[Objective] This study reveals the epistemological rationale underlying George Gabriel Stokes’ cautious and reserved stance in his review of Osborne Reynolds’ groundbreaking 1895 paper proposing the Reynolds-Averaged Navier-Stokes (RANS) equations. While Reynolds’ methodology has become a cornerstone of turbulence modeling in engineering practices, Stokes—co-developer of the Navier-Stokes (N-S) equations—notably refrained from offering an endorsement during its first-round review. Through an interdisciplinary investigation combining archival analysis, theoretical fluid dynamics, and philosophy of science, it is revealed that Stokes’ reservations stemmed not from technical negligence but from a profound understanding of the N-S equations’ physical completeness and the inherent epistemological limitations of turbulence closure models. [Methods] Three complementary approaches were employed: 1. Fundamental theory reconstruction: the N-S equations were reconstructed based on Stokes’ original axiomatic framework — Newton’s law of viscosity, the assumption of stress isotropy, and the law of mass conservation — confirming their physical completeness. However, introducing additional independent laws to close the unclosed terms derived from Reynolds averaging procedure would fracture the physical completeness of the N-S equations. 2. Theoretical framework comparison: Stokes’ derivation of viscous stress based on physical laws was juxtaposed with Reynolds’ empirical stress closure schemes, revealing a fundamental epistemological asymmetry between the physical law-based N-S equations and phenomenologically approximation methods. 3. Modern computational validation: Contemporary Direct Numerical Simulation (DNS) demonstrated that turbulent dynamics could naturally emerge from N-S equation solutions without auxiliary models, confirming Stokes’ intuition about the equations’ inherent prediction capability. [Results] 1. Closure paradox: unlike the viscous stress governed by Newtonian mechanics in the N-S equations, Reynolds stress lacks a definitive physical closure law. Any imposed closure model constitutes a departure from the N-S framework’s physical completeness. 2. Epistemological boundaries: Turbulence models essentially belong to engineering phenomenology rather than fundamental physics, with parameters relying on calibration and validation against domain-specific observational data rather than universal principles. 3. Computational confirmation: DNS technology validates Stokes’ foresight that turbulence is an inherent property of the Navier-Stokes equations, demonstrating that vortex dynamics and flow transition are natural solutions rather than modeling artifacts. [Conclusion] Stokes’ reserved position reflects a form of prescient scientific conservatism, recognizing that although RANS models have engineering utility, their operation has exceeded the epistemological boundary of first-principles physics. The physical completeness of the N-S equations essentially excludes the possibility of establishing an independent closure law for Reynolds stress, making turbulence models inherently approximate and limited in application. This study bridges historical insights with contemporary controversies in turbulence modeling, demonstrating that mathematical parameterization cannot compensate for the absence of physical laws. While RANS remains indispensable in engineering analysis, Stokes’ implicit critique continues to highlight the unresolved fundamental challenges in fluid mechanics.
[Objective] A bibliometric analysis is conducted using data from China National Knowledge Infrastructure (CNKI) to examine the application of remote sensing technology in monitoring river and lake morphology and water bodies (including runoff monitoring, sediment monitoring, water level monitoring, water surface monitoring, and water volume estimation). The study focuses on discussing the temporal distribution of research publications, spatial distribution of study areas, types of sensors used, and variations in research methods within China. It summarizes key applications and development trends of remote sensing technology in China’s river and lake evolution and management, and compares them with literature on similar topics published between 2014 and 2023 from the Web of Science (WOS) Core Collection. [Methods] Using the advanced search tool of the CNKI database, 25 topics were selected, including “evolution”, “erosion and deposition”, “sediment”, “turbidity”, “main channel”, “fluvial facies”, “bank collapse”, “river regime”, “shrinkage”, “expansion”, “wetland”, “riparian zone”, “connectivity”, “unmanned aerial vehicle (UAV)”, and others. Using the Advanced Search tool in the WOS, this study retrieved relevant literature from the WOS Core Collection of the past decade on similar topics. After excluding literature irrelevant to “river-lake system evolution”, this study ultimately selected 284 articles from CNKI and 745 from WOS for analysis. [Results] In the CNKI dataset, the quantity of literature on river and lake evolution studies using remote sensing technology has shown fluctuating increase since 2002, peaking in 2023 with annual literature quantity of 33 papers. In the WOS dataset, literature quantity has increased steadily since 2018, reaching its peak between 2020 and 2022. Earlier co-occurring keywords included “wetland” and “sediment transport”, while more recent keywords included “Surface Water and Ocean Topography (SWOT)”, “human activities”, “river morphology”, “bank erosion”, and “Google Earth Engine”. Further statistical analysis of the remote sensing data sources used in these studies reveals that Landsat satellite data were the most commonly used, followed by platforms such as MODIS, Chinese Resources Satellites, Environmental Satellites, Sentinel satellites, and Gaofen series. [Conclusion] The application of remote sensing technology in river and lake evolution studies in China has transitioned from reliance on single-source passive optical sensors (visible to infrared spectrum) to multi-source remote sensing through the integration of optical and microwave multi-satellite synergy. This development overcomes limitations of traditional methods for observation, simulation, and management of river-lake systems. Remote sensing technology provides long-term image data, and with further improvement in image interpretation capabilities, more accurate methods for identifying water bodies, vegetation, and other features are expected to further support research. Leveraging remote sensing to deepen the understanding of river-lake ecosystems is of great significance for achieving integrated watershed management.
[Objectives] The sedimentation of rivers and lakes poses a persistent challenge to water resource management. Dredging, while effective for removing excess sediment and restoring channel capacity, often triggers the resuspension of contaminated bed material, leading to secondary pollution and ecological disturbance. Among various dredging techniques, grab-type dredging is widely used for its adaptability to diverse bed conditions, but its impact on local flow fields and sediment dynamics remains underexplored. This study addresses this gap by employing a full-scale two-dimensional numerical simulation using the FS3M (Fluid-Structure-Sediment-Seabed Interaction Model) to investigate the hydrodynamic and sediment suspension responses during grab bucket descent. The aim is to identify descent strategies that minimize sediment resuspension and contribute to more environmentally friendly dredging operations. [Methods] The simulation framework integrates Large Eddy Simulation (LES) for turbulent flow, a Volume of Fluid (VOF) method for water-sediment interface tracking, and a sediment transport module (STM) for modeling both suspended and bedload sediment processes. A 23 m3 environmentally friendly grab bucket is modeled descending in a symmetric two-dimensional domain that includes a 3-meter-thick sand bed. Multiple descent cases are considered: a baseline with constant velocity (1.0 m/s) and six modified cases where the grab decelerates at different heights (1.0 m, 3.0 m, 5.0 m) above the bed, with secondary descent speeds of either 0.33 m/s or 0.50 m/s. Bed deformation, flow velocity, and sediment concentration distributions are monitored over time to assess each strategy’s environmental performance. [Results] Simulation results show that the grab bucket generates significant flow disturbances during its descent, especially near the sediment bed, causing bed erosion and sediment entrainment. In the baseline scenario, rapid descent leads to high flow velocities at the bed surface and the formation of vortices that promote sediment resuspension and diffusion. In contrast, cases involving velocity reduction prior to bed contact exhibit a marked decrease in sediment disturbance. Specifically: 1)Lowering the descent speed reduces the near-bed flow velocity and suppresses the entrainment of suspended sediment. 2)Starting the deceleration at 3.0 meters above the bed (Case D3) with a reduced speed of 0.33 m/s achieves the best balance between operational efficiency and environmental performance. 3)Cases with deceleration starting at 5.0 meters do not significantly improve sediment control compared to the 3.0-meter point, suggesting diminishing returns for earlier deceleration. 4)The presence of a movable bed significantly alters flow patterns compared to fixed-bed simulations, emphasizing the importance of accounting for sediment feedback in modeling. [Conclusions] This study demonstrates that modifying the descent speed of a grab bucket is an effective way to reduce sediment resuspension during dredging operations. Key conclusions are as follows: 1)Environmental Impact Mitigation: Gradually reducing the grab’s descent speed before it reaches the sediment bed effectively decreases near-bed turbulence and sediment entrainment, thereby mitigating secondary pollution. 2)Recommended Strategy: Decelerating to one-third of the initial speed (0.33 m/s) starting at 3.0 m above the bed is the optimal descent profile among the cases studied, achieving substantial reduction in suspended sediment without compromising operational feasibility. 3)Modeling Advances: The integration of fluid, structural, and sediment dynamics through the FS3M model provides a powerful tool for analyzing complex interactions in dredging scenarios, capturing realistic behavior that conventional monitoring methods cannot resolve. 4)Future Work: Further studies should extend the modeling to include sediment excavation and lifting processes, and explore dynamic descent control strategies based on real-time sediment feedback.
[Objective] Current research on water-sediment characteristics of the Huaihe River mainstream mainly focuses on single channels, while studies on water-sediment characteristics, relationships, and diversion patterns in its bifurcated channels are limited. This study selects the typical bifurcated section from Wangjiaba to Nanzhaoji (hereinafter referred to as “Mengwa section”) in the middle reaches of the Huaihe River, aiming to clarify the variations in water-sediment characteristics and diversion patterns of typical bifurcated channels. [Methods] A combination of cumulative anomaly analysis, Mann-Kendall (M-K) trend test, R/S analysis, and Morlet wavelet analysis was used to study the water-sediment inflow characteristics of the bifurcated channels in the Mengwa section from 1985 to 2020. The driving factors of abrupt changes and variation trends in water and sediment conditions were explored. The water-sediment coordination relationships and sediment transport capacity variations were evaluated using water-sediment relationship curves, and quantitative ratios of flow and sediment diversion across bifurcated channels of the Mengwa section were provided. [Results] The annual runoff at Wangjiaba station (total) showed no significant increasing or decreasing trend, while the sediment concentration displayed a pronounced decreasing trend, stabilizing below 0.15 kg/m3 after 2010 and continuing to decrease in the future. An abrupt change occurred around 1995. Sediment retention by reservoirs, agricultural land use changes altering underlying surfaces, and soil and water conservation measures were the primary driving factors of sediment concentration reduction. The sediment coefficient showed a decreasing trend, with external influence coefficient “a” gradually decreasing and sediment transport fitting coefficient “b” gradually increasing. This indicated a continuous reduction in sediment inflow intensity and an enhancement of the channel’s sediment transport capacity, promoting channel scouring. Meanwhile, the main channel cross-section exhibited sustained expansion, indicating an ongoing erosional state in this river section. The flow diversion ratio of the Menghe River was generally positively correlated with total flow in this section. At 2 000 m3/s (low-to-medium flow level), the main channel on the Huaihe River’s southern branch served as the primary flow passage. As the flow increased, the weight diverted through the Meng River progressively rose. Below the flow level of 6 000m3/s, its diversion capacity slightly declined, while at 6 000m3/s, the flow achieved equitable flow diversion with the mainstream of the Huaihe River. The sediment concentration ratios of each bifurcated channel were approximately equal to the ratios of their respective flow sediment transport capacity. [Conclusion] These findings provide theoretical support for sediment concentration calculation models in bifurcated channels during numerical simulations of water and sediment dynamics in the middle reaches of the Huaihe River, while offering a scientific basis for adopting long-distance dredging schemes in the river’s channel regulation strategies.
[Objective] This study focuses on the Yangtze River Economic Belt and constructs a water resources carrying capacity evaluation system that covers four subsystems: water resources, society, economy and ecological environment. The aim is to reveal the current status and future development trend of water resources carrying capacity in the Yangtze River Economic Belt, and to provide a scientific basis and decision-making reference for the rational planning and utilization of water resources, the adjustment and optimization of industrial structure, and ecological environment protection within the region. [Methods] The spatiotemporal evolution characteristics of water resources carrying capacity in the Yangtze River Economic Belt from 2012 to 2021 were analyzed using the TOPSIS method and the standard deviation ellipse method. Combined with the coupling coordination degree model, the coordinated development level among the subsystems within the water resources carrying capacity system was further investigated. To better understand the future development trend of water resources carrying capacity, the grey prediction model was applied to predict its trend over the next five years. [Results] The study revealed the dynamic changes in water resources carrying capacity in the Yangtze River Economic Belt during the study period, along with its spatial distribution characteristics and evolution trends. Between 2012 and 2021, the water resources carrying capacity showed an overall fluctuating upward trend, gradually improving from an alert state to a good state, indicating a significant enhancement in the region’s water resources carrying capacity. Spatially, the center of water resources carrying capacity shifted southwestward toward areas with relatively lower capacity, which may be related to regional economic development patterns, industrial restructuring, and differences in water use efficiency. Regarding system coupling and coordination, except for 2012, the coupling degree between subsystems reached a high coupling stage, and the coupling coordination evaluation gradually shifted from near disorder to good coordination, demonstrating continuously improving coordinated development and enhanced synergy among the subsystems. Analysis of influencing factors identified the proportion of tertiary industry, urbanization rate, and per capita daily domestic water consumption as the three factors most strongly correlated with water resources carrying capacity. Changes in these factors significantly affected its increase or decrease. The water resources carrying capacity was projected to show a positive development trend over the next five years. [Conclusions] It is recommended that the upstream areas develop water-saving irrigation, control fertilizer usage, and enhance urbanization levels; the midstream areas develop reclaimed water use, strengthen sewage treatment, and accelerate industrial transformation; and the downstream areas control population growth, promote water conservation and environmental protection, restore ecosystems, and increase forest coverage. The research findings provide a valuable scientific basis for the efficient management and utilization of water resources in the Yangtze River Economic Belt,as well as for promoting the coordinated development of the regional economy and society,and for achieving sustainable development goals in the region.
[Objective] Taking the Shiyang River Basin, a typical arid inland river basin, as the study area, this study aims to explore the spatial distribution and matching patterns of agricultural water and soil resources under different scenarios of future land use change, identify the supply-demand imbalance and its causes in the river basin, and provide support for the planning and decision-making of sustainable agricultural development at the river basin scale. [Methods] Using the FLUS model, this study simulated the spatial patterns of land use of the Shiyang River Basin in 2035 under three scenarios: cropland protection, natural development, and ecological conservation. By introducing the agricultural water and soil resource equivalent coefficient, this study established a matching assessment model for future agricultural water and soil resources in the Shiyang River Basin. Combined with the water yield module of the InVEST model, this study predicted spatiotemporal variations in water yield under three scenarios in 2035 and evaluated the spatiotemporal matching relationships of agricultural water and soil resources in the Shiyang River Basin. [Results] (1) All seven county-level administrative regions in the Shiyang River Basin showed varying degrees of severe water shortage, indicating an overall imbalance in agricultural water and soil resources, with water supply unable to meet the demand of cropland-based agricultural production. (2) The spatial pattern of water and soil resource matching in the Shiyang River Basin was generally better in the west than in the east of the basin. The Gini coefficient ranged from 0.2 to 0.3, showing a slightly increasing trend but still indicating a relatively balanced condition. The average water and soil resource matching coefficient was projected to be 797 m3/hm2 in 2035 under different scenarios, compared to 640 m3/hm2 in 2020, showing an overall improvement. (3) Although water yield increased to some extent within each county-level region under different scenarios in 2035, the imbalance in actual water utilization and distribution continued to deepen over time. The continuous expansion of cropland under the natural development and cropland protection scenarios made it more difficult to balance the supply and demand of agricultural water and soil resources in Gulang County, Minqin County, and Liangzhou District. [Conclusion] For regions with poor balance between precipitation and evaporation, such as Liangzhou District, a typical resource-based water-scarce region, it is recommended to alleviate water shortage through interregional water transfer and the introduction of external water sources. In regions where agricultural development is dominant, it is advisable to accelerate agricultural modernization, reduce water consumption per hectare, and adjust crop structures. For regions with poor matching between water and soil resources, such as Minqin County, where both resource-based and engineering-related water scarcity coexist, it is proposed to address the imbalance through interregional water diversion and transfer, systematically improving the efficiency of water resource development and utilization.
[Objectives] This study aims to analyze the applicability of existing precipitation, temperature, and runoff data in data-scarce regions, and to develop and evaluate a deep learning hybrid model driven by multi-source information for improving the accuracy of monthly runoff forecasting. [Methods] Based on historical precipitation, temperature, and runoff sequences from the Yulongkashi River, a Convolutional Neural Network-Bidirectional Gated Recurrent Unit-Attention (CNN-BiGRU-Attention) model was developed. An Improved Particle Swarm Optimization (IPSO) algorithm was used to optimize this model, forming the IPSO-CNN-BiGRU-Attention hybrid model. The performance of this model was compared with that of the Gated Recurrent Unit (GRU) model and the ABCD water balance model. [Results] The IPSO-CNN-BiGRU-Attention model that incorporated precipitation and temperature data overall outperformed the CNN-BiGRU-Attention and GRU models, showing better agreement with the observed values. As the predication period increased, the proposed model achieved a root mean square error (RMSE) of 2.11 m3/s, a mean absolute error (MAE) of 1.32 m3/s, a mean absolute percentage error (MAPE) of 73.76%, and a Nash-Sutcliffe efficiency (NSE) coefficient of 0.94. The highest forecast accuracy was observed in the first three months. [Conclusions] The IPSO-CNN-BiGRU-Attention model effectively integrates precipitation, temperature, and runoff information, significantly enhancing the accuracy of monthly runoff forecasts in data-scarce regions. The model demonstrates robust performance across different forecast horizons, particularly suitable for short-term predictions of 1-3 months. This approach offers a practical and reliable tool for hydrological forecasting and flood control/drought management in data-scarce basins.
[Objective] Traditional dredging methods for reservoir sedimentation can cause resuspension of sediments, leading to the release of nutrients, and then affect the water environment. Proposing a reasonable and feasible ecological dredging scheme is important to prevent water environmental pollution caused by sediment dredging, which is a fundamental requirement for the sustainable exploitation of reservoir sediments. To address the issues of sedimentation in the Three Gorges Reservoir and secondary water pollution caused by traditional dredging methods, this study focuses on typical sediment-accumulated river sections and explores ecological dredging technologies suitable for deep-water and complex environments. [Methods] This study comparatively evaluated the characteristics, applicability, and environmental friendliness of existing reservoir dredging technologies. Based on the segmented sedimentation characteristics of the Three Gorges Reservoir, it proposed an environmentally friendly ecological dredging technology suitable for the reservoir. Typical sediment-deposited river sections in Fuling and Zhongxian were selected as representative areas. A two-dimensional hydrodynamic-suspended sediment mathematical model was established to simulate the dredging effects under different dredging equipment, and an ecological dredging technical scheme for these areas was developed. [Results] The results showed that ecological dredging technology outperforms traditional methods in precision control, pollution prevention, and resource utilization. The study recommended using pneumatic dredging for the near-dam section, pneumatic or jet dredging for the middle section, and pneumatic or eco-friendly cutter suction dredging for the upper section and fluctuating backwater area. Simulations indicated that pneumatic dredging had the least impact on suspended sediment concentration and diffusion. Based on the simulation results, comprehensive dredging recommendations were proposed, including equipment selection, construction timing, residual water treatment, and sediment resource utilization. [Conclusion] The ecological dredging scheme proposed in this paper can provide a reference for ensuring the storage capacity of the Three Gorges Reservoir and its long-term effective use, as well as sustaining comprehensive benefits. It shows strong potential for promotion and practical engineering application value.
[Objective] As the uppermost section of the lower Yangtze River, the water quality changes in the Anhui section have attracted significant attention. Investigating the spatiotemporal variation characteristics of water quality and the underlying influencing factors in this region over recent years can provide clearer guidance for future water environment management in the lower Yangtze River. [Methods] Based on daily water quality data from 29 national assessment sections in the Anhui section of the Yangtze River from 2021 to 2023, this study adopted the comprehensive water quality index method to evaluate water quality, and integrated principal component analysis, correlation analysis, and other methods to explore the spatiotemporal variation and influencing factors of water quality. [Results] (1) The daily data values of different water quality indicators at various monitoring sections in the Anhui section from 2021 to 2023 exhibited varying degrees of fluctuation. Additionally, the WQI showed a significant positive correlation with pH and dissolved oxygen (DO) (P<0.01), while it exhibited a significant negative correlation with permanganate index (CODMn), ammonia nitrogen (NH3-N), total nitrogen (TN), and total phosphorus (TP) (P<0.01). (2) Overall, the water environment quality in the upstream basin in the Anhui section was superior to that of the downstream basin, with several downstream sections having WQI values above 80. The overall water quality in the Anhui section deteriorated progressively from the upstream to the downstream (flowing from the southwest to the northeast). (3) From 2021 to 2023, the overall water quality showed an upward trend, with annual average WQI values of 70.49, 72.24, and 72.49, respectively. Additionally, the quarterly trend within each year was characterized by an initial decline followed by an increase, with average WQI values for the first, second, third, and fourth quarters being 72.21, 71.74, 69.18, and 73.55, respectively. [Conclusion] (1) The overall average WQI value in the Anhui section of the Yangtze River is 71.65, indicating good water quality. CODMn, NH3-N, and TN are identified as the primary indicators influencing the water environment quality of the region. (2) Spatially, the water quality of the upstream basin sections (except for XK section) is better than that of the downstream basin, which may be attributed to differences in the connectivity of upstream and downstream lake systems, the degree of mineral resource exploitation and development, and the scale of agriculture. (3) Temporally, influenced by meteorological factors such as temperature and precipitation, water quality exhibits a trend of first decreasing and then increasing across the four quarters, with better water quality in winter and spring compared to summer and autumn.
[Objective] Accurately estimating the carbon sources and sinks of ecosystems and exploring their spatiotemporal evolution patterns are of great significance for optimizing territorial space management and promoting the low-carbon transition in Hebei Province. [Methods] This study utilized energy consumption data, remote sensing data, carbon density data, water carbon flux data, and salt marsh and coastal aquaculture data to calculate the carbon emissions from energy consumption, terrestrial ecosystem carbon sinks, and water carbon fluxes in Hebei Province. Additionally, a scientific analysis of the degree of carbon neutrality was conducted. [Results] (1) The overall carbon emissions from energy consumption in Hebei Province showed a continuous upward trend from 2000 to 2019, with emissions in 2019 reaching approximately four times those of 2000, at an average annual growth rate of about 6.98%. (2) The total NEP (Net Ecosystem Production) in Hebei Province from 2000 to 2020 showed significant fluctuations but an overall upward trend. The interannual variations in carbon fluxes from inland waters were minimal, showing a slight increasing trend. Blue carbon from marine aquaculture demonstrated overall growth, increasing from 6 600 tons in 2000 to 35 600 tons in 2020. (3) A comprehensive analysis of the carbon sources and sinks in Hebei Province’s territorial space revealed that the total ecosystem carbon sinks in 2020 could offset approximately 3.54% of the carbon emissions from energy consumption. [Conclusion] This suggests that Hebei Province currently has a relatively low carbon neutrality capacity, below the national average (15%), and faces enormous pressure to reduce carbon emissions and increase carbon sinks.
[Objective] Reservoir construction has severely degraded the ecological environment of reservoir banks. The high-frequency, large-amplitude water level fluctuations make ecological restoration in the drawdown zone particularly challenging. After the operation of Henan Tianchi Pumped Storage Power Station, the water level exhibits significant weekly regulation fluctuations, resulting in large areas of exposed concrete on reservoir banks, severe fragmentation of the drawdown zone, and extreme habitat stress that greatly impedes vegetation restoration. This study focuses on the ecological restoration of the rocky slope drawdown zone in the Henan Tianchi Pumped Storage Power Station reservoir to ensure water resource security. [Methods] To address the severely impaired ecological function of the drawdown zone, this study conducted systematic analysis of habitat characteristics, including hydrological patterns, bank characteristics, non-point source pollution, and plant communities. Focusing on the critical need for ecological restoration in rocky slope drawdown zones of pumped storage reservoirs, this study investigated regreening approaches targeting growth substrate construction, plant community rehabilitation, and vegetation management. [Results] After more than one year of implementation, vegetation in the drawdown zone showed robust growth. No slope failure or soil erosion was observed. Plants exhibited strong resilience in terms of post-submersion recovery, expansion, and colonization, achieving an overall survival rate of 83.2%. Bamboo Willow (Salix sp), Bamboo Willow cuttings (Salix sp), Zhongshan Fir (Taxodium hybrid), Wallich Willow (Salix wallichiana), Chaste Tree (Vitex negundo), Lax-flowered Myricaria (Myricaria laxiflora), Variegated Willow cuttings (Salix variegata), Small Dogwood (Swida paucinervis), and Chinese Distylium (Distylium chinense) all achieved survival rates exceeding 85% and exhibited long-term tolerance to complete submersion. Planting Variegated Willow (Salix variegata) using cuttings was recommended to enhance its survival rate. Through practical restoration efforts within the test area, 13 plant species tolerant to submersion, drought, and barren conditions were selected: Zhongshan Fir (Taxodium hybrid), Bamboo Willow (Salix sp), Wallich Willow (Salix wallichiana), Lax-flowered Myricaria (Myricaria laxiflora), Variegated Willow (Salix variegata), Small Dogwood (Swida paucinervis), Chinese Distylium (Distylium chinense), Chaste Tree (Vitex negundo), Bermuda Grass (Cynodon dactylon), Indian Shot (Canna indica), Lamb’s Quarters (Chenopodium album), Violet Orychophragmus (Orychophragmus violaceus), and Cosmos (Cosmos bipinnatus). [Conclusion] Ecological restoration of rocky slope drawdown zones in pumped storage reservoirs requires an integrated approach combining engineering and biological measures. Engineering measures provide the essential soil substrate for plant growth and ensure vegetation survival. Based on a comprehensive consideration of topography, geology, and water level fluctuation patterns, the geogrid + ecological bag + hanging net composite technique is applied in permanently exposed and alternately submerged zones, while the long-fiber ecological bag + mesh reinforcement composite technique is used in permanently submerged zones. Vegetation measures should adopt a tree-shrub-herb configuration model tailored to the degree of submersion stress and the desired landscape effect. ①Permanently exposed zone. Trees: Bamboo Willow (Salix sp), Zhongshan Fir (Taxodium hybrid), Wallich Willow (Salix wallichiana)+Shrubs: Chaste Tree (Vitex negundo) +Herbs: Cosmos (Cosmos bipinnatus), Violet Orychophragmus (Orychophragmus violaceus), Lamb’s Quarters (Chenopodium album), Indian Shot (Canna indica), and Bermuda Grass (Cynodon dactylon). ②Alternately submerged zone. Trees: Bamboo Willow (Salix sp), Zhongshan Fir (Taxodium hybrid) +Shrubs: Variegated Willow (Salix variegata), Small Dogwood (Swida paucinervis), and Lax-flowered Myricaria (Myricaria laxiflora) +Herbs: Bermuda Grass (Cynodon dactylon). ③Permanently submerged zone. Shrubs: Variegated Willow (Salix variegata), Small Dogwood (Swida paucinervis), and Chinese Distylium (Distylium chinense) +Herbs: Bermuda Grass (Cynodon dactylon). The findings hold significant implications for scientifically guiding regreening efforts in rocky slope drawdown zones of pumped storage power station reservoirs.
Foundation scour is one of the primary causes of hydraulic failures in river-crossing bridges. By integrating flume experiments, prototype observations, numerical simulations, and artificial intelligence methods, this study reviews research on foundation scour of river-crossing bridges over the past six decades, summarizes progress in three aspects of general scour, contraction scour, and local scour, analyzes the limitations in existing research, and proposes future research directions. In terms of physical mechanisms, most existing studies focus on bridge foundation scour under simplified boundary conditions such as straight channels, non-cohesive riverbeds, and cylindrical structures. However, cohesive sediments prevalent in natural rivers exhibit complex force interactions and high randomness, resulting in scour processes for bridge foundations that differ significantly from those in non-cohesive riverbeds. Moreover, in common natural channels such as braided, branching, confluence, and alternating wide-narrow channels, water-sediment dynamics and riverbed evolution involve numerous factors with strong uncertainties, making scour mechanisms for bridge foundations more complex than those in straight channels. Therefore, future research must focus on scour mechanisms under more boundary conditions commonly found in natural rivers to improve the theoretical framework for foundation scour of river-crossing bridges. Regarding scour prediction methods, existing research primarily relies on flume experiments and prototype observations of specific bridges. The former’s prediction accuracy is severely affected by scale effects, while the latter has limited applicability. To date, there is a lack of predictive formulas or analytical models that quantitatively consider the scale effects on bridge foundation scour. Data-driven models such as artificial neural networks and deep learning can effectively compensate for the inability of conventional prediction methods for bridge foundation scour to account for complex boundary conditions. In particular, multi-module multilayer perceptrons (multi-module MLPs) can construct hybrid neural networks incorporating physical scour mechanisms, showing great potential in addressing the challenges of predicting scour under complex boundary conditions. In numerical modeling, existing methods are often applicable to low Reynolds number conditions, with insufficient accuracy in capturing turbulence at high Reynolds numbers and absence of standardized grid size criteria. Sediment transport is frequently computed using empirical formulas, and dynamic grid technologies often suffer from low precision. Existing numerical methods exhibit inadequate coupling between turbulence models and sediment transport models. Moreover, current numerical simulations are limited to non-cohesive riverbeds, with few models applicable to cohesive riverbeds and virtually no reported models suitable for stratified riverbeds. Therefore, numerical models for bridge foundation scour require in-depth investigation to address these issues in the future, improving their applicability and reliability under complex boundary conditions. In addition, intensified human interventions—including sand mining, channel regulation, and dam construction—have triggered rapid riverbed degradation in many rivers. These degradation events often occur at scales, rates, and complexity far beyond conventional understanding of general riverbed degradation, resulting in highly destructive and abrupt changes. Future research should systematically investigate riverbed evolution under human disturbances. To build a more comprehensive understanding of foundation scour of river-crossing bridges, future studies should better integrate flume experiments, prototype monitoring, numerical modeling, theoretical analysis, artificial neural networks, and deep learning methods. This will enable systematic investigation of bridge scour under human disturbance and complex boundary conditions, thereby improving the theoretical system and developing more widely applicable and reliable scour design methods.
[Objectives] Traditional culvert designs often result in excessively high flow velocities within the channel, impeding the upstream movement of weak-swimming fish species. Installing small triangular baffles inside culverts has the potential to provide upstream passage for small fish while maintaining discharge capacity. This study aims to clarify the hydraulic effects of triangular baffles by arranging multiple small baffles along one side of a flume to simulate internal culvert structures and verify the hydraulic effects through flume experiments. [Methods] Three-dimensional velocity data were collected using an Acoustic Doppler Velocimeter (ADV) to analyze the distribution patterns of turbulent kinetic energy and Reynolds stress. The quadrant analysis method was employed to quantitatively assess the impact of the baffle system on flow velocity distribution, turbulence characteristics, and momentum transport modes. [Results] The results showed that the triangular baffles created stable low velocity zones (LVZs) along the sidewall, with longitudinal velocities ranging from -4 to 15 cm/s, and velocities at the outer edge of the baffles around 25 cm/s, below the critical swimming speed of small fish such as Rhinogobius giurinus. In the mainstream zone, the lateral profiles of longitudinal velocity were nearly identical, ranging from 25 to 30 cm/s, indicating that the small triangular baffles had minimal impact on mainstream flow and thus preserved discharge capacity, achieving synergistic optimization of hydraulic efficiency and ecological function. The proportion of the low velocity zone area remained relatively consistent along the flow path, accounting for 14.80%-18.07% of the total cross-sectional area, demonstrating the feasibility of using triangular baffles to stably expand LVZs. The baffles significantly enhanced turbulence intensity in the region near the baffle-side sidewall, generating clockwise vortices and positive horizontal Reynolds stress that play an important role in maintaining swimming stability. Although the turbulent kinetic energy and Reynolds stress in downstream LVZs were higher than those in high-speed regions without baffles, they remained below the threshold of fish swimming preferences. This moderate turbulence enhancement not only provided energy for swimming but also avoided excessive turbulence that could impair the sense of direction or balance. Momentum exchange was dominated by jetting (Q2) and sweeping (Q4) events, whose dominance increased with higher threshold parameter H0 (with a contribution rate of about 60% at H0=4). The transient vortices formed had planes parallel to the fish’s spine and body axis, reducing energy loss during upstream movement and improving swimming efficiency through vortex energy transfer. This provided a more favorable flow environment for weak-swimming fish species. [Conclusions] This study identifies the distribution patterns of mean flow and turbulence characteristics and introduces quadrant analysis into the study of culvert turbulence-fish behavior interactions. It reveals the promoting effect of small baffle structures in fish upstream migration and addresses the lack of detailed flow field and turbulence structure analyses in previous research. The findings offer a feasible hydraulic optimization paradigm and model reference for the design of eco-friendly culverts.
[Objective] To address the issue that conventional river regulation structures struggle to dynamically adapt to the highly variable characteristics of natural rivers, this study develops an innovative active flow-regulating vane system. [Methods] The system combined a vertically adjustable and rotatable vane structure with a remote intelligent control module. It allowed real-time monitoring and dynamic adjustment of flow parameters, thereby overcoming the limitations of traditional fixed structures such as spur dikes and deflector vanes. To investigate its applicability in curved river channels, the flow-regulating vanes were arranged in a 180°U-shaped bend model. The verified RNG k-ε turbulence model and VOF method were used to conduct numerical simulations of the bend’s flow field characteristics before and after the vane installation. The impact of the flow-regulating vanes on the hydrodynamic structure of the bend was analyzed. [Results] 1) Numerical results showed that when the top of the flow-regulating vanes was flush with the free water surface (at a flow rate of 7.9 L/s), the longitudinal velocity near the convex bank region increased by 21.67% compared to the original bend, while the maximum transverse velocity in the central region decreased by 70.33%, effectively weakening the transverse circulation. When the vanes were submerged to 0.3 times the water depth (at a flow rate of 15.8 L/s), the longitudinal velocity still increased by 13.64%, and the transverse velocity decreased by 37.63%. 2) Analysis of the flow field structure revealed that the vanes could split the original single clockwise vortex circulation structure within the bend into two vortices rotating in the same direction, which reduced the flow’s kinetic energy, lowered the circulation velocity, and decreased transverse sediment transport. 3) The distribution of bed shear stress showed that, after the installation of the flow-regulating vanes, the bed shear stress within the bend was uniformly distributed along the convex bank side, which helped alleviate sedimentation on the convex bank while avoiding concentrated scouring. Moreover, the suspended design of the vanes reduced flow obstruction at the bend bottom, solving the sedimentation problem caused by decreased flow velocities around traditional structures fixed to the riverbed, making it a viable option for flow regulation in hardened bend channels.
[Objective] The flow patterns of energy dissipation inside tunnels are complex, and theoretical calculations cannot meet design requirements. This research aims to: (1) verify the rationality of design parameters for energy dissipation in diversion tunnels at canal head based on hydraulic model tests; (2) propose an energy dissipation layout suitable for specific projects through model optimization to address high wave height inside the tunnel, insufficient clearance below the tunnel crown, and cavitation and erosion. [Methods] A hydraulic model test with a scale of 1∶1.5 was selected to simulate the diversion channel, pressurized tunnel, in-tunnel gate chamber, energy dissipation section, and a downstream section of free-flow tunnel. Additionally, an emergency gate shaft and the ventilation pipe behind the gate were simulated. A water tank was used as the model reservoir. The project involved three different discharge conditions, each with varying reservoir water levels, resulting in eight typical working conditions for testing. Then, based on the hydraulic model test results under different conditions, the downstream flow pressure characteristics, cavitation characteristics of the weir surface behind the operating gate, pressure characteristics of the gradually expanding stilling basin floor and sidewalls, flow connection patterns, and energy dissipation performance were obtained. Finally, the dimensions of the stilling basin section and the free-flow tunnel were improved, and wave suppression measures were optimized based on the test results. [Results] The hydraulic model test revealed shortcomings in the original energy dissipation scheme and proposed a combined layout of “stilling basin + wave suppression beam” suitable for in-tunnel energy dissipation. The test results showed: 1) the maximum wave height inside the free-flow tunnel was reduced by 67%, and the tunnel crown clearance met safe water conveyance requirements; 2) The local minimum cavitation number of the water flow at the curved section of the weir surface and the expanded section of the sidewalls behind the operating gate was about 0.37, indicating a low likelihood of cavitation erosion; 3) The root mean square of fluctuating pressure at measuring points along the stilling basin floor did not exceed 1.0×9.81 kPa, meeting structural design requirements. [Conclusion] This study proposes a combined energy dissipation method of “stilling basin + wave suppression beam” to address problems of high wave height and insufficient tunnel crown clearance in the original scheme. Compared with traditional submerged energy dissipators, the combined method significantly improves dissipation efficiency and has better energy dissipation characteristics. Hydraulic model tests verify the feasibility of the optimized scheme. The energy dissipation scheme is effective in solving the problems of large waves and insufficient tunnel crown clearance in similar projects. It is effective under multiple reservoir water levels and discharge conditions, and the wave suppression beam, as an in-tunnel energy dissipation structure, has little impact on tunnel flow capacity, demonstrating certain universality.
[Objective] This study aims to break through traditional limitations by quantifying the influence mechanism of crack penetration rate on the strength characteristics of expansive soil through laboratory experiments. It seeks to establish a predictive model for shear strength based on penetration rate, providing a scientific basis for evaluating the stability of engineering slopes. [Methods] A novel method was employed to simulate cracks using geomembranes. Triaxial specimens with varying crack penetration rates (0%, 33.3%, 50.0%, 66.7%) were prepared and subjected to consolidated drained triaxial tests. During the tests, interface strength parameters between the geomembrane and the soil were obtained through direct shear interface friction tests. Combined with the Mohr-Coulomb strength criterion and strength calculation methods for cracked surfaces, a composite strength analysis framework for the “soil block-crack” structure was established. Compared to traditional crack simulation methods, this technique enables precise control of crack geometry, effectively reproducing the crack development process and providing robust data support. [Results] Crack penetration significantly affected the mechanical behavior of expansive soils. As penetration rate increased, the stress-strain curves of the specimens exhibited a transition from strain hardening to strain softening. When the penetration rate increased from 0% to 66.7%, a distinct peak appeared under high confining pressure (400 kPa), and the peak strength decreased by 60.73%, indicating a pronounced increase in brittle failure characteristics. Under low confining pressure, the specimens exhibited no obvious peak strength and were mainly subject to plastic failure, with the stress-strain curve displaying mild strain softening. The ultimate deviatoric stress at failure was influenced by both confining pressure and crack penetration. With increasing penetration rate, the soil’s resistance to shear failure diminished, and the ultimate deviatoric stress decreased accordingly. This decline became more pronounced as confining pressure increased. When cracks were introduced into the specimen, they altered the stress concentration zones, promoting shear failure along the cracks. Obvious shear cracks appeared along the shear plane, and the failure mode shifted from bulging failure to dislocation failure along the crack surface. Shear strength was a key mechanical property representing soil failure characteristics. In this study, the strength parameters of specimens with cracks were calculated using the cracked-surface strength method, yielding accurate shear strength indices. When the crack penetration rate was 0%, the shear strength indices represented intact soil, with cohesion and internal friction angle of 37.6 kPa and 22.0°, respectively. When the penetration rate increased to 33.3%, cohesion and internal friction angle decreased to 30.7 kPa and 20.1°, down by 18.4% and 8.6% compared to the 0% case. At 50.0% penetration rate, these values further dropped to 27.6 kPa and 16.4°, decreasing by 26.6% and 25.5%, respectively. As penetration rate increased, the actual contact area between soil particles and crack surfaces grew, reducing frictional resistance along the shear plane. When the penetration rate reached 66.7%, cohesion and internal friction angle declined to 21.8 kPa and 15.2°, down by 42.0% and 30.9% from the 0% condition, indicating that cracks exerted a greater control over shear strength. Therefore, with increasing penetration rate, the shear strength parameters of the soil-crack surface consistently decreased. To further illustrate that the variation in shear strength parameters under different penetration rates was the result of the combined effect of soil blocks and cracks, this study established a comprehensive calculation formula for shear strength along the failure surface. A comparative analysis of the calculated and predicted shear strength values under different penetration rates showed that the deviation of the internal friction angle prediction from the experimental value ranged from -2.5% to 6.7%, and that of cohesion ranged from -19.7% to -3.3%, all within the allowable experimental error. [Conclusion] This study uses a novel simulation material to quantitatively analyze the influence of cracks on the strength properties of expansive soil, investigating the effect of cracks on shear failure patterns and strength characteristics. A comprehensive strength calculation formula is proposed to validate the influence of the integrated behavior of soil along the shear surface. The findings enrich the theoretical system of expansive soil crack mechanics and provide a reference for slope stability analysis in similar hydraulic engineering projects.
[Objective] With the advancement of rainwater and sewage diversion projects in cities along the river, trenchless pipe jacking technology has been widely adopted due to its efficiency and environmental advantages. However, pipe jacking in the river-crossing sections faces challenges posed by complex hydrogeological conditions, which can cause riverbed surface displacement and even lead to engineering accidents such as water inrush or blowout. There is still a lack of systematic analysis of the mechanisms influencing surface displacement in the river-crossing sections during pipe jacking construction. Most existing studies are based on assumptions of semi-infinite elastic bodies or static stratum conditions, making it difficult to accurately reflect the disturbance patterns under dynamic changes of parameters such as bulk density, cohesion, and internal friction angle of geomaterials in river-crossing sections. This study focuses on a pipe jacking project in the river-crossing section of a city along the Yangtze River, investigating the displacement patterns of the riverbed surface under fluid-solid interaction. It aims to reveal the influence mechanisms of key parameters, thereby providing theoretical support for safe construction. [Methods] A combination of theoretical analysis, numerical simulation, and empirical formula comparison was adopted. First, the strength reduction method was applied to reflect the soil weakening effect under fluid-solid interaction by reducing the geotechnical mechanical parameters (cohesion c and internal friction angle φ). Then, a 3D numerical model was established using COMSOL Multiphysics. The model simulated actual operating conditions through roller supports and fixed boundary conditions. Considering soil elastoplasticity, the grouting layer, and hydrostatic pressure boundary conditions, this model simulated stress redistribution and surface deformation during the pipe jacking process. In addition, Peck’s empirical formula was introduced to predict settlement, and the results were compared with the numerical simulation to verify the reliability of the model. Finally, the single-factor analysis method was used to systematically study the influence patterns of pipe diameter, grouting pressure, and soil elastic modulus on riverbed surface displacement. [Results] (1) Characteristics of soil stress distribution: During the pipe jacking process, the stress in the soil around the pipe exhibited a near “M”-shaped distribution, with the minimum stress at the pipe axis and the stress on both sides increasing first and then decreasing. The closer to the pipe, the narrower the “M”-shaped trough became. At 38 meters of jacking distance, the maximum stress value increased by about 60% compared to the initial state, concentrated mainly at the pipe bottom and pipe crown. (2) Riverbed surface subsidence pattern: The surface subsidence trough followed a “U”-shaped normal distribution, with the maximum subsidence located directly above the pipe axis. At 38 meters of jacking, the maximum subsidence reached 1.352 mm, closely matching the prediction of 1.313 mm by the Peck formula. However, due to the influence of high water pressure and soil parameter weakening, the simulation result was slightly conservative. (3) Influence of parameters: Increasing pipe diameter from 1.8 m to 2.4 m raised the maximum settlement by approximately 40% and widened the subsidence trough by 23%, indicating that large pipe diameters significantly intensified soil disturbance. Raising grouting pressure from 0.1 MPa to 0.3 MPa reduced the maximum subsidence by 35%, and the support and lubrication effect of the slurry sleeve effectively inhibited soil loss. Increasing the soil elastic modulus from 7.2 MPa to 14.4 MPa reduced the maximum subsidence by 46%, indicating that hard soil had significantly stronger deformation resistance compared to soft soils. [Conclusion] Under the disturbance caused by pipe jacking construction, the soil stress redistribution exhibits an “M”-shaped pattern, and the surface subsidence trend is consistent with the predictions of the Peck empirical formula, validating the applicability of the numerical model. (1) Pipe diameter, grouting pressure, and soil elastic modulus are key parameters influencing surface displacement. In engineering practice, it is necessary to balance the selection of pipe diameter (large diameters improve jacking efficiency but increase subsidence risk), optimize grouting pressure (to suppress subsidence and avoid excessive uplift), and improve the disturbance resistance of soft soil through reinforcement (such as pre-grouting). (2) This study is the first to construct a 3D fluid-solid interaction model for pipe jacking in the river-crossing section, combining the strength reduction method and parameter sensitivity analysis to provide a theoretical basis for similar projects. Its limitation lies in the lack of field monitoring data for validation. In the future, site monitoring should be incorporated to further improve model accuracy. The findings can provide guidance for design optimization and risk control of pipe jacking projects along the Yangtze River Economic Belt and under similar hydrogeological conditions, contributing to the implementation of the “joint efforts for environmental protection” strategy.
[Objective] Under the influence of climate change and engineering activities, the thermodynamic stability of subgrade engineering in permafrost regions faces severe challenges. To investigate the influence of seasonal temperature boundary conditions on the thaw consolidation characteristics of frozen soil subgrade, this study modifies the three-dimensional nonlinear large-deformation melting-thaw consolidation theory. [Methods] By introducing seasonal temperature boundary conditions and using the Mohr-Coulomb criterion to describe the plastic settlement deformation of thawed soil, a three-dimensional nonlinear plastic thaw consolidation theory incorporating seasonal temperature effects was developed. The theoretical model was numerically implemented using the FLAC3D simulation platform. Taking a typical high ice-content frozen soil subgrade section of the Qinghai-Tibet Highway as the research object, the thaw consolidation evolution patterns under seasonal temperature boundary conditions were systematically analyzed. The validity of the theoretical model was verified through comparison with field-measured data. [Results] The results showed that the settlement deformation of the frozen soil subgrade exhibited a periodic variation pattern with seasonal surface temperature changes, representing the most significant characteristic of thaw consolidation under seasonal temperature boundary conditions. Due to self-weight of subgrade soil, the distribution scope of vertical effective stress expanded with time. The calculation model considering plastic deformation demonstrated higher prediction accuracy. As plastic deformation accumulated continuously during thaw consolidation, its effect could not be neglected in long-term deformation predictions for high-ice-content frozen soil engineering. Through the study of the pore water pressure distribution during the consolidation process, it was found that the pore water in the shallow thawed area of the subgrade dissipated during initial operation. In the subsequent long-term operation, the continuous development of the thaw and settlement of frozen soil subgrade primarily resulted from the dissipation of the newly thawed pore water at the thaw front. [Conclusion] The improved theoretical model proposed in this study can more reasonably describe the thaw consolidation characteristics of high-ice-content frozen soil subgrades under seasonal temperature boundary conditions, providing a critical theoretical basis for the design and maintenance of subgrade engineering in frozen soil regions.
[Objectives] Large-scale urban underground space development has led to numerous anti-floating problems. Groundwater level is a key parameter in the anti-floating design of underground structures, but it is inherently dynamic and influenced by various factors. This study aims to investigate how groundwater level in fractured rock layers dynamically responds to rainfall. [Methods] Field monitoring was conducted along a subway line, with seven groundwater level monitoring points and two meteorological monitoring points installed. Real-time data of groundwater level in fractured rock layers and rainfall at the site were collected. Based on these data, the annual variation patterns of groundwater level and rainfall were analyzed. Groundwater level increments under moderate to heavy rainfall conditions (daily rainfall ≥10.0 mm) were extracted, and a linear fit was performed between rainfall and groundwater level increments. [Results] Groundwater level variations were closely related to rainfall, rising during wet periods and falling during dry periods, with peak-to-valley amplitudes ranging from 3.34 to 17.55 meters. Additionally, the slope of the linear fitting between groundwater level increment and rainfall ranged from 0.006 to 0.025, indicating varying response speeds of groundwater level changes to rainfall. These differences were mainly influenced by rainfall intensity, site topography, surface water systems, and excavation activities. Based on the permeability of the rock layers, recommendations for anti-floating design were proposed: when the permeability coefficient of fractured rock exceeds 20 m/d, underground structures should strengthen passive anti-floating measures or increase active drainage and pressure relief measures; when the permeability coefficient ranges from 10 to 20 m/d, the anti-floating safety factor should be appropriately increased; when the coefficient is below 10 m/d, standard design practices are sufficient. [Conclusions] The study identifies the main factors influencing groundwater level fluctuations, quantifies the response of groundwater level to rainfall, and proposes an anti-floating design method that accounts for the permeability coefficient of rock layers. This approach addresses the limitations of traditional anti-floating designs that assume a uniform design water level and provides practical guidance for the anti-floating design of subway stations.
[Objective] Underground oil storage caverns are typically located in areas with hard crystalline rock, where the stability of surrounding rock mainly manifests as localized block instability. Traditional rock mass classification methods focus solely on analyzing and evaluating the overall stability of the surrounding rock, often neglecting the problem of block instability caused by unfavorable combinations of structural planes. [Methods] Block theory, utilizing geometric topological analysis to evaluate rock blocks formed by intersecting structural planes and their stability characteristics, serves as an effective approach for assessing the stability of underground caverns. Building on this block theory, this study utilized the whole-space stereographic projection method to identify removable blocks formed by the combinatorial intersection of various structural planes. The residual sliding force of these removable blocks was then used to determine whether they were key blocks requiring support. Subsequently, key blocks underwent maximum block morphology analysis to eliminate non-engineering-support blocks. Finally, positional block analysis was performed on blocks requiring support. [Results] This study developed a comprehensive flowchart for on-site block prediction analysis during engineering rock mass excavation. The specific analysis process was as follows. First, the development patterns of structural planes in the main cavern were analyzed and summarized based on geological mapping data obtained from preliminary surveys and the excavation of the main cavern’s top layer. Next, structural planes were combined, and the whole-space stereographic projection method was employed to identify potential removable blocks and key blocks that may form on the middle and lower sidewalls of the main cavern for each combination. Then, the geometric morphology of these key blocks was analyzed using their maximum block shape. Finally, blocks requiring support were identified based on their maximum block morphology, and corresponding support schemes were proposed. [Conclusion] The main conclusions are as follows: (1) through full-space stereographic projection analysis of various combinations of structural planes, the removable blocks and key blocks formed by these combinations on the left and right sidewalls were identified. (2) Based on the maximum block morphology of each key block, “shallow-buried” and “slender” types of non-support key blocks were eliminated, leaving only the “compact” type of blocks requiring support. (3) Support schemes were proposed based on the actual morphology of the identified “compact” blocks. The findings provide a theoretical foundation for the support design of cavern surrounding rock and hold significant value for broader applicability in rock underground engineering construction.
[Objective] To promote the application of large-aggregate asphalt concrete in water conservancy projects, this study investigates the stress-strain and dilatancy characteristics of large-aggregate asphalt concrete under the same mix ratio but under varying influencing factors. [Methods] Under large shear deformation conditions (εa=30% ), static triaxial tests were carried out on asphalt concrete with Dmax=26.5, 31.5, and 37.5 mm. The dilatancy characteristics were elucidated from the perspectives of confining pressure and different maximum aggregate sizes. The relationship between the phase transformation stress ratio (Mpt) of asphalt concrete and confining pressure as well as different maximum aggregate sizes was comparatively analyzed, and an expression for determining whether dilatancy occurred in the specimen based on initial parameters was established. To further demonstrate the applicability of large-aggregate asphalt concrete, the Dmax=19 mm asphalt concrete in the core wall was replaced with Dmax=37.5 mm asphalt concrete. Based on a finite element model that ignored the contact and dilatancy between the core wall and the rockfill body, stress-deformation calculations were performed on the asphalt concrete core wall of a typical project in Xinjiang to simulate the behavior of the core wall with large-aggregate asphalt concrete and analyze the influence of maximum aggregate size on the calculation parameters. [Results] (1) With increasing aggregate size, the stress-strain curve of asphalt concrete changed from the softening type to the hardening type. (2) Under the same confining pressure conditions, the tangent modulus Et of large-aggregate asphalt concrete was lower than that of Dmax=19 mm asphalt concrete. As the confining pressure increased, both the maximum deviatoric stress and the maximum volumetric strain of Dmax=37.5 mm asphalt concrete decreased compared to Dmax=19 mm asphalt concrete, indicating that appropriately increasing the maximum aggregate size could weaken the shear dilatancy. (3) An empirical expression for calculating the phase transformation stress ratio Mpt based on initial physical parameters (confining pressure, different maximum aggregate sizes) was proposed, which could serve as a criterion for the transformation between shear contraction and dilatancy in asphalt concrete. A larger Mpt value indicated stronger shear dilatancy. (4) Furthermore, the finite element analysis results showed that there were almost no differences in settlement rate, maximum minor principal stress, and maximum major principal stress of the core walls. The dilatancy characteristics of large-aggregate asphalt concrete met the requirements of high-stress and deep overburden conditions for high dam projects. [Conclusion] Under the conditions of this study, increasing the maximum aggregate size in the asphalt concrete core wall has almost no effect on its stress condition. The experimental results provide a theoretical basis for the promotion and application of large-aggregate asphalt concrete in high dam projects under high-stress and deep overburden conditions.
[Objectives] This study aims to investigate the lateral bearing characteristics of bucket foundation breakwaters, focusing on their failure modes, ultimate bearing capacity, the relationship between rotation and displacement, soil-structure interaction, and cyclic bearing behaviors. The goal is to improve computational theories of bucket foundation breakwaters and support their engineering design and applications. [Methods] Based on the actual structural configurations, a 1∶20 large-scale test model was designed, along with a foundation bed model simulating the sandy soil conditions of port areas, to simulate the service performance of bucket foundation breakwaters. The loading process covered the entire phase from post-installation to failure. While validating the test conditions using the finite element analysis, supplementary finite element analysis was conducted for different structural configurations and soil conditions, enabling a systematic study of the bearing characteristics and load response of bucket foundation breakwaters. [Results] (1) In the early stage of installation, the sidewall friction increased linearly, with the average friction measured in the test being 41.23 kPa and the average friction coefficient 0.405. (2) The failure mode was general shear failure. The displacement pattern at the limit state obtained from numerical analysis was consistent with the test results. When the displacement reached 150.3 mm, the maximum displacement of the soil on the rear side was 54.2 mm. (3) The ultimate bearing capacity obtained from the model test was 14.26 kN, while the finite element analysis calculated 15.07 kN, with a relative error of 5.68%. The deformation process of bucket foundation breakwaters could be divided into three stages: quasi-elastic stage, plastic stage, and failure stage. In the quasi-elastic stage, the displacement increased linearly, with an elastic limit displacement of about 1.0%L and a plastic limit displacement of about 3.0%L. (4) Before failure, earth pressure in the passive zone increased with displacement, reaching a maximum increment of 74.2 kPa. Earth pressure in the active zone was significantly smaller, with a maximum increment of 10.2 kPa. The variation trends of earth pressure on the connecting wall and the cylinder wall were consistent, and the deformation coordination between the foundation and the internal soil was relatively good. (5) The bearing capacity of bucket foundation breakwaters in sandy soil was better than in silty clay, which was better than in silt. Under the same displacement, rotation was more pronounced in sandy soil, while under identical loading conditions, the most significant rotation occurred in silt. (6) The ultimate bearing capacity of the bucket foundation breakwaters was negatively correlated with both the length-to-height ratio and width-to-height ratio, but positively correlated with the length-to-height ratio. (7) Under lateral cyclic loading, the bucket foundation breakwaters showed cyclic hardening during positive rotation and cyclic degradation during negative rotation. The stiffness reduction was more pronounced during positive rotation. [Conclusions] The deformation of bucket foundation breakwaters has three stages: quasi-elastic, plastic, and failure stages. The overall failure mode is general shear failure, and there is a high degree of deformation coordination between the foundation and the soil. Soil type significantly affects bearing capacity, with sandy soil performing the best and silt the worst. In addition, the geometry layout greatly influences performance. Under cyclic loading conditions, the bucket foundation breakwaters exhibit enhanced plastic deformation capacity, good energy dissipation, and excellent seismic performance.
[Objective] The attitude of a shield machine is a critical parameter that significantly affects tunnel construction, directly determining construction safety and project quality. To ensure that shield tunneling closely aligns with the designed alignment and to improve engineering construction quality, this study proposes a novel shield attitude prediction model, called WM-CTA, based on deep learning technology. [Methods] The WM-CTA model primarily consists of two frameworks: a data preprocessing module (Wavelet Transform and Maximum Information Coefficient) and a prediction module (Convolutional Neural Network and Attention Mechanism). The preprocessing module, composed of Wavelet Transform (WT) and the Maximum Information Coefficient (MIC) algorithms, was used to perform noise reduction and parameter correlation analysis on the raw data, thereby generating enhanced inputs. The Convolutional Neural Network (CNN) integrated with a channel-wise attention mechanism explored parameter weight differences and extracted local data features. Subsequently, the Temporal Convolutional Network (TCN) was employed to capture temporal dependencies and dynamic variations in the data. Finally, the Attention Mechanism (AM) was applied to extract key temporal node information. The model’s prediction performance was validated using monitoring data from a section of a shield tunnel under construction in Shenyang. Experiments were conducted on data for noise reduction and correlation analysis, followed by analysis of the model’s prediction performance and generalization ability. [Results] Experimental results showed that the monitoring curves processed with wavelet transform had improved smoothness with reduced frequency of abrupt changes between data points. Correlation analysis indicated that shield construction parameters exerted greater influence on shield attitude than soil parameters, enabling dimensionality reduction of input parameters. Compared with four baseline models, the proposed WM-CTA model achieved minimum MAE and RMSE and maximum R2 value. [Conclusion] The experiments verify that the WM-CTA model delivers optimal prediction performance with high computational efficiency. Furthermore, the model exhibits strong generalization ability, providing valuable references for similar future engineering projects.
[Objective] This study investigates the mechanical properties and microstructural evolution of coarse-grained sulfate saline soils in the arid inland regions of Northwest China, modified with lignin fiber (LF) and polypropylene fiber (PP). It aims to clarify the effects of fiber dispersion methods, salt dissolution behavior, and fiber-salt interactions on soil strength with different sodium sulfate (Na2SO4) contents, thereby providing engineering strategies to mitigate soil-related hazards in construction. [Methods] Lignin fiber (hydrophilic) and polypropylene fiber (hydrophobic) were incorporated into saline soils using dry and wet mixing methods, respectively, to ensure uniform dispersion. A series of laboratory tests were performed, including fiber water absorption measurements, scanning electron microscopy (SEM) for microstructural observation, energy dispersive X-ray spectroscopy (EDS) for elemental analysis, and unconfined compressive strength (UCS) tests on soil samples with Na2SO4 contents ranging from 0% to 6%. The effects of salt content, fiber type (LF or PP), dosage, and their interactions on compressive strength were evaluated through multifactor analysis of variance (ANOVA) using SPSS software. [Results] (1) Fiber characteristics: The lignin fiber, hydrophilic and flat with a ribbon-like structure, had a porous, rough surface, demonstrating a water absorption ratio of 6.70 in pure water (an 8% reduction in saline solutions). Salt crystals adhered to its surface in the form of scales or layers, leaving minimal salt in soil pores. In contrast, the polypropylene fiber, hydrophobic and smooth with a cylindrical shape, exhibited a lower water absorption ratio (4.25 in pure water, 63% of that of LF), with further reduction (7%-23%) in saline conditions. Salt crystallized within the soil pores rather than on the fiber surface. (2) Salt dissolution dynamics: At salt contents ≤3%, complete salt dissolution occurred regardless of fiber type. At 6% salt content, approximately 83% dissolved, while the remaining 17% formed needle-like crystalline clusters that reinforced the soil skeleton. Lignin fiber increased the optimal water content in high-salt soils, promoting nearly complete salt dissolution. Polypropylene fiber had no significant effect on salt dissolution. (3) Strength behavior: Salt content primarily influenced UCS trends. Strength peaked at 1.5% salt (a 40.3% increase compared to untreated soil), then declined sharply, with a 37% reduction at 6% salt. Stress-strain curves shifted from strain-softening to strain-hardening behavior as salt content increased. Polypropylene fiber consistently enhanced UCS and residual strength. Optimal dosages were 0.35% for low-to-moderate salt soils (<3%, with strength increases of 150%-213%) and 0.45% for hypersaline soil (6%). Its smooth structure allowed salts to remain dissolved, while the fiber network facilitated load redistribution. Lignin fiber improved strength in low-to-moderate salt soils (12%-118% increase at 2%-4% dosage, optimal at 2%) but weakened high-salt soils (4%-17% decrease at 6%) due to salt aggregation on its rough surface. (4) Statistical significance (ANOVA): For LF-modified soils, salt content had the most significant effect on strength, followed by the interaction between salt content and fiber dosage. In PP-modified soils, salt content and fiber dosage were significant independent factors, with minimal interaction effects. [Conclusion] (1) Fiber performance hinges on microstructure and hydrophilicity. Polypropylene fiber, with its hydrophobic nature and load-distributing network, strengthens soil across all salt levels but requires higher dosages in hypersaline conditions. Lignin fiber enhances the strength of low-to-moderate salt soils by promoting salt dissolution but destabilizes high-salt soils due to surface-induced salt crystallization. (2) Salt dissolution and crystallization play a critical role in the mechanical properties. At high salt contents, undissolved crystals become part of the soil structure, while the fiber type influences both salt solubility and distribution. (3) Engineering strategies must align fiber selection with salt content. Polypropylene fiber is recommended for hypersaline soil, while lignin fiber proves more effective under moderately saline conditions. This study provides practical guidelines for managing sulfate saline soils in arid regions, emphasizing microstructure-driven design approaches.
[Objective] The aim of this study is to investigate the effects of acid-base conditions on the mechanical properties of expansive soil. [Methods] Expansive soil from Section C003 of the Yangtze-to-Huaihe Water Diversion Project was taken as the research object. A self-developed leaching test device was employed to leach expansive soil samples with acid-base solutions of varying pH values. After leaching, the relationship between strength changes of expansive soil and pH values of solutions was investigated using critical water content tests and consolidated drained triaxial shear tests. Chemical composition analysis and X-ray diffraction tests were conducted to investigate the underlying mechanism driving the variations in physical and mechanical properties. [Results] (1) After 7-day leaching with acid and alkali solutions, the samples showed different changes in morphology and form. Specifically, during acidic solution leaching, microbubbles formed on the sample surface, which developed into numerous pores after 7 days of leaching. In contrast, during alkaline solution leaching, no significant surface changes were observed initially, but after 7 days of leaching, the samples exhibited volume expansion and white crystals formed on the surface. (2) Critical water content and triaxial compression tests revealed that after 7 days of acidic solution leaching, the physical and mechanical properties of expansive soil blocks progressively deteriorated with decreasing pH values (compared to samples leached with pH=7 solution). Specifically, as pH values decreased, the liquid limit, plastic limit, and plasticity index decreased, the cohesion showed a significant decrease, and the internal friction angle showed a minor decrease. After 7 days of alkaline solution leaching, the physical and mechanical properties of expansive soil blocks gradually strengthened with increasing pH values (compared to samples leached with pH=7 solution). Specifically, as pH values increased, the liquid limit, plastic limit, and plasticity index increased, the cohesion showed a significant increase, and the internal friction angle showed a slight increase. (3) XRD tests and chemical composition analysis of expansive soil blocks after acid and alkali solution leaching revealed that the interaction mechanisms between the acid and alkali solutions and the soil primarily involved ion exchange and reactions between soil minerals and solutions. These processes modified the double-layer thickness between soil particles and the content of free oxide cements and water-soluble salts, thereby changing the interparticle contact patterns and soil microstructure. After acidic solution treatment, the diffuse double-layer became thinner, the cements were dissolved, and the soil structure deteriorated, leading to progressively deteriorating physical and mechanical properties with decreasing pH. After alkaline solution treatment, the diffuse double-layer became thicker, accompanied by the formation of new cements that filled pores of various sizes inside the soil, making the soil structure more compact, leading to systematically enhanced physical and mechanical properties with increasing pH.
[Objective] Pile-soil stress ratio is a key parameter in the design of rigid pile composite foundations for shallow-buried rock and soft soil foundations, but the rules governing its value and influencing factors remain unclear. [Method] Based on a concrete sluice dam project, this study carried out 7 sets of scaled indoor physical model tests, systematically studied the bearing characteristics of soft soil single-pile composite foundations and the pile-soil stress ratio, analyzed the influences of factors such as cushion type, pile loading conditions, pile spacing and pile end bearing stratum, and obtained the variation trend of pile-soil stress ratio with load and the pile-soil stress ratio corresponding to bearing capacity. [Results] In the initial loading stage, the P-S curves of the tested single-pile composite foundations exhibited linear changes, and the soil under the bearing plate was in an elastic deformation state. With the increase of load, a sudden change in slope appeared in the P-S curve of the bearing pile at the lower end of the cement-soil cushion, and the characteristic value of foundation bearing capacity should be inferred according to the proportional limit. The P-S curves of friction piles under the cement-soil cushion and friction piles and end-bearing piles under the gravel cushion mainly exhibited a gradual change characteristic, and the characteristic value of foundation bearing capacity should be estimated according to the relative deformation value of 1% of the side length of the bearing plate. Under the two cushion conditions, the characteristic values of the bearing capacity of the single-pile composite foundation of end-bearing piles could meet the design requirements, while those of friction piles could not. The pile-soil stress ratio of end-bearing piles basically showed a monotonous increase with load, while that of friction piles showed an initial increase followed by a decrease. The maximum pile-soil stress ratio of end-bearing piles in the cement-soil cushion was 16.8, and that of friction piles was 13.7, with an increase of about 22.6% for end-bearing piles. The pile-soil stress ratio of end-bearing piles corresponding to the design bearing capacity of 290 kPa could be taken as 9.7, and that of friction piles could be taken as 8.1. Therefore, for shallow buried rock-soft soil foundations, rigid pile composite foundations should adopt end-bearing piles embedded in rock. The bearing capacity of end-bearing piles in the cement-soil cushion was close to that in the gravel cushion, but the pile-soil stress ratio decreased from 16.8 to 8.2, a decrease of about 51.2%, indicating that the gravel cushion had a better stress adjustment capacity. The pile end bearing stratum and pile spacing were key design parameters. When the pile spacing was adjusted from 1.4 m to 1.8 m, and the pile tip bearing stratum was adjusted from weakly weathered rock to strongly weathered rock, the pile-soil stress ratio decreased by 42.3%, but the bearing capacity still met the design requirements, which was more economical. [Conclusion] The cement-soil cushion significantly improves the bearing capacity of the composite foundation and the pile-soil stress ratio, and its maximum pile-soil stress ratio is about twice that of the gravel cushion. The strength of the pile end bearing stratum and the pile spacing have a significant influence on the pile-soil stress ratio, and the scheme can be optimized by increasing the pile spacing and adjusting the pile end bearing stratum. The bearing capacity of the end-bearing pile composite foundation under the cement-soil cushion is close to that under the gravel cushion, but the pile-soil stress ratio is higher. A composite embedded cushion layer can meet both seepage control and stress adjustment requirements. The research results can provide a theoretical basis for the optimal design of rigid pile composite foundations in shallow buried rock-soft soils.
[Objective] Shear strength serves as a key parameter in soft soil engineering, and accurately obtaining shear strength can greatly optimize project design and enhance construction safety. To investigate the shear strength characteristics of soft soils in the Nansha District of Guangzhou, geotechnical investigation data are collected from dozens of on-site survey projects. The data include both linear projects like rail transit systems and planar projects such as civil construction sites. [Methods] The collected data were statistically analyzed according to burial depths of 0-10, 10-20, and 20-30 m to obtain the quick shear strength parameters of silt and silty soil. Linear regression was performed on in-situ vane shear test results to determine the consolidated quick shear strength parameters. Triaxial compression tests were conducted on local soft soils to obtain consolidated undrained and consolidated drained strength parameters. The undrained shear strength was obtained through unconfined compressive strength tests and vane shear tests. Correlation analysis was conducted between the quick shear and consolidated quick shear strength parameters from direct shear tests. Additionally, comparative analysis was performed on the unconsolidated undrained, consolidated undrained, and consolidated drained shear strength from triaxial compression tests. Sensitivity analysis was applied to the unconfined compressive strength and vane shear test results to estimate the shear strength of remolded soil. [Results] (1) The thickness of soft soil in the study area mainly ranged from 5 to 25 m, with coastal regions in the southwestern part of Nansha District exhibiting thicknesses exceeding 45 m. (2) The quick shear strength parameters of the local soft soil were determined as follows. For silt at 0-10 m depth, the cohesion cq and internal friction angle φq were measured at 6.40 kPa and 4.10°, respectively, while those at 10-20 m depth were 8.50 kPa and 6.10°. For silty soil, the corresponding values were found to be 7.60 kPa and 5.10° at 0-10 m depth, and 8.60 kPa and 6.30° at 10-20 m depth. (3) The consolidated quick shear strength ccq of soft soil at 0-10 m depth ranged from 11.06 to 11.98 kPa, with an internal friction angle φcq varying between 2.40° and 3.11°. At 10-20 m depth, ccq exhibited a range of 5.56-13.70 kPa, while φcq ranged from 1.25°-4.76°. (4) In triaxial tests, the consolidated drained shear strength parameters (c', φ') of soft soil were determined as 13.75 kPa and 14.76°, respectively, while the consolidated undrained strengths (ccu, φcu) were 13.13 kPa and 11.50°, respectively. (5) The undrained shear strength of undisturbed soil obtained from vane shear tests and unconfined compression tests was 14.84 kPa and 15.83 kPa, respectively, indicating close agreement between the two methods. The undrained shear strength of remolded soil obtained from vane shear tests and unconfined compression tests was 4.99 kPa and 7.63 kPa, respectively. The vane shear strength of remolded soil was much lower than that from unconfined compression tests. The strength of remolded soil was approximately 1/3 to 1/2 of the strength of undisturbed soil. (6) The cohesion of soft soil under consolidated quick shear conditions increased by over 45% compared to that under unconsolidated quick shear conditions. The internal friction angle in the consolidated quick shear showed a decreasing trend compared to the unconsolidated quick shear, with most values declining by 20%-40%. Notably, at the same burial depths, the quick shear strength and consolidated quick shear strength of silty soil were greater than those of silt. (7) The cohesion values derived from triaxial unconsolidated undrained, consolidated undrained, and consolidated drained shear tests showed strong consistency. Based on the consolidated undrained shear strength, the internal friction angle of consolidated drained shear increased by approximately 30%. (8) Unconfined compression tests revealed that the sensitivity of soft soil mainly ranged from 1.4 to 3.0, while vane shear tests indicated a sensitivity range mainly from 2.0 to 4.2. Both sets of data indicate medium sensitivity. Sensitivity increased with depth initially, but began to decrease beyond a certain depth. [Conclusion] These findings provide valuable insights for soft soil engineering in the region and offer practical references for geotechnical investigation, design, and construction. Certain anomalies and unconventional patterns are observed in the dataset, including the opposite variation trends in the consolidated quick shear strength of both silt and silty soil with increasing depth, as well as the difference in the rate of strength change for silt at depths of 10 m≤h<20 m under consolidated quick shear compared to direct shear conditions. Future research should focus on collecting additional soft soil test samples to obtain more definitive conclusions.
