The widespread use of antibiotics has significantly increased their presence in aquatic environments,particularly in sensitive Karst River systems.In this study,the distribution and ecological,human health,and resista...The widespread use of antibiotics has significantly increased their presence in aquatic environments,particularly in sensitive Karst River systems.In this study,the distribution and ecological,human health,and resistance selection risk assessment of 44 antibiotics in the typical Karst River,Lijiang River,were investigated during the influenza season,a period marked by heightened antibiotic usage.27 antibiotics could be found in the water of Lijiang River,among which azithromycin showing the highest concentrations.The concentrations of total antibiotics were in the range 171.70–2003.75 ng/L,with an average value of 704.76 ng/L.Macrolide was the predominant class,constituting an average of 57.65%of the total antibiotic concentrations.Risk assessments revealed that certain antibiotics,especially macrolides,posed moderate to high ecological risks to algae,displayed potential human health risks at low levels and contributed to antimicrobial resistance.Among all the antibiotics,azithromycin was the only one could cause ecological risk to algae,human health risk towards infants and antimicrobial resistance selection risk,which should be identified as the priority antibiotic for control in the Lijiang River during the influenza season.There was no difference in the concentrations,human health and antimicrobial resistance selection risk of antibiotics between mainstream and tributaries of Lijiang River.This study contributes to a better understanding of antibiotic pollution and provides insights into potential risk management practices in vulnerable aquatic systems worldwide.展开更多
Gassy soils are distributed in relatively shallow layers the Quaternary deposit in Hangzhou Bay area. The shallow gassy soils significantly affect the construction of underground projects. Proper characterization of s...Gassy soils are distributed in relatively shallow layers the Quaternary deposit in Hangzhou Bay area. The shallow gassy soils significantly affect the construction of underground projects. Proper characterization of spatial distribution of shallow gassy soils is indispensable prior to construction of underground projects in the area. Due to the costly conditions required in the site investigation for gassy soils, only a limited number of gas pressure data can be obtained in engineering practice, which leads to the uncertainty in characterizing spatial distribution of gassy soils. Determining the number of boreholes for investigating gassy soils and their corresponding locations is pivotal to reducing construction risk induced by gassy soils. However, this primarily relies on the engineering experience in the current site investigation practice. This study develops a probabilistic site investigation optimization method for planning investigation schemes (including the number and locations of boreholes) of gassy soils based on the conditional random field and Monte Carlo simulation. The proposed method aims to provide an optimal investigation scheme before the site investigation based on prior knowledge. Finally, the proposed approach is illustrated using a case study.展开更多
Large-scale and heavily jointed rocks have inherent planes of anisotropy and secondary structural planes,such as dominant joint sets and random fractures,which result in significant differences in their failure mechan...Large-scale and heavily jointed rocks have inherent planes of anisotropy and secondary structural planes,such as dominant joint sets and random fractures,which result in significant differences in their failure mechanism and deformation behavior compared to other rock types.To address this issue,inherent anisotropic rocks with large-scale and dense joints are considered to be composed of the rock matrix,inherent planes of anisotropy,and secondary structural planes.Then a new implicit continuum model called LayerDFN is developed based on the crack tensor and damage tensor theories to characterize the mechanical properties of inherent anisotropic rocks.Furthermore,the LayerDFN model is implemented in the FLAC3D software,and a series of numerical results for typical example problems is compared with those obtained from the 3DEC,the analytical solutions,similar classical models,laboratory uniaxial compression tests,and field rigid bearing plate tests.The results demonstrate that the LayerDFN model can effectively capture the anisotropic mechanical properties of inherent anisotropic rocks,and can quantitatively characterize the damaging effect of the secondary structural planes.Overall,the numerical method based on the LayerDFN model provides a comprehensive and reliable approach for describing and analyzing the behavior of inherent anisotropic rocks,which will provide valuable insights for engineering design and decision-making processes.展开更多
To cope with the problems that edge detection operators are liable to make the detected edges too blurry for synthetic aperture radar(SAR)images,an edge detection method for detecting river in SAR images is proposed b...To cope with the problems that edge detection operators are liable to make the detected edges too blurry for synthetic aperture radar(SAR)images,an edge detection method for detecting river in SAR images is proposed based on contourlet modulus maxima and improved mathematical morphology.The SAR image is firstly transformed to a contourlet domain.According to the directional information and gradient information of directional subband of contourlet transform,the modulus maximum and the improved mathematical morphology are used to detect high frequency and low frequency sub-image edges,respectively.Subsequently,the edges of river in SAR image are obtained after fusing the high frequency sub-image and the low frequency sub-image.Experimental results demonstrate that the proposed edge detection method can obtain more accurate edge location and reduce false edges,compared with the Canny method,the method based on wavelet and Canny,the method based on contourlet modulus maxima,and the method based on improved(ROEWA).The obtained river edges are complete and clear.展开更多
According to the measured data after impoundment and operation of the Three Gorges Reservoir,the reservoir sediment deposition and downstream river channel scouring are described briefly and compared with the research...According to the measured data after impoundment and operation of the Three Gorges Reservoir,the reservoir sediment deposition and downstream river channel scouring are described briefly and compared with the research results achieved in the demonstration stage.It is indicated through analysis that the reservoir sediment deposition and downstream river channel scouring during 8-year impoundment and operation are still within the original forecast,so the original forecasting results are feasible.The further observation and comparison should be conducted because the comparison between the observed data and the original forecast is not so sufficient in time and the prototype observation and related research work should be strengthened in the future.展开更多
The construction and operation of the Three Gorges Reservoir and the cascade reservoirs upstream have significantly altered the processes offlow and sediment in the main and tributary channels of the Yangtze River.Thi...The construction and operation of the Three Gorges Reservoir and the cascade reservoirs upstream have significantly altered the processes offlow and sediment in the main and tributary channels of the Yangtze River.This has led to substantial adjustments in the riverbed through erosion and deposition,thereby impactingflood protection,water resource utilization,navigation,and the aquatic environ-ment in the Yangtze River basin.In this study,prototype measurements were used to analyze the variations in runoff and sediment load in the main channel of the Yangtze River,as well as the changes and evolution of the riverbed.Mathematical modeling was done to predict the trends in reservoir sedimentation and riverbed adjustments.The results indicate that,apart from the significantly increased runoff and sediment load in the river source region(Zhimenda station)over the past two decades,there is no clear unidirectional trend of increasing or decreasing in the main and tributary annual runoff of the Yangtze River.However,the release of reservoir outflows undergoes significant changes throughout the year due to reservoir regulation.Suspended sediment load in the upper Yangtze River has been decreasing since the 1990s,especially after the operation of the Three Gorges Reservoir and the four cascade reservoirs in the lower reach of the Jinsha River.The factors influencingflow and sediment variations include mainly climate change and human activities such as reservoir operation and soil and water conservation.The significant changes inflow and sediment conditions have disrupted the original relative equilibrium state of the main channel of the Yangtze River,leading to riverbed adjustments.The river sections in the upper reach,located within reservoir areas,have shifted from erosional state under natural conditions to accumulative state,while the middle and lower reaches have transitioned from a relatively equilibrium state to a process dominated by erosion and reconstruction.Overall,the river regime in the reservoir area and downstream of the Three Gorges Dam remains relatively stable,but there have been adjustments in some local river sections,for example,in the curved sections,particularly in the sharply curved sections downstream of the Three Gorges Dam,where gradual or abrupt chute cutoff has occurred.In the foreseeable future,the river channel downstream of the Three Gorges Dam will remain in an unsaturated state regarding sediment transport.The process of river channel erosion will persist for a long time and have far-reaching consequences.Some long straight sections,multiple bifurcation sections,and sections with large curvature are expected to undergo certain adjustments in the river regime,necessitating continuous observation,long-term monitoring,and timely river management and channel governance.展开更多
Hyperconcentrated floods in the Yellow River usually accompanied with some peculiar phenomena that cannot be explained by general conceptions of ordinary sediment-laden flow (e.g., downstream increase in peak discharg...Hyperconcentrated floods in the Yellow River usually accompanied with some peculiar phenomena that cannot be explained by general conceptions of ordinary sediment-laden flow (e.g., downstream increase in peak discharge, instability flow, ripping up the bottom). Up to date, the mechanisms for the abnormal phenomena are not well understood. The aim of this paper is to facilitate a new insight into the abnormal downstream increase in peak discharge of hyperconcentrated floods in the lower Yellow River. Numerical model experiments have been conducted on a typical flood occurred in August 1992 in the Lower Yellow River during which the peak discharge at Huayuankou station was 1690 m3/s larger than the value at Xiaolangdi station at upstream. It is found that a fully coupled model that incorporates the contribution of bed evolution to the mass conservation of the water-sediment mixture, can reasonably well capture the characteristics of peak discharge rise and severe bed scour, while separate numerical experiment using a decoupled model, which ignores the feedback effects of bed evolution, shows no rise in the peak discharge. This leads us to comment, if only briefly, that the entrainment of sediment due to bed erosion is the main reason for causing peak discharge increase along downstream course.展开更多
Layered rock mass is a type of engineering rock mass with sound mechanical anisotropy,which is generally unfavorable to the stability of underground works.To investigate the strength anisotropy of layered rock,the Moh...Layered rock mass is a type of engineering rock mass with sound mechanical anisotropy,which is generally unfavorable to the stability of underground works.To investigate the strength anisotropy of layered rock,the Mohr-Coulomb and Hoek-Brown criteria are introduced to establish the two transverse isotropic strength criteria based on Jaeger's single weak plane theory and maximum axial strain theory,and parameter determination methods.Furthermore,the sensitivity of strength parameters(K 1,K 2,and K 3)that are used to characterize the anisotropy strength of non-sliding failure involved in the strength criteria and confining pressure are investigated.The results demonstrate that strength parameters K 1 and K 2 affect the strength of layered rock samples at all bedding angles except for the bedding angle of 90°and the angle range that can cause the shear sliding failure along the bedding plane.The strength of samples at any bedding angle decreases with increasing K 1,whereas the opposite is for K 2.Except for bedding angles of 0°and 90°and the bedding angle range that can cause the shear sliding along the bedding plane,K 3 has an impact on the strength of rock samples with other bedding angles that the specimens'strength increases with increase of K 3.In addition,the strength of the rock sample increases as confining pressure rises.Furthermore,the uniaxial and triaxial tests of chlorite schist samples were carried out to verify and evaluate the strength criteria proposed in the paper.It shows that the predicted strength is in good agreement with the experimental results.To test the applicability of the strength criterion,the strength data of several types of rock in the literature are compared.Finally,a comparison is made between the fitting effects of the two strength criteria and other available criteria for layered rocks.展开更多
Terracing is a widely adopted agricultural practice in mountainous regions around the world that aims to conserve soil and water resources.Soil nutrients play a crucial role in determining soil quality,particularly in...Terracing is a widely adopted agricultural practice in mountainous regions around the world that aims to conserve soil and water resources.Soil nutrients play a crucial role in determining soil quality,particularly in landscapes prone to drought.They are influenced by factors such as land-use type,slope aspect,and altitude.In this study,we sought to examine the impact of terracing on soil nutrients(soil organic content(SOC),total nitrogen(TN),nitrate-nitrogen(NO_(3)^(-)-N),ammonium nitrogen(NH_(4)^(+)-N),total phosphorus(TP),available phosphorus(AP),total potassium(TK),and available potassium(AK))and how they vary with environmental factors in the Chinese Loess Plateau.During the growing season,we collected 540 soil samples from the 0 to 100 cm soil layer across five major land-use types,different slope aspects,and varying altitudes.Additionally,a meta-analysis of literature data further corroborated the effective accumulation of soil nutrients through terracing in the Loess Plateau.Our findings are as follows:(1)Terraced fields,regardless of land-use type,showed a significant improvement in SOC and TN content.(2)Soil nutrient contents within terraced fields were predominantly higher on sunny slopes.(3)Terraces at lower altitudes are characterized by elevated SOC concentrations.(4)A meta-analysis of literature data pertaining to terracing and soil nutrients in this region confirmed the effective accumulation of soil nutri-ents through terracing.The elucidated outcomes of this study offer a profound theoretical underpinning for the accurate planning and management of terraces,the scientific utilization of land resources,and the enhancement of land productivity.展开更多
The far-field microdynamic disturbance caused by the excavation of deep mineral resources and underground engineering can induce surrounding rock damage in high-stress conditions and even lead to disasters.However,the...The far-field microdynamic disturbance caused by the excavation of deep mineral resources and underground engineering can induce surrounding rock damage in high-stress conditions and even lead to disasters.However,the mechanical properties and damage/fracture evolution mechanisms of deep rock induced by microdynamic disturbance under three-dimensional stress states are unclear.Therefore,a true triaxial multilevel disturbance test method is proposed,which can completely simulate natural geostress,excavation stress redistribution(such as stress unloading,concentration and rotation),and subsequently the microdynamic disturbance triggering damaged rock failure.Based on a dynamic true triaxial test platform,true triaxial microdynamic disturbance tests under different frequency and amplitudes were carried out on monzogabbro.The results show that increasing amplitude or decreasing frequency diminishes the failure strength of monzogabbro.Deformation modulus gradually decreases during disturbance failure.As frequency and amplitude increase,the degradation rate of deformation modulus decreases slightly,disturbance dissipated energy increases significantly,and disturbance deformation anisotropy strengthens obviously.A damage model has been proposed to quantitatively characterize the disturbance-induced damage evolution at different frequency and amplitude under true triaxial stress.Before disturbance failure,the micro-tensile crack mechanism is dominant,and the micro-shear crack mechanism increases significantly at failure.With the increase of amplitude and frequency,the micro-shear crack mechanism increases.When approaching disturbance failure,the acoustic emission fractal dimension changes from a stable value to local large oscillation,and finally increases sharply to a high value at failure.Finally,the disturbance-induced failure mechanism of surrounding rock in deep engineering is clearly elucidated.展开更多
Using flexible damping technology to improve tunnel lining structure is an emerging method to resist earthquake disasters,and several methods have been explored to predict mechanical response of tunnel lining with dam...Using flexible damping technology to improve tunnel lining structure is an emerging method to resist earthquake disasters,and several methods have been explored to predict mechanical response of tunnel lining with damping layer.However,the traditional numerical methods suffer from the complex modelling and time-consuming problems.Therefore,a prediction model named the random forest regressor(RFR)is proposed based on 240 numerical simulation results of the mechanical response of tunnel lining.In addition,circle mapping(CM)is used to improve Archimedes optimization algorithm(AOA),reptile search algorithm(RSA),and Chernobyl disaster optimizer(CDO)to further improve the predictive performance of the RFR model.The performance evaluation results show that the CMRSA-RFR is the best prediction model.The damping layer thickness is the most important feature for predicting the maximum principal stress of tunnel lining containing damping layer.This study verifies the feasibility of combining numerical simulation with machine learning technology,and provides a new solution for predicting the mechanical response of aseismic tunnel with damping layer.展开更多
At present,the major problems facing the water resource environment worldwide include water pollution,water resource shortage,and water ecosystem degradation.The discharge of industrial wastewater,agricultural non-poi...At present,the major problems facing the water resource environment worldwide include water pollution,water resource shortage,and water ecosystem degradation.The discharge of industrial wastewater,agricultural non-point source pollution,and the discharge of urban sewage lead to a serious decline in water quality,which directly affects the safety of human drinking water and the living environment of aquatic organisms.Additionally,the unbalanced distribution and excessive exploitation of water resources lead to the problem of water shortage in many areas,which then leads to social and economic contradictions and ecological crises.In terms of ecosystems,the phenomena of water ecological degradation and reduction of biodiversity are increasingly obvious,and the carrying capacity of aquatic ecosystems are gradually declining.This paper aims to analyze the natural,social,and economic factors affecting the water resource environment,and propose effective strategies to protect the water ecology.To provide a theoretical basis and practical guidance for the sustainable utilization of water resources and the long-term development of the water ecosystem.展开更多
This paper describes a study on the combined impacts of antecedent earthquakes and droughts on disastrous debris flows.This is a novel attempt in quantifying such impacts using the effective peak acceleration(EPA)(to ...This paper describes a study on the combined impacts of antecedent earthquakes and droughts on disastrous debris flows.This is a novel attempt in quantifying such impacts using the effective peak acceleration(EPA)(to represent earthquakes) and standardized precipitation index(SPI)(to represent droughts).The study is based on the analysis of 116 disastrous debris flow events occurred in China's Mainland in the last 100 years covering a wide spectrum of climate types and landforms.It has been found that the combined impacts from earthquakes and droughts on disastrous debris flows do exist and vary from low to very high according to different climate conditions and terrains.The impacts from earthquakes increase with the increased terrain relief,and the impacts from droughts are strongest in semi-humid climate condition(with reduced impacts in humid and semi-arid /arid climate conditions).Hypothetical explanations on the study discoveries have been proposed.This study reveals the possible reasons for the disastrous debris flow distributions around the world and has significant implications in paleo-climate-seismicanalysis and disastrous debris flow risk management.展开更多
Gully erosion has caused soil degradation and even reduced soil productivity. However, only few studies on the effects of gully erosion and artificial controlling measures on soil degradation in the Black Soil Region ...Gully erosion has caused soil degradation and even reduced soil productivity. However, only few studies on the effects of gully erosion and artificial controlling measures on soil degradation in the Black Soil Region of Northeast China are available. Thus, this study explores the relationships between gully erosion, gully filling and soil parameters. Two sets of soil samples were collected in the field at： （1） 72 sample points in the gully erosion study area, 60 sample points in the ephemeral and classical gully erosion area （3,518 m2）, 12 sample points in the deposition zone （443 m2）, （2）1o reference points along a slope unaffected by gully erosion representing the original situation before the gully was formed. All soil samples were analyzed for gravel content （GC）, soil organic matter （SOM）, total nitrogen （TN）, available nitrogen （AN）, available phosphorus （AP）, and available potassium （AK）. The soil property values on unaffected slope were fitted by the polynomial curves as the reference values in no gully erosion area. The interpolated soil property values in gully eroded study area were compared with these polynomial curves, respectively, and then, changes of soil property values were analyzed. Gully erosion caused an increase in GC and a decrease in SOM, TN, AN, AP and AK. The change of GC, SOM, TN, AN, AP, AK was 8.8%, -9.04 g kg-1, -0.92 g kg-1, -62.28 mg kg-1, -29.61 mg kg% -79.68 mg kg-1. The soil property values in the study area were below optimal values. Thus, we concluded that gully erosion and gully filling caused both on-site and off-site soil degradation. Soil degradation area was 0.65 % of the cultivated land. In addition, it was proved that gully filling were an improper soil and water conservation measure, which seems to exacerbate the problem. Thus, it is suggested that soil where soil is deep is moved to fill the gully, and then the area around the filled gullies should be covered by grass for preventing the formation and development of the gully.展开更多
Vegetation patterns are important in the regulation of earth surface hydrological processes in arid and semi-arid areas. Laboratory-simulated rainfall experiments were used at the State Key Laboratory of Soil Erosion ...Vegetation patterns are important in the regulation of earth surface hydrological processes in arid and semi-arid areas. Laboratory-simulated rainfall experiments were used at the State Key Laboratory of Soil Erosion and Dryland Farming on the Loess Plateau, Yangling, northwestern China, to quantify the effects of Artemisia capillaris patterns on runoff and soil loss. The quantitative relationships between runoff/sediment yield and vegetation parameters were also thoroughly analyzed using the path analysis method for identifying the reduction mechanism of vegetation on soil erosion. A simulated rainfall intensity of 90 mm/h was applied on a control plot without vegetation （Co） and on the other three different vegetation distribution patterns： a checkerboard pattern （CP）, a banded pattern perpendicular to the slope direction （BP）, and a single long strip parallel to the slope direction （LP）. Each patterned plot received two sets of experiments, i.e. intact plants and roots only, respectively. All treatments had three replicates. The results showed that all the three other different patterns （CP, BP and LP） of A. capillaris could effectively reduce the runoff and sediment yield. Compared with Co, the other three intact plant plots had a 12%-25% less runoff and 58%-92% less sediment. Roots contributed more to sediment reduction （46%-70%）, whereas shoots contributed more to runoff reduction （57%-81%）. BP and CP exhibited preferable controlling effects on soil erosion compared with LP. Path analysis indicated that root length density and plant number were key parameters influencing runoff rate, while root surface area density and root weight density were central indicators affecting sediment rate. The results indicated that an appropriate increase of sowing density has practical significance in conserving soil and water.展开更多
The properties of low-heat Portland cement concrete（LHC） were studied in detail. The experimental results show that the LHC concrete has characteristics of a higher physical mechanical behavior, deformation and dura...The properties of low-heat Portland cement concrete（LHC） were studied in detail. The experimental results show that the LHC concrete has characteristics of a higher physical mechanical behavior, deformation and durability. Compared with moderate-heat Portland cement（MHC）, the average hydration heat of LHC concrete is reduced by about 17.5%. Under same mixing proportion, the adiabatic temperature rise of LHC concrete was reduced by 2 ℃-3 ℃,and the limits tension of LHC concrete was increased by 10× 10^-6-15×10^-6 than that of MHC. Moreover, it is indicated that LHC concrete has a better anti-crack behavior than MHC concrete.展开更多
The numerical manifold method(NMM)can be viewed as an inherent continuous-discontinuous numerical method,which is based on two cover systems including mathematical and physical covers.Higher-order NMM that adopts high...The numerical manifold method(NMM)can be viewed as an inherent continuous-discontinuous numerical method,which is based on two cover systems including mathematical and physical covers.Higher-order NMM that adopts higher-order polynomials as its local approximations generally shows higher precision than zero-order NMM whose local approximations are constants.Therefore,higherorder NMM will be an excellent choice for crack propagation problem which requires higher stress accuracy.In addition,it is crucial to improve the stress accuracy around the crack tip for determining the direction of crack growth according to the maximum circumferential stress criterion in fracture mechanics.Thus,some other enriched local approximations are introduced to model the stress singularity at the crack tip.Generally,higher-order NMM,especially first-order NMM wherein local approximations are first-order polynomials,has the linear dependence problems as other partition of unit(PUM)based numerical methods does.To overcome this problem,an extended NMM is developed based on a new local approximation derived from the triangular plate element in the finite element method(FEM),which has no linear dependence issue.Meanwhile,the stresses at the nodes of mathematical mesh(the nodal stresses in FEM)are continuous and the degrees of freedom defined on the physical patches are physically meaningful.Next,the extended NMM is employed to solve multiple crack propagation problems.It shows that the fracture mechanics requirement and mechanical equilibrium can be satisfied by the trial-and-error method and the adjustment of the load multiplier in the process of crack propagation.Four numerical examples are illustrated to verify the feasibility of the proposed extended NMM.The numerical examples indicate that the crack growths simulated by the extended NMM are in good accordance with the reference solutions.Thus the effectiveness and correctness of the developed NMM have been validated.展开更多
Biological soil crusts(biocrusts)are important landscape components that exist in various climates and habitats.The roles of biocrusts in numerous soil processes have been predominantly recognized in many dryland regi...Biological soil crusts(biocrusts)are important landscape components that exist in various climates and habitats.The roles of biocrusts in numerous soil processes have been predominantly recognized in many dryland regions worldwide.However,little is known about their effects on soil detachment process by overland flow,especially in humid climates.This study quantified the effects of moss-dominated biocrusts on soil detachment capacity(Dc)and soil erosion resistance to flowing water in the Three Gorges Reservoir Area which holds a subtropical humid climate.Potential factors driving soil detachment variation and their influencing mechanism were analyzed and elucidated.We designed five levels of coverage treatments(1%–20%,20%–40%,40%–60%,60%–80%,and 80%–100%)and a nearby bare land as control in a mossdominated site.Undisturbed soil samples were taken and subjected to water flow scouring in a hydraulic flume under six shear stresses ranging from 4.89 to 17.99 Pa.The results indicated that mean Dc of mosscovered soil varied from 0.008 to 0.081 kg m^-2 s^-1,which was 1.9 to 21.0 times lower than that of bare soil(0.160 kg m^-2 s^-1).Rill erodibility(Kr)of mosscovered soil ranged from 0.0095 to 0.0009 s m^-1,which was 2 to 20 times lower than that of bare soil(0.0187 s m^-1).Both relative soil detachment rate and Kr showed an exponential decay with increasing moss coverage,whereas the critical shear stress(τc)for different moss coverage levels did not differ significantly.Moss coverage,soil cohesion,and sand content were key factors affecting Dc,while moss coverage and soil bulk density were key factors affecting Kr.A power function of flow shear stress,soil cohesion,and moss coverage fitted well to estimate Dc(NSE=0.947).Our findings implied that biocrusts prevented soil detachment directly by their physical cover and indirectly by soil properties modification.Biocrusts could be rehabilitated as a promising soil conservation measure during ecological recovery to enhance soil erosion resistance in the Three Gorges Reservoir Area.展开更多
Pipe cooling is an effective method of mass concrete temperature control, but its accurate and convenient numerical simulation is still a cumbersome problem. An improved embedded model, considering the water temperatu...Pipe cooling is an effective method of mass concrete temperature control, but its accurate and convenient numerical simulation is still a cumbersome problem. An improved embedded model, considering the water temperature variation along the pipe, was proposed for simulating the temperature field of early-age concrete structures containing cooling pipes. The improved model was verified with an engineering example. Then, the p-version self-adaption algorithm for the improved embedded model was deduced, and the initial values and boundary conditions were examined. Comparison of some numerical samples shows that the proposed model can provide satisfying precision and a higher efficiency. The analysis efficiency can be doubled at the same precision, even for a large-scale element. The p-version algorithm can fit grids of different sizes for the temperature field simulation. The convenience of the proposed algorithm lies in the possibility of locating more pipe segments in one element without the need of so regular a shape as in the explicit model.展开更多
The stability of slope rock masses is influenced by freeze-thaw cycles in cold region,and the mechanism of stability deterioration is not clear.In order to understand the damage and progressive failure characteristics...The stability of slope rock masses is influenced by freeze-thaw cycles in cold region,and the mechanism of stability deterioration is not clear.In order to understand the damage and progressive failure characteristics of rock masses under the action of freezing and thawing,a model test was conducted on slope with steep joint in this study.The temperature,frost heaving pressure and deformation of slope rock mass were monitored in real-time during the test and the progressive failure mode was studied.The experimental results show that the temperature variations of cracking and the rock mass of a slope are different.There are obvious latent heat stages in the temperature-change plot in the crack,but not in the slope rock masses.The frost heaving effect in the fracture is closely related to the constraint conditions,which change with the deformation of the fracture.The frost heaving pressure fluctuates periodically during freezing and continues to decrease during thawing.The surface deformation of the rock mass increases during freezing,and the deformation is restored when it thaws.Freeze-thaw cycling results in residual deformation of the rock mass which cannot be fully restored.Analysis shows that the rock mass at the free side of the steep-dip joint rotates slightly under the frost heaving effect,causing fracture propagation.The fracture propagation pattern is a circular arc at the beginning,then extends to the possible sliding direction of the rock mass.Frost heaving force and fracture water pressure are the key factors for the failure of the slope,which can cause the crack to penetrate the rock mass,and a landslide ensues when the overall anti-sliding resistance of the rock mass is overcome.展开更多
基金Knowledge Innovation Program of Wuhan-Shugung Project,Grant/Award Number:2023020201020363。
文摘The widespread use of antibiotics has significantly increased their presence in aquatic environments,particularly in sensitive Karst River systems.In this study,the distribution and ecological,human health,and resistance selection risk assessment of 44 antibiotics in the typical Karst River,Lijiang River,were investigated during the influenza season,a period marked by heightened antibiotic usage.27 antibiotics could be found in the water of Lijiang River,among which azithromycin showing the highest concentrations.The concentrations of total antibiotics were in the range 171.70–2003.75 ng/L,with an average value of 704.76 ng/L.Macrolide was the predominant class,constituting an average of 57.65%of the total antibiotic concentrations.Risk assessments revealed that certain antibiotics,especially macrolides,posed moderate to high ecological risks to algae,displayed potential human health risks at low levels and contributed to antimicrobial resistance.Among all the antibiotics,azithromycin was the only one could cause ecological risk to algae,human health risk towards infants and antimicrobial resistance selection risk,which should be identified as the priority antibiotic for control in the Lijiang River during the influenza season.There was no difference in the concentrations,human health and antimicrobial resistance selection risk of antibiotics between mainstream and tributaries of Lijiang River.This study contributes to a better understanding of antibiotic pollution and provides insights into potential risk management practices in vulnerable aquatic systems worldwide.
文摘Gassy soils are distributed in relatively shallow layers the Quaternary deposit in Hangzhou Bay area. The shallow gassy soils significantly affect the construction of underground projects. Proper characterization of spatial distribution of shallow gassy soils is indispensable prior to construction of underground projects in the area. Due to the costly conditions required in the site investigation for gassy soils, only a limited number of gas pressure data can be obtained in engineering practice, which leads to the uncertainty in characterizing spatial distribution of gassy soils. Determining the number of boreholes for investigating gassy soils and their corresponding locations is pivotal to reducing construction risk induced by gassy soils. However, this primarily relies on the engineering experience in the current site investigation practice. This study develops a probabilistic site investigation optimization method for planning investigation schemes (including the number and locations of boreholes) of gassy soils based on the conditional random field and Monte Carlo simulation. The proposed method aims to provide an optimal investigation scheme before the site investigation based on prior knowledge. Finally, the proposed approach is illustrated using a case study.
基金supported by financial support from the National Natural Science Foundation of China(Grant Nos.52309122 and U2340229)the Innovation Team of Changjiang River Scientific Research Institute(Grant No.CKSF2024329/YT).
文摘Large-scale and heavily jointed rocks have inherent planes of anisotropy and secondary structural planes,such as dominant joint sets and random fractures,which result in significant differences in their failure mechanism and deformation behavior compared to other rock types.To address this issue,inherent anisotropic rocks with large-scale and dense joints are considered to be composed of the rock matrix,inherent planes of anisotropy,and secondary structural planes.Then a new implicit continuum model called LayerDFN is developed based on the crack tensor and damage tensor theories to characterize the mechanical properties of inherent anisotropic rocks.Furthermore,the LayerDFN model is implemented in the FLAC3D software,and a series of numerical results for typical example problems is compared with those obtained from the 3DEC,the analytical solutions,similar classical models,laboratory uniaxial compression tests,and field rigid bearing plate tests.The results demonstrate that the LayerDFN model can effectively capture the anisotropic mechanical properties of inherent anisotropic rocks,and can quantitatively characterize the damaging effect of the secondary structural planes.Overall,the numerical method based on the LayerDFN model provides a comprehensive and reliable approach for describing and analyzing the behavior of inherent anisotropic rocks,which will provide valuable insights for engineering design and decision-making processes.
基金Supported by the CRSRI Open Research Program(CKWV2013225/KY)the Open Project Foundation of Key Laboratory of the Yellow River Sediment of Ministry of Water Resource(2014006)+2 种基金the Open Project Foundation of Key Lab of Port,Waterway and Sedimentation Engineering of the Ministry of Transportthe State Key Lab of Urban Water Resource and Environment(HIT)(ES201409)the Priority Academic Program Development of Jiangsu Higher Education Institution
文摘To cope with the problems that edge detection operators are liable to make the detected edges too blurry for synthetic aperture radar(SAR)images,an edge detection method for detecting river in SAR images is proposed based on contourlet modulus maxima and improved mathematical morphology.The SAR image is firstly transformed to a contourlet domain.According to the directional information and gradient information of directional subband of contourlet transform,the modulus maximum and the improved mathematical morphology are used to detect high frequency and low frequency sub-image edges,respectively.Subsequently,the edges of river in SAR image are obtained after fusing the high frequency sub-image and the low frequency sub-image.Experimental results demonstrate that the proposed edge detection method can obtain more accurate edge location and reduce false edges,compared with the Canny method,the method based on wavelet and Canny,the method based on contourlet modulus maxima,and the method based on improved(ROEWA).The obtained river edges are complete and clear.
基金support from the Technology Pillar Program during the"Eleventh Five-year Plan"Period (No.2006BAB05B02No.2006BAB05B03) are acknowledged
文摘According to the measured data after impoundment and operation of the Three Gorges Reservoir,the reservoir sediment deposition and downstream river channel scouring are described briefly and compared with the research results achieved in the demonstration stage.It is indicated through analysis that the reservoir sediment deposition and downstream river channel scouring during 8-year impoundment and operation are still within the original forecast,so the original forecasting results are feasible.The further observation and comparison should be conducted because the comparison between the observed data and the original forecast is not so sufficient in time and the prototype observation and related research work should be strengthened in the future.
基金Changjiang Water Science Research Joint Fund of the National Natural Science Foundation of China,Grant/Award Numbers:U2240206,U2240224Research Project on Major Scientific and Technological Issues in Watershed Water Management of MWR of China,Grant/Award Number:CKSC2020791/HL+2 种基金Fundamental Research Funds for Central Public Welfare Research Institutes of China,Grant/Award Number:CKSF2023328/HLKey Laboratory of Water-Sediment Sciences and Water Disaster Prevention of Hunan Province of China,Grant/Award Number:2021SS01Natural Science Foundation of Hubei Province,Grant/Award Number:2021CFB146。
文摘The construction and operation of the Three Gorges Reservoir and the cascade reservoirs upstream have significantly altered the processes offlow and sediment in the main and tributary channels of the Yangtze River.This has led to substantial adjustments in the riverbed through erosion and deposition,thereby impactingflood protection,water resource utilization,navigation,and the aquatic environ-ment in the Yangtze River basin.In this study,prototype measurements were used to analyze the variations in runoff and sediment load in the main channel of the Yangtze River,as well as the changes and evolution of the riverbed.Mathematical modeling was done to predict the trends in reservoir sedimentation and riverbed adjustments.The results indicate that,apart from the significantly increased runoff and sediment load in the river source region(Zhimenda station)over the past two decades,there is no clear unidirectional trend of increasing or decreasing in the main and tributary annual runoff of the Yangtze River.However,the release of reservoir outflows undergoes significant changes throughout the year due to reservoir regulation.Suspended sediment load in the upper Yangtze River has been decreasing since the 1990s,especially after the operation of the Three Gorges Reservoir and the four cascade reservoirs in the lower reach of the Jinsha River.The factors influencingflow and sediment variations include mainly climate change and human activities such as reservoir operation and soil and water conservation.The significant changes inflow and sediment conditions have disrupted the original relative equilibrium state of the main channel of the Yangtze River,leading to riverbed adjustments.The river sections in the upper reach,located within reservoir areas,have shifted from erosional state under natural conditions to accumulative state,while the middle and lower reaches have transitioned from a relatively equilibrium state to a process dominated by erosion and reconstruction.Overall,the river regime in the reservoir area and downstream of the Three Gorges Dam remains relatively stable,but there have been adjustments in some local river sections,for example,in the curved sections,particularly in the sharply curved sections downstream of the Three Gorges Dam,where gradual or abrupt chute cutoff has occurred.In the foreseeable future,the river channel downstream of the Three Gorges Dam will remain in an unsaturated state regarding sediment transport.The process of river channel erosion will persist for a long time and have far-reaching consequences.Some long straight sections,multiple bifurcation sections,and sections with large curvature are expected to undergo certain adjustments in the river regime,necessitating continuous observation,long-term monitoring,and timely river management and channel governance.
文摘Hyperconcentrated floods in the Yellow River usually accompanied with some peculiar phenomena that cannot be explained by general conceptions of ordinary sediment-laden flow (e.g., downstream increase in peak discharge, instability flow, ripping up the bottom). Up to date, the mechanisms for the abnormal phenomena are not well understood. The aim of this paper is to facilitate a new insight into the abnormal downstream increase in peak discharge of hyperconcentrated floods in the lower Yellow River. Numerical model experiments have been conducted on a typical flood occurred in August 1992 in the Lower Yellow River during which the peak discharge at Huayuankou station was 1690 m3/s larger than the value at Xiaolangdi station at upstream. It is found that a fully coupled model that incorporates the contribution of bed evolution to the mass conservation of the water-sediment mixture, can reasonably well capture the characteristics of peak discharge rise and severe bed scour, while separate numerical experiment using a decoupled model, which ignores the feedback effects of bed evolution, shows no rise in the peak discharge. This leads us to comment, if only briefly, that the entrainment of sediment due to bed erosion is the main reason for causing peak discharge increase along downstream course.
基金the financial support from the National Natural Science Foundation of China(Grant No.51979008)the National Natural Science Foundation of China(Grant No.51779018)the Innovation team of Changjiang River Scientific Research Institute(Grant No.CKSF2021715/YT).
文摘Layered rock mass is a type of engineering rock mass with sound mechanical anisotropy,which is generally unfavorable to the stability of underground works.To investigate the strength anisotropy of layered rock,the Mohr-Coulomb and Hoek-Brown criteria are introduced to establish the two transverse isotropic strength criteria based on Jaeger's single weak plane theory and maximum axial strain theory,and parameter determination methods.Furthermore,the sensitivity of strength parameters(K 1,K 2,and K 3)that are used to characterize the anisotropy strength of non-sliding failure involved in the strength criteria and confining pressure are investigated.The results demonstrate that strength parameters K 1 and K 2 affect the strength of layered rock samples at all bedding angles except for the bedding angle of 90°and the angle range that can cause the shear sliding failure along the bedding plane.The strength of samples at any bedding angle decreases with increasing K 1,whereas the opposite is for K 2.Except for bedding angles of 0°and 90°and the bedding angle range that can cause the shear sliding along the bedding plane,K 3 has an impact on the strength of rock samples with other bedding angles that the specimens'strength increases with increase of K 3.In addition,the strength of the rock sample increases as confining pressure rises.Furthermore,the uniaxial and triaxial tests of chlorite schist samples were carried out to verify and evaluate the strength criteria proposed in the paper.It shows that the predicted strength is in good agreement with the experimental results.To test the applicability of the strength criterion,the strength data of several types of rock in the literature are compared.Finally,a comparison is made between the fitting effects of the two strength criteria and other available criteria for layered rocks.
基金the National Natural Science Foundation of China(Grants No.42201100,U21A2011,41991233)the Central Public-Interest Scientific Institution Basal Research Fund(Grant No.CKSF2023301)the Knowledge Innovation Program of Wuhan-Basic Research(Grant No.2022020801010236).
文摘Terracing is a widely adopted agricultural practice in mountainous regions around the world that aims to conserve soil and water resources.Soil nutrients play a crucial role in determining soil quality,particularly in landscapes prone to drought.They are influenced by factors such as land-use type,slope aspect,and altitude.In this study,we sought to examine the impact of terracing on soil nutrients(soil organic content(SOC),total nitrogen(TN),nitrate-nitrogen(NO_(3)^(-)-N),ammonium nitrogen(NH_(4)^(+)-N),total phosphorus(TP),available phosphorus(AP),total potassium(TK),and available potassium(AK))and how they vary with environmental factors in the Chinese Loess Plateau.During the growing season,we collected 540 soil samples from the 0 to 100 cm soil layer across five major land-use types,different slope aspects,and varying altitudes.Additionally,a meta-analysis of literature data further corroborated the effective accumulation of soil nutrients through terracing in the Loess Plateau.Our findings are as follows:(1)Terraced fields,regardless of land-use type,showed a significant improvement in SOC and TN content.(2)Soil nutrient contents within terraced fields were predominantly higher on sunny slopes.(3)Terraces at lower altitudes are characterized by elevated SOC concentrations.(4)A meta-analysis of literature data pertaining to terracing and soil nutrients in this region confirmed the effective accumulation of soil nutri-ents through terracing.The elucidated outcomes of this study offer a profound theoretical underpinning for the accurate planning and management of terraces,the scientific utilization of land resources,and the enhancement of land productivity.
基金the financial support from the National Natural Science Foundation of China(No.52109119)the Guangxi Natural Science Foundation(No.2021GXNSFBA075030)+2 种基金the Guangxi Science and Technology Project(No.Guike AD20325002)the Chinese Postdoctoral Science Fund Project(No.2022M723408)the Open Research Fund of State Key Laboratory of Simulation and Regulation of Water Cycle in River Basin(China Institute of Water Resources and Hydropower Research)(No.IWHR-SKL-202202)。
文摘The far-field microdynamic disturbance caused by the excavation of deep mineral resources and underground engineering can induce surrounding rock damage in high-stress conditions and even lead to disasters.However,the mechanical properties and damage/fracture evolution mechanisms of deep rock induced by microdynamic disturbance under three-dimensional stress states are unclear.Therefore,a true triaxial multilevel disturbance test method is proposed,which can completely simulate natural geostress,excavation stress redistribution(such as stress unloading,concentration and rotation),and subsequently the microdynamic disturbance triggering damaged rock failure.Based on a dynamic true triaxial test platform,true triaxial microdynamic disturbance tests under different frequency and amplitudes were carried out on monzogabbro.The results show that increasing amplitude or decreasing frequency diminishes the failure strength of monzogabbro.Deformation modulus gradually decreases during disturbance failure.As frequency and amplitude increase,the degradation rate of deformation modulus decreases slightly,disturbance dissipated energy increases significantly,and disturbance deformation anisotropy strengthens obviously.A damage model has been proposed to quantitatively characterize the disturbance-induced damage evolution at different frequency and amplitude under true triaxial stress.Before disturbance failure,the micro-tensile crack mechanism is dominant,and the micro-shear crack mechanism increases significantly at failure.With the increase of amplitude and frequency,the micro-shear crack mechanism increases.When approaching disturbance failure,the acoustic emission fractal dimension changes from a stable value to local large oscillation,and finally increases sharply to a high value at failure.Finally,the disturbance-induced failure mechanism of surrounding rock in deep engineering is clearly elucidated.
基金Project(2023YFB2390400)supported by the National Key R&D Programs for Young Scientists,ChinaProjects(U21A20159,52079133,52379112,52309123,41902288)supported by the National Natural Science Foundation of China+5 种基金Project(2024AFB041)supported by the Hubei Provincial Natural Science Foundation,ChinaProject(QTKS0034W23291)supported by the Key Laboratory of Water Grid Project and Regulation of Ministry of Water Resources,ChinaProject(2023SGG07)supported by the Visiting Researcher Fund Program of State Key Laboratory of Water Resources Engineering and Management,ChinaProject(2022KY56(ZDZX)-02)supported by the Key Research Program of FSDI,ChinaProject(SKS-2022103)supported by the Key Research Program of the Ministry of Water Resources,ChinaProject(202102AF080001)supported by the Yunnan Major Science and Technology Special Program,China。
文摘Using flexible damping technology to improve tunnel lining structure is an emerging method to resist earthquake disasters,and several methods have been explored to predict mechanical response of tunnel lining with damping layer.However,the traditional numerical methods suffer from the complex modelling and time-consuming problems.Therefore,a prediction model named the random forest regressor(RFR)is proposed based on 240 numerical simulation results of the mechanical response of tunnel lining.In addition,circle mapping(CM)is used to improve Archimedes optimization algorithm(AOA),reptile search algorithm(RSA),and Chernobyl disaster optimizer(CDO)to further improve the predictive performance of the RFR model.The performance evaluation results show that the CMRSA-RFR is the best prediction model.The damping layer thickness is the most important feature for predicting the maximum principal stress of tunnel lining containing damping layer.This study verifies the feasibility of combining numerical simulation with machine learning technology,and provides a new solution for predicting the mechanical response of aseismic tunnel with damping layer.
基金The Knowledge Innovation Program of Wuhan-Shuguang Project(Project No.2023020201020361).
文摘At present,the major problems facing the water resource environment worldwide include water pollution,water resource shortage,and water ecosystem degradation.The discharge of industrial wastewater,agricultural non-point source pollution,and the discharge of urban sewage lead to a serious decline in water quality,which directly affects the safety of human drinking water and the living environment of aquatic organisms.Additionally,the unbalanced distribution and excessive exploitation of water resources lead to the problem of water shortage in many areas,which then leads to social and economic contradictions and ecological crises.In terms of ecosystems,the phenomena of water ecological degradation and reduction of biodiversity are increasingly obvious,and the carrying capacity of aquatic ecosystems are gradually declining.This paper aims to analyze the natural,social,and economic factors affecting the water resource environment,and propose effective strategies to protect the water ecology.To provide a theoretical basis and practical guidance for the sustainable utilization of water resources and the long-term development of the water ecosystem.
基金funded by the Ministry of Science and Technology of China (Grant No. 2011BAK12B02)the National Natural Science Foundation of China (Grant No. 41190084)+2 种基金the National Key Technology R&D Program (Grant No 2012 BAK10B04)the Non-Profit Industry Financial Program of MWR (Grant No. 201301058)the Changjiang River Scientific Research Institute of Sciences Innovation Team Project (Grant No. CKSF2012052/TB)
文摘This paper describes a study on the combined impacts of antecedent earthquakes and droughts on disastrous debris flows.This is a novel attempt in quantifying such impacts using the effective peak acceleration(EPA)(to represent earthquakes) and standardized precipitation index(SPI)(to represent droughts).The study is based on the analysis of 116 disastrous debris flow events occurred in China's Mainland in the last 100 years covering a wide spectrum of climate types and landforms.It has been found that the combined impacts from earthquakes and droughts on disastrous debris flows do exist and vary from low to very high according to different climate conditions and terrains.The impacts from earthquakes increase with the increased terrain relief,and the impacts from droughts are strongest in semi-humid climate condition(with reduced impacts in humid and semi-arid /arid climate conditions).Hypothetical explanations on the study discoveries have been proposed.This study reveals the possible reasons for the disastrous debris flow distributions around the world and has significant implications in paleo-climate-seismicanalysis and disastrous debris flow risk management.
基金supported by National Basic Research Program of China (973 Program) (Grant no. 2007CB407204)Innovation project of Changjiang River Scientific Research Institute (CKSF2012052/TB)basic scientific research project of Changjiang River Scientific Research Institute (CKSF2011008)
文摘Gully erosion has caused soil degradation and even reduced soil productivity. However, only few studies on the effects of gully erosion and artificial controlling measures on soil degradation in the Black Soil Region of Northeast China are available. Thus, this study explores the relationships between gully erosion, gully filling and soil parameters. Two sets of soil samples were collected in the field at： （1） 72 sample points in the gully erosion study area, 60 sample points in the ephemeral and classical gully erosion area （3,518 m2）, 12 sample points in the deposition zone （443 m2）, （2）1o reference points along a slope unaffected by gully erosion representing the original situation before the gully was formed. All soil samples were analyzed for gravel content （GC）, soil organic matter （SOM）, total nitrogen （TN）, available nitrogen （AN）, available phosphorus （AP）, and available potassium （AK）. The soil property values on unaffected slope were fitted by the polynomial curves as the reference values in no gully erosion area. The interpolated soil property values in gully eroded study area were compared with these polynomial curves, respectively, and then, changes of soil property values were analyzed. Gully erosion caused an increase in GC and a decrease in SOM, TN, AN, AP and AK. The change of GC, SOM, TN, AN, AP, AK was 8.8%, -9.04 g kg-1, -0.92 g kg-1, -62.28 mg kg-1, -29.61 mg kg% -79.68 mg kg-1. The soil property values in the study area were below optimal values. Thus, we concluded that gully erosion and gully filling caused both on-site and off-site soil degradation. Soil degradation area was 0.65 % of the cultivated land. In addition, it was proved that gully filling were an improper soil and water conservation measure, which seems to exacerbate the problem. Thus, it is suggested that soil where soil is deep is moved to fill the gully, and then the area around the filled gullies should be covered by grass for preventing the formation and development of the gully.
基金funded by the National Natural Science Foundation of China (41301298)the State Key Program of National Natural Science Foundation of China (41030532)the Special Fund of Strategic Priority Research Program of Chinese Academy of Sciences (XDA05060300)
文摘Vegetation patterns are important in the regulation of earth surface hydrological processes in arid and semi-arid areas. Laboratory-simulated rainfall experiments were used at the State Key Laboratory of Soil Erosion and Dryland Farming on the Loess Plateau, Yangling, northwestern China, to quantify the effects of Artemisia capillaris patterns on runoff and soil loss. The quantitative relationships between runoff/sediment yield and vegetation parameters were also thoroughly analyzed using the path analysis method for identifying the reduction mechanism of vegetation on soil erosion. A simulated rainfall intensity of 90 mm/h was applied on a control plot without vegetation （Co） and on the other three different vegetation distribution patterns： a checkerboard pattern （CP）, a banded pattern perpendicular to the slope direction （BP）, and a single long strip parallel to the slope direction （LP）. Each patterned plot received two sets of experiments, i.e. intact plants and roots only, respectively. All treatments had three replicates. The results showed that all the three other different patterns （CP, BP and LP） of A. capillaris could effectively reduce the runoff and sediment yield. Compared with Co, the other three intact plant plots had a 12%-25% less runoff and 58%-92% less sediment. Roots contributed more to sediment reduction （46%-70%）, whereas shoots contributed more to runoff reduction （57%-81%）. BP and CP exhibited preferable controlling effects on soil erosion compared with LP. Path analysis indicated that root length density and plant number were key parameters influencing runoff rate, while root surface area density and root weight density were central indicators affecting sediment rate. The results indicated that an appropriate increase of sowing density has practical significance in conserving soil and water.
基金the National Natural Science Foundation of China(No.50539010)
文摘The properties of low-heat Portland cement concrete（LHC） were studied in detail. The experimental results show that the LHC concrete has characteristics of a higher physical mechanical behavior, deformation and durability. Compared with moderate-heat Portland cement（MHC）, the average hydration heat of LHC concrete is reduced by about 17.5%. Under same mixing proportion, the adiabatic temperature rise of LHC concrete was reduced by 2 ℃-3 ℃,and the limits tension of LHC concrete was increased by 10× 10^-6-15×10^-6 than that of MHC. Moreover, it is indicated that LHC concrete has a better anti-crack behavior than MHC concrete.
基金supported by the National Key R&D Program of China (Grant No.2018YFC0407002)the National Natural Science Foundation of China(Grant Nos.11502033 and 51879014)
文摘The numerical manifold method(NMM)can be viewed as an inherent continuous-discontinuous numerical method,which is based on two cover systems including mathematical and physical covers.Higher-order NMM that adopts higher-order polynomials as its local approximations generally shows higher precision than zero-order NMM whose local approximations are constants.Therefore,higherorder NMM will be an excellent choice for crack propagation problem which requires higher stress accuracy.In addition,it is crucial to improve the stress accuracy around the crack tip for determining the direction of crack growth according to the maximum circumferential stress criterion in fracture mechanics.Thus,some other enriched local approximations are introduced to model the stress singularity at the crack tip.Generally,higher-order NMM,especially first-order NMM wherein local approximations are first-order polynomials,has the linear dependence problems as other partition of unit(PUM)based numerical methods does.To overcome this problem,an extended NMM is developed based on a new local approximation derived from the triangular plate element in the finite element method(FEM),which has no linear dependence issue.Meanwhile,the stresses at the nodes of mathematical mesh(the nodal stresses in FEM)are continuous and the degrees of freedom defined on the physical patches are physically meaningful.Next,the extended NMM is employed to solve multiple crack propagation problems.It shows that the fracture mechanics requirement and mechanical equilibrium can be satisfied by the trial-and-error method and the adjustment of the load multiplier in the process of crack propagation.Four numerical examples are illustrated to verify the feasibility of the proposed extended NMM.The numerical examples indicate that the crack growths simulated by the extended NMM are in good accordance with the reference solutions.Thus the effectiveness and correctness of the developed NMM have been validated.
基金funded by the National Natural Science Foundation of China(Grant No.41877082)the Fundamental Research Funds for Central Public Welfare Research Institutes(Grant No.CKSF2019410TB)+2 种基金the National Natural Science Foundation for Young Scientists of China(Grant No.41701316,51909011)the National Key R&D Program of China(Grant No.2017YFC050530302)the Demonstration Project of Water Conservancy Technology(Grant No.SF-201905)。
文摘Biological soil crusts(biocrusts)are important landscape components that exist in various climates and habitats.The roles of biocrusts in numerous soil processes have been predominantly recognized in many dryland regions worldwide.However,little is known about their effects on soil detachment process by overland flow,especially in humid climates.This study quantified the effects of moss-dominated biocrusts on soil detachment capacity(Dc)and soil erosion resistance to flowing water in the Three Gorges Reservoir Area which holds a subtropical humid climate.Potential factors driving soil detachment variation and their influencing mechanism were analyzed and elucidated.We designed five levels of coverage treatments(1%–20%,20%–40%,40%–60%,60%–80%,and 80%–100%)and a nearby bare land as control in a mossdominated site.Undisturbed soil samples were taken and subjected to water flow scouring in a hydraulic flume under six shear stresses ranging from 4.89 to 17.99 Pa.The results indicated that mean Dc of mosscovered soil varied from 0.008 to 0.081 kg m^-2 s^-1,which was 1.9 to 21.0 times lower than that of bare soil(0.160 kg m^-2 s^-1).Rill erodibility(Kr)of mosscovered soil ranged from 0.0095 to 0.0009 s m^-1,which was 2 to 20 times lower than that of bare soil(0.0187 s m^-1).Both relative soil detachment rate and Kr showed an exponential decay with increasing moss coverage,whereas the critical shear stress(τc)for different moss coverage levels did not differ significantly.Moss coverage,soil cohesion,and sand content were key factors affecting Dc,while moss coverage and soil bulk density were key factors affecting Kr.A power function of flow shear stress,soil cohesion,and moss coverage fitted well to estimate Dc(NSE=0.947).Our findings implied that biocrusts prevented soil detachment directly by their physical cover and indirectly by soil properties modification.Biocrusts could be rehabilitated as a promising soil conservation measure during ecological recovery to enhance soil erosion resistance in the Three Gorges Reservoir Area.
基金supported by the National Natural Science Foundation of China(Grant No.51109071)
文摘Pipe cooling is an effective method of mass concrete temperature control, but its accurate and convenient numerical simulation is still a cumbersome problem. An improved embedded model, considering the water temperature variation along the pipe, was proposed for simulating the temperature field of early-age concrete structures containing cooling pipes. The improved model was verified with an engineering example. Then, the p-version self-adaption algorithm for the improved embedded model was deduced, and the initial values and boundary conditions were examined. Comparison of some numerical samples shows that the proposed model can provide satisfying precision and a higher efficiency. The analysis efficiency can be doubled at the same precision, even for a large-scale element. The p-version algorithm can fit grids of different sizes for the temperature field simulation. The convenience of the proposed algorithm lies in the possibility of locating more pipe segments in one element without the need of so regular a shape as in the explicit model.
基金supported by the National Natural Science Foundation of China(Project No.52179110,41877280 and 51309025)the Fundamental Research Funds for Central Public Welfare Research Institutes(CKSF 2019180/YT)the Research Funding of Wuhan Polytechnic University(NO.2021RZ028)。
文摘The stability of slope rock masses is influenced by freeze-thaw cycles in cold region,and the mechanism of stability deterioration is not clear.In order to understand the damage and progressive failure characteristics of rock masses under the action of freezing and thawing,a model test was conducted on slope with steep joint in this study.The temperature,frost heaving pressure and deformation of slope rock mass were monitored in real-time during the test and the progressive failure mode was studied.The experimental results show that the temperature variations of cracking and the rock mass of a slope are different.There are obvious latent heat stages in the temperature-change plot in the crack,but not in the slope rock masses.The frost heaving effect in the fracture is closely related to the constraint conditions,which change with the deformation of the fracture.The frost heaving pressure fluctuates periodically during freezing and continues to decrease during thawing.The surface deformation of the rock mass increases during freezing,and the deformation is restored when it thaws.Freeze-thaw cycling results in residual deformation of the rock mass which cannot be fully restored.Analysis shows that the rock mass at the free side of the steep-dip joint rotates slightly under the frost heaving effect,causing fracture propagation.The fracture propagation pattern is a circular arc at the beginning,then extends to the possible sliding direction of the rock mass.Frost heaving force and fracture water pressure are the key factors for the failure of the slope,which can cause the crack to penetrate the rock mass,and a landslide ensues when the overall anti-sliding resistance of the rock mass is overcome.
