Abstract:For the phenomenon of transient flow with entrapped air pockets, which often arises in the process of water filling pipelines in long distance water conveyance system, considering the elasticity of water, compressibility of air, dynamic movement of the air-water interface and the multiple-air-pocket interaction, a numerical model is developed to simulate the pipeline filling with multiple entrapped air pockets. A local grid interpolation method is proposed to track the dynamic air-water interface, which is solved by the Methods of Characteristics (MOC). Comparison between the calculated results and the experimental results verifies that the model can accurately simulate the transient pressures of multiple entrapped air pockets. Case analysis shows that for the situation with only one entrapped air pocket, the maximum air pressure first rises and then drops with the increase of air length, and also gradually rises as the blocking water column length increases. However, for the situation with two entrapped air pockets, the maximum pressure alternately arises within the upstream and downstream air pocket as the blocking water column length increases.

Abstract:In order to obtain the influence law of stand column types on flow and separation performance in a vortex settling basin (VSB), VSBs without column support system, with II-type and VSB H-type stand columns were studied by model experiments respectively. The results show that in the case without columns, the air core penetrates through the flushing bottom with the largest air core diameter, the maximal clean water area and the strongest spiral flow intensity. The air core offsets the flushing bottom after the installation of II-type columns, leading to smaller air core diameter, clean water area reduction and lower spiral flow intensity. The offset distance of air core is the largest after installation of type-H columns, leading to the smallest air core diameter, minimum clean water area and weakest spiral flow intensity. Compared with H-type columns, the sediment trapping efficiency, flushing efficiency, sediment deposition in the basin, water abstraction ratio under the II-type column system are similar to those without columns under deflector. II-type columns can be used as the support body shape to ensure the safety of the deflector and a higher sediment trapping efficiency.

Abstract:In order to provide scientific basis for the engineering structure design and working condition control for the main tunnel system of a deep tunnel drainage system, numerical simulation was carried out combined with physical model test. A three-dimensional numerical model of the main tunnel system including two shafts and a connected main tunnel section was established, which had the same body structure as the physical model. A three-dimensional dynamic simulation of the inflow process was performed under two extreme large inflow conditions. The results show that the water intake process of the main tunnel system under large flows can be summarized into 4 stages, flow entering into the main tunnel from two shafts, flow colliding to form surface waves which are transmitted and superimposed in the main tunnel, lower and upper side tunnel ports blocked successively, and inflow stopped. The inflow mainly affects the seal degree of the port in the main tunnel system, the phenomenon of hysteretic gas and the process time of each inflow stage. The seal degree of the port in the main tunnel system and the phenomenon of hysteretic gas is more serious under larger inflow condition, and the process time of each inflow stage is substantially reduced.

Abstract:Sedimentation model testes were carried out on dredged slurry treated by calcareous flocculants at high initial water content. The influences of calcareous flocculants on the self-weight sedimentaiton characteristics of dredged slurry were discussed based on the test results. The results show that the settling of dreged slurry with calcareous flocculants undergoes flocculatin, hindering settling and self-weight consolidation. The addition of calcareous flocculant would result in a decrease of the settling time, while the stable settlement amounts induced by self-weight sedimentation vary with the properties and dosages of calcareous flocculants. For the CaCl2, it mainly affects the self-weight sedimentation characteristics of dredged slurry by the ion exchange and electrical neutralization. Unlike the CaCl2, the effects of Ca(OH)2 on the self-weight sedimentation characteristics of dredged slurry is primarily controlled by flocculantion at the earlier stage, and then by the pozzolanic reaction, resulting in a substantial reduction of the stable self-weight settlement value for dredged slurry pretreated with Ca(OH)2.

Abstract:The effects of polymer curing agent on vegetation growth and erosion resistance of sandy soil after composite improvement were studied by adding different concentration of curing agent and fibers to a sandy slope. The mechanism of improvement was analyzed by scanning electron microscopy, and the results show that with the increase of curing agent concentration, the germination rate of seeds decreases, and the growth of plants is better when polypropylene fiber is added. The sand slope surface strengthened by macromolecule curing agent and plant has better erosion resistance, and the cohesion and internal friction angle of the soil are obviously enhanced. The polymer curing agent sprayed on the surface of sandy soil forms a certain thickness solidifying layer on the surface of the slope, which makes the reinforced sandy soil have better erosion resistance. The plant stems and leaves on the slope can intercept rainfall, avoid the direct impact of water droplets on the surface of sandy soil. The plant roots play a reinforcing role that can effectively enhance the strength of soil, so that the sandy slope surface strengthened by macromolecule solidifying agent and vegetation has better erosion resistance.

Abstract:In order to construct monitoring and evaluation indexes of tobacco drought disaster in Guizhou region, a linear regression equation was established for the water deficit rate and yield reduction rate of Guizhou tobacco during different growth periods. According to the classification criteria of agricultural drought grade, the drought indexes of tobacco during different growth periods were obtained. The results indicate that when the ranges of the water deficit rate in the whole period were ≤15%, (15%，35%］, (35%，55%］ and >55%, light drought, moderate drought, severe drought and extreme drought occurred, and the corresponding reduction rates were ≤10%, (10%，20%］, (20%，30%］ and >30%, respectively. When the ranges of the water deficit rate in the flourishing period were ≤35%, (35%，70%］ and >70%, light drought, moderate drought and severe drought occurred, and the corresponding reduction rates were ≤10%, (10%，20%］ and (20%，30%］, respectively. When the ranges of the water deficit rate in the maturing period were ≤35%, (35%，75%］ and >75%, light drought, moderate drought and severe drought occurred, and the corresponding reduction rate were ≤10%, (10%，20%］ and (20%，30%］, respectively.

Abstract:In order to improve the problems of low training efficiency, easy over-fitting, and poor parameter sensitivity in traditional modeling methods, an extreme gradient boosting (XGBoost) algorithm is introduced, combined with a Bayesian optimization method based on Gaussian process (GP), to improve the learning efficiency and the prediction accuracy.The dam deformation prediction model based on the proposed method was established and the prediction effect was compared with the traditional statistical model and the neural network model. The results show that the monitoring model based on this method has high prediction accuracy and fast iteration speed. Overfitting can be effectively avoided by adjusting the regular term parameters.

Abstract:In view of the problems that the maximum main dam height of a pumped storage power station is 182.3m, the soil and stone material source of the upper reservoir is scarce, the geological conditions of the dam foundation are complex, the bank slope fluctuation is large, and the reliability requirements of the dam deformation and anti-seepage structure are high, a zoning optimization scheme of the main dam section was studied to improve the safety performance. The stones excavated by the stone factory in the upper reservoir is fully considered to build the dam. The slope ratio of the upstream and downstream rockfill boundary is set to be 1∶0.4. Modulus-increased zone is set below the dam crest. In order to ensure the structural safety, the connecting plate is translated into the reservoir with a reduction of the turning section curvature, and the foundation cushion is optimized into special cushion with special transition material.

Abstract:In order to study the anti-seismic capacity of asphalt concrete core wall dams, taking the Niya Reservoir in Xinjiang as an example, the dynamic characteristics of dam materials were analyzed by large-scale triaxial apparatus dynamic modulus damping ratio and permanent deformation test, and the seismic response of dam body was analyzed by using equivalent linear viscoelastic model and hyperbolic residual deformation model of Dalian Institute of Technology. The results show that the maximum dynamic shear modulus of sand gravel and transition material is 4% to 11% higher than that of rockfill material, and the maximum damping ratio of rockfill material is 4% to 14% higher than that of sand gravel and transition material. The maximum dynamic shear modulus of asphalt concrete increases with the increase of confining pressure and consolidation ratio. During the earthquake dynamic response, the maximum displacement, acceleration and maximum permanent deformation of the dam body occur at the dam crest, and the maximum displacement along the river is 0.042m with the maximum acceleration of 4.98m/s2. The upstream and downstream soils of the dam may cause tensile stress failure along the river, the maximum permanent deformation of the core wall occurs at the top of the dam, and the maximum settlement of the dam body is 0.035m higher than that of the core wall, showing strong coordinated deformation ability of the dam body and the core wall. According to the research, the gold rimming silver structure of the Niya asphalt concrete core wall dam has good seismic performance.

Abstract:Based on a statistical model of dam displacement, the form of hydration heat component was proposed to quantify the influence of hydration heat on dam displacement. According to the data of dam displacement, water level and dam body thermometer, the statistical model of dam displacement was established by using backward elimination-partial least square (BE-PLS) method. The displacement component caused by temperature was separated from the measured displacement data. Then, the periodic term was used as the expression of environmental temperature component, and the approximate solution of one-dimensional heat conduction equation was used to construct the model of hydration heat component. The two terms were used to fit the temperature displacement component to realize quantitative analysis of the influence of hydration heat on dam displacement. Calculation of an engineering case shows that the statistical model established by BE-PLS can effectively overcome the influence of multicollinearity among various factor variables on the fitting accuracy of the model. The proposed formula of hydration heat component is applicable, and the dam displacement caused by residual hydration heat should not be ignored.

Abstract:In dam leakage monitoring, due to the complexity of influencing factors, certain interference exists for data interpretation. Two groups of typical geoelectric models of dam leakage were established, and their response characteristics were analyzed by forward modeling. The combination analysis of apparent resistivity pseudo sections and inversion results can eliminate some false anomaly interference and improve the recognition of target. In the anomaly seepage monitoring of a dam, combined with the measured data and inversion results, through continuous tracking of the low resistance abnormal body, the causes of abnormal seepage and the location of the leakage passage were deduced, providing basis for engineering treatment in the next step.

Abstract:Aiming at the problem of inefficient and risky manual detection of cracks in concrete dams, a crack analysis method for concrete dams based on LabVIEW + VDM was proposed. The Vision Assistant (VA) of the Vision Development Module (VDM) was used to process the crack images. The skeleton function of VDM is combined with the morphological operation to extract the skeleton of the crack, and the particle analysis method was used to calculate the crack length, crack width and crack area. The processing method implemented in VA was used to generate script code, and then imported into the programming platform LabVIEW for debugging and GUI design. The results show that the VDM can independently complete the detection function of concrete dam cracks. The program developed based on LabVIEW helps industry personnel quickly detect and analyze cracks in concrete dams, timely diagnose and eliminate hidden safety hazards.

Abstract:In order to solve the problem that the traditional image segmentation algorithm is difficult to segment the dam surface crack images with serious noise pollution, a dam surface crack recognition and segmentation algorithm based on adaptive region growing and local K-Means clustering was proposed. Firstly, bilateral filtering to initially reduce noise in crack greyscale images is used, then the adaptive region growing algorithm to obtain the rough segmentation image of cracks is applied. Secondly, the isolated noises like points and groups are removed by morphological eroding and largest connected domain extracting. Finally, the precise segmentation image of cracks is obtained by local K-Means clustering algorithm. The proposed algorithm, Otsu threshold algorithm and other three algorithms are used to segment three crack images which have stain noise, concrete surface burr noise, block noise and strip noise respectively. The results show that the completion index and accuracy index of the segmentation results obtained by the proposed algorithm are above 0.95, which is better than the other three algorithms. The proposed algorithm has good anti-noise performance and strong adaptability, which can realize the accurate identification and segmentation of dam surface cracks.

Abstract:Aiming at the problem of seepage consolidation in saturated clay around a single pile,the inhomogeneous boundary condition of the water head was established considering the influence of water level change of river or reservoir near the site. The influence of confined-water bearing layer of sand and gravel, or the measures of pumping water from sand wells to accelerate consolidation and drainage was included, and the boundary condition of hydraulic gradient was established. Based on the boundary conditions, the definite solution conditions reflecting the dissipation of excess pore water pressure in saturated clay around the pile were established.The homogeneous operation was then carried out and the solution was deduced. According to the derived theoretical solution, the pore-water pressure variation with boundary and initial condition wasobtained. The contour and the velocity vector diagram were drawn for intuitive comparison and analyzing the rationality of the solution. The actual bearing capacity of a single pile was used to convert the consolidation degree data to verify the correctness of the solution.

Abstract:The characteristics of raindrops from May to October in 2019 and from June to July in 2020 were analyzed by using distrometers, and the results were also compared with the measured data of 0.1mm and 0.5mm resolution rain gauges calibrated in the experimental field. The raindrop velocity and diameter and the relationship between them were obtained. The distribution of raindrop diameters in different rainfall intensities was investigated. The results show that the raindrops with the highest frequency of about 0.5mm diameter accounts for more than 20%, and the raindrops with diameter less than 0.7mm accounts for about 65% from May to October in 2019. The distribution histogram shows a more obvious double peak phenomenon in moderate and heavy rainfall patterns. With the increase of rainfall intensity, triple peak phenomenon occurs in storm rain pattern while single peak phenomenon occurs in light rain pattern. The frequency of the rainfall intensity less than 0.5mm/min is over 90% from May to October in 2019 and during the rainy season in 2020, which requires the factory calibration of rain gauges under weak rainfall intensity.