Abstract:The surface spillway is generally short for high arch dams due tothe thin dam crest. Discharge capacity can be affected if flaring gate piers are applied to surface spillway in high arch dams. Numerical simulation was carried out on the basis of the Dongzhuang water conservancy project to explore the flaring gate piers that can meet the design requirements for discharge capacity. The effects of plunge angles, contraction ratios, deflection angles on discharge capacity and the relationship between discharge capacity and Froude number along the surface spillway were studied. The results show that the discharge capacity of surface spillway decreases with the decrease of plunge angles, contraction ratios and the horizontal distance between starting flare and weir crest but it increases with the decrease of deflection angles. A comprehensive influence coefficient k_综 is proposed to reflect the effect of the shape parameters of flaring gate piers and water head over the weir. For k_综≥2, flaring gate piers have no effect on the discharge capacity of a surface spillway. For k_综<2, the effect on discharge capacity is gradually enhanced with a decreasing k_综. There is a knee point on the curve of Froude number along the surface spillway in the upstream of the starting flare. The discharge capacity is less affected by higher Froude number at the knee point.

Abstract:The Particle Image Velocimetry(PIV)technique is applied to explore the flow structures behind a hollow bridge pier. Hydrodynamic characteristics of the flow field past the pier with a rectangular hollow slot are examined in both horizontal and vertical planes. The result shows that the motion of the wake flow at the height of the slot can be changed. The development and movement of large-scale vortex is restrained and the upward motion trajectory of the bottom flow behind the pier is cut off by the strong shear effect that is generated due to the interaction between the high-speed flow pass through the hole and the low-speed flow in the lateral and back region of the pier. Characteristics of periodicity and high intermittency exist in the instantaneous flow field behind the pier.

Abstract:An empirical estimation formula for the maximum water elevation of the impact wave generated by the landslide in a V-shaped river valley is presented. Using the Flow-3D software, a numerical model of the impact wave resulting from the landslide in a V-shaped river valley was established and numerical experiments under 96 conditions were carried out. Effects of the inserting velocity of landslide into water, landslide volume, time of underwater sliding, inserting angle and climbing angle on the maximum water elevation were analyzed respectively. The fitting formula of the maximum water elevation was obtained by regression analysis. The new formula was used to evaluate the maximum water elevation for the Gongjiafang landslide event, and it is shown that the calculated result is very close to the value of the physical experiment.

Abstract:In this paper, sediment samples of fine partiles were olleted from three rivers, the Nanjing reah of the Yangtze River, the Bengbu reah of the Huai River and the Yong River Estuary. Isothermal equilibrium adsorption experiments were arried out to study the variation of Zeta potential of sediment after phosphorus adsorption. It an be onluded that the absolute value of Zeta potential inreases with the inreasing equilibrium phosphorus adsorption amount per unit mass of sediment, resulting in an enhaning stability that restrains floulation. Zeta potential variation is proportional to the equilibrium phosphorus adsorption amount, but the ratio is different for sediments with different origins. This ratio ranks from high to low respetively for sediments from the Yong River, the Huai River and the Yangtze River. Moreover, the relative variation of Zeta potential is proportional to the relative adsorption amount of phosphorus, and the ratio is the largest for sediment from the Yong River Estuary, followed by that from the Yangtze River and the Huai River, whih have similar values.

Abstract:To evaluate the calcium leaching for the concrete subjected to aggressive water, a two-dimensional calcium leaching model of concrete is established based on the leaching mechanism of concrete under the effects of soft water and nitric acid. The tortuosity and the constrictivity of the concrete are incorporated into the model. The effect of the interface transition zone(ITZ)on the porosity is also considered. The reliability of the model is validated by the comparisons between numerical and experimental results. The theoretical model was solved using COMSOL software and the characteristics of the two-dimensional calcium leaching of concrete was analyzed. It shows that the leaching depths of concrete subjected to soft water and nitric acid are proportional to the square root of time.

Abstract:Aiming at reducing the strong subjectivity caused by single value scores in seepage behavior assessment of concrete dams, the methods based on interval grading are suggested. The weight factors are introduced to represent the difference among evaluation levels of the experts. The degree of the disagreement on seepage behavior is described by an interval probability distribution function and the subjective weight is corrected based on the interval width. The Monte Carlo simulation method is then introduced into the comprehensive evaluation of the seepage behavior. The proposed method was applied to assess the seepage condition of the No. 7 section in a concrete dam and the probability of the assessment grade belonged to basic normal and above normal was 99.9%. The assessment result is basically normal and consistent with actual operation, showing the interval assessment method based on Monte Carlo simulation is feasible to evaluate the seepage behavior of concrete dams and it can also be applied to project assessment with high uncertainty in which single value grading is difficult to be applied.

Abstract:Forthe problem that the rehabilitation degree of dangerous reservoirs is difficult to be accurately evaluated, a two-layer index system was established. The fuzzy gray clustering and combination weighting method are combined to quantitatively evaluate the rehabilitation degree of reservoirs. Firstly, the subjective and objective weights of each evaluation index are calculated by entropy method and analytic hierarchy process, and a combination weight containing subjective and objective implications is obtained using the combination weighting method. Secondly, the gray clustering method is used to evaluate the rehabilitation degree of each rehabilitation type. The clustering coefficient of each rehabilitation type is adopted to create the fuzzy evaluation matrix, and then the weight of each rehabilitation type is calculated. Finally, the comprehensive evaluation method is utilized to accurately assess the rehabilitation degree of dangerous reservoirs after reinforcing. The method is applied to the reinforcement assessment of three reservoirs in Henan and Jiangxi Province and the results agree well with the practical situation of the reinforcement assessment and the acceptance conclusions, indicating a great value in engineering applications.

Abstract:According to the 4 years(2009-2014)daily rainfall data of mainland china from the China Meteorological Data Service Center(CMDC), the precision of TRMM precipitation data is evaluated by indicators such as error, correlation coefficient, and relative error on the time scale of months and years respectively. The results show the TRMM precipitation data is of high accuracy on the monthly and annual scales. The monthly correlation coefficient is 0.99 and the annual correlation coefficient reaches to 0.86. The accuracy of TRMM precipitation data is mainly affected by precipitation intensity and altitudes. In arid and high-altitude regions the accuracy of the TRMM precipitation data is low.

Abstract:In order to investigate the permeability anisotropy and stress-seepage coupling effect of the filled tube assemblage for geotube dams, a large-scale model experiment on stress-seepage coupling was used to study the effect of overburden pressure on the permeability and its anisotropy of the geotube assemblage under different arrangement modes. The experimental results show that the joints between geotubes are the main seepage channel of the assemblage. If the joints between geotubes are arranged parallel to the direction of seepage, the permeability coefficient of the assemblage is much larger than that of the vertical arrangement, and seepage damage is easy to occur. With the increase of the overburden stress, the permeability coefficient of the assembly decreases gradually and the anisotropy of permeability gradually increases. The influence of overburden pressure increase on permeability is different for different arrangement modes.

Abstract:To investigate the effect of silica fume and limestone powder on the crack resistance for roller compacted concrete(RCC)and its mechanism, silica fume was added into the limestone powder-fly ash-based RCC. Indicators such as the split tensile strength, tension-compression ratio and elastic modulus-compression ratio were used for the experimental analysis with the technology of scanning electron microscopy(SEM), thermal gravimetric analysis(TGA)and mercury injection(Hg). It is suggested that adding 5% silica fume into the limestone powder-fly ash-based RCC of 40% admixture can increase the density of the microstructures, optimize the pore structures and effectively improve the overall crack resistance performance of the material.

Abstract:Defect-induced leakage of geomembranes may have negative effect on the anti-seepage safety of geomembrane faced earth-rock dams. Finite element theory of saturated-unsaturated seepage was employed for the 3D simulation of the seepage field of a typical geomembrane faced earth-rock dam in the condition that defects are in random distribution on the upstream dam surface. The quantity, types, location, sizes and distribution of geomembrane defects were considered reasonably, and the change rules of infiltration capacity, defect-induced leakage and phreatic line were analyzed emphatically. The results indicate that in the condition that the geomembrane is intact, the seepage flux changes little for both single and multiple defects on the geomembrane. However, when the geomembrane is under multiple defects, the defect-induced leakage increases significantly, leading to the increase of total seepage flux. Multiple defects will raise the phreatic surface in the dam body, and the variation of local phreatic surface height is related to the quantity and location of the defects. The more and lower the defects are, the more obvious the uplift of the phreatic surface can be. Further, the local distribution of water head behind the geomembrane is related to the cross effect of leakage of adjacent defects.

Abstract:The relationship between the secondary consolidation coefficient and pressure for soft soil is studied by indoor compression test. It is found that the secondary consolidation coefficient-pressure curve of over-consolidated soil and normal consolidated soil can be fitted by a power function and a hyperbola function, respectively. Based on the experiment, the conventional secondary consolidation formula was corrected and a modified one was proposed considering the effect of pressure and the convergence characteristic of calculation. The results of its application to an engineering project show that the new formula can better reflect the secondary consolidation characteristic of soft soil, indicating great engineering value.

Abstract:In order to study the application and the effect of ecological dredging and silt disposal in deep-water reservoirs, the ecological dredging and regulation engineering of Tongjiqiao reservoir was taken as an example. The influence of dredging on the pollutant diffusion in bottom sediment of the reservoir was analyzed through tracking and monitoring the water quality near the cutter suction dredger and reservoir intake. The moisture content of the dry soil after plate and frame filtration treatment and the residual water index was also tested and analyzed. The result shows that the ecological dredging only causes sediment disturbance within 20 meters from the ecological cutter with a short duration, which has no obvious influence on the water quality near the reservoir intake. The moisture content of the silt obtained by dredging can be reduced to 40%-60% after the rapid dehydration treatment, which meets the requirement of sediment transport and resource utilization. The residual water also meets the standard emission requirements during this process.

Abstract:A multi-beam bathymetry system was introduced from marine surveying and mapping to the hydropower station detection industry so that non-destructive testing for the erosion damage effect of the flood energy dissipating system can be carried out. The multi-beam bathymetry system combined with the video filmed by an underwater robot was applied to detect the erosion damage of the cement concrete mulch and side walls of a hydropower station. Through analysis of the testing process and data, the application conditions of no signal shielding was determined. Detailed detection characteristics such as scouring, wearing and caving were summarized and the result shows the multi-beam bathymetry system has good detection effects for erosive wear especially for the faulting of slab ends of which the scope and degree can be clearly estimated. The multi-beam bathymetry system also has good detection effects for erosive caving and the underwater topography around the scouring pit can be accurately plotted with a better estimation for the scouring scope and depth.

Abstract:To obtain the time evolution of the local scour of bridge piers and to explore the scouring characteristics of piers with different cross sections, the user-defined function and the dynamic mesh updating technique of the computational fluid dynamics software FLUENT were used. The bed shear stress considering the enhancement effect of turbulence vortex and the critical shear stress considering the influence of the bed slope were calculated to obtain the sediment transport rate. The dynamic variation of bed topography with time was achieved by the relationship between sediment transport rate and bed elevation. Simulation distortion and numerical instability caused in the condition that the bed slope is greater than the sediment repose angle can be overcome through the adjustment of sediment collapse. It shows that the maximum scour depth, the shape of the scour hole and the flow structures by numerical simulation are in good agreement with the experimental results. With the same maximum pier width, the scour depth of the streamlined piers is about 45% and 40% lower than that of the round-ended piers and the sharp-nosed piers respectively, and the range of the scour hole is also reduced.

Abstract:The safety operation of a pump station is directly affected by the siphon formation time of a siphon outlet pipe. In order to investigate the siphon formation time characteristics and the impact of the improvement on siphon formation time, RNG k-ε turbulence model with structured grids were used to simulate the siphon outlet pipe of a pump station. The numerical simulation results show that the duration of the hydrodynamic phase is related to the inflow flux. In the hydroponic phase, the exhausting rate is related to the velocity at the water air interface. During the siphon formation process, the generation of airbags is very unfavorable for the siphon formation and configuration of a splitter plate at the top of the hump section can effectively improve the flow rate distribution in the siphon, which can accelerate the discharge of the airbags, shorten the siphon formation time and minimize the influence on the hydraulic loss.