s River scouring is the primary cause of impulsive riverbank failure. Its direct effect is to cause catastrophic changes in the structure of the riverbank slope, which then leads to riverbank collapse. However, its internal evolution mechanism is unclear. To solve this problem, a continuous-discontinuous deformation analysis method that can reveal the evolution mechanism has been developed based on the Discontinuous Deformation Analysis (DDA) method. It discretizes the soil into Voronoi-shaped sub-blocks, forces the displacement coordination of the continuous medium through the defined bar element between the sub-blocks, and simulates the evolution from continuum to discontinuum through the bar element failure. At the same time, the open-close iteration algorithm is still used to deal with the contact between the real block boundaries and there is no need to judge the contact between sub-blocks. Then, for the first time, a generalized model of riverbank collapse caused by flow erosion is built, the entire failure process is simulated, and the effects of different soil strengths and slope ratios on the failure mode are discussed. The results indicate that it is insufficient to explain the mechanism of riverbank collapse only by using the concept of circular slip failure of a traditional soil slope.
Soil organic carbon (SOC) plays a vital role in mitigating climate change and ensuring food security. In this study, a legacy database containing analytical data for 216 soil profiles collated from the most recent soil series survey in China was used to clarify the spatial distribution and storage of soil organic carbon in the Dongting Lake basin. The results showed that the SOC contents decreased with increasing depth of the soil. The spatial distributions of SOC contents decreased from the central to the northeast part of the basin, and the spatial variation trend of each layer was consistent. Elevation, normalized difference vegetation index, topographic position index, and land use intensity were the key factors affecting SOC contents. Natural forests contributed more to SOC sequestration than plantations did in medium slope areas (6°–25°). For the 0–100 cm soil layer, the average density and total storage of SOC were 12.71 kg C m⁻² and 3.32 Pg, respectively. The study suggested that an improved algorithm for SOC estimation and effective ecological restoration policy is needed in the future.
Land use change may alter roots and soil properties, thus greatly affecting soil detachment. Previous research mainly focused on quantifying soil detachment, while few studies have analyzed the soil detachment variation mechanism and its dominant factors under different land uses. The objective of this study was to investigate the response mechanism of the soil detachment capacity (SDC) to hydrodynamic parameters and root-soil composite properties across different land uses. Undisturbed soil samples were collected from four different land uses (cropland, orchard, grassland and woodland). The samples were subjected to flow scouring through hydraulic flume experiments under six different stream powers. The results showed that the SDC of cropland and orchard, with a mean value of 0.46 kg·m⁻²·s⁻¹, was significantly higher than that of grassland and woodland, with a mean value of 0.10 kg·m⁻²·s⁻¹. The dominant factors affecting the SDC differed among different land uses. For cropland, the dominant factor was hydrodynamic parameters, while it was root and soil properties for orchards, grassland and woodland. The SDC variation with root length density (RLD) was greatly influenced by hydrodynamic conditions in farmland. There was a clear zoning phenomenon for SDC variation with RLD in grassland and woodland. The critical conditions of different zones were also quantified. Different dominant factors affected the SDC within different zones: the dominant factor was roots when the RLD in root-soil composites was higher; the dominant factor was soil properties when there was lower RLD and better soil structure; and the dominant factor included both hydrodynamic parameters and roots under other conditions. Based on stream power, RLD, root mass density, clay content and organic matter, SDC prediction models suitable for different land uses were developed (Nash–Sutcliffe efficiency = 0.92, Decision coefficient = 0.92). This study provides a scientific basis for analyzing the varying mechanisms of soil erosion involved in the land use transfer process.
Due to their special geographical locations and environments, plateau lakes play a key role in maintaining regional water balance, but lake water storage changes are upsetting this balance. Based on data from lakes on the Tibetan Plateau (TP), this study used the Spatial Processes in Hydrology (SPHY) model to simulate the runoff process in the Siling Co basin from 2000-2016 and estimated the changes in water storage of Siling Co and the contribution of each component of runoff into the lake. The results showed that the water storage capacity of Siling Co has increased by 1.157 billion m /yr, declines in precipitation have significantly reduced baseflow(BF), rainfall runoff(RR), and Snow runoff(SR), while temperature increases have raised glacier runoff(GR). The simulated average runoff showed that BF, GF, RR, and SR contribute 24%, 22%, 16%, and 38%, respectively, of the flow into Siling Co. Based on hypothetical climate change scenarios and two Shared Socioeconomic Pathways (SSP1-2.6 and SSP3-7.0) from the MRI-ESM2-0 GCMs, this study estimated that a 10% increase in precipitation could lead to a 28.45% increase in total runoff, while a 1 °C increase in temperature could lead to a 9.49% decrease in runoff. The average runoff depth of the basin is expected to increase by 29.77-39.13 mm, since the temperature and precipitation may increase significantly from 2020-2050. The intensification of glacial melting caused by the increase in temperature continues, posing a greater challenge to many water resources management problems caused by the expansion of lakes.
Land use/cover change (LUCC) affects regional climate not only through its direct changes of land surface properties, but also through its further modifications of land–atmosphere interactions. Urban land expansion is a typical case of LUCC in highly populated areas and has been widely discussed about its impacts on regional air temperature, notably known as urban heat island (UHI) effects. Besides temperature, atmospheric humidity, as another key variable in hydrometeorology and climate, would be inevitably affected by LUCC as well. However, the impacts of LUCC on atmospheric humidity seem to have not been investigated as much as those on temperature. We examined atmospheric humidity changes by trend and change point analyses of humidity and heat content indicators of three representative urban agglomerations in the Yangtze River Economic Belt, China during 1965–2017, and found the evident urban dry island (UDI) effects which are characterized by significant humidity decrease and vapor pressure deficit increase. In urban cores with different levels of development, the severity of UDI is different. Furthermore, strong positive correlations between transpiration and evaporation (TEVP) and humidity, and between leaf area and TEVP were recognized during 2001–2017 when cities entered the accelerated stage of land expansion, indicating that LUCC affects regional climate through an ecohydrological way. We speculated that the UDI effect will not appear until urban land expands to a certain scale, for urbanization-induced LUCC may exert a larger influence on UDI than on UHI by considerably altering the latent heat flux in the later period of current urban expansion. The increasing impacts of urbanization on atmospheric humidity should attract wider attention in the future, so as to mitigate climate change and maintain sustainable development.
Soil erosion is very pronounced during late winter and early spring when frozen soil thaws on the Loess Plateau of China. The alternating action of seasonal freeze–thaw and wind erosion provides sufficient material sources for water erosion in the rainy season, greatly increasing the risk and intensity of soil erosion. To quantify the effect of seasonal freeze–thaw, wind erosion and their alternating action on runoff and sediment of different slopes, rainfall tests of different slopes (control, seasonal freeze–thaw, wind erosion and seasonal freeze–thaw + wind erosion of sandy loam, silty loam and clay loam) were carried out indoors. The results showed that the mean runoff and sediment yield start times of sandy loam (9.84 and 12.75 min) were significantly greater than those of silty loam (8.92 and 9.98 min) and clay loam (4.92 and 5.98 min, P < 0.05). The start time of runoff yield after wind erosion, freeze–thaw and alternating action slopes increased by 1.14, 1.35 and 1.62 times, respectively, and the time of runoff and sediment yield on the control slope were all the lowest. The runoff rates under different slopes all substantially increased first and then gradually stabilized. On different slopes, the mean runoff rates of the three soils decreased in the order of wind erosion > alternating action > freeze–thaw > control slopes. The minimum value occurred on the alternating action slope with silty loam (161.56 ± 24.78 g/(m² min)), and the maximum occurred on the wind erosion slope with clay loam (360.77 ± 35.98 g/(m² min)). The process of sedimentation was similar to that of runoff. The mean sediment yield values of sandy loam (4.82 ± 0.83 kg) and silty loam (4.66 ± 0.58 kg) were much greater than those of clay loam (0.65 ± 0.17 kg). In addition, the sediment yield increase magnitudes of silty loam under freeze–thaw, wind erosion and their alternating action slopes (58.86 %, 17.47 % and 58.18 %, respectively) were higher than those of sandy loam (29.96 %, 3.23 % and 44.28 %, respectively) and clay loam (20.50 %, 13.16 % and 46.19 %, respectively). The contribution rate to sediment yield of soil types was greatest (84.01 %), followed by freeze–thaw (9.56 %) and wind erosion (0.79 %). This study can provide a reference for the study of compound erosional mechanisms and soil and water conservation in seasonal freezing-thaw zones.
The current paper evaluates the response of a tunnel subjected to strike-slip fault rupture with experimental and numerical approaches. Some state-of-art techniques were adopted in the analysis. A new formula containing sodium silicate was used for the similar material. Endoscope technique was used in the model test to log the crack propagating inside the tunnel. And hybrid discrete–continuous modeling was introduced to perform a sophisticated numerical investigation. Two small-scale model tests were carried out, in which the interaction of the tunnel with the fault rupture, the deformation pattern, and the strain evolution and crack propagation in the tunnel liner were observed. The model tests indicate that the failure of the tunnel mainly resulted by the faulting-induced circular cracks concentrated in the vicinity of the shear zone and longitudinal cracks at the passive side portion. Then, the hybrid DEM-FDM model was constructed and calibrated based on the experimental data, with which the response and mechanism of the tunnel subjected to strike-slip fault rupture were numerically investigated to identify the influences of some important factors. The longitudinal and transverse deformation profiles of the tunnel were found to be dominated by the rock mass condition and the buried depth of the tunnel. And the tunnel’s design factors have significant effects on the stress and failure mode of the liner. For a soft or thin tunnel liner, the failure zones were more concentrated. The tunnel would fail in a ‘shear’ mode. In contrast, for a hard or thick liner, the magnitude of the tensile strain is less, yet the tension failure area is larger. The tunnel would fail in a ‘squeeze’ mode. Based on the obtained results, suggestions on the design of tunnel liner against the strike-slip fault rupture were proposed.
This paper presented the role of supplementary cementitious materials (SCMs), including fly ash (FA), granulated blast-furnace slag (GBFS), and silica fume (SF) in long-term resistance to external sulfate attack (ESA) of cement mortar at atmospheric temperature. The cement mortars were immersed in 5% sodium sulfate solution at a temperature of 20 °C for 36 months. The results showed that the amount of deterioration products and pore characteristics were the two critical factors affecting sulfate resistance. The pore characteristics played more integral roles in influencing the long-term sulfate resistance than the amount of deterioration products. FA maintained excellent sulfate resistance after exposure to ESA for 36 months. SF exhibited higher sulfate resistance than FA because it primarily supported total porosity and percentage of harmless pore, rather than the portlandite removal by the pozzolanic reaction. On the contrary, the addition of GBFS accelerated the deterioration process and exhibited the worst sulfate resistance because the total porosity and percentage of harmless pore occurred massive changes.
Most flash floods in countries around the world occur in poor rural mountainous areas and typically cause more casualties and economic losses due to monitoring challenges and early warning difficulties. In mountainous regions, reservoir projects are a very effective measure for mitigating the risk of flash floods and can also be used for water supplies and irrigation, but there is a lack of research on the comprehensive benefit assessments of reservoirs. In this paper, we simulate the inundation extents of flash floods for the Wangmo Basin in China, where flash floods frequently occur, under different return periods using the HEC-HMS (HEC-Hydrologic Modelling System) model and FLO-2D model and compare the resulting housing losses with and without reservoirs. The results indicate that using dam and reservoir operations for flood control in the Wangmo River Basin decreases the flooded housing area in the county centre by approximately 12.9 %–30.2 %, which results in housing losses reductions of 19.7 %–45.7 %.These dams and reservoirs will begin to make a profit during the 38th year of operation, and the average annual net benefit reaches 101.76 million RMB in 50 years, which is equivalent to 1.43 % of the GDP of Wangmo County; the net benefits of flood control, water supply and irrigation accounted for 0.4 %, 1.0 % and 0.03 %, respectively. Priority should be given to planning and building these water conservation measures to help these poor mountainous areas. The construction of dams and reservoirs can contribute to decreasing losses in poverty and disaster-prone regions. The effectiveness evaluation framework for dams and reservoirs presented in this study can be applied to other mountainous basins for flood control and local development.
In this article, the rheological and thixotropic properties of fresh cement pastes (fcps) with nonionic polyacrylamide (PAM) are investigated through the coaxial rotary method. The B-HB model is resorted to fit the shear stress versus shear rate diagram, from which the slurry plastic viscosity is particularly discussed. The results show that with the development of PAM, the plastic viscosity increases first, then decreases, and then increases again, exhibiting the “up-down-up” trend, which is consistent with the fcps fluidity. The adsorption, lubrication, and entanglement mechanisms of PAM are successfully used to interpret this phenomenon. Combined with the suspension density, the relationship among plastic viscosity, flowability, and density is successfully established follower via a multivariate linear regression method. The Durbin-Watson coefficient, variance inflation factor, μ significance, ρ significance, and R 2 are 2.122, 1.024, 0.014, 0.004, and 0.776, respectively, demonstrating the feasibility of fitting formula. Besides that, the PAM containing slurry which exhibits the explicit thixotropy is also found according to the appeared hysteresis curve during one shearing cycle. With the increase of PAM dosage, the thixotropic indexes including Th1 and Th2 decreased, until the PAM exceeded 0.5%-0.6% dosage, both of them yielded negative values. The phenomenon that the fcps final shear stress exceeds its initial value occurs.
Dye adsorption by magnetic modified biochar has now received growing interest due to its excellent adsorption performance and facile separation for recycling. In this study, nano iron oxide–modified biochar was fabricated via the successive hydrothermal-pyrolyzing method using Chlorella vulgaris (Cv) and FeSO4·7H2O as raw materials, and its adsorption on Rhodamine B (RhB) in aqueous solution was studied. Multiple techniques such as X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Brunauer–Emmett–Teller (BET), vibrating sample magnetometry (VSM) and X-ray photoelectron spectroscopy (XPS) were employed to comprehensively characterize the structure, morphology and physicochemical properties of the adsorbent. The as-synthesized nano iron oxide–modified biochar (CBC-Fe(II)) exhibited a large surface area (527.6 m2/g) and high magnetic saturation value (13.7 emu/g) to facilitate magnetic separation. Compared with CBC and CBC-Fe(III), CBC-Fe(II) exhibited superior adsorption ability towards RhB in aqueous solution, with a maximum adsorption capacity of 286.4 mg/g. The adsorption process of RhB onto CBC-Fe(II) was well described by the pseudo-second-order kinetic model and Langmuir isotherm model, indicating monolayer chemisorption behaviors for the adsorption system. Facile preparation, great adsorption performance and magnetic recovery properties endow CBC-Fe(II) to be a promising adsorbent for dye removal.
The ocean is the main driver of internal climate variability. However, the relatively short length of the historical record limits our ability to study the impact of large-scale oscillations on the regional climate. This work uses the output from the Canadian Earth System Model large ensemble (CanESM2-LE) to study the impact of three large-scale oscillations on temperature and precipitation anomalies over North America. The 50-member ensemble provides data series covering 2500 years to study the superpositions between ENSO, AMO, and PDO over the 1961–2010 period. The main characteristics of all three oscillations are well reproduced by CanESM2-LE. The impact of each oscillation is considered independently (with the others in their neutral phases), as well as combined with the other two (e.g., all three in non-neutral phases). The results outline a dominant role of ENSO in annual precipitation and of AMO in temperature over most of North America. PDO has a minimal impact on precipitation and temperature. The dominant roles of ENSO on precipitation and AMO on temperature are enhanced by superpositions between these patterns. These combined impacts are consistent with their independent ones. Even though this study is conducted in a model world, the superpositions are mostly consistent with our understanding derived from observations. The results therefore extend our understanding of the relationship between large-scale oscillations and climate variability over North America and highlight the importance of considering the superpositions between oscillations to better understand internal hydroclimatic variability.
Porewater is the primary carrier of sediment nitrogen and a crucial source of overlying water nitrogen; its separation thus is essential for restraining nitrogen release from sediment to overlying water. We developed a novel device using electrokinetic geosynthetics to drain porewater with nitrogen and restrain nitrogen release. A batch experiment lasted 1120 h (about 47 days) was conducted with 20 cm depth of overlying water under three conditions, i.e., undrained at 0 V/cm voltage gradient (control), drained at 0 V/cm, and drained at 0.5 V/cm. Under the pulsed direct current, once porewater drained, overlying water replenished sediment pore space and supplied porewater. Along with porewater drainage, sediment nitrogen concentration was reduced by 11%–30%, decreasing nitrogen release from sediment to overlying water from 83 mg/m² in the first 100 h to −95 mg/m² after about 600 h. Processes such as electroosmosis, electromigration, and redox reaction contributed to the restraint on nitrogen release. This research revealed the potentiality of applying electrokinetic geosynthetics to in-situ restraint on sediment nitrogen release in eutrophic waterbodies such as fishponds.
In recent years, the operation of cascade reservoirs in the upper reaches of the Yangtze River led by the Three Gorges Reservoir has significantly changed the low water level of Dongting Lake, which has had an adverse impact on the water resources and ecological security in the lake area. As a result, the low water level situation of Dongting Lake is drawing more and more attention. Based on the abundant and long-term daily observation data of Dongting Lake and main stream of the Yangtze River, the spatial and temporal evolution characteristics of low water level in the Dongting Lake area since the 1950s were analyzed in this study, especially during the storage period of the Three Gorges Reservoir. In addition, the influence of the jacking effect of the Yangtze River on Dongting Lake was also discussed to analyze the impact of the Three Gorges Reservoir. The results show that the annual minimum water level in the Dongting Lake area over the years generally occurs from January to February and December. Since it is not within the storage period of the Three Gorges Reservoir, it is not affected by the Three Gorges Reservoir. However, the average water level in September and October during the main storage period of the Three Gorges Reservoir has significantly reduced, and the closer it is to the main stream of the Yangtze River, the greater the influence is. In recent years, affected by the advance of the impounding period, the average water level has decreased further in September. In addition, the low water level of Dongting Lake is obviously affected by the jacking effect of the main stream of the Yangtze River. After the impoundment of the Three Gorges Reservoir, the water surface slope of the Dongting Lake area has decreased, while that of the main stream of the Yangtze River has increased. This has strengthened the jacking effect of the main stream. The research results can provide reference for the solution of water resource and ecological crises in the Dongting Lake area.
Engineering rock mass in cold regions has obvious freeze–thaw damage as a result of extreme differences in temperature, rainfall, snow, and other factors, which is one of the main causes of frequent geological disasters. Therefore, it is important to investigate the deterioration mechanism and evolution laws of rock mass freeze–thaw damage. Considering a hydropower station’s left bank slope in a cold region, model testing and numerical testing of slope rock mass failure under freeze–thaw conditions are here carried out by developing a generalized model. The results reveal that heat is transmitted from the outside to the inside of the slope and that the rate of temperature change varies with depth; the frost-heave force causes tensile cracks in the rock mass, with crack propagation taking the form of a circular arc; the presence of an original structural plane influences the propagation direction of the frost-heave crack, whereas the freezing rate of the fissure water influences the amplitude and growth rate of the frost-heave force. Additionally, a novel method of measuring frost-heave force is proposed. The largest frost-heave force caused by water–ice phase change is 19.3 kPa, which is equivalent to 3.17 MPa of the actual slope.
This paper proposes a displacement sensing method based on magnetic flux measurement. A bridge-structured magnetic circuit, formed by permanent magnets and two ferromagnetic cores, is designed and discussed. The analyses of the equivalent magnetic circuit and three-dimensional finite element simulations showed that the magnetic flux density changes linearly with the reciprocal of the sum of a constant and the displacement. A prototype sensor of the bridge structure is developed that consists of four permanent magnets as excitation, a Hall sensor as reception, and two ferromagnetic cores as the connection. Experiments have validated the feasibility of this method. The measured results show a good linearity between the sensor’s output and the reciprocal of the sum of a constant and the displacement, with a correlation coefficient greater than 0.9995 across different measurement ranges. Additionally, the measured results significantly indicate that the proposed sensor is compatible with different ferromagnetic materials with a worst-case error of less than 5%. The proposed sensor has the advantages of low cost and good linearity; however, the test object is limited to ferromagnetic materials.
To evaluate the influence of confining pressure on the rock-breaking force required by the cutter and provide a new possible method for ground stress prediction, the rock breakage mechanism under TBM cutters is studied through theoretical analysis and numerical simulation. A theoretical model for peak penetration force required for rock breakage prediction is established with confining pressure considered. The rock breakage by cutters under different confining pressures is simulated by PFC and compared with the theoretical analysis results. The numerical simulation results are in good agreement with the theoretical analysis, which verifies the validity of the established mechanical model. The peak penetration force increases significantly with the increase of the confining pressure that is perpendicular to the cutting direction and increases slowly with the increase of the confining pressure that is parallel to the cutting direction. Considering the effect of biaxial confining pressure, the impact factor is introduced to modify the theoretical formula for peak penetration force prediction. Besides, we discuss the variation of specific energy and found that increasing confining pressure improves rock fragmentation efficiency at high confining pressure though the effect is less evident when it exceeds a critical value.
Indoor point cloud includes wall, ceiling, floor and many other indoor objects. Extraction of wall, ceiling, floor and many objects in the room is the key for many applications including object identification, facility management and reconstruction of building. In view of this, this paper uses exponential function to construct density clustering model according to the local density within cutoff distance. First, the distances between boundary and indoor point cloud are used to construct the constraint condition of wall density clustering. Second, ceiling and floor are extracted according to the density clustering of z direction and local density model. Third, the distance δi is determined according to the size of local density. Simultaneously, we find that the cluster centers are recognized as points for which the product value of the local density and distance δi is anomalously large. Finally, the cluster belonging of each point to the cluster center is determined according to the distance between each point and cluster center. Finally, indoor objects extraction is achieved by judging the distance between neighboring clusters. We conduct the extraction of indoor objects of different type scenes and compare with clustering and deep learning methods. Comparison results show that the proposed method is superior to the clustering and deep learning methods when adjacent objects are not close to each other, but inferior to the deep learning methods when they are next to each other. Additionally, the extraction accuracy, recall and F1-score are calculated according to the matching rate, TP, FP and FN. It illustrates that the performance of the proposed method is affected by the degree of closeness between objects.
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