Abstract:The hydrological principle of the structure and parameters of watershed hydrological models, the physical coupling relationship between the structure and parameters, and the essential difference between lumped and distributed watershed hydrological models were investigated. The characteristics of the solution methods for these two models, and the reasons causing the phenomenon of equifinality for different parameters during the calibration of the watershed hydrological models, as well as methods to alleviate the effects of this phenomenon, are discussed. A method for verification and comparison of the watershed hydrological models is proposed.

Abstract:The urban river network in Tianjin City has stagnant or slow-flow water, which leads to water quality variations different from natural rivers. Multivariate statistical analysis methods, including the cluster analysis method, factor analysis method, and multiple linear regression method, were used to evaluate the water quality data from 11 sites in four main rivers of Tianjin, the Haihe River, Jinhe River, Weijin River, and Waihuai River, for 39 weeks during the period from 2008 to 2009. The results show that the water quality variation exhibited specific temporal and spatial characteristics. Water quality data from May to August were worse than during other months, especially for the ammonia nitrogen and total phosphorous concentrations, which severely exceeded the water quality standards. Water quality deteriorated from the Haihe River to Jinhe River, Weijin River, and, finally, Waihuan River gradually. Nitrogen and phosphorous pollutants were the main pollution sources of the Haihe River, Jinhe River, and Weijin River, while organic pollutants were the main pollution sources of the Waihuan River.

Abstract:Change in the flow resistance coefficient of underwater hammers was analyzed through comparison of common types of hammers in multiple projects based on the LS-DYNA fluid-structure coupling numerical simulation method. The results show that, when the hydrostatic pressure on the bottom surface of the hammer is a fixed value, the flow resistance coefficient decreases with the increase of the hammer mass. The hammer fall velocity in the water increases with the drop distance, but the growth rate gradually decreases and tends toward a stable value. The energy usage ratio of the hammer decreases with the increase of the drop distance. When the hydrostatic pressure on the bottom surface is a fixed value, the energy dissipation rate increases with the decrease of the hammer mass.

Abstract:In order to investigate the structural characteristics of turbulent flow over sand waves on a complicated riverbed, a numerical model for simulating flow over three-dimensional sand waves was established using the Fluent software based on the Reynolds-averaged Navier-Stokes(RANS)equations and the k-ω turbulence model. The model was verified using experimental data. The results show that the established model can depict the turbulent characteristics over sand waves well. The three-dimensional properties of the sand waves are important factors influencing the turbulent structure of flow. The shear stress and bed form resistance are much more sensitive to the transversal phase difference φ₂ than to the longitudinal phase difference φ₁. With the increase of φ₂, the sand waves become interlaced, and the shear stress and bed form resistance both decreased.

Abstract:In order to verify the feasibility and stability of pore fluids used to manufacture transparent soil and provide references for relevant transparent soil model tests, the relationships of the refractive index and viscosity coefficient with the mass ratio of the solution were determined for four water-based inorganic solutions(calcium bromide, potassium pyrophosphate, potassium phosphate, and magnesium chloride hexahydrate)and one oil-based organic solution(the mixture of mineral oil No.15 and dodecane). The calcium bromide solution and the mixture of mineral oil No.15 and dodecane are two typical pore fluids in model tests. Experiments on the influence of the two pore fluids on the size deformation and tensile strength of latex membrane and solid granular particles were carried out. The results show that the refractive indices of the water-based inorganic solutions linearly increase with the mass ratio of the solution, and the viscosity coefficients nonlinearly increase with the mass ratio. Under the same conditions, the length change rates of the latex membranes after being immersed in the calcium bromide solution and the mixture of mineral oil No.15 and dodecane are 0.47% and 37.81%, respectively, their width change rates are -1.09% and 40.50%, respectively, and their tensile strengths decrease by 13.5% and 89.4%, respectively. The effect of the pore fluids on the fused silica sand is smaller than that on the amorphous silica. The effect of the mixture of mineral oil No. 15 and dodecane on the solid particles is basically the same as that of the calcium bromide solution.

Abstract:Two groups of hydraulic fracturing tests were carried out on concrete specimens of different strengths with a single initial crack under different stresses. The effects of stress state and loading pattern on the crack propagation process of concrete specimens were studied. The evolution law of water pressure within crack along the crack propagation path was analyzed, and the quantitative relation for the critical fracturing pressure prediction model of concrete specimens was obtained. Results show that damages induced by hydraulic fracturing occurred to the two groups of specimens under different stresses. Besides, the differences between the critical fracturing pressure and axial pressure of the two groups of specimens were less than the splitting strength of the specimens, and the development of the sharp cutting edge under water pressure lagged behind that of the dry crack.

Abstract:Using the FLAC3D multi-fracture constitutive relation, a numerical model of anisotropic failure characteristics of a layered rock slope was established. With the strength reduction method, the relationships between the slope safety coefficient and the interlayer weak plane dip angle β, slope angle α, slope height H, and shear strength of the rock mass were determined, and the impacts of various factors on the safety coefficient were investigated with the grey correlation method. Results show that for a bedding slope(with the slope direction consistent with the obliquity of the rock layer)at β ≤15°, damage is mainly caused by tensile cracking-shear-slippage failure, and a sliding surface does not occur along the interlayer weak plane; bedding slippage failure appears at 15°<β<α; and the top of the slope slips along the weak plane, and bending failure appears at the slope foot at β≥α. For a reverse slope(with the slope direction opposite to the obliquity of the rock layer), the compression-shear failure is the main failure mode at β<50°, and toppling failure appears when β is larger(β≥50°). With the increase of β, the safety coefficient of the bedding slope shows a tendency to decrease first, then increase, and then decrease again, and the stability of the horizontal layered slope is higher than that of the vertical one. The safety factor change tendency of the reverse slope is opposite to that of the bedding slope. In the case of β>α, the stability of the bedding slope is higher than that of the reverse slope at the same dip angle. For a bedding slope, the slope height has the greatest impact on the stability, followed by the cohesion of the weak plane and slope angle, and the influences of the dip angle and friction angle of the weak plane are relatively small; for a reverse slope, the influence of each factor on its stability is ranked by the friction angle of the weak plane, slope angle, slope height, and cohesion and dip angle of the weak plane.

Abstract:Based on hydraulic model tests of a reinforcement project, the water flow pattern, velocity distribution, maximum depth-averaged velocity of a typical section, and scouring characteristics downstream of the sluice were measured, and the cause of water flow pattern deterioration and scour severity under the design scheme were analyzed. The cause is considered to be the change of the flow boundary condition after reinforcement of the downstream wing wall, which concentrates the main flow downstream of the sluice, increases the velocity locally, and intensifies scouring. Through comparison of different energy dissipation and scour prevention schemes, the method of using partition piers to eliminate the flow accumulation is put forward. Partition piers can eliminate the main flow extrusion by the boundary, improve the flow pattern downstream of the sluice, homogenize the velocity distribution downstream of the sluice, reduce the maximum velocity of the river bed, and decrease scour downstream of the sluice. The partition piers have a simple structure and construction.

Abstract:In order to study the two-dimensional(2D)flow in the Yazidang Reservoir, terrain pretreatment was carried out using the image processing method and Google Earth(GE)software. The initial terrain of the reservoir was obtained through image mosaicking, mathematical morphology, and measured data. A 2D RNG k-ε turbulence model was established, reasonable boundary conditions and initial conditions of the flow module of the established model were set, the equations were discretized using the finite volume method, and a mesh was divided using the advancing-front method. The flow field in the reservoir and the depth-averaged velocity at sections near the water inlet and the water power were simulated. The results show that accurate and detailed reservoir terrain can be obtained using the image processing method and the GE software. The numerical simulation results of the flow field and the depth-averaged velocity at critical positions show that the simulated and measured values are in strong agreement.

Abstract:In order to improve the flow pattern in the foreway of a pump station, the RNG k-ε turbulence model based on the Fluent software was used to simulate the flow pattern in the front inflow forebay of a pump station with a single row of square columns, and the effect of geometric parameters of these square columns on the flow pattern in the foreway was analyzed. The results show that a single row of square columns leads to flow separation, the water flowing through the square columns disperses to the two sides of the foreway, and vortices form behind the square columns. Without rectification measures, the flow pattern is disorderly in the forebay, but it is significantly improved when a single row of square columns are arranged in the forebay. These square columns should be arranged in the forepart and middle of the forebay, not in the backflow zone at the two sides. The flow separation effect decreases and the approach velocity is more non-uniform with the decrease of the width of square columns.

Abstract:Based on the optimized mixture ratio of core wall asphalt concrete, asphalt concrete specimens were prepared using 12% limestone powder, 6% cement and 6% limestone powder, and 12% cement, respectively. The effect of cement fillers on long-term water stability of core wall asphalt concrete with the natural gravel aggregate was studied. The results show that the water stability coefficient of the specimen with 12% limestone powder decreases with the increase of the immersion time, and the water stability coefficient decreases to 0.88 when the immersion time is 75h, indicating that it does not meet the requirement that the water stability coefficient of core wall asphalt concrete be greater than or equal to 0.90. The water stability coefficients of the specimens with 12% cement or 6% cement and 6% limestone powder first increase and then decrease with the increase of the immersion time, and reach their maximum values of 1.02 and 0.98, respectively, when the immersion time is 375h. The water stability factor can still meet the specification requirements when the immersion time is 1500h. It can effectively improve the long-term water stability of core wall asphalt concrete to use cement to replace limestone powder.

Abstract:In order to promote the method of vacuum preloading combined with electro-osmosis using electric vertical drain(EVDs)in large dredger fill foundation reinforcement, field tests on marine dredger fill in Wenzhou City reinforced by this method were conducted. Comparisons of this method with the method of vacuum preloading combined with electro-osmosis using metal electrodes and the conventional vacuum preloading method were performed. Changes in the vacuum pressure, surface settlement, current, and voltage were analyzed, and as was the growth rule of bearing capacity of the foundation after reinforcement. The test results show that EVDs can obtain the same reinforcement effect as metal electrodes, that their use is effective and feasible for electro-osmosis, and that their arrangement has an influence on the reinforcement effect. The surface settlement of the method of vacuum preloading combined with electro-osmosis using EVDs is over 9% larger than that of the conventional vacuum preloading method, and the bearing capacity of the foundation of the former is over 21.4% larger than that of the latter. The bearing capacity of the deep soil increases, and the reinforcement effect is significant.

Abstract:In order to study the bearing characteristics of the interface between the anchor and rock in the anti-pullout process of a rock-socketed anchor, according to the failure mechanisms of the rock-socketed anchor in the rock foundation, the mechanical behavior of the interface between the anchor and surrounding rock was simulated using a two-segment linear function. The formulas of axial force, side resistance, and top vertical displacement of the rock-socketed anchor were derived based on the load transfer theory. The influence of the comprehensive influence coefficient η on the anti-pullout bearing characteristics of the rock-socketed anchor was analyzed, and the method for determining the value of η was provided. The axial force, side resistance, and P-S curve for an engineering example were analyzed using the presented calculation method. Results show that, when the uplift load is small, the side resistance of the rock-socketed anchor shows a hyperbolic distribution. When the uplift load is larger, the plastic zone appeares. The side resistance shows a uniform distribution in the plastic zone and a hyperbolic distribution in the elastic zone.

Abstract:Advances in research of mechanisms of tailings dam failure-induced disasters, mechanical properties of tailings and hyperconcentrated flow after dam failures, the range of influence of tailings dam failures, and measures of early-warning and disaster prevention are summarized and analyzed. On the whole, studies on tailings dam failures have made some progress, and certain experiences have been obtained. However, further in-depth and systematic studies are required in many areas. At present, research on tailings is mainly performed on specific projects, in contrast to research on the conventional soil material. Systematic study on mechanical properties of tailings helps to enhance the level of safety evaluation of tailings dams. Physical model tests and the numerical simulation method are the main means to predict the range of influence of tailings dam failures. Some key problems for further research of tailings dam failures and disaster control are pointed out, i. e. , seeking breakthroughs with new testing technology, properties of tailings and hyperconcentrated flow after dam failures, and dam construction methods.

Abstract:A summary of the current status of concrete dams impacted by leakage dissolution is provided. In view of material science, the leakage dissolution process and the degradation of mechanical properties of concrete in hydraulic structures are reviewed based on results of experimental and theoretical research. In view of engineering structures, the spatial evolution law of mechanical properties of concrete for dam bodies impacted by leakage dissolution is summarized. Furthermore, the spatial variability of physical and mechanical parameters of concrete dams is analyzed, and advances in the random field model for description of the spatial variability of dam body mechanical performance and the random finite element method for evaluation of dam body dynamic performance are discussed. Finally, three important topics for further research, including the mechanism of leakage dissolution causing damage to concrete structures under multiple environmental and load factors, the spatial random field model for description of the mechanical performance of concrete dams impacted by leakage dissolution, and the seismic safety analysis method for assessment of the dynamic performance of aged concrete dams under the influence of leakage dissolution, are proposed.