The calculation of sediment transport capacity is of great importance in modelling of morphodynamic processes in alluvial rivers. Recently, worldwide fluvial sediment load is reducing especially in the Lower Yellow River (LYR), while the commonly used formulas of sediment transport capacity are specially developed for relatively high sediment-laden flow, which needs some improvement for the varying flow and sediment regime. The measurements during a long period (1956–2020) covering 4974 datasets in a quasi-equilibrium state were collected at seven hydrometric stations of the LYR, and the hydrodynamic variables related to suspended bed-material load were classified, in order to determine the critical parameters (K and M) in the widely used formula proposed by H.W. Zhang. The calculation relations were firstly developed between K and M and the comprehensive flow-sediment factor (STP), under various combinations of flow and sediment, which reduce the uncertainty related to modifying model input parameters. The improved formula was further applied to simulate the morphodynamic processes in the LYR. Results indicated that the improved formula presented the best accuracy in the simulation of morphodynamic processes induced by low or high incoming sediment amount, compared with the other two formulas. This improved formula can be directly applicable to the varying flow-sediment regime and achieves the accurate simulation of the hydrograph of low sediment concentration in the LYR.
The key factor influencing flood evolution and the progression of riverbed erosion and silting in the wide floodplain of the Lower Yellow River (LYR) is channel roughness. The distribution law of channel roughness has changed since the implementation of water storage and sand control in Xiaolangdi Reservoir in 2002, and the change in roughness has had a number of effects on the design of flood control projects and ecological environment protection planning of the lower reaches. Manning's formula was used to calculate the roughness based on cross-section data and hydrological data collected by typical hydrological stations in the wide floodplain of the LYR from 2002 to 2020. The evolution law and influencing factors of channel roughness of typical sections before and after floods were also examined. The findings indicate that: (1) The post-flood roughness was slightly higher than the pre-flood roughness in the same area. The post-flood roughness in the Huayuankou and Sunkou sections significantly increased compared to the pre-flood roughness, with an increase rate of 14.64% and 19.37%, respectively. (2) The time-to-space variation of roughness in the wandering section exhibits a decreasing trend, whereas the time-to-space variation of roughness in the transition section exhibits a slightly increasing trend. (3) The channel roughness decreases with an increase in Froude number, but there is no clear relationship between the roughness and sediment content. (4) Using Huayuankou and Gaocun stations as examples, the channel roughness is inversely proportional to the flow, the average sectional velocity, and the cross-section area of the flow. The channel roughness of the wandering section is inversely proportional to the ratio of width to depth, and the channel roughness of the transition section is proportional to the ratio of width to depth. Roughness and average velocity were determined to have the best-fitting connection, with R2 values of 0.62 and 0.78, respectively. (5) The main elements impacting channel roughness in the wide floodplain of the LYR are section shape and flow condition.
Sediment is one of the main factors affecting the ecological environment of rivers, and its eco-environmental effect plays an important role in maintaining the balance of water environment and aquatic biodiversity. Sediment in mountain rivers has obvious characteristics such as wide gradation, which has unique impacts on the ecological environment. In addition, the increasingly intense human activities in mountain rivers, such as the construction and operation of large-scale cascade reservoirs, lead to further complicated changes in the ecological and environmental effects of sediment. In this paper, the environmental effects of mountain river sediment in adsorption, desorption and transport and the ecological effects on aquatic microorganisms, animals, plants and the entire food web were systematically reviewed. The problems existing in relevant researches were discussed, and the research prospects were presented, in order to provide guidance for the protection of mountain rivers.
Under the action of earthquake, concrete-filled steel tubular（CFST） columns are often subjected to torsion action or combined action of compression-bending-shear-torsion.The existence of torque will aggravate the damage of CFST columns.In order to study the pure torsional failure and size effect behavior of CFST columns, a numerical model of CFST columns on pure torsional failure was established by using the three-dimensional meso-scale numerical simulation method, considering the meso-heterogeneity of concrete and the contact between steel tube and concrete.The influence of structural size, confinement coefficient and cross-sectional shape on torsional failure of CFST columns with different sizes were analyzed.Finally, the Ba6ant size effect law was compared and revised, and the formula for the nominal torsion strength in the full size range was proposed.The results show that:（1）Pure torsion failures of plain concrete columns show significant brittle failure characteristics, while pure torsion failures of CFST columns show certain ductile failure characteristics;（2）The pure torsion failure of the CFST column has the size effect, and the size effect of the square columns is stronger than that of the circular columns;（3）Under low constraints（use confinement coefficient to mark）,the size effect of the pure torsion failure of the CFST column is more obvious, with the increase of the confinement coefficient, the size effect of the nominal torsion strength is weakened.
The Yellow River is the “mother river” of the Chinese nation.The unbalanced relationship between water and sediment and frequent flood disasters have always been the main challenges in the governance of the Yellow River Basin or YRB.In recent years, the Yellow River channel have undergone major changes caused by the fluctuated water-sediment relationship, meanwhile, along with frequent extreme weather events, the social economy in the basin has developed rapidly.Under this changing environment, a river health diagnosis for the YRB becomes essential.In this study, methods such as information entropy and entropy weight method are adopted to study the characteristics of the healthy development and evolution of the Yellow River Basin through a new index “River Health Index”,shortly RHI.The study results indicate:（1） A health analysis of the river system shows that the YRB was in a healthier state from 1980 to 1986 and was generally unhealthy from 1987 to 1999;and from 2000 to 2019,the river system developed towards a healthy and well-aligned direction.（2） An analysis of the trend of the RHI finds that the river system developed better from 1980 to 1984,showed an increasingly unhealthy trend from 1984 to 1999,and a positive trend from 2000 to 2019;（3） The sensitive factor of the river system was the flood capacity of the main channel of the Ningxia-Inner Mongolia river section before 1986;from 1987 to 1999,the sensitive factors were the flood capacity of the main channel of the Ningxia-Inner Mongolia river section and the total water volume of Huayuankou; since the 21st century, the sensitive factors are the total scouring and silting as well as the incoming sediment of the lower reaches of the Yellow River.For the entire period, the sensitive factors are the total scouring and silting of the lower Yellow River and the flood capacity of the main channel of the Ningxia-Inner Mongolia river section.These results can provide support for the ecological conservation and high-quality development of the YRB.
The development of new river channel projects and its design is important to solve difficult control of the Yellow River regime and high emergency costs problem.Analyze the defects of traditional engineering and elaborate the structural form of the new steel pile dam project combining with data from 2021 and 2022,showing that the combined pile dam demonstration project in the downstream river can achieve the river control goal and solve the problem of large shortage of funds for rock throwing and rescue.In the engineering design of Shaojiaqiao and Hongyazi prototype test, the steel structure shaped dam’s sheet pile length of 12m and the lower steel pipe pile length of 19m were determined according to the overturning stability calculation; The design of steel permeable pile dam in the form of double-row and overall interconnection in the lower extension of the control guide can increase the shape of the support area, which can effectively strengthen the overall stability while improving the effect of slow flow and siltation and restricting flow and sending guide.
To study the water and nitrogen transport characteristics during the infiltration process of fertilizer solution（ammonium nitrate） in wide furrows, the HYDRUS-2D model was used in laboratory experiments.The soil hydraulic characteristics parameters and solute transport parameters were derived by the numerical inversion method under different fertilizer concentrations.The water and nitrogen transports under different water contents and fertilizer concentrations were simulated.The results showed that the parameters obtained by the numerical inversion method were very accurate, and the HYDRUS-2D model was able to simulate nitrogen transport in furrow irrigation.Nitrate nitrogen was more likely to move with water, and ammonium nitrogen was more easily adsorbed by soil.The cumulative infiltration and wetting front migration distance under the condition of 600mg·L -1 fertilizer concentration increased by 7.51% and 3.98%,respectively, compared with 300mg·L -1 fertilizer concentration; and the cumulative infiltration and wetting front migration distance under the condition of 900mg·L -1 fertilizer concentration increased by 14.36% and 9.6%,respectively, compared with 300mg·L -1 fertilizer concentration.The content of nitrate nitrogen and ammonium nitrogen under the condition of 600mg·L -1 fertilizer concentration increased by 101.6% and 84.62%,respectively, compared with 300mg·L -1 fertilizer concentration; and the content of nitrate nitrogen and ammonium nitrogen under the condition of 900mg·L -1 fertilizer concentration increased by 224.7% and 176.71%,respectively, compared with 300mg·L -1 fertilizer concentration.The nitrate nitrogen and ammonium nitrogen in soil were redistributed after 5 days: the content of nitrate nitrogen and ammonium nitrogen in shallow soil decreased gradually, and the nitrification rate of ammonium nitrogen was lower than the rate of nitrate nitrogen moving to deep soil with water.
In order to utilize and dispose vegetable wastes（VWs） by ensiling in a timely and safe manner, the aim of this work is to investigate the inoculation of Lactobacillus plantarum（LP） on the ensiling quality of cauliflower wastes at different temperature（20℃,25℃,30℃,35℃,40℃ and 45℃） in terms of organic components, fermentation quality and microbial community.On this basis, the correlation between microbial community and ensiling quality parameters during ensiling were established.The addition of LP can significantly increase the content of dry matter, crude protein and lactic acid accompanied by the decrease of pH and ammonia nitrogen content for the silages.The dry matter, soluble carbohydrate and crude protein contents in LP were significantly higher than those in the control group（no additive, CK） under medium and low temperatures（20～35℃）.the contents of lignocellulosic fractions such as neutral detergent fiber, acid detergent fiber and cellulose in LP group were significantly higher than those in CK,which resulted in the significant decrease for relative forage value under high temperatures（40℃ and 45℃）.The ratios of lactic acid/acetic acid and lactic acid/total organic acid in LP were lower than those in CK,indicating that the fermentation intensity of lactic acid bacteria in LP was weakened at high temperature.Firmicutes in silages were dominant at phyla, and the abundance of lactic acid bacteria（LAB） in LP was significantly higher than that in CK（except 45℃）,especially the abundance of LAB in LP exceeded 90% at 30℃ and 35℃,indicating that a well lactic acid fermentation was formed, which suppressed the undesirable microorganisms.Lactobacillus is the main genus of LAB,and its abundance is negatively correlated with the content of neutral detergent fiber and acidic detergent lignin, and positively correlated with the content of lactic acid.In conclusion, the temperature and Lactobacillus plantarum had a significant effect on the ensiling quality, the ensiling of cauliflower wastes inoculated with lactobacillus plantarum at middle-low temperature could effectively improve the ensiling quality and relative feed value.Therefore, the ensiling disposition of cauliflower wastes at 20～35℃ was recommended preferentially.
After the M s 6.4 earthquake in Yangbi, Yunnan, on May 21,2021,the seismic damage survey, mobile strong motion observation of aftershocks, and characteristic analysis of ground motion and building damage were carried out.The characteristics of building damage in the earthquake-stricken region especially in the meizoseismal area were summarized, the correlation between the building damage and the ground motion characteristics was explored, the effect and mechanism of topographic condition and ground motion directivity on the building seismic damage characteristics and disaster distribution were revealed.Due to the topographic effect of local site, buildings located on the steep slope and the top of mountains were encountered more severe damage than those on the mountain foot.The directivity effect of ground motion is the main reason for the damage difference of buildings with different orientations.By summarizing the seismic damage characteristics in this earthquake, measurements and suggestions for improving the seismic performance of the mud and wood houses in Yunnan Province were proposed.
In recent decades, ecological environment has changed greatly, and net primary productivity of vegetation（NPP） of vegetation has become an important indicator to characterize the carbon sink status.In this study, the Heihe River Basin in the arid region of inland China was used as the research area, temporal and spatial variation characteristics of annual NPP was analyzed using monthly grid NPP,precipitation and average temperature data from 1985 to 2015,by applying Mann-Kendall trend test method and Pettitt change-point test method.The response of the annual NPP gravity shift to the climate factors gravity shift in different grids was investigated based on the fishing nets and the center of gravity shift model, the contribution rates of climate change and non-climatic factors to changes in NPP was quantified, and the influence of landform and climate factors on annual NPP changes was finally discussed.The results show that:（1） the annual NPP from 1985 to 2015 in 44.98% of the Heihe River Basin has a significant increase, while 35.27% of the basin has a significant decrease;（2） 80.12% of the total area has significant change-points from 1989 to 2010;（3） the shifting direction of the annual NPP gravity center from 1985 to 2015 is consistent with that of the annual precipitation and the annual average temperature in 21.69% and 26.78% of the grid numbers, respectively;（4） the average contribution rates of climatic factors and non-climatic factors to the annual NPP change are 16.13% and 83.87%,respectively.The research results are conducive to understanding the temporal and spatial characteristics of vegetation carbon sinks, thereby further providing a certain scientific basis for the formulation of environmental protection policies and plans in the Heihe River Basin.
Outburst floods caused by the breaching of landslide dams pose severe threats to lives and properties downstream.Rapid and accurate prediction of peak breach flow is vital for scientific assessment of the potential disaster consequences after landslide dam breaching and emergency response.Based on the investigation data of landslide dam breach cases, scholars worldwide have proposed a series of parametric models to predict the peak breach utilizing regression analysis.However, the existing parametric models cannot consider the effect of the grain composition of landslide dam deposits on the peak breach flow.Based on 86 worldwide landslide dam cases with grain-size distribution curves, the grain composition characteristics of three types of landslide dams（soil type, mixed type, and block stone type） are analyzed, and quantitative classification indexes of landslide dam types are proposed.Using experimental test results and field breach cases with measured data, the relationships between landslide dam type, morphology, dammed lake volume, and peak breach flow, dam height, dam width, dammed lake volume, and self-defined erosion factor considering the grain composition are selected as input parameters.A rapid prediction model for the peak breach flow of landslide dams is developed using multiple regression analysis.Five recent landslide dam breach cases are adopted to verify the proposed model in this study, and a comparison study with the existing typical parametric models is conducted.The calculation results show that the proposed model’s relative errors of peak breach flow are all within ±20%.Overall, the proposed model has several advantages, such as quick computation time and better accuracy compared to previous models.
In order to investigate the fracture mechanism of loaded jointed rock in the cold region, the freeze-thaw cycles and uniaxial compression tests were conducted on the sandstone specimens containing multiple flaws.The energy characteristic parameters were introduced to quantify energy conversion of the specimens containing multiple flaws and intact specimens under the different number of freeze-thaw cycles.Based on the statistic damage theory and strain equivalent principle, the damage model of loaded jointed rock under freeze-thaw cycle was established to study the correlation between the damage and energy conversion.The failure modes of specimens containing multiple flaws before and after freeze-thaw cycles are tensile and shear mixed failure.An exponential decay relationship is found between the mechanical properties and the number of freeze-thaw cycles.The energy storage limit and post-peak conversion rate of strain energy for specimens containing multiple flaws and intact specimens decrease with the increase of the number of freeze-thaw cycles.For the same number of freeze-thaw cycles, the energy characteristic parameters are larger for specimens containing multiple flaws than those of intact specimens.These indicate that the energy is released more slowly due to the effects of freeze-thaw cycles and the existence of multiple flaws.The relationship between the damage value at peak stress and the number of freeze-thaw cycles obeys an exponential growth function.The damage values of specimens containing multiple flaws are greater than those of the intact specimens.This is because the damage of freeze-thaw cycling is aggravated by multiple flaws.Data fitting further verified a high negative correlation between the damage value at peak stress and the post-peak conversion rate of strain energy.The higher the degree of rock freeze-thaw damage, the smaller the post-peak energy conversion rate.
Remote sensing water indices are important basis for surface eco-environment analysis, and are critical to large-scale waterbody interpretation and hydrological monitoring.A variety of water indices focus on large-scale, short-term, non-urbanized regions, while the extraction of urban water bodies has been plagued by the applicability of these indices.The study collected Landsat images from 1986 to 2020 in Shenzhen city, and adopted three commonly used water indices（TCW,NDWI,MNDWI） and five improved water indices（WI2015,AWEInsh, ANDWI,MBWI,WI2020）.The interpretation ability of these water indices in the urban noise area were analyzed by taking five regions of building shadow, high albedo building, low albedo building, tidal-flat and mountain shadow as examples.The results show that:（1）Producer accuracy of water indices are negatively correlated with user accuracy（Otsu threshold）,and TCW,NDWI,ANDWI,AWEInsh can effectively filter architectural noise and mountain shadow, but unrecognize small river water bodies, MNDWI,WI2015,MBWI,WI2020 are the opposite;（2）The spectral transformation type and difference type water indices consider the absolute value of multiple bands with low separability, and they are suitable for high-quality image mapping.The ratio type and logical operation type water indices calculate the relative value of multiple bands, and suitable for long-term monitoring;（3）The method of multi-temporal sampling verification in typical cases highlights the interpretation ability and threshold applicability of water indices, and the NDWI is most applicable in urbanized areas, while the WI2020 achieves the highest interpretation accuracy in non-urbanized areas.The above research provides a certain theoretical reference and practical basis for the selection of water index and accuracy verification for urban hydrological monitoring.
Taking runoff from the Yingluoxia hydrological station in the upper reaches of Heihe River from 1944 to 2017 as the research object, combining recurence plot theory with chaos theory, the chaotic characteristics of runoff time series were effectively identified under different time scales.The recurence plot and slip window recurrence quantification analysis（RQA） method were used to obtain dynamic information of the original series and extracted the relevant recurence features.Then, drawing the runoff recurence plot under different scales to qualitatively describe runoff chaotic characteristics.Finally, RQA method was used to calculate and quantitatively describe runoff chaotic characteristics.The results showed that runoff chaotic degree varies in different stages, and determinism（DET） of sliding window can describe runoff chaotic degree together with recurence plot.Shannon entropy（ENTR） of sliding window showed that runoff chaotic degree gradually increases with the increase of time scale.And Laminarity（LAM） of sliding window can be tested with coefficient of variation（C v ）,and can be used as a new parameter to measure runoff overall dispersion.The recurence plot theory realizes the visualization of runoff chaotic characteristics and is an effective tool to identify the chaotic characteristics of runoff time series.
Due to the ‘pile groups effect’,pile groups show dynamic time-history response law different from the single pile under seismic dynamic load.Through large-scale shaking table model test, 5002wave, 5010wave, El-Centro wave, and Kobe wave with the intensity of 0.35g are selected to study the time-history response law and fundamental frequency damage of rock-socketed pile groups.The shaking table test results show that the seismic wave spectral characteristics have a significant influence on the dynamic response parameters of rock-socketed pile groups.The pile groups’ peak acceleration under the El-Centro wave is large, and the peak value of the pile top is lagging behind.Under the action of Kobe wave, the horizontal relative displacement of pile top and the peak value of bending moment are large, but they all appear the earliest in El-Centro wave.The bending moment peak values do not exceed its ultimate bending capacity.The fundamental frequency of pile groups does not change obviously, indicating that there is no damage to pile groups under the strong earthquake.Therefore, the seismic performance of rock-socketed group piles can be optimized through seismic waves with different spectral characteristics, and corresponding engineering suggestions can be put forward.
The hydration mechanism and behavior of composite cementitious system with low water-binder ratios（W/B） are different from those of ordinary cementitious system, and the traditional conclusions about cement hydration are no longer appropriate under this condition.The hydration heat of composite cementitious system of cement-fly ash-slag with different low W/B ratios was measured in 7 days, based on which the effects of low W/B ratio and mineral admixture content on its hydration behavior and mechanism were explored by the cement hydration kinetics.TEM and XRD were also conducted to analyze the hydration products difference of composite cementitious system with low W/B ratio.Results show that the early and late hydration exothermic rates of the composite cementitious system do not change significantly when its W/B ratio is 0.2 and the fly ash-slag content is less than 50%,and the compound mineral admixture could slightly promote the cement hydration under this condition.The addition of fly ash and slag inhibits the hydration of composite cementitious system in 10～17h when the W/B ratio is 0.25 or 0.3.The maximum hydration exothermic rate of the cementitious system increases with the decrease of W/B ratio from 0.3 to 0.2,and the hydration process changes from NG-I-D to NG-D,no longer experiencing the phase boundary reaction.With the decrease of W/B ratio, the fibrous hydrated calcium silicate（C-S-H） will transform into spherical structures after hydrating 28 days.
A two-dimensional（2D） floating slab track-tunnel-ground coupled model was adopted to analyze the vibration characteristics of floating slab track in the metro tunnel.By introducing displacement potential functions and using double Fourier transformations, response solution of the 2D model under moving harmonic load was derived.It indicates that there are three resonant frequencies in the 2D model, the ground displacement response mainly concentrates in the low frequencies, with a peak value frequency around 1Hz, and the changes of vertical ground displacement under different load frequencies are different.The ground acceleration response mainly concentrates in the middle and low frequencies and reaches its maximum value at the second resonant frequency.Adopting the floating slab track is unable to reduce the ground displacement but is effective to reduce the ground acceleration response in which the load frequency is above 1.414 times of the second resonant frequency.Increasing the floating slab mass and decreasing the steel spring stiffness are able to reduce the ground acceleration response and realize the vibration attenuation goal while the ground acceleration is trivially affected by changing stiffness of the rail pad or floating slab.The present research can provide reference to a quick evaluation for the train-induced environmental vibration.
To evaluate the benefits of soil and water conservation and adjust ecological and environmental policies in the middle reaches of the Yellow River, the relationships between precipitation and changes in vegetation index, and water and sediment flows were analyzed using precipitation, runoff, sediment transport and remote sensing data in the Longtong region from 1957 to 2019.The cumulative anomaly method and double cumulative curve were used to analyze the relationship between precipitation and changes in vegetation index, and water and sediment flows.The results showed that precipitation in the Longtong region did not exhibit an apparent decline with time, but runoff and sediment transport exhibited a significant decline with time.The abrupt change to runoff, from abundant to dry, occurred in 1985,and the abrupt change to sediment transport, from abundant to dry, occurred in 1985 and 2002.The normalized vegetation index（NDVI） exhibited a recovery, with an annual increase of 1.7%,and the spatial NDVI exhibited fluctuations in a generally increasing value.Vegetation cover in the southern part of the basin was the best.Compared with the reference period A（1957～1985）,the contribution of precipitation to runoff in period B（1986-2019） was 26.21%,while the contribution of anthropogenic to runoff was 73.79%.Compared with the reference period A（1957～1985）,the contribution of precipitation in periods B（1986～2019） and C（2003～2019） to sediment transport was 22.80% and 11.73%,respectively, while the contribution of anthropogenic sediment transport were 77.20% and 88.27%,respectively.
Bedding yellow sandstone is a common rock in tunnel construction, and the surrounding rock is under cyclic loading-unloading for a long time due to tunnel excavation and later operation.To explore the damage and fracture characteristics of bedding yellow sandstone under cyclic loading-unloading compression, the triaxial cyclic loading-unloading compression of bedding yellow sandstone with different confining pressures and dip angles was constructed with the help of PFC 2D .The stress-strain curve and fracture process were analyzed.A group of micro-parameters was obtained, which can simulate the mechanical behavior of bedding yellow sandstone under triaxial compression, and the strength and fracture characteristics obtained by numerical simulation is similar to that obtained by experiment.The stress-strain curves of specimens under cyclic loading-unloading compression can reflect the mechanical behavior of bedding yellow sandstone, and the stress-strain curve of specimens under cyclic loading-unloading compression are similar to that under monotonic loading.Fracture characteristics of sandstone samples with different dip angles are different under cyclic loading, the shear crack across the matrix when α=0°,which is similar to that under monotonic loading.Whereas when α=60°,the shear across the bedding and with the destruction in the matrix on the sides of the bedding.Under cyclic loading-unloading compression, the width of shear crack is more than that under monotonic loading.
Forecast of the discharge process of dam break flood routing to the downsrteam section is extremely important for scientifically response to flood disasters such as barrier lake or dam break.In view of the dam break flood characteristics of Unsteady Rapidly Varied Flow, the dynamic coordinate method of discontinuous wave is used to transform the unstready flow issure of dam break flood routing into stready flow issue.The calculation of dam break flood and routing to downstream section applied the microelement method to put foward a dam-break flood routing analysis model based on dicontinuous wave, which is verified by the“10·11” Baige barrier lake breach flood routing.The results show that the measured peak discharge of Baige barrier lake breach flood in Yebatan Hydropower Station, which routed to Suwalong Hydropower Station just has an error of 1.44% with the time is 10 min ahead, the peak discharge error of the flood routing to Benzilan, Shigu and Liyuan hydropower stations are around 10%.The feasibility and rationality of the model are verified.This work also demonstrated the efficiency and stability of the discontinuous wave flood routing model, it can effectively support emergency disposal decisions.
