Abstract:Based on the principle of local scour of bridge piers, and on the basis of the anti-scour measures of horizontal collars, a new anti-scour protection measure, called ridged collar, which can change the water flow around the piers was designed. In order to explore the protective effect of the ridged collar on the local scour of cylindrical bridge piers, indoor physical model tests were conducted using ridged collars of different shapes, and the scour characteristics and hydraulic properties around the pier were studied. The test results show that, the protection effect is the best for a ridged collar installed on the bed surface with a height of 1 cm and an angle of 135°. Compared with cases of no protective measures, after the ridged collar is installed on the bridge pier, the maximum scour depth reduction can reach 62.2%, and the vertical flow velocity and vertical turbulence intensity at the bottom of the pier can be significantly reduced. Through multivariate analysis, an empirical equation for calculating the non-dimensional maximum scour depth around the pier is established, which is applicable to both open channel flows and flows under ice sheet.

Abstract:In order to study the impacts of different width-depth ratios and radius-width ratios on the hydrodynamic characteristics at open-channel confluences with bend flow, a three-dimensional numerical model was established by using the volume of fluid (VOF) method for the free surface capture and adopting the RNG k-ε model for the governing equations closure. The water surface pattern, velocity distribution, secondary flow and shape of separation zone were analyzed after the simulations of five combined cases with three width-depth ratios and three radius-width ratios. The results indicate that the degree of water level drop near the intersection decreases with the increase of the width-depth ratio or the decrease of the radius-width ratio. Compared to the radius-width ratio, the width-depth ratio has a stronger impact on the non-uniformity of velocity distribution at the confluence and the downstream area. When the width-depth ratio increases, the longitudinal flow rate increases and the non-uniformity of velocity distribution increases with enhanced flow deflection effect. When the width-depth ratio or radius-width ratio increases, the reflux structure at the bend is enhanced, the size of the separation zone increases with narrower and longer horizontal form.

Abstract:To investigate the process of pollutant transport in sinuous open channel flow, a 3D hydrodynamic-pollutant coupled large-eddy simulation model was established according to the scalar tracer experiment. The influence of different release positions in transverse and vertical directions of point source on the concentration distribution in the downstream was analyzed. The results show that the streamwise velocity, vorticity and turbulent kinetic energy have clear relations and the secondary currents exert dominant impact on transport and mixing. Besides, the variance in transverse and vertical position of point source has significant influence on mixing efficiency and spatial distribution of pollutant. Specifically, the point source placed near the center of cross section in transverse direction or near the bottom of channel in vertical direction will result in a higher mixing efficiency and a wider influence range. There exists a positive correlation relationship between mixing rate and distribution range in the near field. The variance of point source position in a sinuous open channel mainly influences the pollutant’s mixing within a single period.

Abstract:To deeply analyze the influence factors of ship lift deformation, a method for building ship lift deformation monitoring model based on quantile regression is proposed. Based on the structural characteristics of the ship lift, the influence factors such as air temperature and mean value of upstream water level in early stages are introduced into the candidate influence factor set. Adaptive elastic net penalized quantile regression is used for choosing the influence factors of ship lift deformation and building the quantile regression model. The optimal model can be obtained based on the principle of good fitting and validity check. Example verification shows that compared with traditional stepwise regression model, the proposed optimized model has low volatility for prediction accuracy with strong stability, indication a good ability for long term prediction.

Abstract:To reveal the influence of delayed-peak rainfall infiltration on ultimate bearing capacity of an unsaturated foundation rapidly, the following research work was carried out. The Gardner’s permeability coefficient function and the soil-water characteristic curve model were introduced to simplify the Richards unsaturated seepage control equation, and the Laplace transform was adopted to derive the transient analytical solution of matrix suction for foundation under delayed-peak rainfall infiltration with rain intensity, which was verified with the finite element numerical simulation results. Based on the theory of shear strength for unsaturated soil and the transient analytical solution of matrix suction, the expression of transient ultimate bearing capacity for foundation was obtained under delayed-peak rainfall infiltration. The mapping relationship between the ultimate bearing capacity and the initial rain intensity, the rain intensity variation coefficient, and the rainfall duration was established. With the analytic solution of the ultimate bearing capacity, the evolution characteristics of the bearing capacity for foundation were studied during the delayed-peak rainfall, and the effects of the initial rain intensity and the rain intensity coefficient on the ultimate bearing capacity for foundation were analyzed. The results show that during delayed-peak rainfall infiltration, the ultimate bearing capacity decreases gradually with a nonlinear velocity from low to high, which is different from the near linear reduction when encountering uniform rainfall. When the rain intensity coefficient is constant, ultimate bearing capacity for foundation decreases faster with the greater initial rain intensity. When the initial rain intensity is constant, the ultimate bearing capacity for foundation decreases faster with greater rain intensity variation coefficient.

Abstract:Aiming at the problem that there is no standard test method for the shear strength of cement-based repair material and concrete interface, a double L direct shear test device was designed, which can effectively avoid the influence of bending stress and make pure shear failure at the interface. Based on this test device, the effects of concrete surface roughness, water content and interfacial agent type on the shear strength of mortar-concrete interface were studied. The results show that moderate roughness treatment is conducive to the improvement of shear strength, and the shear strength decreases when the roughness is too large. The higher the surface moisture content of concrete, the lower the interfacial shear strength will be, and the surface moisture content has a significant influence on the shear strength. The use of interfacial agent can strengthen the structure of interface transition zone, and the selection of appropriate interfacial agent according to the dry and wet conditions of concrete surface is helpful to improve the shear performance of the bonding interface.

Abstract:In order to study the influence of Duncan-Chang E-B model parameters and their interactions on dam deformation, the global sensitivity of parameters in Duncan-Chang E-B model was studied using the improved response surface method for a homogeneous loess dam. Firstly, five parameters including R f, γ, φ 0, K b and K , which have significant influence on the deformation of earth dam were screened out by fractional factorial design. Then the central composite design in the response surface method was used to conduct further global response surface analysis on the screening results and investigate the influence of parameters and their interaction on the deformation of earth dams. The results show that R f, γ and φ 0 are the three most sensitive parameters to dam displacement, and the interaction between them is also significantly sensitive to dam deformation, which is greater than the sensitivity of a single factor. Therefore, the interaction between the parameters should be considered in similar engineering calculations.

Abstract:Based on the economic design index of single 5% cement, the triaxial test of improved aeolian sand static in mixed cement silt was carried out.The stress-strain and strength characteristics of improved aeolian sand sample under different confining pressures were analyzed, based on which the change law of the viscosity and internal friction angle of different doping ratios, the failure form of improved aeolian sand, and the shear failure mechanism were revealed. The main results show the stress-strain relationship curves of improved aeolian sand are all strain softening curves.The elastic modulus and failure intensity are positively correlated with confining pressure, and elastic modulus reaches to its peak value when the amount of silt mixing is increased to 15%.The value of failure intensity is positively correlated with the amount of silt.The cohesion of modified aeolian sand is the largest under 10% silt mixture, and the internal friction angle increases monotonously with silt mixing amount. The reason is that cement hydrate is wrapped in the surface of sand particles, increasing the surface roughness and forming a network structure in the gap between sand particles.The sand particles are linked together and the relative movement of sand grains is hindered.Incorporating an appropriate amount of silt can fill the gaps between sand particles and hydrates, but excessive silt will restrict the hydration reaction, and at the same time, alkaline ions and hydrates react to produce sodium silicate and sodium aluminate with poor cementing capacity, resulting in a decrease in the overall performance of improved aeolian sand.

Abstract:Taking the rural Fushanchang village around a drinking headwater reservoir in western Hubei montane as a research example, an investigation was carried out on the current situation of rural domestic sewage discharge and treatment in western Hubei montane through on-site investigation and water quality testing.The results show that rural wastewater in western Hubei montane is mainly treated by three methods, including centralized micro-powered station, small micro-powered facility for three-household combined discharge, and three-format fermenting tanks.After treatment, the sewage is discharged into surface ditches, weirs and ponds or infiltrated into the ground. The test results of the effluent water quality of the three wastewater treatment methods cannot meet the requirements of rural domestic wastewater discharge water quality, and it has a certain impact on the water quality of the adjacent water source reservoir.The micro-powered sewage treatment facilities have high operating costs, complex operation and maintenance procedures, negligent management and short effective operation time, making it difficult to achieve the appropriate sewage treatment effect.Therefore, the study of new rural domestic wastewater treatment methods based on the characteristics of rural terrain and domestic wastewater discharge in western Hubei montane is imperative to ensure the safety and quality of the rural water environment.

Abstract:In order to accurately detect the location and range of dam leakage channels and reduce the influence of the limitation and uncertainty of single method on the detection result, a method of combining high-density electrical method and comprehensive tracer method to detect the hidden dangers of dam leakage is proposed. The verification of a pumped storage power station example shows that, the results of the high-density electrical method can be verified by the comprehensive tracer method through several tracing tests. The dam leakage channel detection technology combined with high-density electrical method and comprehensive tracer method accurately reveals the location and range of the hidden danger of dam leakage, overcomes the non-unique defect of single method detection result. The combination of high-density electrical method and comprehensive tracer method for dam leakage channel detection has high efficiency and accuracy.

Abstract:In hydrogeological survey, the situation of multiple aquifers is often encountered in borehole testing, and it is necessary to use packer system to isolate and detect each aquifer. Due to the inconvenience for field operation and high drilling conditions required, a multi-aquifer seepage tracing model without packer system was proposed. Considering different conditions of aquifer inflow and out flow without using plugging system, an electric conductivity tracer model for a multi-aquifer seepage system was established to determine the permeability parameters by measuring the conductivity of each aquifer during pumping. When only the outflow aquifer exists, the flow rate can be calculated directly by using the proportion relation between the area of conductivity curve and solute mass. When both outflow layer and inflow layer appear in borehole, the position of inflow layer can be found accurately according to the slope of electrical conductivity curve, and then the flow rate of aquifers can be calculated by the change of slope. In a field test, the hydrogeological parameters such as permeability coefficient, hydrostatic head, seepage velocity and water conductivity coefficient of each aquifer were calculated by using three methods. The results show that the detection results obtained by the conductivity tracing model is in good agreement with the isotope tracer test and water injection test, and the proposed model is simpler to operate, which can greatly improve the detection efficiency of aquifer hydrogeological parameters.

Abstract:To quickly and accurately predict the temperature history during the concrete construction period, a prediction model based on the long short-term memory (LSTM) network algorithm was proposed combined with the principal component analysis (PCA).Taking the baseboard of the Siyaogang Sluice and Bayaogang Sluice in Shanghai Chongming Island as an example, the PCA method was used to reduce the number of the possible influencing factors of the concrete temperature field, and then the LSTM prediction model of temperature history based on the temperature data of the Siyaogang Sluice baseboard was established to train the input principal components. Then the trained model was used for the fitting and prediction of the temperature history of the Bayaogang Sluice and was compared with the measured results. The results show that the predicted value fits well with the measured one with the RSM error within 2℃ and the coefficient of determination close to 1, meeting the requirements of engineering accuracy. The proposed method can partially be an alternative for FEM back-analysis, which can increase the efficiency for concrete temperature field prediction of pump and sluice projects.

Abstract:Aiming at the uncertainty in the results of the scheming optimization process influenced by subjective factors and the problem of optimal scheme selection during asphalt concrete mix designing, taking the mix design of the Qiaolabula asphalt concrete core wall project as an example, the projection pursuit regression(PPR) modelling technique combined with the TOPSIS comprehensive evaluation method based on entropy weights (PPR-TOPSIS analysis method) was proposed for the comprehensive benefits of the mix evaluation indexes. The results show that the established PPR model for asphalt concrete evaluation indexes is highly accurate in calculation, with a pass rate of 93.1% and an average relative error of 2.01%, which can accurately predict the evaluation indexes of the mix ratio schemes with different combinations of factor levels. The test results of the best mix ratio scheme analyzed by the PPR-TOPSIS comprehensive evaluation method can satisfy the specification criteria. Compared with the traditional design method, the influence of human subjective factors can be reduced and the solution search and quantitative evaluation of the combination of all test factors can be realized by the proposed method, and the obtained ratio solution is more reasonable.

Abstract:Surface cracks in the impervious concrete panel of a concrete faced rockfill dam were examined by employing several non-destructive testing methods, including ground penetrating radar, impact echo and ultrasonic plane inspection. The characteristics of electromagnetic response of different types of cracks were analyzed, the effects and influencing factors of impact echo and ultrasonic plane measurement upon different cracks were assessed with error analysis. By comparing with direct drilling results, the effectiveness and accuracy of integrated non-destructive method, which was established by incorporating holistic rapid inspecting and local accurate measurement, were discussed in crack detection. The results indicate that ground penetrating radar, with its intuitive and high efficiency, can achieve an overall investigation of impervious panel cracks, and quickly indentify their distribution and physical properties. The impact echo and ultrasonic plane mearsuring method, with their accuracy and flexibility, can further determine the crack depth. Through reasonably combining testing methods and scientifically laying out survey lines, the proposed methods can identify the distribution, basic properties, scope and size of cracks, whilst improving the comprehensiveness, accuracy and precision of detection.

Abstract:In order to deeply mine the dynamic correlation between the front and back information in the time series data,explore the internal influence mechanism of dam deformation, and effectively improve the prediction accuracy of the model, a bidirectional gated recurrent unit (BiGRU) prediction model based on mixed attention mechanism and whale optimization algorithm (WOA) was constructed. WOA was used to optimize the hyperparameters of BiGRU to effectively mine the deep information of deformation data in the time dimension.A mixed attention mechanism that combines factor attention mechanism (FATT) and temporal attention mechanism (TATT) was introduced to calculate the contribution rate of each impact factor, so as to visualize the model and improve the ability to capture the dynamic changes of environmental factors. Taking a high arch dam as an example, the prediction results of this model were compared with those of various commonly used models. The results show that the prediction accuracy of this model is significantly improved, and the calculation of contribution rate is in line with the research results of dam deformation, which verifies the superiority and rationality of the model in dam deformation prediction.

Abstract:To solve the problem that the internal correlation between multiple measuring points cannot be considered by traditional single measuring point monitoring models, which is difficult to reflect the regional characteristics of high arch dam deformation in space. A high arch dam deformation prediction model based on clustering partition and a multi-output least square support vector regression machine (MO-LSSVR) algorithm is proposed. Based on the composite similarity index between the measuring points, the clustering partition of spatial correlation measuring points is realized by hierarchical agglomerative clustering (HAC) algorithm. The MO-LSSVR algorithm integrating the correlation characteristics of measuring points is then used to model the points in the partition. The engineering example results show that the clustering partition results are consistent with the spatial distribution characteristics of dam deformation. The MO-LSSVR model based on the reasonable partition results has high accuracy and robustness, which provides a new method to accurately predict the dam deformation and monitoring the overall safety state of the dam from the multi-measuring points correlation dimension.

Abstract:Aiming at the problem of gross errors and abnormal measurements in the deformation monitoring data of concrete dams, a data anomaly identification and reconstruction model is proposed. The association rules are used to quantify the correlation between deformation sequences and water level sequences, and the monitoring data are input into the DBSCAN clustering algorithm to find the abnormal points.The association results are used to classify the data abnormal points into two categories, coarse error points and points reflecting the dam morphology.The points reflecting the dam morphology are retained and the coarse error points are eliminated, and modified wavelet neural network is used to reconstruct the coarse difference data to ensure the integrity of the monitoring sequence. The application results of an arch dam deformation monitoring data show that the model can accurately identify the abnormal values in the monitoring data and can obtain more accurate reconstructed data, providing a new analysis method for the evaluation of measured properties of a dam.