Abstract: Geomaterials are known to be non-associated materials. Granular soils therefore exhibit a variety of failure modes, with diffuse or localized kinematical patterns. In fact, the notion of failure itself can be confusing with regard to granular soils, because it is not associated with an obvious phenomenology. In this study, we built a proper framework, using the second-order work theory, to describe some failure modes in geomaterials based on energy conservation. The occurrence of failure is defined by an abrupt increase in kinetic energy. The increase in kinetic energy from an equilibrium state, under incremental loading, is shown to be equal to the difference between the external second-order work, involving the external loading parameters, and the internal second-order work, involving the constitutive properties of the material. When a stress limit state is reached, a certain stress component passes through a maximum value and then may decrease. Under such a condition, if a certain additional external loading is applied, the system fails, sharply increasing the strain rate. The internal stress is no longer able to balance the external stress, leading to a dynamic response of the specimen. As an illustration, the theoretical framework was applied to the well-known undrained triaxial test for loose soils. The influence of the loading control mode was clearly highlighted. It is shown that the plastic limit theory appears to be a particular case of this more general second-order work theory. When the plastic limit condition is met, the internal second-order work is nil. A class of incremental external loadings causes the kinetic energy to increase dramatically, leading to the sudden collapse of the specimen, as observed in laboratory.
Abstract: The water requirement pattern for tobacco (Yun 85) was identified based on analysis of data obtained from pot experiments in a canopy at the Xiuwen Irrigation Test Central Station in Guizhou Province, China. The results showed that the tobacco water requirement and the tobacco water requirement intensity throughout the growth period in pot experiments were significantly lower than those in field production. In pot experiments, the tobacco water requirement throughout the growth period ranged from 159.00 to 278.90 mm, with a reduction in the range of 241–441mm, as compared with that in field production. Also, the average water requirement intensity at the vigorous growing stage was 1.97 mm/d, and the water requirement and water requirement module were 33.80–72.60 mm and 16.39%–33.09%, respectively, at the group stage, almost equal to their values at the vigorous growing stage. The patterns of the tobacco water requirement and water requirement module in pot experiments were different from those in field production. In pot experiments, the tobacco water requirement and water requirement module ranked the highest at the mature stage, followed by those at the group/vigorous growing and rejuvenation stages, while the water requirement intensity ranked the highest at the vigorous growing stage, followed by those at the mature, group, and rejuvenation stages. The pattern of the water requirement intensity in pot experiments was consistent with that in field production. In addition, the response of the tobacco water requirement to water deficit was also analyzed. Serious water deficit at the vigorous growing stage and continuous water stress at the group, vigorous growing, and mature stages can greatly influence the tobacco water requirement. Water deficit led to reductions in the water requirement and water requirement intensity at each growth stage. The vigorous growing stage exhibited the highest sensitivity to water deficit. The lower limit of moderate soil water stress at the vigorous growing stage was 65% of the field capacity. Results of this study can help to establish a reasonable irrigation schedule for tobacco production in Guizhou Province, China.
Abstract: As demands on limited water resources intensify, concerns are being raised about water resources carrying capacity (WRCC), which is defined as the maximum sustainable socioeconomic scale that can be supported by available water resources and while maintaining defined environmental conditions. This paper proposes a distributed quantitative model for WRCC, based on the principles of optimization, and considering hydro-economic interaction, water supply, water quality, and socioeconomic development constraints. With the model, the WRCCs of 60 subregions in Henan Province were determined for different development periods. The results showed that the water resources carrying level of Henan Province was suitably loaded in 2010, but that the province would be mildly overloaded in 2030 with respect to the socioeconomic development planning goals. The restricting factors for WRCC included the available water resources, the increasing rate of GDP, the urbanization ratio, the irrigation water utilization coefficient, the industrial water recycling rate, and the wastewater reuse rate, of which the available water resources was the most crucial factor. Because these factors varied temporally and spatially, the trends in predicted WRCC were inconsistent across different subregions and periods.
Abstract: Field experiments and laboratory analysis were carried out to determine the effects of controlled drainage (CTD) and conventional drainage (CVD) technologies on drainage volume, concentrations of , , and total phosphorus (TP), nitrogen and phosphorus losses, rice yield, and water utilization efficiency. Results show that CTD technology can effectively reduce drainage times and volume; , , and TP concentrations, from the first to the fourth day after four rainstorms decreased by 28.7% to 46.7%, 37.5% to 47.5%, and 22.7 to 31.2%, respectively, with CTD. These are significantly higher rates of decrease than those observed with CVD. CTD can significantly reduce nitrogen and phosphorus losses in field drainage, compared with CVD; the reduction rates observed in this study were, respectively, 66.72%, 55.56%, and 42.81% for , , and TP. Furthermore, in the CTD mode, the rice yield was cut slightly. In the CVD mode, the water production efficiencies in unit irrigation water quantity, unit field water consumption, and unit evapotranspiration were, respectively, 0.85, 0.48, and 1.22 kg/m3, while in the CTD mode they were 2.91, 0.84, and 1.61 kg/m3—in other words, 3.42, 1.75, and 1.32 times those of CVD. Furthermore, the results of analysis of variance (ANOVA) show that the indicators in both the CVD and CTD modes, including the concentrations of , , and TP, the losses of , , and TP, irrigation water quantity, and water consumption showed extremely significant differences between the modes, but the rice yield showed no significant difference.
Abstract: In order to study the relationship between nutrient pollutants and suspended sediment (SS) in the upper reaches of the Yangtze River and two tributaries, water samples were collected from September 1, 2010 to September 30, 2011 at the Zhutuo, Cuntang, Beibei, Wulong, Qingxichang, Wanxian, and Fengjie cross-sections. In the laboratory, the SS concentration and the concentration of SS whose particle size was smaller than 0.02 mm were measured. Phosphorus (P), nitrogen (N), and permanganate index (CODMn) concentrations in the natural water sample, the settled water sample, and two types of filtered water samples obtained through filter membranes with pore sizes of 0.02 mm and 0.45 µm were monitored synchronously. The results show that there are strong relationships between the P and CODMn concentrations and the SS concentration. P mainly exists in particulate form, while N mainly exists in dissolved form. SS whose particle size is smaller than 0.02 mm accounts for a high proportion of sediment in the Yangtze River and has a strong effect on water quality. At the seven cross-sections, the amounts of P, N, and CODMn in particulate form in the wet season are higher than in the dry season and the adsorption amounts of P, N, and CODMn per unit mass of sediment are higher in the dry season than in the wet season.
Abstract: To evaluate the effect of benthic algae on soluble reactive phosphorus (SRP) release from sediments in shallow lakes, experiments on SRP release with and without benthic algae in sediment cores and an experiment on SRP uptake by benthic algae were conducted using the radioisotope (32P) tracing method. The dissolved oxygen (DO) concentration in sediment cores was also investigated. The results show that benthic algae effectively reduce the release of SRP from sediments to overlying water. The uptake of SRP by benthic algae, which is the direct way in which benthic algae affect the SRP release from sediments, is low in filtered water and increases with the SRP concentration. However, in the experiment, the increased uptake rate lasted for a short time (in one hour), and after that it returned to a low rate. Benthic algae make the DO concentration and the oxic layer thickness increased, which can indirectly reduce the SRP release from sediments. These findings indicate that benthic algae can reduce the SRP release from sediments in both direct and indirect ways. It seems that the indirect way also plays an important role in reducing the SRP release from sediments.
Abstract: The distribution of persistent organic pollutants (POPs) in ice and the release of POPs from ice during ice melting have an important influence on the eco-environment and water quality of a river. Through laboratory simulation experiments, the distribution and release of 2,4,5-trichlorobiphenyl (PCB29) in ice and the partition coefficients of PCB29 in ice water at different temperatures, concentrations, and pH levels were studied. The results showed that, at different temperatures and concentrations, the concentration of PCB29 in ice increased progressively with depth. The modes of release of different concentrations of PCB29 from ice were obtained. A large amount of PCB29 was released rapidly in the first melting period, and then the remaining PCB29 was released uniformly. The pH value dominated both the distribution and late release of PCB29 in ice. In ice water, at different temperatures, concentrations, and pH levels, the majority of PCB29 entered the water, and a lesser amount remained in the ice. Finally, laboratory experiment results were verified with field investigations. A theoretical framework is provided by this research of the behavior of POPs in ice under different environmental conditions, but a more quantitative understanding of the behavior of POPs in ice will need to be developed through further laboratory studies combined with field investigations.
Abstract: Degradation of bisphenol A (BPA) in aqueous solution using sulfate radicals was investigated using the Fe(Ⅱ)-activated peroxydisulfate (PDS) process, electrochemical process, electrochemical process with 2.5 mmol/L Na2S2O8 without Fe(Ⅱ), and electrochemical assistant Fe(Ⅱ)-activated PDS process. It was found that the electrochemical assistant Fe(Ⅱ)-activated PDS process performed best in the degradation of BPA. The variables considered to influence the degradation efficiency of BPA were the initial concentration of Fe2+, the initial concentration of Na2S2O8, and the current density. More than 97% of the BPA removals were achieved within 120 min under the optimum operational condition. The degradation of BPA was accompanied by the formation of phenol, hydroquinone, and small-molecule compounds such as succinic acid. The electron transfer was the principal step in the oxidation of BPA.
Abstract: The receptivity of plane Poiseuille flow to local single-period micro-vibration disturbances with different phases at the top and bottom walls was investigated through direct numerical simulation of three-dimensional incompressible Navier-Stokes equations. Results show that the disturbance presents a symmetrical distribution in the spanwise direction when the micro-vibration on the wall ends, and the initial disturbance velocities and spatial distribution of the disturbance structure are different at the top and bottom walls. The disturbance’s velocity, amplitude, and high- and low-speed streaks increase with time, and the amplitude of streamwise disturbance velocity is larger than those of spanwise and vertical disturbance velocities. However, no significant Tollmien-Schlichting wave was found in the flow field. The number of disturbance vortex cores gradually increases with the disturbance area. High-speed disturbance fluid concentrates near the wall and its normal velocity largely points to the wall, while low-speed disturbance fluid largely deviates from the wall. Furthermore, the streamwise velocity profiles near the top and bottom walls both become plump because of the existence of the disturbances, and the streamwise velocity profiles show a trend of evolving into turbulent velocity profiles. The shear stress near the wall increases significantly. The local micro-vibration disturbance on the wall in plane Poiseuille flow can induce the development of a structure similar to turbulent spots.
Abstract: Both cracks in clay liner and the complex composition of landfill leachate might have effects on the hydraulic conductivity of a compacted clay liner. In this study, the hydraulic conductivities of natural clay and bentonite-modified clay with and without desiccation cracks were measured, respectively, using three types of liquids as permeating liquid: 2 500 mg/L acetic acid solution, 0.5 mol/L CaCl2 solution, and tap water. When tap water was adopted as the permeating liquid, desiccation cracks resulted in increases in the average value of hydraulic conductivity: a 25-fold increase for the natural clay and a 5.7-fold increase for the bentonite-modified clay. It was also found out that the strong self-healing capability of bentonite helped to reduce the adverse impact of cracks on hydraulic performance. In contrast to tap water, simulated leachates (acetic acid and CaCl2 solutions) show no adverse effect on the hydraulic conductivities of natural and bentonite-modified clays. It is concluded that desiccation cracks and bentonite have more significant effects on hydraulic performance than simulated leachates.
Abstract: In conjunction with association rules for data mining, the connections between testing indices and strong and weak association rules were determined, and new derivative rules were obtained by further reasoning. Association rules were used to analyze correlation and check consistency between indices. This study shows that the judgment obtained by weak association rules or non-association rules is more accurate and more credible than that obtained by strong association rules. When the testing grades of two indices in the weak association rules are inconsistent, the testing grades of indices are more likely to be erroneous, and the mistakes are often caused by human factors. Clustering data mining technology was used to analyze the reliability of a diagnosis, or to perform health diagnosis directly. Analysis showed that the clustering results are related to the indices selected, and that if the indices selected are more significant, the characteristics of clustering results are also more significant, and the analysis or diagnosis is more credible. The indices and diagnosis analysis function produced by this study provide a necessary theoretical foundation and new ideas for the development of hydraulic metal structure health diagnosis technology.
Abstract: Slope excavation is one of the most crucial steps in the construction of a hydraulic project. Excavation project quality assessment and excavated volume calculation are critical in construction management. The positioning of excavation projects using traditional instruments is inefficient and may cause error. To improve the efficiency and precision of calculation and assessment, three-dimensional laser scanning technology was used for slope excavation quality assessment. An efficient data acquisition, processing, and management workflow was presented in this study. Based on the quality control indices, including the average gradient, slope toe elevation, and overbreak and underbreak, cross-sectional quality assessment and holistic quality assessment methods were proposed to assess the slope excavation quality with laser-scanned data. An algorithm was also presented to calculate the excavated volume with laser-scanned data. A field application and a laboratory experiment were carried out to verify the feasibility of these methods for excavation quality assessment and excavated volume calculation. The results show that the quality assessment indices can be obtained rapidly and accurately with design parameters and scanned data, and the results of holistic quality assessment are consistent with those of cross-sectional quality assessment. In addition, the time consumption in excavation project quality assessment with the laser scanning technology can be reduced by 70%−90%, as compared with the traditional method. The excavated volume calculated with the scanned data only slightly differs from measured data, demonstrating the applicability of the excavated volume calculation method presented in this study.
