Abstract:Three basic essentials, which affect the inversion results of mechanical parameters, were systematically summarized for earth-rockfill dams, including inversed parameters, inversion methods and measured data. Recent research progress on inversion technology were also reviewed in four aspects, which can be summarized as follows. (1)Intelligent back analysis algorithms were developed. (2)Multi-parameter decoupling methods were put forward for multi-material and multi-model inversion problems. (3)Optimization methods for measuring points arrangement were developed, as well as the pre-treatment methods for measured data, including observation error treatment and virtual measurement supplement. (4)The uniqueness of inversion results can be evaluated by correlation analysis and trial simulation, which is closely related to the engineering characteristics and essentials of parameter inversion. Along with the expansion of earth-rockfill dam’s scale and the innovation of material and structure, it is necessary to develop new real-time inversion techniques and suitable inversion method for the dams with new materials or structure.

Abstract:The application of hydrology-hydrodynamic-water environmental integrated models can provide the whole process simulation of regional water resources from the source to the water body, which is of great significance for the development and utilization of water resources and comprehensive decision-making management. In order to deeply understand the development and evolution of the basin coupling simulation system, the structure and characteristics of hydrological, hydrodynamic and water environmental models were summarized and the role of the models in the coupling system was discussed. The advantages and disadvantages of one-way coupling, two-way coupling and interface transmission coupling were summarized and reviewed, and the spatial and time scale matching problems in the coupling model was discussed. The problems such as loose structure, difficult parameter calibration and unclear application standard in the current coupling model were pointed out. Model coupling system can be an important measure to solve intelligent basin management and decision making in the future.

Abstract:Considering the problems of current water shortages and the weakness in the existing research, this study scientifically revealed the spatiotemporal varieties of water resources metabolism efficiency and driving factors in nine provinces (cities) in the Beijing-Tianjin-Hebei region, central and western regions of China from 1990 to 2015 in the perspective of heterogeneous resource endowments. The main results show that the water resources metabolism efficiency changed little from 1990 to 1995, and the overall trend has been obviously improved since 2000 from the time scale. From the perspective of spatial distribution, in the early stages, water resources metabolism efficiency was low with unobvious regional differences. Since 2005, more obvious regional differences occurred in the Beijing-Tianjin-Hebei region than in other regions. Waste virtual recycling use ratio, total retail sales of consumer goods of unit water use, forest coverage and fresh water recovery rate are the main driving factors of regional water resources metabolism efficiency.

Abstract:In order to reveal the law of flood evolution in the lower reaches of Nenjiang River and its impact on the vegetation in the floodplain, a one and two-dimensional hydrodynamic coupling model from Jiangqiao to Dalai river section was established using MIKE FLOOD. The measured data during the flood seasons of 1998 and 2013 were selected to calibrate and verify the roughness of the river section, and the flood process in typical river section with four different return periods were simulated. Based on the MOD13Q1 data set of the MODIS satellite from 2000 to 2019, the vegetation indices(NDVI, EVI)of the submerged range of different flood frequencies were obtained, and the impact of flood disturbances in the lower reaches of Nenjiang River in different return periods on vegetation was evaluated. The results show that the simulation effect of the model during the calibration and verification period meets the accuracy of Class A prediction, and the simulation accuracy of the model is high. The vegetation index in different return periods has a strong seasonal variation, and floods have obvious destructive effects on vegetation. The destructive effect has a relatively short periodicity in Nenjiang River Basin, indicating that the vegetation in this area is highly recoverable. At the same time, affected by the degree of frequent flooding, the vegetation index of different return periods conforms to the moderate interference hypothesis.

Abstract:Taking the dewatering treatment method of hydraulic dredged silt in the river system of Fuyang urban area as a research object, through model test and theoretical analysis, the water yield in the dewatering process was collected, and the relationship among the vacuum dewatering method, horizontal electroosmosis method and joint vacuum and horizontal electroosmosis method was analyzed. The dehydration quantity calculation of hydraulic dredged silt based on joint vacuum and horizontal electroosmosis method was proposed. The results show that, under the action of vacuum dewatering method, the dewatering process of hydraulic dredged silt can be divided into two stages, rapid dewatering and stable drainage, in which the mass ratio between liquid water and vaporous water is about 3∶5. Under the action of horizontal electroosmosis, the dewatering rate of hydraulic dredged silt has a linear relation with the current intensity and the silt conductivity has a linear, exponential or quadratic relationship with water content, of which the linear relationship is the best fitting. The dewatering amount of hydraulic dredged silt by joint vacuum and horizontal electroosmosis dewatering method can be comprehensively calculated by superposition of vacuum and horizontal electroosmosis dewatering amounts.

Abstract:The hydraulic characteristics of the curves under the conditions of ice flow were simulated by establishing bend channels with different curvatures based on the volume of fluid(VOF)technology, the RNG k-ε turbulence model and the Lagrangian particle model. The results show that the ice mainly concentrates on the outer bank after passing the curve with obvious gather. The existence of ice increases the lateral circulation of the surface current on the outer bank, which affects the development of the large circulation at the bottom of the inner bank to a certain extent. The maximum water surface velocity at the inlet section of each curve is greater than the outlet. With the increase of the curvature, the outer bank area of the low-velocity flow and the high turbulent kinetic energy area of the ice flow stream continue to increase, and the mainstream area of the curved top section gradually shifts to the inner bank.

Abstract:In order to reduce the uncertainty of the numerical model, the particle filter method is introduced into the calculation of one-dimensional unsteady flow to establish a multivariable correction method for water quantity simulation. The optimal estimation of the state variables is realized by statistically estimating the water state particles. Taking the flood process of a single channel as an example, the performance of the proposed method was discussed and the influence of particle number, state variable disturbance and uncertainty of the boundary condition on the filtering effect was analyzed. The performance of particle filter and ensemble Kalman filter was compared in terms of accuracy, stability and efficiency. The results show that 100 particles can guarantee both the filtering effect and computational efficiency. The best filtering effect can be obtained when the water level disturbance variance and the flow disturbance variance are both 10 percent of the actual value. When the relative error of the boundary condition is within 20%, the simulated precision can be over 94%. The particle filter is slightly less accurate and stable than the ensemble Kalman filter, but its computational efficiency is about 2. 3 times higher than that of the Kalman filter. Application to the river network water quantity correction in the Taihu Basin shows that particle filter can significantly improve the simulation accuracy.

Abstract:Through the unconfined compressive strength test, shrinkage test, X-ray diffraction(XRD)test, mercury injection porosimetry(MIP)test and scanning electron microscopy(SEM)test, the cement-modified expansive soil was systematically studied in the aspects of macroscopic mechanical properties, phase evolution and the micro-structure characteristics. The results show that cement addition can effectively improve the strength, swelling and shrinkage characteristics of expansive soil. After the cement addition, the microstructure of expansive soil changes significantly, and the gel phase hydration products of C-S-H during hydration reaction increase with the cement content. The soil particles can form a larger flocculent body and can benefit the pore distribution. The volume fraction of micro holes(diameter less than 100 nm)in modified expansive soil increases, indicating that the amount of hydration products is the key factor to soil strength, microscopic pore structure characteristics and shrinkage characteristics of cement-modified expansive soil.

Abstract:In view of the lack of long-term river monitoring data in river source regions, it is difficult to determine the migration rate of river bends. Through field investigation and sampling in the Yellow River source region in 2016 and 2017, nine river bends of the Baihe River, a typical meandering river, were selected as research examples. The ages of trees were determined by tree rings analysis, and a method for estimating the migration rate of river bends based on the relationship between tree positions and tree ages according to vegetation succession of trees growing on scroll bars in convex bank was used. The migration rates of nine river bends of the Baihe River were estimated to be 0. 38-6. 10 m/a, and the migration rates were found to be related to the flow rate, channel slope, height of the concave bank and width of the river valley. The maximum migration rate appears in the No. 9 river bend where the river curvature is the smallest.

Abstract:To solve the problem of slow convergence speed and easy falling into local optimum for general optimization algorithms during parameter inversion of constitutive parameters of earth-rock dams, the adaptive chaotic mutation particle swarm optimization(ACMPSO)algorithm was improved by using dynamic variation coefficient and OpenMP parallel instructions, and the improved ACMPSO algorithm was validated by a case. The results demonstrate that the improved ACMPSO parallel algorithm can effectively prevent algorithm from falling into local optimum and reduce the calculation time significantly. The algorithm has the characteristics of fast convergence, high inversion accuracy and good stability, which is suitable to solve complex parameter inversion problems with high dimensions and huge computation.

Abstract:To solve the problem that the low bearing capacity of fresh dredger fill foundation that cannot meet the requirement of mechanical construction, a kind of electroosmosis electrode was developed for rapid crust of freshly dredger fill based on the characteristics of fast consolidation of soil in the anode area in electroosmosis consolidation. Laboratory tests of different combination of electroosmosis and vacuum with the electrode were carried out, and the soil parameter indexes such as soil discharge, electroosmotic energy consumption, final moisture content, shear strength and bearing capacity were comparative analyzed. The results show that the moisture content of the dredger fill is reduced by 31. 0% to 61. 4% after the treatment of electroosmosis electrode, and the bearing capacity of the surface layer is up to 192 kPa. After electroosmotic treatment, the shear strength of the soil layer decreases along the depth. Under the combined action of electroosmosis and vacuum, the shear strength of soil layer is higher and more uniform. The developed electroosmosis electrode can realize rapid reinforcement of the near-surface layer of fresh shallow dredger fill with high water content.

Abstract:Based on the characteristics of the bottom mud of the Liangxi River, the technology of online dewatering for dredged mud was designed and tested. Through settling column tests and type selection tests for chemicals by computer operation, the turbidity of the supernatant and the volume of the settling column, and the solid content of mud cakes and the discharging time were compared respectively. The chemical selection and dosage were thus analyzed and determined. Through type selection tests for the air permeability of the filter cloth, the solid content of mud cakes and the permeability time under different air permeability were compared. Accordingly, the air permeability of filter cloth was determined. Finally, by applying the data from the above tests on on-site operation of the plate and frame machine, the eigenvalue of the final displacement corresponding to the optimal feeding and back pressure time was determined and used as a reference for pump termination. According to the results of engineering practice, the online dewatering process for dredged mud can meet the design requirements of mud loss rate not less than 50%, mud cake solid content not less than 60%, and mud cake thickness not less than 25 mm, indicating feasibility of the technics.

Abstract:In order to study the hydraulic fracture characteristics of cement mortar under sulfate attack, four test conditions were designed using a three-field coupling test system. The mechanical properties and hydraulic fracture resistance of cement mortars in sulfate solutions with different pH values and with different erosion times were analyzed. The experimental results show that the cement mortars in sulfate solutions with different pH values has different effects on the mechanical properties of hydraulic fracture. In the later stage of erosion, the deterioration degrees of hydraulic fracture properties of mortar in the 0. 1 mol/L Na₂SO₄ solution with pH values of 7, 3 and 1 gradully decrease. It was found that the hydraulic fracturing resistance of cement mortar under sulfate attack has a significant cubic function relationship with the erosion time.

Abstract:In order to avoid the phenomenon of over fitting and low prediction accuracy of conventional time series model which does not consider the non-linear and random environmental quantity, an integrated empirical mode decomposition(EEMD)method was used to decompose the actual monitoring seepage flow of the water measuring weir. Multiple groups of stable eigenmode functions(IMF)and residual quantities(R)were generated, and then the IMF series and R were fitted and predicted by the correlation vector machine(RVM). Finally, the IMF series and R were added by equal weight to get the predicted value of the seepage flow. The number and length of the training set, the choice of the prediction set number and the treatment of the jump points were also discussed. The results of an engineering application case show that the EEMD-RVM model has high prediction accuracy, and is significantly higher than RVM model and GA-BP model, which verifies the feasibility of the model.