Gongcheng Kexue Yu Jishu/Advanced Engineering Science

To study the mechanical properties of ferronickel slag–clay–cement (FNSCC) modified soil, the undrained triaxial compression tests of FNSCC modified soil under different ferronickel slag mixing ratios, moisture content and curing times were carried out. The stress-strain curve and secant elastic modulus of FNSCC modified soil samples under different working conditions were obtained, and the influence mechanism and failure mode of mechanical properties were analyzed. Based on the experimental results, the modified Duncan–Chang constitutive model suitable for FNSCC modified soil was established. The results show that the stress-strain curve of FNSCC modified soil has obvious strain softening characteristics. The peak strength first increases and then decreases with the increase of water content. The swelling failure of the sample with a water content of approximately 15 % is particularly obvious. The peak strength of FNSCC modified soil increases with the decrease of the ferronickel slag incorporation ratio. With the increase of the ferronickel slag incorporation ratio, the failure mode of specimens changed from bulging failure to shear failure. With the increase of curing time, the failure mode changes from a plastic failure such as bulging deformation to a brittle failure such as local tension crack. The secant elastic modulus of FNSCC modified soil decreases with the increase of axial strain. When the axial strain is less than 2%, the addition ratio of ferronickel slag, water content, and curing time have a great influence on the secant elastic modulus. When the axial strain is greater than 2%, each factor has little effect on the secant elastic modulus. The modified Duncan–Chang model can better reflect the strain softening phenomenon of FNSCC modified soil. The model parameters m, n and l are approximately linear with confining pressure. The model parameter m is most affected by the ratio of FNSCC modified soil, followed by the curing time, and the moisture content is the smallest. The curve calculated by the modified Duncan–Chang model is in good agreement with the measured curve, which verifies the rationality of the fitting parameters

The rapids abating hydraulic index generally refers to the combination of the maximum route flow velocity and gradient of a ship which can sail through the rapids by itself under the condition of rated load and rated main engine power. It is the critical flow condition to determine whether the ship can sail through the rapids by itself, and it is the reference basis for analyzing the effect of rapids regulation. This paper analyzes the defects of the existing methods to determine the rapids abating hydraulic index, and points out the shortcomings of the existing expressions of comprehensive rapids abating hydraulic index, such as unreasonable selection of key parameters, unclear relationship between influencing factors and main variables, etc. Based on the basic relationship between flow resistance and flow velocity, gradient resistance and gradient, and according to the basic principle of the balance between ship thrust and navigation resistance, from the perspective of overcoming the existing shortcomings of the calculation and expression of the rapids abating hydraulic index, a traditional expression and pre-estimation formula of dimensionless rapids abating hydraulic index were derived. Applying the test results of 500-ton ship at hydrostatic speed in Lancang River, the variation law between the ratio of actual propeller speed to the rated propeller speed with the advancing coefficient was obtained. When calculating the rapids abating hydraulic index, the propeller speed should not be taken as the rated speed. The results show that there is an obvious deviation between the flow resistance calculated by the Zvankov formula and the ship thrust. The correction curve of the resistance correction coefficient with the ship Froude number was plotted. It is pointed out that the calculation formula of Zvankov flow resistance needs to be properly modified according to the results of full-scale ship test. The rapids abating hydraulic indexes of various types of motor ships in Lancang River were analyzed and calculated, and the rationality of the traditional expression of dimensionless rapids abating hydraulic index were verified. It is proved that the dimensionless parabola is more appropriate to describe the relationship between flow velocity and gradient in the rapids abating hydraulic index. Based on the principle of dimensional analysis and through the numerical regression analysis of the rapids abating hydraulic indexes of various motor ships in Lancang River, the pre-estimation formula of dimensionless rapids abating hydraulic index was established, which can significantly improve the calculation efficiency of the rapids abating hydraulic index.

In conventional dam displacement monitoring models, forecast precision is below the standard, the fitting residual sequence contains chaotic components, and information mining of dam prototype observation data is limited. In consideration of the chaotic characteristics of the fitting residual sequence in regression model, the multi-scale wavelet analysis is used to decompose and reconstruct the residual sequence in this study; back propagation neural network and autoregressive integrated moving average model are used to forecast the reconstructed residual sequence by identifying the high-frequency and low-frequency characteristics of signals. By superimposing the residual forecast value with the forecast value of regression model, the combination forecast model for concrete dam displacement considering residual correction is proposed. Examples show that, compared with conventional models, the proposed combination model is better in fitting precision and convergence speed. Forecast capability is significantly improved for dam displacement forecast when effective components contained in residual sequence are considered. A new method of displacement forecast for high slope and other hydraulic structures is presented.

Saccharin (SAC) is an emerging contaminant, widely detected in the environment, with potential ecotoxicity risks to aqueous organisms and human beings. Wastewater treatment plants (WWTPs) are key sources and sinks of SAC, and play a vital role in eliminating SAC entering the environment. An overview is provided of the potential ecotoxicity of SAC, its occurrence in the aqueous environment, and its degradation performance in WWTPs. SAC treatments, including physical, chemical (mainly advanced oxidation processes AOPs), biological, and hybrid processes, and possible degradation mechanisms are also considered. Of the various SAC removal processes, we find that adsorption-based physical methods exhibit relatively poor performance in terms of SAC removal, whereas chemical methods, especially hydroxy radical-mediated oxidation processes, possess excellent capacities for SAC elimination. Although biological degradation can be efficient at removing SAC, its efficiency depends on oxygen supply and the presence of other co-existing pollutants. Hybrid aerobic biodegradation processes combined with other treatments including AOPs could achieve complete SAC reduction. Furthermore, novel adsorbents, sustainable chemical methods, and bioaugmentation technologies, informed by in-depth studies of degradation mechanisms and the metabolic toxicity of intermediates, are expected further to enhance SAC removal efficiency and enable comprehensive control of SAC potential risks

The dynamic characteristics of water and sediment in a meandering channel are more complex than that in a straight channel. The bed evolution and the characteristics of overbank floods in bend are affected by the changes of flood and sediment discharge. The laboratory experiment was carried out in a curved flume under several flow discharges and sediment supplies in this paper. The water surface elevation, bed topography, water level of bend and longitudinal velocities along the main channel and the floodplain were measured in detail, and the effects of flow discharges and sediment supplies on bed evolution and overbank floods in the meandering channel were discussed. The calculation results of Lan Yunchang formula, Zhang Hongwu formula and Mao Peiyu formula for the water surface superelevation of the curved channel were compared, Lanyunchang formula could better predict the water surface elevation of the curved reaches with stable bedform under different flow and sediment discharges. The sediment supply had little effect on bed evolution in bend with inbank flows, for that most of the sediment supply was deposited in the upstream straight reach or transported to the downstream reach and only a small amount of recharge sediment was deposited in the bend reach. More upstream sediment was transported to the curved reach and deposited by overbank flows. With the increase of sediment supply, the sediment deposition in the curved main channel increased, which however had little effect on the water level and flow velocity in bend. When the flood discharge increased, the water level in the bend and the flow velocity in the concave bank increased significantly. The results indicated that the flood discharge was the key factor affecting the water level in the bend and the flow velocity in floodplain, and the upstream sediment supply was the secondary influencing factor. The flow velocity in floodplain in the 30-60° of 90° bend reach was higher than that in the main channel and upstream reach. The maximum flow velocity in the floodplain occurred in section 50°, which could reach 1.3 times of the upstream flow velocity. The above results are of great significance for flood control and disaster reduction of meandering rivers