providing a scientific basis for reservoir water quality management, ecological protection, and so on. [Methods] In 2023, prototype observations of water temperature were carried out in Danjiangkou Reservoir during four typical hydrological periods, including the dry season (February), the normal flow season (June), and the flood season (September and October). A total of 16 observation sections were deployed throughout the entire reservoir, including one section in front of the dam, seven along the mainstream of the Hanjiang River, and eight along the mainstream of the Danjiang River. Based on the observation data, multiple discriminant methods such as water residence time (Tr), runoff-storage capacity ratio (α), reservoir width-depth ratio (R), and densimetric Froude number (Fr) were comprehensively applied to systematically analyze the thermal stratification structure of the reservoir and its spatiotemporal evolution characteristics, and to further explore the influence mechanisms of meteorological, hydrological, and topographic factors on thermal stratification. [Results] (1) The vertical thermal stratification structure of Danjiangkou Reservoir exhibited a significant seasonal variation pattern: during the dry season (February), the water body was well mixed with no obvious stratification. During the normal flow season (June), stable stratification formed, and increased air temperature and enhanced inflow strengthened vertical mixing of the water body, resulting in a double-thermocline type vertical water temperature structure in the Han Reservoir, with a surface-to-bottom temperature difference of approximately 20 ℃. During the flood seasons (September-October), the thermocline deepened, and thermal stratification was the most stable and exhibited greater thickness. (2) The reservoir’s surface water temperature was highly correlated with air temperature (R2=0.976), whereas variations in middle and bottom water temperatures exhibited a lag, regulated by heat transfer within the water body and hydrological processes. (3) The Dan Reservoir and the Han Reservoir exhibited significantly different hydrological and hydrothermal characteristics. The Han Reservoir had a shorter water residence time (257 days), a larger runoff-storage capacity ratio (α=1.47), and stronger hydrodynamic forcing, exhibiting characteristics of a riverine reservoir. Its thermocline was mainly controlled by inflow dynamics, with isotherms showing an inclined pattern. The Dan Reservoir had a longer water residence time (336 days), a smaller runoff-storage capacity ratio (α=1.04), and slower water flow conditions, showing characteristics of a lacustrine reservoir. Its thermocline was primarily controlled by solar radiation and meteorological conditions, with more horizontally distributed isotherms and a more stable and persistent stratification structure. (4) Operation of the intake in front of the dam had an impact on the local thermal structure, and clustering of isotherms was observed at depths near the intake. [Conclusion] Through systematic prototype observations, this study comprehensively reveals the complex spatiotemporal thermal stratification structure of Danjiangkou Reservoir, particularly confirming the existence of a double thermocline during the normal flow season and the essential differences in stratification mechanisms between the Dan Reservoir and the Han Reservoir. This study innovatively demonstrates that two thermal stratification modes, lacustrine (Danjiang Reservoir) and riverine (Hanjiang Reservoir), coexist within the Danjiangkou Reservoir, providing an important foundation for understanding migration and transformation of nitrogen and phosphorus, algal growth, and seasonal water quality changes in the reservoir area.
[Objective] Rural ditches are major pathways through which agricultural nitrogen and phosphorus pollutants enter surface waters. Ditch ecological landscape systems typically consist of multiple interconnected units, including buffer zones, constructed wetlands, and ecological ponds. The overall spatial allocation of these systems critically determines their performance. This study addresses this issue by developing a methodological framework for optimizing the spatial allocation of ditch ecological units in plain regions, thereby overcoming subjectivity and the lack of theoretical and data-driven approaches in traditional designs. [Methods] Representative rural ditches in the Chezhegou watershed of the Huaibei Plain were selected for the spatial optimization of ecological units. A coupled modeling framework was developed in MATLAB, integrating a spatial optimization model of rural ditch ecological units with pollutant proxy functions. The computational procedure involved three key steps: (1) spatial parameters of suitable construction areas for ecological units at each node were input together with hydrological and water quality data under rainfall scenarios; (2) proxy functions were developed using multiple linear regression based on simulation data from 13 ecological units; and (3) a cost-constrained optimization model was developed to maximize pollutant removal efficiency under practical budget limitations. Using TN and TP as key performance indicators, the model aimed to optimize multiple pollutant reduction in rural ditch systems while satisfying prescribed cost constraints. Optimization was conducted using a bi-level particle swarm optimization (BPSO) algorithm to obtain the optimal allocation solution. [Results] (1) Implementation of ecological landscape systems effectively reduced the total pollutant load within rural ditch systems. Although higher construction costs improved pollutant removal efficiency, diminishing marginal returns on investment were observed. Specifically, the incremental improvement in purification efficiency per unit investment decreased progressively with additional spending.(2) Comprehensive analysis under different budget scenarios indicated that buffer zones B and C, together with wetlands D, C, G, and E, achieved superior pollutant reduction performance in the Huaibei Plain, providing valuable guidance for future rural ditch management strategies.(3) This study proposed a novel optimization framework for the spatial allocation of rural ditch ecological units. By integrating optimization algorithms with proxy functions, the framework reduces the subjectivity and empirical limitations of traditional design approaches. The method improved the scientific rigor of spatial allocation schemes and enhanced pollutant removal efficiency across multiple scenarios, demonstrating its feasibility and effectiveness. [Conclusion] The effectiveness of integrating the BPSO algorithm with proxy functions for optimizing the spatial allocation of ditch ecological units is demonstrated. This approach overcomes the limitations of previous designs, including subjectivity and limited theoretical and data support. Nevertheless, several challenges remain, including (1) high data demands, as the model requires extensive preprocessing and detailed input parameters for the target area; (2) uncertainty-related limitations, since simplifications are still necessary to accommodate uncertainties in pollutant removal simulations and surface runoff dynamics in plain regions; and (3) scalability constraints, as large-scale applications may encounter data scarcity and computational challenges due to the extensive and complex nature of rural landscapes. Future research should prioritize the development of high-resolution terrain and land-use databases tailored to rural environments, aim to streamline data requirements for the ecological unit spatial allocation module, and enhance the computational efficiency and generalizability of the optimization framework.
[Objective] This study aims to conduct a scientific and objective dynamic assessment of ecological quality in megacities to monitor the spatiotemporal changes and to analyze the effects of land use transition on ecological quality, thereby providing insights and recommendations for addressing the safety and ecological issues arising from spatial expansion and spatial factor aggregation in megacities. [Methods] We selected the urban area of Wuhan, Hubei Province, which was newly designated as a megacity in 2022, as the research subject. First, we collected Landsat remote sensing images, digital elevation model (DEM), land use data, and other required datasets from reliable online scientific repositories. Subsequently, the remote sensing ecological index (RSEI) method was applied to systematically process and analyze the remote sensing images to extract the spatiotemporal dynamics of urban ecological quality. Second, Moran’s I was used to perform spatial autocorrelation analysis of the RSEI results to quantify the spatial dependence and clustering characteristics of ecological environment changes, enabling the identification of hotspots and coldspots of ecological quality changes. Finally, ecological quality changes were spatially coupled with land use change data using spatial overlay analysis and statistical correlation methods to derive the quantitative relationship between spatiotemporal changes in ecological quality and land use transition processes. [Results] (1) During the study period, Wuhan’s overall ecological quality exhibited a fluctuating upward trend, with the mean value increasing from 0.57 in 2014 to 0.63 in 2023. The improvement was most pronounced from 2014 to 2017, when the mean RSEI rose from 0.57 to 0.64. (2) Moran’s I for Wuhan’s ecological quality was 0.32, and the “high-high” clusters in the local spatial autocorrelation analysis exhibited spatial continuity, indicating that the ecological quality of Wuhan showed a pronounced spatial clustering pattern. (3) Ecological degradation was mainly concentrated on the periphery of the central urban area, indicating that construction expansion in Wuhan contributed to an overall decline in ecological quality. Meanwhile, ecological quality improved along the shorelines at the confluence of the Yangtze River and the Han River and around wetlands such as East Lake and Liangzi Lake, demonstrating the effectiveness of Wuhan’s ecological restoration initiatives. (4) Analysis of ecological quality changes across land use types further showed that disparities within Wuhan’s built environment widened during the study period. Specifically, the gap in ecological quality between construction land and cultivated land increased from 0.34 in 2014 to 0.38 in 2023, suggesting that the ecological cost of converting cultivated land to construction land increased. [Conclusion] (1) Wuhan’s riverbank and wetland restoration activities have a significant positive impact on ecological quality improvement. Therefore, future efforts should continue to promote ecological governance initiatives such as landscape enhancement in urban renewal areas, riverbank protection, and wetland conservation. (2) In subsequent ecological governance, Wuhan should, while following socioeconomic development, consider the spatial agglomeration characteristics of regional ecological quality changes and adopt region-specific measures for hotspots with sharp ecological degradation, such as appropriate artificial restoration and landscape enhancement. (3) From the perspective of ecological quality advancement, Wuhan, as a megacity, should place greater emphasis on intensive urban development by slowing its expansion pace in line with socioeconomic needs and promoting the ecological renewal of existing urban built-up spaces to improve the ecological quality of human settlements. (4) The data indicate a significant ecological quality gap between cultivated land, forest land, and other ecological spaces and construction land. Therefore, Wuhan should strengthen the supervision and protection of cultivated land and forest land during urban construction and development to mitigate substantial ecological losses arising from land transition.
[Objective] To address the lack of carbon footprint accounting and insufficient multi-objective synergy in evaluating existing gray-green infrastructure in Sponge Cities, this study proposes a game theory-based method for life-cycle synergistic optimization evaluation of water-carbon-economic performance. [Methods] By analyzing the synergistic relationships among water environment improvement, carbon emission reduction, and economic cost over the life cycle of gray-green infrastructure, a three-dimensional (3D) indicator system—“water environment-carbon reduction-economic cost”—was developed. This system integrated key indicators such as runoff reduction rate, pollutant removal rate, life-cycle carbon emissions, and economic cost. The entropy weighting method and the analytic hierarchy process (AHP) were integrated with a game theory model to optimize indicator weights based on multi-source weighting and multi-criteria decision-making theory. The Nash equilibrium was applied to balance conflicting objectives, and the TOPSIS method was employed for the comprehensive evaluation of multiple schemes. [Results] The main campus of Hebei University of Water Resources and Electric Engineering was selected as a case study, with seven gray-green infrastructure combination schemes designed. The results indicated that Scheme 5 (a combination of storage tank, sunken green space, and rain barrel) achieved effective runoff reduction, pollutant removal rates above 48%, low economic cost, and a significant carbon sink effect, demonstrating the best overall performance. The subsequent ranking of schemes was: Scheme 3, Scheme 7, Scheme 6, Scheme 1, Scheme 4, and Scheme 2. Sensitivity analysis confirmed that Scheme 5 exhibited good stability. [Conclusion] Case study indicates that, in the game theory-based comprehensive weighting model, the carbon emission indicator carries the highest weight. This highlights the critical importance of advancing low-carbon development goals within the current decision-making framework. Concurrently, the study reveals a significant divergence in the weighting of the life-cycle cost indicator between subjective and objective weighting methods. This reflects inherent differences arising from distinct evaluation perspectives—namely, expert judgment versus quantitative data. Notably, the advantage of the game theory model lies in its ability to integrate and balance the contributions of these two methods through an equilibrium optimization mechanism, thereby effectively mitigating potential systemic biases inherent in single weighting methods. Importantly, water environment indicators, such as runoff reduction rate and pollutant removal rate, play an essential “bottom-line” role within the entire evaluation system. In pursuing low-carbon goals, these critical water environment performance indicators cannot be compromised, and the core requirements for water environment management must be strictly maintained. This research addresses the limitations of traditional methods that overemphasize technology at the expense of synergy, providing methodological support for transforming and upgrading Sponge Cities from “engineering compliance” to achieving “synergistic benefits in water-carbon-economic performance”. It provides both theoretical foundations and practical pathways for promoting low-carbon development of Sponge Cities and facilitating their synergy with the “dual carbon” goals (carbon peaking and carbon neutrality).
[Objective] Shared approach channels were formed during the reconstruction and expansion of ship locks due to limited spatial conditions. This study focuses on the complex unsteady flow induced by water discharge from multi-line ship locks and its impact on navigation safety. Taking the double-line ship locks of the Sanjiang approach channel at the Gezhouba Project as the research object, this study systematically investigates the superposition patterns of flow fluctuations and flow velocity variations within the shared approach channel under different water discharge combinations using a mathematical model. The objective is to reveal the hydrodynamic response characteristics of the shared approach channel during coordinated operation of multi-line ship locks, thereby providing a theoretical basis for optimizing the operation scheduling of multi-line ship locks, improving navigation flow conditions, and enhancing navigation safety. [Methods] Based on the N-S equations for two-dimensional incompressible flow, a two-dimensional hydrodynamic mathematical model covering the downstream area of the Gezhouba Project and the Sanjiang approach channel was established. The model was validated using measured hydrological data and showed good accuracy and reliability. By setting different water discharge combination scenarios, various operation modes were simulated, including simultaneous discharge and staggered discharge of the double-line ship locks. The water level fluctuation process, flow velocity distribution, and their variation patterns within the shared approach channel were analyzed. Special attention was given to the staggered discharge conditions, under which the spatiotemporal interactions and response characteristics of the fluctuations generated by successive discharges were investigated. The superposition characteristics of wave crests and troughs and their effects on the flow regime within the shared approach channel were further examined. [Results] Under staggered water discharge conditions, the forward flow generated by the later-discharging ship lock met the reverse flow produced by the earlier-discharging ship lock within the approach channel, which significantly reduced the reverse flow velocity in the shared approach channel and was beneficial to ship navigation control. Compared with single-line ship lock discharge, during double-line ship lock discharge, the increment of water level wave crests in the approach channel first increased and then decreased with increasing staggered time, and finally tended to remain unchanged at zero. The difference in wave troughs was positive at first and then became negative, and ultimately tended to remain stable. When the double-line ship locks discharged with a staggered time of 12-22 minutes, smaller wave troughs occurred in the approach channel, which were favorable for ship navigation. In terms of wave superposition, the wave crests in the first cycle exhibited a pronounced linear superposition characteristic. Under specific staggered discharge conditions, the superposition effect of wave troughs showed only minor differences from the results of linear superposition, whereas nonlinear characteristics were observed at other staggered times. In addition, different discharge combinations produced distinct effects on the longitudinal flow velocity distribution along the shared approach channel. Significant variations in velocity gradients and flow directions were observed, particularly in the lock gate area and the middle section of the approach channel. [Conclusion] Staggered water discharge can regulate the reverse flow velocity within the approach channel and can further reduce wave troughs in the shared approach channel within specific staggered time intervals. The findings provide guidance for optimizing the layout of shared approach channels for existing and reconstructed multi-line ship locks, formulating reasonable discharge timing schemes, and mitigating the adverse effects of complex flow conditions on navigation safety. The results also offer scientific reference for improving navigation flow conditions in the Gezhouba navigation capacity expansion project and similar hydraulic hubs.
[Objective] The unsteady motion of secondary flow, namely Dean vortices, in bent pipes can induce thermal fatigue and mechanical fatigue, posing a serious threat to the safe operation of industrial piping systems. In recent years, the swirl switching phenomenon, as a fundamental fluid mechanics issue in turbulent flow through 90° bends, has gradually attracted widespread academic attention. However, most existing studies focus mainly on time-averaged hydraulic characteristics such as pressure distribution and mean velocity distribution in bends, while research on the unsteady dynamic characteristics of secondary flow in pipes remains relatively limited. [Methods] Through the extensive literature review, this study collected and organized existing research results on the swirl switching phenomenon in turbulent flow through 90° bends. From the perspectives of upstream inflow conditions, flow separation in bends, flow structures, oscillation characteristic frequencies, the influence range of secondary flow, and flow control, the research progress on the swirl switching phenomenon is systematically summarized. [Results] The correlation between the swirl switching phenomenon and upstream inflow conditions in spatially developing turbulent flow through 90° bends still requires further verification. Flow separation on the inner side of the bend is not a necessary condition for triggering Dean vortex oscillation. Significant discrepancies remain regarding the dominant proper orthogonal decomposition modes representing Dean vortex oscillation. The characteristic frequencies of the swirl switching phenomenon extracted using POD analysis are lower than those obtained by other analysis methods, and extracting characteristic frequencies based on variations of single local physical quantities exhibits considerable randomness. The spatial scale of Dean vortex oscillation, its interaction with the streamwise main flow, and its spatiotemporal evolution mechanisms still require further investigation. The triggering mechanism of the swirl switching phenomenon remains unclear, and how to effectively control it also requires more in-depth research on the underlying flow mechanisms. [Conclusion] Current domestic and international understanding of the swirl switching phenomenon remains incomplete. Its dynamic characteristics and spatio-temporal evolution mechanisms are still unclear, and high-precision three-dimensional flow field data are lacking. It is proposed that further exploration and investigation of the triggering mechanisms, intrinsic modes, characteristic oscillation frequencies, spatial structures, and flow control methods of the swirl switching phenomenon should be conducted using high-fidelity direct numerical simulations and advanced three-dimensional time-resolved flow field measurement techniques.
[Objective] This study aims to investigate the relationship between shear wave velocity and physical-mechanical indices in saturated red clay. [Methods] Triaxial saturated specimens exhibiting varying dry densities were meticulously prepared. Utilizing a specifically modified triaxial bender element apparatus,consolidated undrained (CU) triaxial tests combined with shear wave velocity measurements were conducted on the red clay to identify the primary controlling factors influencing shear wave velocity characteristics within saturated red clay specimens. Subsequently,leveraging the quantitatively established relationships between shear wave velocity and physical-mechanical parameters,an evaluation model for shear wave velocity in saturated red clay was ultimately developed. [Results] (1) The shear wave velocity of saturated red clay generally exhibited an initial ascending phase followed by a progressive decline as dry density increased. Conversely,the shear wave velocity demonstrated a consistent monotonic enhancement in response to escalating confining pressure and effective stress. The interrelationships between these parameters (confining pressure and effective stress) and shear wave velocity were mathematically modeled employing power function formulations. Correlation coefficients exceed 0.92 (R2>0.92),indicating that a positively correlated power-law functional dependence governs the associations between confining pressure/effective stress and shear wave velocity. (2) Linear regression,quadratic polynomial approximation,power function formulation,and exponential function modeling were individually applied to analyze the experimental data. Power function modeling demonstrated higher precision than exponential function modeling,which in turn surpassed quadratic polynomial approximation,with linear regression exhibiting the lowest degree of accuracy. The quantitative interrelationship between shear modulus and effective stress conforms to a power-law functional dependence,thereby establishing a foundational theoretical framework essential for the systematic development of subsequent shear wave velocity predictive models. (3) A comprehensive evaluation model for shear wave velocity was ultimately constructed. This sophisticated model incorporated specific gravity,void ratio,and effective stress as its primary input variables. Implementation of this framework facilitated rigorous nonlinear surface regression analysis applied to experimental datasets,yielding a coefficient of determination of R2=0.91. Precisely 89.9% of the data points demonstrated relative errors between measured and calculated values below the 10% threshold,whereas the remaining 11.1% exhibited relative deviations exceeding 10%,which confirms the model’s elevated predictive accuracy. [Conclusion] A robust correlation exists between the shear wave velocity of saturated red clay and the physical properties of the soil. The evaluation of soil physical parameters through shear wave velocity measurements demonstrates practical feasibility. Concurrently,the developed shear wave velocity model establishes a quantitative relationship between the shear wave velocity of saturated red clay and its physical-mechanical parameters. This achievement provides a significant theoretical foundation for in-depth exploration of the monitoring and early-warning mechanisms for lateritic landslides.
[Objective] In subgrade widening projects in loess areas, the soil squeezing effect induced by high-pressure jet grouting pile construction easily leads to soil displacement and settlement deformation of existing lines, seriously threatening the control accuracy of track geometry and operational safety. This study aims to clarify the influence mechanisms of single-pile and group-pile high-pressure jet grouting construction on existing lines in loess areas, and to quantify soil lateral displacement, line settlement, and heave deformation, thereby providing a reference for construction optimization and safety control of such projects. [Methods] Based on a foundation treatment project for an existing line widening section in a loess area, a combination of on-site real-time monitoring and theoretical analysis was adopted. The variations in soil lateral displacement under single-pile and group-pile high-pressure jet grouting construction were investigated, the settlement evolution of the existing line during different construction stages of high-pressure jet grouting was analyzed, and the effects of high-pressure jet grouting construction on the service condition of the existing line were examined. [Results] (1) The soil lateral displacement induced by high-pressure jet grouting pile construction exhibited a significant decreasing trend with increasing pile depth and showed a negative correlation with the distance from the pile center. Within the normalized radial distance range of 0-4d0 (where d0 was the pile diameter), the lateral displacement attenuated most rapidly; beyond this range, the attenuation trend became gradual. (2) The influence range of high-pressure jet grouting pile construction on the surrounding soil was determined to be approximately 11 times the pile radius, providing a clear basis for defining construction safety distances and monitoring layout ranges. (3) During pile group construction, the ground surface heave exhibited a “double-peak” distribution pattern. The heave amplitude was inversely proportional to the distance between the construction area and the existing subgrade, and the locations of the “double peaks” were related to the pile group construction sequence and pile layout. (4) The adoption of the alternate pile construction method effectively reduced the impact of the soil squeezing effect on the service condition of the existing line. [Conclusion] This study systematically elucidates the influence pattern of high-pressure jet grouting pile construction on existing lines in subgrade widening sections in loess areas, and quantifies the attenuation characteristics of soil lateral displacement, the construction influence range, and the “double-peak” distribution pattern of group-pile-induced heave. An engineering reference value of 11 times the pile radius for the influence range is proposed. The results provide important theoretical guidance, prediction methods, and process optimization recommendations for the design and construction of high-pressure jet grouting pile foundation treatment under similar engineering conditions, and have direct engineering application value for ensuring the operational safety and high track smoothness of existing lines.
[Objective] Traditional piles with uniform cross-sections have inadequate properties of the bearing stratum at pile tip or difficulties in penetrating into rock when used in soft soil areas or karst regions. Based on the concept of transforming end-bearing piles into mid-bearing piles, this study proposes a novel discontinuous variable cross-section thorn pile, aiming to systematically reveal the mechanisms by which thorn length and the number of thorn layers affect the compressive bearing properties of thorn piles through indoor model tests, thereby providing a theoretical basis for establishing a performance-based optimized design method. [Methods] Using a self-developed loading device, a geometric similarity ratio of 1∶75 was adopted, and PVC hollow circular pipes and 304 stainless steel cylindrical pins were used as the model piles and pile thorns, respectively. Using the controlled variable method, a total of 21 test groups were designed, and indoor model tests with different thorn lengths and number of thorn layers were conducted to investigate the compressive bearing properties of thorn piles in sand. [Results] (1) compared with smooth piles, thorn piles exhibited superior compressive bearing and settlement resistance. Under sand conditions, the ultimate bearing capacity of the 17-layer Type-38 thorn pile increased by 278% compared with that of the smooth pile. (2) Both thorn length and the number of thorn layers showed positive correlations with the bearing capacity of the pile foundation; compared with thorn length, the number of thorn layers was more sensitive to the ultimate bearing capacity of a single pile and the pile shaft resistance. (3) From an engineering economic perspective, when the thorn spacing was approximately one-eighth of the pile length and the thorn length was about equal to the pile diameter, the thorn pile exhibited optimal compressive bearing properties. [Conclusion] (1) The presence of thorn structures increases the interlocking effect between thorns and soil as well as the effective stress of the surrounding soil, delays the softening of pile shaft resistance, expands the influence range of the surrounding soil, and effectively redistributes the applied load, thereby significantly enhancing the overall bearing capacity of the pile foundation. (2) The concept of mid-bearing degree is introduced to quantify the mid-bearing contribution of pile thorns, and a calculation method for the ultimate bearing capacity of a single thorn pile is proposed, laying a foundation for subsequent theoretical studies. (3) Future research may consider the effects of layered foundations, soil squeezing during thorn formation, and thorn geometry on the compressive bearing properties of thorn piles, so as to further improve the comprehensiveness of bearing mechanisms and the applicability of theoretical models. The findings of this study have important theoretical and practical value in promoting the transformation of modern pile foundation engineering toward green and intelligent development, and their application will profoundly influence future modes of underground space development.
[Objective] To address the challenges of difficult coring, high cost, and high data dispersion in traditional mechanical testing for deep rock engineering, as well as the conflict between testing efficiency and accuracy in existing indentation techniques that rely on multi-point array statistics, this study aims to propose a new, efficient, and accurate method for determining the elastic modulus of rocks. This method enables the rapid acquisition of mechanical parameters without the need for intact cores. [Methods] An innovative macroscopic indentation testing scheme was adopted, featuring continuous cyclic loading and unloading at a single indentation point. Tight sandstone from the Tarim Basin at burial depths of 6 500-8 038 m was used as the research object. Standard cylindrical specimens (for uniaxial compression benchmark tests), rectangular specimens, and solidified drilling cutting specimens (simulating field application scenarios) were prepared simultaneously. The experiments combined the Oliver-Pharr theory with the Hertz contact model. Through a three-factor, three-level orthogonal experimental design (maximum load: 50, 100, 200 N; loading rate: 0.03,0.06,0.09 mm/min; load holding time: 0, 10, 30 s), the influence of key experimental parameters on the elastic modulus measurement results were systematically investigated. Thirty cycles of loading and unloading were performed at each indentation point to collect a greater amount of load-displacement data. Initial indentation deviations and dispersion were corrected through linear fitting. After removing outliers, statistical characteristic values were calculated and compared with the results from uniaxial compression tests for validation. The experiments were conducted using a modified WANCE 503A electronic universal testing machine to ensure high-precision acquisition of load and displacement data. [Results] The maximum load had a significant impact on measurement accuracy. The indentation elastic modulus under a 50 N load showed the best agreement with the uniaxial compression reference value, with an error of only 9.70%. In contrast, the errors increased to 12.18% and 24.74% under loads of 100 N and 200 N, respectively. The loading rate had a secondary influence, with the lowest rate of 0.03 mm/min providing the best data stability (coefficient of variation <7.5%), effectively reducing dynamic effect interference. A load holding time of 10 s achieved a balance between contact stability and deformation instantaneity, resulting in a low error of 4.73%. No holding time (coefficient of variation 9.2%) or excessively long holding time (30 s) both led to increased data dispersion. The elastic modulus exhibited a gradual increasing trend within 30 cycles and tended to stabilize after 20 cycles, with an increment ≤20%, which was consistent with the patterns of rock cyclic hardening and micro-damage accumulation. The error of the elastic modulus measured by this method was <10%, significantly better than the 13.5%-15% error level of traditional indentation tests. Drilling cuttings, after simple solidification treatment, could meet the testing requirements without the need for intact cores, greatly improving testing efficiency compared to traditional multi-point array indentation. Under uniaxial compression, tight sandstone exhibited typical splitting failure, with the main fracture plane parallel to the axial direction. During the cyclic loading and unloading process, the proportion of plastic deformation gradually decreased with increasing cycle number and eventually approached a purely elastic response, verifying the rationality of the physical mechanisms of the method. [Conclusion] The core innovation of this study lies in proposing a “single indentation point with continuous cyclic loading and unloading” testing mode. This approach overcomes the limitations of traditional indentation techniques that rely on multi-point array statistics and simultaneously improves data density and accuracy through multiple tests at a single point, thereby resolving the conflict between efficiency and accuracy. The determined optimal experimental parameters (maximum load of 50 N, loading rate of 0.03 mm/min, load holding time of 10 s) can ensure the accuracy and stability of measurement results. The method features a simple experimental procedure, portable equipment, and eliminates the need for deep coring. It enables the rapid acquisition of elastic modulus directly from drilling cuttings, with errors controlled within an engineering-acceptable range. This provides an efficient and reliable technical pathway for on-site mechanical parameter testing in deep rock engineering. Its applicability covers brittle rocks such as sandstone, limestone, and granite. Future integration with digital image correlation techniques can further reveal the dynamic relationship between rock microstructure and elastic modulus under cyclic loading.
[Objective] Compacted bentonite is a critical buffer material for the deep geological disposal of nuclear waste and landfill engineering. Its swelling characteristics are directly affected by cation exchange with groundwater or landfill leachate. While existing research has clarified cation-related hydration and swelling mechanisms in bentonite powder or via molecular dynamics simulations, studies on the influence of interlayer cations on compacted samples remain limited. This study aims to fill this gap by investigating the influence of interlayer cations on the macroscopic swelling behavior of compacted bentonite, thereby providing technical support for engineering design and safety assessment. [Methods] The test material was bentonite from Shouguang, Shandong Province, containing a montmorillonite content exceeding 95% and exhibiting excellent swelling and adsorption properties. Four types of homoionic bentonite (Na-based, K-based, Ca-based, Mg-based) were prepared via cation exchange by mixing bentonite with 1 mol/L solutions of NaCl, KCl, CaCl2, or MgCl2. The samples were compacted to a dry density of 1.1 g/cm3 with an initial moisture content of 20%. A self-developed integrated consolidation-swelling device was used for volume-constrained swelling pressure tests and unconfined swelling strain tests. Complementary characterizations included X-ray diffraction (XRD) to measure interlayer spacing (d001) and scanning electron microscopy (SEM) to observe microstructural changes. [Results] The final swelling pressure of the four types of homoionic bentonite followed a distinct hierarchy: Mg-based (5.98 MPa) > Ca-based (5.79 MPa) > Na-based (4.49 MPa) > K-based (3.61 MPa). Swelling pressure curves exhibited a “rise-decline-stabilization” trend: rapid growth occurred within 0-2 h, with Mg/Ca-based samples peaking at 6.21 MPa and 5.18 MPa, respectively, followed by a slight decline due to aggregate splitting and pore filling, and finally stabilizing after 18 h. Na/K-based samples stabilized after 22 h without an early decline. The ratio of time to swelling pressure showed a strong linear correlation with time. This correlation enabled the prediction of the maximum swelling pressure, and the predicted values were highly consistent with the measured values. For swelling strain, the order was Na-based (72.7%) > K-based (51.5%) > Ca-based (47.0%) ≈ Mg-based (48.7%). Swelling strain curves exhibited three stages: slow growth (0-0.06 h, clay particle hydration), rapid growth (0.06-10 h, dominant interlayer swelling), and stabilization. The swelling strain of Mg/Ca-based samples stabilized faster than that of Na/K-based ones. The ratio of time to swelling strain also showed excellent linearity with time, and the reciprocal of slope could be used to predict the maximum strain. XRD results showed that after swelling pressure tests, Mg/Ca-based samples had larger interlayer spacings (18.62 Å/18.10 Å, 3 layers of interlayer water) than Na/K-based ones (15.63 Å/15.39 Å, 2 layers). After swelling strain tests, Na/K-based samples adsorbed over 4 layers of water, resulting in larger spacings (23.68 Å/20.98 Å). SEM images revealed that Na/K-based samples had thin, curled lamellar aggregates with uniform pores, while Ca/Mg-based samples had thicker aggregates and more macropores. [Conclusion] Interlayer cations regulate the macroscopic swelling behavior of compacted bentonite through their hydration energy and interaction with the crystal layers. Divalent cations (Ca2+ and Mg2+) have higher hydration energy than monovalent cations (Na+ and K+), enabling stronger interlayer swelling under volume-constrained conditions and consequently resulting in higher swelling pressure. The minimum swelling pressure recorded for K-based bentonite stems from the matching of its ionic radius with the montmorillonite crystal cavity, which promotes the formation of stable interlayer structures. Under unconfined conditions, monovalent cations (Na+ and K+) have weaker interaction with the crystal layers, allowing more interlayer water adsorption and intense osmotic expansion. This accounts for the larger swelling strain of Na- and K- based samples. The development rates of swelling pressure and strain have a good linear relationship with immersion time, and the proposed empirical formulas provide a reliable tool for predicting maximum swelling characteristics. Microstructural evolution (aggregate splitting and pore distribution) is closely linked to interlayer cation type, which further determines macroscopic performance. The findings of this study highlight the significant effect of interlayer cations and emphasize the necessity of considering interlayer cation composition of bentonite-based barriers. The differences in the macroscopic swelling pressure and swelling strain of different cationic bentonites should be given high priority in relevant engineering design and evaluation.
[Objective] This study aims to address the limitations of traditional quantitative classification methods for altered granites, which often lead to coarse grade divisions and significant discrepancies in rock degradation between adjacent grades. Focusing on the Hercynian mid-term granites in the North Tianshan Mountains region, where deep-seated alteration is jointly controlled by hydrothermal metasomatism and tectonic dynamics, the research seeks to 1) elucidate the alteration mechanisms through mineralogical and geochemical analyses, 2) develop a refined alteration classification index (Alteration Index for Granite, AIG) by correcting CaO components, and 3) establish a five-grade alteration classification standard for engineering geological evaluations. [Methods] Twelve granite samples (including altered and unaltered rocks) from two depths (240 m and 1250 m) in the F01 area were analyzed. The methodologies included: (1) Thin-section identification to determine mineral composition, optical properties, and structural characteristics;(2) X-ray diffraction (XRD) for quantifying secondary minerals (e.g., chlorite, clay minerals) and validating CaO correction;(3) X-ray fluorescence (XRF) to measure major and trace element oxides (Al2O3, CaO, Fe2O3, MgO, K2O, SiO2, Na2O) following the HJ780-2015 standard;(4) Index formulation to derive the AIG index by refining CaO contributions, excluding interference from apatite and secondary carbonates. This involved a three-step correction: XRF data acquisition, XRD-based secondary mineral quantification, and crystal stoichiometric inversion of primary silicate CaO. [Results] (1) Innovation of the AIG Index: Traditional indices (CIA, CIW, WIP, WIC, WIG) exhibit limitations, such as over-reliance on Al2O3 stability (CIA/CIW) or insensitivity to late-stage alteration (WIP). The AIG index addresses these by decoupling CaO contributions from secondary phases (e.g., apatite, calcite) and integrating multi-component stability (TiO2, Al2O3, Fe2O3). Compared to the suboptimal WIG index, the AIG demonstrates 65% and 160% improvements in overall correlation with CIA and CIW, respectively. Its quantitative accuracy surpasses CIA by 50%, with reduced dispersion (<5%) in high-secondary-mineral samples.(2) Alteration Mechanisms: in terms of dominant alteration types, Low-temperature hydrothermal alteration (150-300 ℃) prevails, characterized by chloritization (K depletion, Mg enrichment) and argillization (Na/Ca depletion). Tectonic dynamic alteration is weak. In terms of mineralogical evolution,a) Chloritization originates from biotite replacement, accompanied by Fe-rich chlorite (Fe/(Mg+Fe)=0.78-0.82) and secondary epidote/sphene; b) Argillization is driven by plagioclase dissolution, forming montmorillonite-illite mixtures and kaolinite under acidic conditions. Fracture networks enhance fluid permeability, intensifying alteration.Secondary alterations: Sericitization (K+ metasomatism), epidotization (Ca2+ migration), and clinozoisitization (selective Ca-Al exchange) occur at lower intensities.(3) Five-Grade Classification Standard: Based on AIG thresholds and petrological features, the altered granites are classified into Grade I (AIG>105): Unaltered, blocky structure, negligible secondary minerals; Grade II (AIG between 100 and 105): Slight chloritization, color transition (gray-black to brown-red); Grade III (AIG between 95 and 100): Moderate alteration with illite/sericite, blurred grain boundaries; Grade IV (AIG between 90 and 95): Enhanced argillization, cataclastic structure; Grade V (AIG <90): Intense alteration with montmorillonite, complete loss of primary texture. AIG thresholds expand the CIA’s theoretical range by 1.7 times, enhancing sensitivity to multi-stage alteration processes. [Conclusion] (1) Theoretical Advancements: The AIG index innovatively resolves CaO interference through mineral-phase decoupling, enabling precise quantification of silicate-driven alteration. Its multi-component framework (Na2O, K2O, MgO, corrected CaO vs. Al2O3+Fe2O3+TiO2) outperforms existing indices in sensitivity and robustness. The study confirms that North Tianshan granites undergo low-temperature hydrothermal alteration dominated by chloritization and argillization, with weak tectonic influence. Elemental migration (Na/Ca loss, K/Mg enrichment) aligns with mineralogical transformations (plagioclase depletion, secondary clay/chlorite growth).(2) Practical Implications: The five-grade AIG classification standard bridges geochemical data with macroscopic engineering properties (e.g., fracturing, water absorption), offering a reliable tool for evaluating altered granite stability in deep engineering projects. Future work should integrate mechanical testing to correlate AIG grades with rock strength and deformability, further refining the model’s predictive capability.(3) Innovative Highlights. AIG Index: a novel geochemical index incorporating XRD-XRF cross-validation to eliminate non-silicate CaO contributions, achieving 65%-160% higher correlation with established indices. Mechanistic Insights: first systematic delineation of chloritization-argillization synergy in Hercynian granites, linking element migration to multi-stage hydrothermal processes.Engineering Relevance: a robust five-grade standard enabling quantitative alteration assessment, critical for mitigating geological hazards in deep underground projects.
[Objective] To facilitate the construction of asphalt concrete core walls in the severe cold regions of Western China, this paper undertakes a systematic investigation into the influence of acidic gravel aggregates on the performance characteristics of hydraulic asphalt concrete. [Methods] The research methodology and evaluation framework were strictly guided by two pivotal Chinese technical standards: Test Code for Hydraulic Asphalt Concrete (DL/T 5362-2018) and the more recent Technical Specification for the Application of Acidic Aggregates in Hydraulic Asphalt Concrete (DL/T 5876-2024). The key performance indicators (mechanical properties, deformation behavior, impermeability, and overall durability) of asphalt concrete incorporating crushed gravel aggregates were evaluated through asphalt concrete water stability tests, direct tensile tests, bending tests, pressure-based impermeability tests for dense-graded asphalt concrete, triaxial compression tests, long-term water immersion stability tests, and long-term freeze-thaw splitting tests. [Results] (1) Complex Composition and Durability Challenge: Gravel aggregates typically exhibited a complex mineralogical composition, encompassing alkaline, neutral, and acidic aggregates, with acidic rock types often being predominant. A primary concern identified was the inherently weak interfacial bonding force between asphalt binder and acidic aggregate surfaces. Under prolonged water immersion, this weak bond facilitated a gradual displacement process where water molecules infiltrated and substituted the asphalt at the aggregate interface, leading to stripping or detachment of the asphalt film from the aggregate surface. This mechanism posed a substantial threat to the long-term durability of the asphalt concrete. Consequently, a thorough durability assessment should be required when considering the application of gravel aggregates-based hydraulic asphalt concrete in critical structures. (2) Enhancement Mechanisms via Cement Filler and Anti-Stripping Agents: The study identified effective methods to mitigate the adhesion issue. Metal ions present in cement, such as Ca2+ and Mg2+, engaged in chemical bonding with oxygen atoms within the asphalt. In the mixing process, this interaction promoted a more robust and durable bond between the asphalt and the aggregates. Furthermore, the use of anti-stripping agents was found to be highly beneficial. These agents operated through multiple synergistic mechanisms, including chemical bonding with the aggregate surface, modification of the interfacial properties, and the creation of a physical barrier against water intrusion. Collectively, these actions significantly enhanced both the durability and the mechanical performance of asphalt concrete made with acidic aggregates. Incorporating cement filler alone, or using a combination of cement filler and non-amine anti-stripping agents, effectively strengthened the adhesive bond between the gravel aggregates and the asphalt matrix, thereby markedly improving the durability of the resulting acidic gravel aggregate hydraulic asphalt concrete. (3) Mechanical Behavior and Modeling: Asphalt concrete was recognized as a temperature-sensitive material. Analysis of triaxial test data revealed that the relationship between lateral strain and axial strain approximated a linear relationship. Specifically for the gravel aggregate asphalt concrete studied, its strength demonstrated a well-defined and favorable linear increase with rising confining pressure. The material's strength could be effectively characterized using the parameters of a linear strength model, namely the cohesion and the angle of internal friction. (4) Overall Performance Improvement: Incorporating cement filler or adding non-amine anti-stripping agents substantially improved the comprehensive performance profile of acidic gravel aggregate asphalt concrete. These enhancements directly translated to superior mechanical properties, increased resistance to water-induced damage, and extended long-term durability. [Conclusion] The application of acidic gravel aggregates in the construction of asphalt concrete core wall dams is demonstrated to be technically feasible. Key performance parameters evaluated in this study, including the long-term water immersion stability coefficient, the freeze-thaw cycle splitting tensile strength ratio, and the failure tensile strain, provide a robust theoretical foundation and essential technical support for the engineering application of this material.
[Objective] With advances in dam construction technology and equipment, faced rockfill dams have emerged as a highly competitive dam type. The development of concrete-faced rockfill dams (CFRDs) in China is progressing toward the goal of “taller dams and larger reservoirs.” For ultra-high CFRDs, a gravity-type concrete high toe wall is incorporated at the upstream heel area of the riverbed, replacing a portion of the lower face slab. This not only reduces the face slab length but also improves maintainability in the lower dam zone. This study aims to further evaluate the rationality and safety of adopting this composite structural scheme for ultra-high CFRDs. [Methods] An ultra-high (250m) CFRD under construction in China was taken as the research subject. Two-dimensional nonlinear finite element analysis was employed to compare the stress and deformation differences between the composite structure with a concrete high toe wall and the conventional structural scheme. A three-dimensional nonlinear finite element model was further applied to examine the mechanical behavior of the composite-structure ultra-high CFRD during staged construction filling and multi-level reservoir impoundment. The rockfill was modeled using Shen Zhujiang’s double-yield-surface elastoplastic constitutive model, while concrete structures—including the face slab, toe slab, and riverbed high toe wall—were simulated with a linear elastic model. Interfaces between rockfill and concrete were modeled using thin-layer elements with low modulus. [Results] The concrete high toe wall significantly restrained the streamwise deformation of the rockfill, reducing the maximum upstream deformation by 23%. Face slab deflection was notably decreased, with a 10% reduction in peak deflection. During staged filling and multi-stage impoundment, the internal stress distribution in the rockfill remained uniform, with low stress levels and no evidence of stress concentration or plastic limit zones. Compressive stresses in the face slab and concrete high toe wall were within the allowable compressive strength of concrete, and all deformations fell within acceptable engineering limits. [Conclusions] (1) The composite “concrete high toe wall-faced rockfill dam” structure, which replaces the lower face slab in the riverbed with a gravity concrete wall, effectively restrains streamwise rockfill deformation, reduces face slab deflection and improves its stress distribution, while also enhancing maintainability at the slab bottom. This scheme provides a new research direction for CFRD construction and merits further promotion and application. (2) Validation and wider adoption of novel dam structural schemes require support from field monitoring data. This study only considered the stress-deformation behavior of the composite-structure CFRD under static water load. In practice, stress and deformation in faced rockfill dams involve complex conditions such as dynamic actions, seepage, and multi-field coupling. The actual performance and feasibility of the composite structural scheme still need to be verified by long-term operational monitoring data from the project.
[Objective] The concrete lining structures of underground air storage caverns in compressed air energy storage (CAES) systems are subjected to the combined effects of periodic air pressure fluctuations and temperature variations during long-term operation. This study aims to systematically reveal the evolution of mechanical properties, the microscopic damage mechanisms, and the macroscopic constitutive behavior of concrete under synchronous temperature-pressure cyclic loading, establish a damage constitutive model that accurately describes its stress-strain response characteristics, and further clarify the synergistic deterioration effect of coupled temperature-pressure cyclic loading. [Methods] A method combining experimental investigation and theoretical modeling was adopted. First, based on the actual operational parameters of CAES caverns, coupled cyclic loading tests were conducted on C50 concrete cylindrical specimens to investigate the individual and combined effects of three key variables: the number of cycles, the upper limit of cyclic temperature, and the upper limit of cyclic stress. After cyclic loading, uniaxial compression tests and SEM observations were performed on the specimens to reveal the changes in macroscopic mechanical properties and the underlying microscopic mechanisms of concrete under such loading. Based on continuum damage mechanics and the equivalent strain principle, and using the Weibull statistical distribution to describe the distribution and evolution of micro-defects within concrete, a damage constitutive model was established. [Results] (1) Temperature-pressure synchronous cyclic loading significantly deteriorated the mechanical properties of concrete. Both the peak compressive strength and the secant elastic modulus of concrete decreased monotonically with the number of cycles, the upper limit of cyclic temperature, and the upper limit of cyclic stress. The most severe performance degradation occurred during the first 30 cycles, and the degradation rate gradually leveled off after 40 cycles. Particularly, the coupled temperature-pressure action produced a significant synergistic deterioration effect, where the combined effect exceeded the sum of individual effects. After 30 synchronous temperature-stress cycles, the peak strength of concrete decreased by approximately 22% compared to the uncycled reference group. In contrast, the same number of single-factor temperature cycles (without stress) or single-factor stress cycles (constant temperature of 25 ℃) resulted in strength reductions of only about 15% and -3%, respectively, with low-level stress cycling exhibiting a slight strengthening effect. This indicated that the synchronous alternating action of temperature and stress was not a simple superposition of independent effects but rather exacerbated the damage accumulation within concrete through mutually reinforcing mechanisms. (2) SEM observations indicated that the difference in thermal expansion coefficients between aggregates and cement mortar was the fundamental cause of thermally induced microcracks. The presence of periodic axial compressive stress generated additional stress at the tips of existing microcracks during the heating/pressurization phase, promoting their further propagation, and induced repeated shearing and friction on crack surfaces during the cooling/depressurization phase, exacerbating the degradation of interfacial bonding. This coupled thermo-mechanical process ultimately led to the accelerated accumulation and interconnection of damage in the interfacial transition zone (ITZ), the weakest link in concrete, which became the dominant mechanism for the sharp degradation of macroscopic mechanical properties. (3) The established damage constitutive model showed good agreement between the theoretically calculated stress-strain curves and the experimental curves under various working conditions. The model accurately reproduced the shape of the ascending branch, the location of the peak point, and the descending branch trend of the concrete stress-strain relationship after different cyclic histories. The damage evolution curves indicated that temperature-pressure synchronous cyclic loading not only significantly increased the initial damage value of concrete but also altered the development of damage during subsequent loading. Compared to reference concrete or concrete subjected only to temperature cycles, concrete that underwent coupled temperature-pressure cycles exhibited a faster development rate of the damage variable before reaching peak stress and a higher degree of damage at the peak stress point. This quantitatively confirmed the dual effects of “acceleration” and “aggravation” of the coupled temperature-pressure loading on the concrete damage process. [Conclusion] Through systematic experimental and theoretical analysis, this study comprehensively explains the performance degradation and damage evolution mechanisms of concrete under the coupled action of synchronous cyclic temperature-pressure loading. It clearly reveals the unique synergistic deterioration effects resulting from the coupling of temperature and stress fields. The established damage constitutive model provides a directly applicable constitutive relationship for nonlinear mechanical analysis and safety assessment of concrete structures in complex service environments such as CAES underground air storage caverns. The results confirm that the coupled effects of temperature-pressure cycles must be considered in the design and durability evaluation of such structures. Extrapolation based solely on single-factor test results may lead to a severe overestimation of the actual service life and safety margin of the structures.
[Objective] Autogenous volume deformation is a key factor affecting the cracking resistance of dam concrete; however, its meso-scale mechanism is often neglected in engineering practice. Meso-scale modeling of full-graded dam concrete has long faced challenges of low efficiency and poor mesh quality, particularly in reconciling, within a unified model, the scale disparity between a maximum aggregate size of up to 150 mm and an interfacial transition zone (ITZ) thickness of only about 50 μm, which prevents accurate representation of the true meso-structural characteristics. To address this issue, we propose a random aggregate batch placement method. [Methods] By optimizing the aggregate generation algorithm and introducing an efficient spatial positioning criterion, rapid placement and high-volume simulation of four-graded aggregates were achieved. An adaptively coordinated meshing technique for the interfacial transition zone was combined with local mesh refinement and geometric smoothing at aggregate-mortar interfaces, thereby constructing a two-dimensional meso-scale analytical model of full-graded dam concrete that accurately captured the micrometer-scale interfacial geometry and mechanical properties. Based on this model, the stress distributions and their evolution within the interfacial transition zone and the mortar matrix were systematically investigated under two autogenous volume deformation modes—shrinkage and expansion—and under different constraint conditions, including single-sided and four-sided constraints. [Results] 1) Different autogenous volume deformation modes governed the spatial distribution characteristics of meso-scale stresses. Under autogenous shrinkage, tensile stresses were concentrated in the cement mortar regions adjacent to sharp aggregate corners because the shrinkage of the mortar matrix was restrained by aggregates, with the local stresses reaching 3.6-4.0 MPa, approaching the tensile strength limit of the mortar. In contrast, under micro-expansion deformation, the restriction of expansion by aggregates caused the tensile stress concentration zones to shift to the specimen surface and the corner regions of internal interfacial transition zones, with a significant increase in the stress concentration factor, indicating that the interfaces became the weak links under expansion conditions. 2) Constraint conditions played a critical role in regulating the stress state of concrete. Compared with a single-sided constraint, the four-sided constraint simulating the strong restraint of a dam foundation significantly amplified the adverse effects of shrinkage deformation, with the shrinkage-induced tensile stresses in the cement mortar generally increasing by 0.8-1.2 MPa, and the local tensile stress at interfaces even exceeding 4.0 MPa, resulting in a sharp increase in cracking risk. Under the same constraint conditions, however, the positive effect of micro-expansion deformation was effectively transformed, causing the concrete as a whole to remain in a compressive stress state and thereby significantly enhancing its cracking resistance. 3) Based on the maximum tensile stress criterion and by comprehensively considering the actual tensile strengths of the mortar and the interfacial transition zone, the safe deformation threshold for high crack-resistant concrete was determined. The autogenous volume deformation of full-graded dam concrete should be strictly controlled within the range of -9×10-6 to 11×10-6. In addition, sensitivity analysis further revealed the influence patterns of key parameters. When the elastic modulus ratio between mortar and aggregate varied by ±20%, the elastic moduli of the mortar and aggregate had a significant effect on the maximum tensile stress of the specimen. Therefore, in dam concrete design, attention should be paid to the coordination between the elastic moduli of mortar and aggregates to prevent excessive tensile stresses induced by autogenous or external deformation. Meanwhile, deformation control indices should be dynamically adjusted according to specific constraint conditions. [Conclusion] Adopting a deformation control strategy of “low shrinkage or micro-expansion” and precisely limiting the deformation magnitude within the above threshold range is an effective approach to enhancing the cracking resistance of dam concrete from the perspective of material design. The established meso-scale model and the obtained quantitative conclusions provide direct evidence for performance-based crack resistance design of concrete. They also offer clear guidance for concrete mix proportion design, optimization of expansive agent dosage, and crack control in practical engineering, and provide a reliable analytical approach for in-depth investigation of deformation coordination and cracking evolution mechanisms of dam concrete at the meso-scale.
[Objective] To address the problems of insufficient 3D scene accuracy, unsatisfactory dynamic water effects, and imprecise hydrodynamic process simulation in existing river-lake digital twins, this study proposes an integrated method for 3D river-lake scene construction and hydrodynamic process simulation based on Unreal Engine 5 (UE5). The proposed method aims to construct a digital twin framework that combines high-fidelity scene representation with high-accuracy hydrodynamic process simulation, and to enhance the visualization, dynamism, and interactivity of river-lake digital twins. [Methods] UE5 was used as the research platform, and a real-scene 3D hydrodynamic process simulation method for river-lake scenarios was proposed and implemented by integrating terrain construction, water body simulation, and dynamic extraction of hydrological parameters. First, high-precision 3D river-lake terrain and environmental scenes were constructed using terrain height maps and high-precision photogrammetric models. Second, the Fluid Flux water simulation plugin in UE5 was modified by incorporating bottom friction factors influenced by the Manning coefficient, as used in engineering analysis, thereby establishing a hydrodynamic process model that better conformed to engineering practice. Finally, Blueprint programs were designed to dynamically extract and compute hydrological process parameters during simulation, enabling real-time calculation and dynamic extraction of key hydrological parameters such as flow velocity, water depth, watershed area, total water volume, and river cross-sections. An interactive user interface was also developed to support parameter visualization and scene interaction. [Results] A complete river-lake digital twin framework was constructed, and its functional effectiveness was verified through multiple experiments. First, a dam-break simulation experiment in a 90° bend was constructed to simulate the diffusion process of dam-break flow. The trends of water level variations at all measurement points showed good agreement with classical experimental data, validating the reliability of the hydrodynamic model. Subsequently, inundation simulation experiments under different vegetation cover conditions were conducted. These experiments reflected the influence of vegetation density on flow resistance and inundation processes in the simulated scenarios, demonstrated the capability of surface roughness variations to affect flow simulation, and verified that the proposed method could simulate the impacts of different vegetation environments on hydrodynamic processes. Finally, a complete 3D river-lake scene integrating 3D scenarios, dynamic water simulation, real-time hydrological parameter extraction, and an interactive interface was presented. Through the interface, users could obtain hydrological parameters such as water depth, flow velocity, cross-sectional morphology, watershed area, and total water volume at any location in real time, facilitating clear data acquisition and subsequent processing. [Conclusion] This study investigates methods for 3D scene construction of rivers and lakes and for hydrodynamic process simulation within such scenes, and successfully constructs a river-lake scene framework that integrates high-precision 3D scenes with hydrodynamic process simulation using UE5. The main innovations of this study lie in clarifying the method for constructing 3D river-lake scenes in the UE5 environment, generating terrain base surfaces using the terrain system and elevation data, and introducing high-precision photogrammetric models to enrich the surface environment, thereby improving the realism of 3D river-lake scene construction. From an engineering analysis perspective, the hydrodynamic model of the Fluid Flux plugin in UE5 is improved by adding a friction term influenced by the Manning coefficient, enabling hydrodynamic process simulation in 3D scenes to more accurately reflect the influence of environmental roughness. Simulation scenarios are also designed to verify the impacts of different terrain and vegetation roughness on flow simulation. In addition, Blueprint programs are designed to dynamically extract and compute various hydrological elements during the simulation of 3D river-lake scenes, forming a complete method for hydrodynamic process simulation in 3D river-lake scenes. The proposed method provides integrated capabilities for scene construction, hydrodynamic process simulation, and hydrological parameter extraction and computation, thereby improving the efficiency of data acquisition and processing during 3D scene simulation.
[Objective] In response to the persistent high-temperature drought of the highest intensity since 1961 that occurred across most of the Yangtze River Basin during the summer and autumn of 2022, the Changjiang Water Resources Commission successively launched two rounds of special campaigns to combat drought, ensure water supply, and secure autumn grain harvest. A digital twin platform for drought relief scheduling in the Yangtze River Basin was developed and scenario simulations for drought defense were conducted, providing technical demonstration for the construction of a digital twin system for drought defense in the river basin. [Methods] The platform was developed in line with the operational requirements of early warning, simulation, and contingency planning. Using the platform, the severe drought in the Yangtze River Basin in 2022 were simulated. [Results] (1) Guided by the requirements of drought relief based on prediction, early warning, simulation, and contingency planning, and combining needs such as drought relief information management, emergency response, drought disaster verification and assessment, drought relief benefit evaluation, and drought relief contingency planning, a digital twin platform for drought relief and water replenishment scheduling was developed. Functions such as monitoring and alarm, prediction and early warning, scheduling simulation, contingency plan consultation, and user management were realized. (2) The severe drought in the Yangtze River Basin in 2022 was selected as a case study. Scenario simulations were conducted along the whole chain and entire process of “current drought diagnosis,future trend analysis,drought relief scheduling simulation,contingency plan consultation and decision-making”. “Current drought diagnosis” included drought monitoring data access, over-limit alarm for monitoring data, and monitoring of drought-related online public opinion, addressing the question of “where is the drought occurring?” “Future trend analysis” included drought prediction data access, prediction model calculation, and over-limit early warning for prediction data, addressing the question of “how will the drought evolve?” “Drought relief scheduling simulation” included the construction of a knowledge base of drought relief scheduling schemes and drought relief scheduling schemes based on knowledge base and scenario simulation, addressing the question of “how should the reservoirs be operated?” “Contingency plan consultation and decision-making” included drought relief emergency plan query, automatic generation of drought relief reports, and intelligent response of drought relief knowledge base, addressing the question of “what actions should be taken for drought relief?” [Conclusion] (1) A digital twin platform for drought relief and water replenishment scheduling is developed, and scenario simulation of the severe drought in the Yangtze River Basin in 2022 is conducted, forming a model case of a basin-level digital twin system for drought defense. (2) Future research should focus on water inflow and demand prediction models for the river basin, big data analysis of online public opinion, and intelligent matching and rolling optimization of drought relief scheduling scenarios, to effectively improve the intelligent level of drought relief and disaster reduction management in the Yangtze River Basin.
