Abstract:“Making Efforts to Protect the Yangtze River Together” is a huge and complex system project based on a scientific understanding of the ecological environment of the Yangtze River. The project involves thoroughly studying and exploring the Yangtze River by means of the following measures: top-level design and implementing of path planning; scientific support and guidance; selection of key engineering and technical measures; construction of a system for systematic monitoring and evaluation; exploring application of the value realization method; innovation using a market-oriented mechanism for operation; protection and supervision by legislation; and construction of an innovative platform for cooperation. These measures together constitute the framework of the “Making Efforts to Protect the Yangtze River Together” project, which are critical to fullfilling the objective of the project.

Abstract:For better understanding the characteristics of colloidal substance and its effect on biogenic element cycle in the hyporheic zone, this review focuses on recent advances of adsorption, release, migration, transformation, and exchange of biogenic elements influenced by colloidal substances. Main content of this review include: (a)the source, composition, temporal-spatial distribution, release, and migration of colloidal substance in the hyporheic zone under the interaction of surface water and groundwater; (b)the effects of physical, chemical, and biological conditions of the hyporheic zone on the properties of colloidal substance; (c)relationship between the distribution of biogenic elements in the hyporheic zone and the influencing mechanism of colloid facilitated-transport of biogenic elements; (d)rationality of present mathematical models for the migration and transformation of colloidal substance and its facilitated-transport of biogenic elements. Some research prospects are proposed based on present trends and deficiencies of researches about the influence of colloidal substances on the transport and transformation of biological elements in the hyporheic zone.

Abstract:A new biological filter reactor with multi-layer fiber ball was designed to overcome the disadvantages of traditional aquaculture, such as the high energy consumption and the complicated process. This reactor removed SS and nitrogen pollutants without changing water, and achieved a high concentration of dissolved oxygen in the effluent water. The results show that the naturally-formed biofilm built an externally-aerobic and internally-anoxic environments in the fiber. Therefore, the reactor could simultaneously accomplish the nitrification process and denitrification process. The influence of different water recirculating rate was discussed. In the case of water circulation rate of three times a day that was the optimal for the reactor, the concentration of NH⁺₄-N in effluent could be reduced to 0. 2 mg/L with the removal rate of 96. 15%. The removal efficiency ofNO^-₃-N was stable at about 70%, and the concentration ofNO^-₂-N in effluent could be reduced to 0. 1 mg/L with the removal rate of 95. 82%. Besides, the concentration of COD in effluent decreased to 4. 0 mg/L and the removal rate reached 60% or higher. At the same time, the SS removal rate was up to 100%. The simultaneous nitrification-denitrification process in the reactor was successfully achieved, and this study provides a new idea for the recirculating aquaculture system.

Abstract:Referring to the definition and classification method of oasis proposed by previous researchers, the artificial and natural oases were extracted in the downstream of the Tarim River. After that, this paper analyzed the area change characteristics, transformation process, gravity center migration, and spatial variation of oasisization and desertification during the period of 1990-2015. The results show that, from 1990 to 2015, the total area of oasis in the downstream of Tarim River Basin decreased firstly and then increased. The area of artificial oasis continued to expand with a 10-year average growth rate of 46. 78 km². The area of natural oasis continued to shrink, but increased after 2000. It is because that the amount of river discharge decreased, resulting in the degradation of grassland and the reduction of natural oasis before the ecological water transport(1990-2000). After the ecological water transport(2000-2015), some unused land was utilized again. The center of the oasis traveled to the northwest, then to the south, and finally to the southeast. In addition, the oasis mainly expanded to the northwest and southeast, while the oasis reduction area was sporadic.

Abstract:To provide more reliable simulations and forecasts using the Xinanjiang model in the semi-humid watersheds, this study introduced three real-time correction methods into the flood forecasting, respectively, including the K-nearest neighbor algorithm(the KNN method), the traditional error autoregression method(the AR method)and the simulating feedback method. The Chenhe Basin, in Shaanxi Province, was selected as the experimental basin. Considering the relative error of flood peak and the coefficient of Nash-Sutcliffe efficiency as evaluation indicators, this study analyzed the results of three correction methods. The results show that all three kinds of correction methods can improve the coefficient of Nash-Sutcliffe efficiency and the simulating feedback method was optimal on the Nash-Sutcliffe efficiency coefficient, while the AR method and the KNN method were the second best. The simulating feedback method allow a remarkable improvement compared with the KNN method in a short forecast period, and both of them can effectively avoid the defect of the AR method in terms of the error correction of flood peak. The results also indicate the KNN method with historical samples yielded better results than the simulation of feedback method on the error correction of flood peak, which can effectively improve the accuracy of flood forecasting.

Abstract:Taking the Baidajie embankment in the mainstream of Nenjiang River as the typical area, the locally encrypted and unstructured triangular calculating grid was generated by the surface water modeling system(SMS)based on the complex river topography and coastline conditions. Then, the third generation of shallow water wave model(simulating wave nearshore, SWAN)was adopted to simulate the effect of wave attenuation forest on the wind-generated waves in river. The results show that the correlation coefficient between the simulated wave height and the measured wave height is 0. 95. The coefficient of wave dissipation is 30. 51% under the condition of a flood once in fifty years. It means that the simulating results are reasonable and the anti-wave effect is significant. Meanwhile, the SWAN model based on the unstructured triangular mesh can effectively simulate the wind-generated wave field in the river of complex topography.

Abstract:In the calculation of seepage or consolidation, if there is a large difference in seepage coefficient of two adjacent materials, the release point, as well as the phreatic line, should be determined by iterations. However, if we set interface elements between two materials, reasonable results of release point can be captured without iterations. In this paper, two seepage cases are investigated, and the composite seepage coefficient of the elements, which are intersected by the phreatic line, is calculated with the Monte Carlo integration method. Two interface elements are set between two materials with great difference in seepage coefficient. The hydraulic relationship between two materials is built based on the seepage matrices of the interface elements, while the location of the phreatic line is then calculated by iterations. Choosing a thin thickness for the interface element(e. g. , 1/4 of the thickness of the adjacent element)could localize the error of calculation, which has little impact to the whole area at the same time. By choosing an appropriate seepage coefficient or permeability rate of the interface element, results close to those obtained through the traditional methods can be acquired, which shows the applicability of the proposed method.

Abstract:Safety monitoring is an important means to ensure the operational safety of long-distance water diversion project, which dynamically generates a large amount of multi-source data. How to organize and display theses data in a vivid way so as to assisted the safety analysis is an essential technical issue. A BIM(Building Information Modeling)–based network method for water diversion project is proposed, which can dynamically integrate and visualize the safety monitoring information. First, the constituent elements of 3D virtual scene for a water diversion project are analyzed to build a 3D BIM model. Then, the BIM model is dynamically coupled with safety monitoring information by the method of key field mapping. Finally, Forge Viewer is used to realize the WEB browsing of the SMI-coupled BIM model based on WebGL. Using the proposed method, a prototype system is developed and applied in the Tianjin South-to-North Water Diversion Project, and the results indicate that the system can realize visualized integration of the safety monitoring with BIM under network environment, which provides support for the engineering safety analysis of water diversion project.

Abstract:Based on engineering practice, this paper proposed a new type of dam, longitudinal reinforced rockfill dam, which is built by a rigid structure(longitudinal reinforced body)with the functions of anti-seepage and bearing stress in the interior of conventional earth and rock dam. This rigid and flexible dam structure improves the operational safety of conventional earth and rock dam. In the analysis of deformation, it is theoretically deduced to consider it as a vertical fixed-end beam that bears the load of upstream and downstream water pressures as well as the force of rock-fill dam, especially the tensile load on the surface of the longitudinal reinforcement caused by the rock-fill settlement. At the same time, the longitudinal reinforcement split the continuous stress and strain of the dam shell material in the upstream and downstream of dam body, and the mechanical performance under various working conditions is closer to the behavior of retaining wall. According to the proposed designing and calculation method of the longitudinal reinforced earth and rockfill dam as well as the engineering practice, this paper mainly introduced the application of the proposed new type of dam in the design of the Fangtianba Reservoir in Tongjiang, Sichuan Province.

Abstract:Particle image velocimetry(PIV)technique is used to accurately determine the location of shear layer and separation zone based on vorticity. Meanwhile, the vortices in the horizontal plane at the confluence are systematically observed and analyzed. It is found that the vortex density within both the shear layer and the separation zone is larger near the water surface and near the bottom than that in the middle of water depth. The vortex density increases with the increase of tributary discharge when the discharge of main channel is fixed. The high density of vortices near the bottom is caused by the wall turbulence. In addition, the shear layer generated by flow shear is dominated by vortices with small swirling strength, while the separation zone generated by the flow separation is dominated by vortices with medium and small swirling strength.

Abstract:A nonparametric regression algorithm, called the multivariate adaptive regression splines(MARS), is adopted to establish a simple and interpretable model to approximate the nonlinear interactions between inputs and outputs. Based on well-documented case data, MARS is capable of producing explicit expressions using the combination of simple linear spline functions, as well as obtaining the relative importance of input parameters. The reliability and accuracy of MARS were validated via the geotechnical applications of pile drivability assessment and stability evaluation of underground caverns. The coefficients of determination for the testing set in the two examples are 0. 921 and 0. 986, respectively, indicating that MARS can effectively fit the correlation between input parameters and target outputs. As for the parametric relative importance, the elasticity modulus of pile and quality of surrounding rock are recognized as the two most influential factors. MARS method can accurately relate the target responses to nonlinear and multivariate inputs; thus, it is useful in the practical engineering construction.

Abstract:Localized vibration caused by the metro operation changes the mechanical properties of underground soft clay, which can cause engineering geological problems, such as continuous subsidence of metro tunnels, but the mechanism is still unclear. In order to study the cause of tunnel’s continuous settlement, this paper studies the flow characteristics of underground soft clay under different water contents, vibration frequencies and confining pressures by the pulling sphere experiment. The experimental results indicate that the flow characteristics of soft clay increase with the increasing water content and vibration frequency, and decrease with the increasing confining pressure. However, the effect of increasing water content on the fluidity of soft clay is more obvious at lower water content, and becomes no longer significant with the gradual increase of water content of soil sample. Confining pressure and vibration frequency have cross-effects on the flow characteristics of soft clay. Under high vibration frequency, the confining pressure has little effect on the flow characteristics of soft clay. At presence of high confining pressure, the increase of vibration frequency will affect the flow characteristics of soft clay only if the vibration frequency exceeds a critical value.

Abstract:Based on the scaled boundary finite element method, the propagation behavior of Lamb waves in a plate encountering multiple cracks, built-in vertical and transverse cracks, and depression was simulated. Different cracking angles, depths of the built-in crack and curvatures of pit were simulated under the A₀ and S₀ excitation mode, in which the mode amplitude of the reflected wave were analyzed. On the same plate, different crack pattern will have different increment for the waveform. The mode amplitude of the reflected wave increases with the increase of the crack depth and the crack angle. As the cracking angle of built-in crack increases, the effect of the mode amplitude in reflected waves is more obvious when the excited mode is antisymmetric A₀ mode. The mode amplitude in the reflected wave decreases as the depression on the plate slows down, which is more obvious when the excited mode is symmetric S₀ mode.

Abstract:The hybrid method was adopted to model the original gradation of a rock-fill material according to the code, and three simulated gradations of rock-fill material have been obtained. By the same token, their equivalent particle diameters are 20 mm, 40 mm, and 60 mm, respectively. With samples prepared under the criterion of a same relative density, the scale effect on strength and deformation characteristics of the rock-fill material were studied by large/medium-scale and consolidated-drained triaxial compression tests. The results show that the nonlinear strength indexes, φ₀ and Δφ, have an increasing trend of a logarithm function with the maximum grain diameter d_max of rock-fill material. Through analyzing the influences of particle size and confining pressure on the axial strains and volumetric strains, some useful conclusion can be drawn as: both the initial elastic modulus E_i and the tangent volumetric modulus B_t increase with the maximum grain size d_max, and there is a good linear relationships between the initial elastic modulus and the maximum grain size as well as that between the tangent volume modulus and the maximum grain size; the initial Poisson’s ratio ν_i decreases with the maximum grain size d_max, and there is a good exponential relationship between the initial Poisson’s ratio and the maximum grain size. Meanwhile, formulas considering the initial elastic modulus, the initial Poisson’s ratio, the tangent volume modulus, the maximum grain size and the confining pressure were obtained, which can roughly estimate the effect of maximum grain size on the initial elastic modulus, the tangent volumetric modulus and the initial Poisson’s ratio.

Abstract:In this paper, two kinds of simplified constitutive integral algorithm are adopted to solve the problem of isotropic plastic damage under three-dimensional stress state based on the Lemaitre damage model. The solving program compiled by the MATLAB was applied to analyze the failure process of materials under different stress states, and then, the accuracy and efficiency of two algorithms were compared. The numerical simulation shows that both the results of two integral algorithms agree well with theoretical solutions, and are capable to the analysis of damage and fracture of a three-dimensional structure under complex stress state. Compared to the updating algorithm that couples the stress and damage, the weak coupling algorithm that decoupling stress updating and damage in incremental step can better improve the computational efficiency.