Abstract:To understand the interaction of titanium dioxide nanoparticles(nTiO₂)and copper(Cu²⁺)and their biological effects, using Daphnia magna as a test animal, we studied the joint toxicity effects of nTiO₂ and Cu²⁺ on Daphnia magna and its internal antioxidant system. The results show that the respective values of 72 h-LC₅₀ and 72 h-EC₅₀ of Daphnia magna exposed to nTiO₂ were 22. 742 and 16. 739 mg/L and the values of Daphnia magna exposed Cu²⁺ were 11. 635 and 10. 129 μg/L. When nTiO₂and Cu²⁺ coexisted, the respective values of 72 h-LC₅₀ and 72 h-EC₅₀ of Daphnia magna exposed to nTiO₂ were 12. 721 and 8. 827 mg/L and the values of Daphnia magna exposed to Cu²⁺ were 12. 405 and 10. 559 μg/L. When Daphnia magna were exposed to both nTiO₂ and Cu²⁺, the activity of superoxide dismutase(SOD)and reduced glutathione(GSH)was first induced and then inhibited, and the malondialdehyde(MDA)content produced during lipid peroxidation increased gradually. This indicated that the antioxidant system had been attacked by reactive oxygen species(ROS), and it could not provide protection for Daphnia magna, which was the key reason for the joint toxicity of Cu²⁺ and nTiO₂.

Abstract:The role of biofilm covering on sediments in the adsorption of three endocrine-disrupting chemicals(EDCs), 17α-ethinyl estradiol(EE2), bisphenol A(BPA), and 4-nonylphenols(4-NP), was investigated. The results indicated that the organic carbon(OC)-normalized distribution coefficients(k_oc)of BPA, EE2, and 4-NP ranged from 10^{1. 78} to 10^{3. 02} L/kg. After the oxidation of sediments by H₂O₂, the k_oc of EE2 was higher(10^{2. 32} L/kg)than before the oxidation(10^{2. 19} L/kg). A two-stage adsorption(fast adsorption and slow adsorption)kinetic model was established(r²>0. 95). The simulation results showed that the fast adsorption section played the main role in the adsorption process, while the slow adsorption section determined the extent of the reaction. The biofilm on the surface of sediments may act as a barrier in mass transfer from water to sediment and seldom improve the adsorption capacity of sediments.

Abstract:Based on the risk categories and self-control capabilities of risks in water source areas, a comprehensive and quantitative risk assessment index system was established using the Zhengrunzhou water source area in Zhenjiang City as an example, and an evaluation method is put forward. The calculation method of the eigenvalue of each index and the risk level grading standards are presented. In calculating eigenvalues, a cumulative risk index was used to represent the impact of the amount and agglomeration intensity of risk sources on the risks of the water source area, and the cumulative risk index was determined using the spatial autocorrelation analysis method. The results show that the risk level of the Zhengrunzhou water source area is at a the medium grade, the main threats influencing the security of this area are the docks located on the shoreline within 20 km upstream of this area, and the directly discharged pollutants from enterprises and sewage plants have less influence on the water source area.

Abstract:This paper presents a review of literature related to project failures, variations of groundwater level, seepage characteristics of soil bodies, and mechanisms of seepage-induced consolidation during the reinforcement process under vacuum negative pressures. Although the seepage-induced vacuum consolidation method has been widely applied, theoretical study of the method lags far behind its practical application and still involves some disputes. Some key issues for future research regarding the method are presented, including new technology for measurement of groundwater levels under negative pressures, mechanisms of seepage-induced consolidation of soil, the effective transmission range of the vacuum degree, and the variation regularity of the zero-pressure surface.

Abstract:For the purpose of application of theoretical calculation to practical vacuum preloading projects and providing guidance in practical application, an equation for soft ground consolidation in the radial direction under vacuum preloading was established by assuming that the vacuum degree attenuated linearly, and formulas for the excess pore pressure and degree of consolidation were developed. Based on study of the effects of the permeability coefficient in smear zones, analytical solutions for the average pore pressure and degree of consolidation were deduced and verified with a constant permeability coefficient and linearly changing permeability coefficient, respectively. Results of analysis show that the smaller the vacuum degree attenuation coefficients, k₁ and k₂, the well resistance factor, n, and the radius ratio of the smear zone to drainage system, s, and the closer the ratio of the permeability coefficients of the undisturbed zone to the smear zone, α, to s, the better the effect of vacuum preloading. The analytical solutions considering the linear attenuation of the vacuum degree and Hansbos solutions were compared with field observations of the degree of consolidation of the foundation under vacuum preloading at the Jiaxing Port. Results show that the analytical solutions are more consistent with field observations, and the solutions considering the linear change of the permeability coefficient in smear zones correspond better with engineering practices.

Abstract:The location of vacuum sources with negative pressures was considered in analysis of the effects of dredger fill foundation reinforcement under vacuum preloading. Model tests were performed to simulate dredger fill foundation reinforcement using the vacuum preloading method, with vacuum sources located at the top and bottom. Over the course of foundation consolidation, the amounts of water drainage and settlement for different soil layers and the vacuum degree at different depths were monitored, and the transmission efficiency of the vacuum degree and consolidation settlement properties for soil layers with vacuum sources located at different depths were studied. Results show that the vacuum preloading method, with vacuum sources located at the bottom of the dredger fill foundation, can enhance the transmission efficiency of the vacuum degree, shorten the drainage path in deep soil layers, change the seepage direction in middle soil layers, and maintain a high vacuum degree in upper soil layers. Meanwhile, deep soil layers can be reinforced effectively, and the consolidation settlement tends to be more uniform. Moreover, this method can increase the effective reinforcement depth to a great extent and reduce the post-construction settlement to a certain degree.

Abstract:In order to investigate the effects of electroosmosis on chemical and mineral compositions of soil, a laboratory electroosmotic consolidation test was carried out using kaolin as an example. The soil samples and drainage water samples before and after the one-dimensional electroosmotic consolidation experiment were collected. The mineral and chemical composition of soil samples were measured using the X-ray diffraction and X-ray fluorescence spectrometry techniques, and the chemical composition of the water samples were measured with inductively coupled plasma mass spectrometry(ICP-MS). The variations of chemical composition in the soil and water samples and the migration phenomenon of different elements during the electroosmosis process were analyzed. The results show that, of the main mineral constituents of kaolin, the dickite content changed significantly, while the quartz, kaolinite, and nacrite contents changed little. The main chemical constituents in the soil samples, SiO₂ and Al₂O₃, did not show obvious change after electroosmosis. There were large changes in CaO, MgO, Na₂O, and K₂O, of which the variation of CaO was the most significant. The analysis of water samples shows that Na and K tended to flow into water in the form of ions, and Ca and Mg tended to generate hydroxide precipitation, which meant that the Ca and Mg ions could not be detected easily.

Abstract:Based on the Fourier and Fourier sequence transforms, and the transfer matrix method, the resonance of a periodically elastically supported continuous beam produced by a series of moving loads and its cancellation effects were investigated. By using the Fourier and Fourier sequence transforms, the dynamic response produced by single moving loads was represented by the integral of the response function over the representative span. The response function and eigenvalue equation of the periodically elastically supported continuous beam were obtained using the transfer matrices between the beam and its elastic supporting points. According to the superposition principle and the expression of the dynamic response of the beam under single moving loads, the dynamic response of the beam under a series of equidistant moving loads was obtained. Using the frequency domain dynamic response of the beam under single moving loads, the resonance and cancellation conditions of the periodically elastically supported continuous beam subject to a series of equidistant moving loads were established. Numerical results show that, when the loading velocity and distance satisfy the resonance condition, resonance will occur; when the condition for resonance cancellation is fulfilled, the effect of resonance cancellation will occur.

Abstract:In order to study the active earth pressure on retaining walls in response to soil arching effects, considering the effect of wall friction angles on the inclination of sliding planes, theoretical analysis was applied to minor principal stress arches. The horizontal width of soil arch differential elements at different depths was calculated, and the expression for the shape of minor principal stress arches was obtained. According to the arch shape obtained, a differential element method was developed, in which differential elements were divided along the axis of minor principal stress arches. Then, this method was used to compute the active earth pressure on retaining walls, and a theoretical formula was obtained. Comparison of the present results with experimental data and results from other theoretical methods shows that the results from the present theoretical formula agree with those of the model test.

Abstract:Compared with the calibration coefficient K of earth pressure cells in practical application in civil engineering, K values provided by manufacturers have certain errors. To solve this problem, calibration tests were performed on different kinds of earth pressure cells, and differences between K values of different kinds of earth pressure cells obtained from calibration tests under the same embedded conditions, as well as the reasons, were analyzed based on their operating principles. Three kinds of typical earth pressure cells(single-film vibrating wire, double-film vibrating wire, and resistance strain gauge earth pressure cells)were selected for calibration tests in sand soil. The test results were compared with the values provided by manufacturers, and a linearly fitting formula based on test results was used to calculate the calibration parameter of different kinds of earth pressure cells in sand soil. Test results show that the K values are 50% smaller than those provided by manufactures for vibrating wire earth pressure cells, however the K values are four times those provided by manufactures for resistance strain gauge earth pressure cells.

Abstract:A tensile fatigue experiment was conducted on Q235 reinforcing steels with different stress levels and fatigue cycles. The steels were soaked in a saturated Ca(OH)₂ solution, and the chloride threshold level(CTL)for corrosion of reinforcing steels was detected by combining the open-circuit potential with electrochemical impedance spectroscopy. The changes of microstructure caused by the tensile fatigue were observed with a scanning electron microscope(SEM). The results show that the CTL of steels degreased with the increase of the stress level and fatigue cycles. The grains of the steels became finer and the amounts of grain boundaries and phase boundaries increased after tensile fatigue. This change became more significant with the increase of the stress level and fatigue cycles. The refinement of grains and increase of the amount of grain boundaries will cause short-circuit diffusion and reduce the CTL of steels.

Abstract:By embedding settlement monitoring instruments in a typical section of a seawall road widening project in a sea area, the impact of the new embankment during its construction on the settlement of the old seawall was studied. Measured results indicate that the construction of the new embankment has caused significant settlement of the old seawall, with a large difference between the amounts of settlement at its left and right road shoulders, which leads to cracking. Simulation analysis using Plaxis finite element software shows that the horizontal displacements in opposite directions, with maximum values of 0. 5 m and 0. 8 m, occur under the old seawall and new embankment, respectively, and that the simulated results agree with the measured data. Thus, appropriate corrective measures should be taken in response to differential settlements during the design of the seawall road widening project.

Abstract:In order to predict the annual variation of the typhoon intensity, a prediction method based on the grey-mean generating function model is proposed. Selecting the maximum wind velocity as the index of typhoon intensity, the prediction models for typhoons arriving or not arriving at coasts are established using data from a Northwest Pacific Ocean typhoon published by the China Meteorological Administration. A five-year prediction was made, and a comparison was made between the predicted results and the observed ones. The results show that the grey-mean generating function model has high accuracy for the prediction of the typhoon intensity. The maximum absolute error of the predicted annual average value is 4. 4 m/s, lower than the average absolute error of forecast results regarding the intensity of 25 typhoons in 2012 obtained from the numerical model. The maximum absolute error of the predicted annual extreme value is 11. 1 m/s, lower than the absolute error of the predicted value obtained from the Shanghai typhoon model.

Abstract:Research progress on the tidal creek system is reviewed in terms of classification, morphological characteristics, and evolution processes of tidal creeks. It is suggested that the classification mode of tidal creeks proposed by Strahler based on the Hortons classification method is relatively reasonable. The total length of the tidal creek is positively correlated with the water catchment area, the tide range is positively correlated with the tidal creek density, and the influence of vegetation on the tidal creek density is inconclusive. Studies on the cross-sectional morphology of the tidal creek focus on the influence of the width-depth ratio, asymmetry, sediment, and vegetation on the cross-sectional morphology of the tidal creek. There are more qualitative results and fewer quantitative results regarding the dynamic mechanisms of tidal creek evolution. It is pointed out that, in future research, more attention should be paid to the complex flow structure in tidal creeks, the stability of side walls of tidal creeks, and the quantitative relationship between morphological characteristics of tidal creeks and their factors through physical model, numerical simulation, and remote sensing analysis techniques.