Abstract: Based on model tests of earthen dam breach due to piping failure, a numerical model was developed. A key difference from previous research is the assumption that the cross-section of the pipe channel is an arch, with a rectangle at the bottom and a semicircle at the top before the collapse of the pipe roof, rather than a rectangular or circular cross-section. A shear stress-based erosion rate formula was utilized, and the arched pipe tunnel was assumed to enlarge along its length and width until the overlying soil could no longer maintain stability. Orifice flow and open channel flow were adopted to calculate the breach flow discharge for pressure and free surface flows, respectively. The collapse of the pipe roof was determined by comparing the weight of the overlying soil and the cohesion of the soil on the two sidewalls of the pipe. After the collapse, overtopping failure dominated, and the limit equilibrium method was adopted to estimate the stability of the breach slope when the water flow overtopped. In addition, incomplete and base erosion, as well as one- and two-sided breaches were taken into account. The USDA-ARS-HERU model test P1, with detailed measured data, was used as a case study, and two artificially filled earthen dam failure cases were studied to verify the model. Feedback analysis demonstrates that the proposed model can provide satisfactory results for modeling the breach flow discharge and breach development process. Sensitivity analysis shows that the soil erodibility and initial piping position significantly affect the prediction of the breach flow discharge. Furthermore, a comparison with a well-known numerical model shows that the proposed model performs better than the NWS BREACH model.
Abstract: Plain reservoirs are shallow, and have low dams and widespread water surfaces. Therefore, wind-wave-induced damage to the dam is one of the important factors affecting the safety of the reservoir. To improve upon unsatisfactory plain reservoir wave-clipping schemes, a numerical method is proposed to predict and analyze waves in the reservoir in the presence of artificial islands, constructed from dredged sediment. The MIKE21 SW model is applied to a specific plain reservoir for finding the optimal artificial island parameters. The simulated wave height attenuation results are seen to agree well with empirically predicted values. Thus, the validity and reliability of the numerical model are established. Artificial islands at suitable locations in the reservoir can attenuate the wave heights by approximately 10% to 30%, which justifies the efficacy of the clipping scheme making use of dredging and island construction.
Abstract: Structural health monitoring is important to ensuring the health and safety of dams. An inverse analysis method based on a novel hybrid fireworks algorithm (FWA) and the radial basis function (RBF) model is proposed to diagnose the health condition of concrete dams. The damage of concrete dams is diagnosed by identifying the elastic modulus of materials using the displacement changes at different reservoir water levels. FWA is a global optimization intelligent algorithm. The proposed hybrid algorithm combines the FWA with the pattern search algorithm, which has a high capability for local optimization. Examples of benchmark functions and pseudo-experiment examples of concrete dams illustrate that the hybrid FWA improves the convergence speed and robustness of the original algorithm. To address the time consumption problem, an RBF-based surrogate model was established to replace part of the finite element method in inverse analysis. Numerical examples of concrete dams illustrate that the use of an RBF-based surrogate model significantly reduces the computation time of inverse analysis with little influence on identification accuracy. The presented hybrid FWA combined with the RBF network can quickly and accurately determine the elastic modulus of materials, and then determine the health status of the concrete dam.
Abstract: Due to the size effects of rockfill materials, the settlement difference between numerical simulation and in situ monitoring of rockfill dams is a topic of general concern. The constitutive model parameters obtained from laboratory triaxial tests often underestimate the deformation of high rockfill dams. Therefore, constitutive model parameters obtained by back analysiswere used to calculate and predict the long-term deformation of rockfill dams. Instead of using artificial neural networks (ANNs), the response surface method (RSM) was employed to replace the finite element simulation used in the optimization iteration. Only 27 training samples were required for RSM, improving computational efficiency compared with ANN, which required 300 training samples. RSM can be used to describe the relationship between the constitutive model parameters and dam settlements. The inversion results of the Shuibuya concrete face rockfill dam (CFRD) show that the calculated settlements agree with the measured data, indicating the accuracy and efficiency of RSM.
Abstract: Extracting implicit anomaly information through deformation monitoring data mining is highly significant to determining dam safety status. As an intelligent singular value diagnostic method for concrete dam deformation monitoring, shallow neural network models result in local optima and overfitting, and require manual feature extraction. To obtain an intelligent singular value diagnosis model that can be used for dam safety monitoring, a convolutional neural network (CNN) model that has advantages of deep learning (DL), such as automatic feature extraction, good model fitting, and strong generalizability, was trained in this study. An engineering example shows that the predicted result of the intelligent singular value diagnostic method based on CNN is highly compatible with the confusion matrix, with a precision of 92.41%, receiver operating characteristic (ROC) curve coordinates of (0.03, 0.97), an area-under-curve (AUC) value of 0.99, and an F1-score of 0.91. Moreover, the performance of the CNN model is better than those of models based on decision tree (DT) and k-nearest neighbor (KNN) methods. Therefore, the intelligent singular value diagnostic method based on CNN is simple to operate, highly intelligent, and highly reliable, and it has a high potential for application in engineering.
Abstract: The effect of hydraulic retention time (HRT) and pH on the biooxidation of ferrous iron during simulated acid mine drainage (AMD) treatment was investigated. The simulated AMD was highly acidic (pH 2.5), rich in iron (about 1700 mg/L) and copper (about 200 mg/L), and contained high concentrations of sulfate (about 4700 mg/L). The biooxidation of ferrous iron was studied in a laboratory-scale upflow packed bed bioreactor (PBR). The HRT was shortened stepwise from 40 h to 20 h, 13 h, and 8 h under the acidic environment at a pH value of 2.2. Then, the influent pH value was changed from 2.2 to 1.2 at a constant suitable HRT. Physiochemical and microbial community structure analyses were performed on water samples and stuffing collected from the bioreactor under different conditions. The results indicate that the efficiency of ferrous iron oxidation gradually decreased with the decrease of HRT, and when the HRT exceeded 13 h, ferrous iron in AMD was almost completely oxidized. In addition, the best efficiency of ferrous iron oxidation was achieved at the influent pH value of 1.8. Microbial community structure analyses show that Leptospirillum is the predominant genus attached in the bioreactor, and low influent pH values are suitable for the growth of Leptospirillum.
Abstract: This paper reviews and discusses the current research status, trends, and future needs in the field of beach morphodynamics under the influence of storm sequences. The paper reviews how the three main research methods, field investigations, numerical modelling, and physical modelling, have been used to study beach morphodynamics during storm sequences. Available quantitative definitions of storm sequences at different sites are presented and discussed. It is shown that the definition of storm sequences is site-specific and requires knowledge of the storm climate, beach characteristics, and the temporal scale of beach recovery. The paper then brings together currently available approaches aimed at describing the effect of storm sequences on beach erosion in a general way. The importance of storm chronology and the effects of an extreme storm within a sequence of storms are highlighted. Following that, the more poorly studied aspect of beach recovery in between storms within a sequence is discussed. Three indicators for defining beach recovery, namely the shoreline, sediment volumes, and the beach state, are identified and compared. Finally, important research needs, including the need for detailed physical modelling, are identified.
Abstract: Confluences play a major role in the dynamics of networks of natural and man-made open channels, and field measurements on river confluences reveal that discordance in bed elevation is common. Studies of schematized confluences with a step at the interface between the tributary and the main channel bed reveal that bed elevation discordance is an important additional control for the confluence hydrodynamics. This study aimed to improve understanding of the influence of bed elevation discordance on the flow patterns and head losses in a right-angled confluence of an open channel with rectangular cross-sections. A large eddy simulation (LES)-based numerical model was set up and validated with experiments by others. Four configurations with different bed discordance ratios were investigated. The results confirm that, with the increasing bed elevation discordance, the tributary streamlines at the confluence interface deviate less from the geometrical confluence angle, the extent of the recirculation zone (RZ) gets smaller, the ratio of the water depth upstream to that downstream of the confluence decreases, and the water level depression reduces. The bed elevation discordance also leads to the development of a large-scale structure in the lee of the step. Despite the appearance of the large-scale structure, the reduced extent of the RZ and associated changes in flow deflection/contraction reduce total head losses experienced by the main channel with an increase of the bed discordance ratio. It turns out that bed elevation discordance converts the lateral momentum from the tributary to streamwise momentum in the main channel more efficiently.
Abstract: Vortices that develop over intakes are a hazardous hydraulic phenomenon. In this study, a 3D model was developed to study the flow field in air-core vortices. This model is based on the spiral pattern of streamlines and the analytical solution of the momentum and continuity equations for deriving the three components of velocity. The model provides equations for free surface profiles and 3D patterns of the streamlines. Moreover, a new relationship was suggested for calculating effective viscosity and its distribution across the vortex flow field. The performance of the proposed analytical model was compared with existing experimental data and the results of previous analytical models. The outcomes indicated that the proposed model could predict characteristics of the vortex flow with good accuracy.
