Abstract:This paper is concerned with the optimal design of the structural section of the geotextile tube dam via application of modern design theories. To realize this objective, a mathematical model for optimal design is proposed, with the key geometric sizes of dam section taken as the design variables, the minimum construction cost as the objective function, and the safety coefficient of slope stability under the working conditions of high and low design water levels and rapid reduction of water level as the main constraint condition. FLAC3D is used for structural analysis and verification of slope stability where the complex method is used to solve the optimal model. The obtained numerical results show that, compared with the original design scheme, the optimal design scheme can reduce the construction cost by 22.7%, the tensile strength of the geotextile tube reaches the critical constraint value, and the performance of the dam structure with stress and deformation is improved, which indicates the helpful effect of section optimization and high economic benefits.

Abstract:The cross-sectional size of an air-cushion surge chamber is usually determined by the critical stability cross-sectional area, and the hydrostatic head, the flow through the generating set, and the thermodynamic process of gas in a surge chamber when there is little perturbation of the water level are three main factors affecting the critical area. Investigations of the heat conduction process between the gas in the surge chamber and the surroundings show that the isothermal change (with a polytropic exponent of 1.0) is most appropriate for simulating the actual conditions when there is little perturbation. Through mathematical analysis of a formula regarding the critical area and a case study, it is concluded that using the maximum hydrostatic head during the normal operation of a hydropower station and the corresponding flow as the calculation conditions can satisfy the fluctuation stability requirement of the water level in the surge chamber of other operation schemes , which would facilitate the safety of projects.

Abstract:Several experiments in which both p (spherical stress) and b (the coefficient of intermediate principal stress) remained constant on theπ-plane were performed on coarse-grained soil by the TSW-40 type true triaxial apparatus at Hohai University. The relationship between the peak value of stress ratio Mb and the value of b in these tests was studied. The test results indicate that Mb decreases with the increase of b, and the influence of b on Mb is greater when b is small, while the influence is small when b is large. The test results also show that Mb decreases with the increase of p under the same value of b, which shows that the strength of coarse-grained soil has nonlinear properties. The failure lines on the π-plane based on five failure criteria, including the failure criterion on a σ3- constant plane, the Mohr-Coulomb criterion, the stress-invariant failure criterion, the Lade-Duncan criterion, and the Matsuoka-Nakai criterion, were drawn and compared with the test results in order to verify the applicability of these criteria to coarse-grained soil. It is shown that the results of the failure criterion on a σ3-constant plane of coarse-grained soil are closer to the test results than those of the Mohr-Coulomb criterion, owing to consideration of the influence of intermediate principal stress, and it is convenient to take strength nonlinearity into account. It is also shown that the results of the stress-invariant failure criterion of coarse-grained soil are between those of the Lade-Duncan criterion and the Matsuoka-Nakai criterion, and they fit the test results better.

Abstract:clay liner (GCL) and attenuation liner (AL) was developed to investigate the transport of organic pollutants in the composite liners. Degradation of the organic pollutants in AL is considered. The analytical solution to the model was obtained, and the results are in good agreement with those from Pollute v7 software, showing the reasonability of the proposed model. The effect of biodegradation on diffusion of organic pollutants was investigated on the basis of the proposed model. The equivalence between GCL+AL and the compacted clay liner (CCL) is discussed with consideration of biodegradation. The results show that the bottom flux of the GCL+AL composite liners is reduced when the degradation half-life of organic pollutants in AL decreases. The standard 0.75 m CCL can be replaced by a combination of a GCL and an AL with a thickness of more than one meter under the calculation conditions described in this paper.

Abstract:To understand the time-variant characteristics of force and deformation of large-size geosynthetic tubes filled with slurry and to provide a calculation basis for tube design, the tension, shape, and height of a geosynthetic tube during the filling process were calculated using the dimensionless method. Two working conditions during the filling process were considered: one was the free filling condition, under which the pressure at the top of the geosynthetic tube was zero, and the other was the pump filling condition, under which the pressure at the top of the geosynthetic tube was greater than zero. It was found that, when a geosynthetic tube with a perimeter of L was filled with slurry with a density of ρ, the critical filling height from the free filling condition to the pump filling condition is 0.1L, the filling volume per unit length of the geosynthetic tube is 0.04L2, and the corresponding tension of the geosynthetic tube is 0.0025ρgL2. After the critical filling height was reached, a continuous increase in the pump pressure was needed to maintain the filling process. Both the required pump pressure and the tension of the geosynthetic tube increase nonlinearly and rapidly with the filling height.

Abstract:Zhenggang deposit talus at Gushui Hydropower Station is in a stable state at present. However, it may become unstable under conditions of rain or earthquakes, which may lead to landslides and even threaten the safety of cavern exits downstream. In order to solve this problem, a typical geological profile was chosen for geological characteristic analysis. Then, a granular discrete element model was built for numerical simulation of landslide reactivation in different cases. The results show that cracks easily occur near the position where the dip angle of the slip surface increases sharply or a fault develops, which also affects the initial landslide position. When the water pressure of three meters is loaded on the slip surface, the deposit talus starts to creep, and when the water pressure reaches five meters, a third-stage landslide may become active aqain. When the seismic strength reaches 0.3g, the deposit talus on the first platform begins to slide, and a third-stage landslide is generated.

Abstract:Based on experiments on concrete specimens subjected to fatigue loading, the applicability of the three- stage deformation law and the invariance of the critical strain in the second stage are inspected. It is demonstrated that the three-stage law is universally applicable and has nothing to do with concrete strength and load form, and that the invariance of the critical strain in the second stage is only suitable for concrete materials with the same strength grade and has nothing to do with the loading history. A formula for calculating the fatigue life is put forward based on the above deformation laws, and the formula can be used to predict the residual fatigue life of existing concrete structures.

Abstract:Dredged material (DM) with different initial water contents and cement contents was solidified. The relationship between the matric suction and the void ratio during drying of the solidified dredged material (SDM) was established by utilizing the soil-water characteristic curves and the shrinkage curves, which were determined through experimental tests. The experimental results show that, during the drying process, the untreated soil and SDM with low cement contents continuously shrink with the increase of matric suction, and the latter exhibits lower shrinkage compared with the former, while SDM with high cement contents show no shrinkage. The increase of matric suction cannot cause further shrinkage when it reaches a specific value φS. It is found that the value of φS is influenced by the initial water content and cement content.

Abstract:An improved method for iterative calculation of the m value is proposed based on the conventional flexibility fulcrum method. In a case study of a deep foundation pit at a subway station in Nanjing City, the results of the two calculation methods were compared with observed data. The results show that the improved flexibility fulcrum method can simulate the changes of the interaction between soil and the supporting structure during the deformation of the supporting structure to a certain extent, which is closer to the reality. The iterative method can better predict the deformation of the foundation pit, which is helpful to the computation theory based on the controlled deformation.

Abstract:The long-term effects of Zn(Ⅱ) on the properties and pollutant removal efficiencies of aerobic granular sludge in sequencing batch reactors (SBR) were investigated systematically. The results show that Zn(Ⅱ) with a concentration less than or equal to 5 mg/ L has a slight effect on the properties and pollutant removal efficiencies of aerobic granular sludge. When the concentration of Zn(Ⅱ) is greater than or equal to 10 mg/ L, the pollutant removal efficiencies of the sludge are reduced, leading to variations of the mass concentration of mixed liquid suspended solids (MLSS) and the sedimentation rate, granular size, and structure of the sludge. Along with the long-term effects of Zn(Ⅱ), the average diameter of granules decreased, the sludge structure loosened, and the sedimentation ability deteriorated, which, finally, resulted in the decrease of the MLSS concentration. After 10 and 15 mg/ L Zn ( Ⅱ) were separately dosed for 76 days, the removal rates decreased to 84.3% and 75.1%, respectively, for NH+4 -N, and 90.1% and 85.7%, respectively, for COD; the MLSS concentration dropped to 3658 and 3225 mg/ L, respectively; the sludge volume index (SVI) increased to 94 and 99 mL/ g, respectively; the average particle size decreased to 0.58 and 0.37 mm, respectively; and parts of the granular sludge disintegrated.

Abstract:In order to manage rivers more effectively, a river ecosystem health early warning model based on the existing study of river ecosystem health and BP artificial neural networks was established and applied in the early warning of the Luanhe River's health status. The results show that the ecosystem health of the Luanhe River will be improved in the next 20 years: in 2015, its health will be in a mild disease state, corresponding to the middle warning level, and in 2020 and 2030, its health will be in a sub-health state, corresponding to the lower warning level. Measures to improve the ecosystem health of the Luanhe River, including water conservation, optimization of water supply projects, and water pollution mitigation, are proposed on the bases of future warning levels and warning sources.

Abstract:This study investigated the change hydrodynamic characteristics at the confluence reach in BaiShi Reservoir area in the Daling River with different factors, based on model testing. The results show that the water depth and flow area increase along the channel, and the flow velocity in the mainstream and tributaries upstream of the confluence zone increases along the channel as well, while the flow velocity downstream of the confluence zone decreases significantly along the channel. The backflow region occurs in the tributaries downstream of the confluence zone, and its range increases with the confluence ratio. When the water level upstream of the dam increases, the absolute value of the velocity and its change rate along the channel decrease in the confluence zone, while the degree of curvature of the main stream line and the backflow region range increase.

Abstract:In order to study the influence of the preferential flow formed in the facture by light non-aqueous phase liquids (LNAPLs) in the unsaturated zone on contamination of the aquifer, we experimentally investigated the migration behavior of the preferential flow formed in a single fracture by LNAPLs with different viscosities in the unsaturated porous media, selecting soybean oil and No. 0 diesel fuel as two LNAPLs with different viscosities. The results indicate that the LNAPL with lower viscosity forms a faster preferential flow in the fracture, and, after entering the capillary zone, the LNAPL migrates more slowly in the vertical direction, and disperses faster in the horizontal direction under the action of uplift force. The preferential flow not only occurs in fractured heterogeneous media, but also exists in homogeneous media in the form of finger flow, and the LNAPL with larger viscosity tends to form more narrow finger flows.

Abstract:To investigate the long-term evolution law and mechanisms of soil moisture content in farmlands of Luancheng District in Shijiazhuang City, the Hurst indices and fractal dimension of soil moisture time series (2002 to 2008) at depths of 10 cm, 80 cm, and 150 cm were calculated by rescaled range analysis. Results show that the Hurst indices of soil moisture at 10cm, 80cm, and 150cm are 0.738, 0.877, and 0.953, respectively, all greater than 0.5, indicating some trends of variations of soil moisture at different depths; and the values of fractal dimension are 1.262, 1.123, and 1.047, respectively, indicating a decreasing trend of the fluctuation amplitude of soil moisture content with the increase of depth, which is consistent with the observed results.

Abstract:Taking the Yangtze Estuary as an example, applicability of the sediment numerical model to prediction of the effect of the reclamation project on accelerating sediment deposition was examined through comparison of the simulated and measured results and reasonableness analysis of predictions. The results show that the plane deposition feature, cross-sectional deposition feature, and deposition amount calculated with the sediment numerical model agree with measurements, indicating that the sediment numerical model is applicable to prediction of the effect of the reclamation project in the Yangtze Estuary on accelerating sediment deposition.

Abstract:Through laboratory experiments of the evolution of an internal solitary wave (ISW) of depression over step topography in a large stratified fluid tank, the propagating characteristics of the ISW along the mutation topography of the seabed of the South China Sea were studied. The process of the interaction of the ISW and the step topography was shown using layered dye-injection techniques and its structure was quantitatively measured with multi-point combined conductivity-probe arrays. The results show that mutation topography can lead to an amplitude increase of the ISW near the step and cause the waveform to steepen. Further, dynamic phenomena, such as the trail wave train and polarity reversal, are generated.

Abstract:Concerning the phenomenon of tidally-induced groundwater fluctuation in a coastal aquifer, based on the new Boussinesq equation derived by Kong et al., the function express and composition of the wave were analyzed using the perturbation method. Analytical research on the influence mechanism of a tidally-induced high-frequency groundwater wave affected by the unsaturated zone aquifer was conducted. The results indicate that, after the groundwater wave propagated into the coastal aquifer, the dominant frequency amplitude decreased exponentially, and the smaller the hydraulic conductivity was, the larger the decay rate of wave energy was. Besides, under the nonlinear effect, a high-frequency wave was generated during the wave propagation process, and the wave energy transformed from a low-frequency wave to a high-frequency wave. Numerical experiment results show that the increase of unsaturated water holding capacity, the decrease of thickness of the unsaturated zone, and the decrease of porosity of soil promote the formation of a high-frequency wave.