Abstract:Using an ensemble forecast product from the European Centre for Medium-Range Weather Forecasts(ECMWF)with a ten-day lead time, forecast data in the Jiangjiaji Catchment of the Huaihe River Basin were extracted and disaggregated to drive a flood forecast model to simulate a flood event in August 2008. In order to study the effect of the flood forecast model driven by the ECMWF ensemble data, the simulated results from this model and the results from a model driven simply by the field precipitation data were compared and analyzed. The results show that the flood forecasting accuracy was improved using the ECMWF ensemble forecasts, and the lead time was extended 48 h. The forecasted discharge hydrographs can provide the uncertainty range of forecast discharges, which provides a scientific decision basis for flood control and disaster mitigation.

Abstract:Using the information entropy theory to characterize the change trend of water consumption structure, using the principal component analysis method to determine the principal components of each influencing factor, and using the grey incidence theory to analyze the correlation coefficient between the principal components and the water consumption structure, a study on the change and driving forces of the water consumption structure in Nanjing City was carried out. The results show that the information entropy increased from 1. 532 nat to 1. 791 nat and the balance degree increased from 0. 787 to 0. 861 from 2000 to 2014, indicating that the water consumption structure is becoming more stable. Factors such as economic structure, water-saving technology, population evolution, and water demand are main driving forces influencing the water consumption structure in Nanjing. Measures for total quantity control of water consumed are put forward to guarantee the reasonable utilization of water resources.

Abstract:The effects of chironomid larvae bioturbation on the concentrations of dissolved oxygen(DO), labile phosphorus(Labile P), and labile iron(Labile Fe), as well as the diffusion flux of Labile P across the sediment-water interface in eutrophic lakes were examined using high-resolution diffusive gradients in thin films(DGT)and microelectrode techniques. The results show that chironomid larvae bioturbation increases the depth of penetration of DO in the sediments, decreases the concentrations of Labile P and Labile Fe, and inhibits the release of Labile P from sediments to the overlying water. Because Labile P is significantly correlated with Labile Fe(R=0. 672 and P<0. 001 for the control group, and R=0. 810 and P< 0. 001 for the chironomid group), it can be inferred that the change of Labile P is controlled by DO and Labile Fe according to the following process: Labile Fe is oxidized to produce the ferric hydration Fe(OOH), which can adsorb Labile P, and this leads to the decrease of the Labile Fe and Labile P concentrations.

Abstract:A large-scale uniaxial compression test was conducted for two types of graded sand-grained materials from the overburden of a dam. The horizontal stress and vertical stress of sand-grained materials were measured using soil pressure boxes with parameters obtained from a calibration method, and then the at-rest lateral pressure coefficient(K₀)was calculated. By studying the applicability of the hydraulic and sand calibration methods, the reliability of the experimental results of K₀ was analyzed. The results show that the sand calibration method is a reliable calibration method for coarse-grained soil. When the vertical stress is large enough, the experimental error of K₀ can be ignored, and the value of K₀ is close to the actual value. The triaxial CD test was conducted for two types of graded sand-grained materials to measure the effective angle of internal friction, and then K₀ was calculated through the relevant empirical formula and compared with the test value to obtain an empirical formula that is suitable for coarse-grained soil. The results show that the relationship expression between the at-rest lateral pressure coefficient and the effective angle of internal friction, which was proposed by Federico and was based on the concept of a mobilized effective angle of internal friction proposed by Terzaghi, is appropriate for coarse-grained soil.

Abstract:In order to study mechanical properties of a carbon fiber grid structure, a type of multilevel grid-stiffened plate was designed, and its mechanical properties were analyzed using theoretical analysis and the finite element method. The grid structure was equivalent to a homogeneous continuous structure. Based on this, an equivalent method for calculation of the grid structure was derived, and the equivalent elastic modulus and the equivalent flexural stiffness of a multilevel grid-stiffened structure were calculated. The results show that the multilevel triangular grid-stiffened structure can improve the anti-buckling ability of ultra-light materials. When the cross-sectional area is the same, the flexural stiffness of the triangular grid is 10% higher than that of the solid structure, indicating that the buckling load of the multilevel grid is higher than that of an ordinary grid.

Abstract:To investigate the nonlinear seismic performance of partially concrete-filled steel bridge piers with thin-wall ribbed box sections during frequent and rare earthquakes, three test specimens, one not filled with concrete, one filled with concrete up to 20% of the height of a bridge pier, and one filled with concrete up to 40% of the height of a bridge pier, were produced and used in the pseudo-dynamic tests using the MTS servo loading system. The JRT-NS seismic wave, the same as that in the Hanshin Earthquake in Japan, was used in the tests, from which the displacement time history curve, load-displacement hysteretic curve, and cumulative energy dissipation time history curve were obtained. The experimental results show the following: all three specimens were in an elastic state under frequent earthquakes; under rare earthquakes, specimens filled with concrete at the base were in an elastoplastic state and showed good seismic performance, without the occurrence of significant destruction; with the increase of the filling ratio of concrete in the plastic-hinge region at the base, the constraint effect of concrete inside the thin-wall steel tube on the local buckling development of the tube gradually increased; and some seismic performance indexes, including the structural stiffness, horizontal bearing capacity, maximum displacement, residual displacement, and energy dissipation capacity of steel piers, were significantly improved.

Abstract:The process of CO₂ sequestration in deep saline aquifers involves fluid migration and pressure transmission. Based on the field data of CO₂ sequestration in saline aquifers in the Frio region of the United States, a two-dimensional multi-lithofacies model was established. The variation characteristics of the rock permeability during CO₂ injection, the variation characteristics of the rock pressure, and the evolution of the CO₂ plume were simulated and analyzed. The results show that the formation of a funnel-shaped diffusion halo was observed when supercritical CO₂ displaced the salt water, and salt precipitation due to evapotranspiration mainly occurred in the single gas phase region near the well. As salt precipitation increased, the permeability near the well decreased and the pressure increased. If the permeability of the cap rock is improved, the pressure in the reservoir will decrease, but the possibility of leakage will increase.

Abstract:Based on research achievements of scholars from China and abroad, fully mechanical model test equipment was independently developed for pile foundations. The equipment is based on a multifunctional loading system and can be used for model tests of compression, uplift, and horizontal loadings on pile foundations. The pile foundation model test system consists of a model tank, a loading system, a measurement system, and other components. The model tank is connected mechanically and can be set to different lengths, widths, and heights according to model test requirements. The fully automatic loading system can meet the requirements of pressure stability for each level of loading. The system is controlled and collected automatically by computer, leading to the high accuracy and reliability of the model test. In addition, the system has the function of loading simultaneously in two or three directions and can simulate the bearing performance of different piles under different conditions. Finally, model tests of compression, uplift, and horizontal loadings on Y-shaped piles were carried out, and the feasibility and reliability of the test equipment and loading system are verified.

Abstract:A case study of the Wusong Jetty during long-term service is presented. Based on the results of field ultrasonic testing, laboratory strength testing, ground-penetrating radar testing, and underwater detection and measurement by divers, the degrees of degradation of sensitivity factors, including the concrete structure for the protective face, the internal rockfill structure, and the variation of the slope and evolution of erosion/deposition on both sides of the jetty, were evaluated. The effect of degradation of the four sensitivity factors on the deformation and stability of the jetty slope was investigated using the finite element numerical simulation method. The results show that the elastic moduli of the concrete structure for the protective face and internal rockfill structure exhibit negative exponential relationships with the maximum horizontal displacement of the jetty; the safety factor of the jetty decreases linearly with the increase of the slope, approximatively; and the maximum displacement of the jetty increases linearly with the increase of elevation induced by deposition on the left side and erosion/deposition on the right side of the jetty. The phenomena should be given more attention in design of schemes for reinforcement and maintenance in practice.

Abstract:The influence of the compaction period, cement content, and curing period on the strength of solidified soil was studied using an unconfined compressive strength test. The results show that a compaction period that is two long makes the solidified soil more easily compacted, but causes a loss of the cementing strength. According to mechanism analysis, it is found that the strength of the remolded solidified soil is related to the dry density of the sample, and a linear equation is fitted to test data. Based on the test results, it is recommended that solidified soil be used as soon as possible after mixing so as to make full use of cementation of cement. Otherwise, it is necessary to improve the degree of compaction in order to achieve the design requirements.

Abstract:In order to solve the problem of large errors in effect quantity prediction caused by small samples in dam safety monitoring, a new approach for prediction of effect quantity, through increasing sample information, was established based on discrete and regression analysis of two-dimensional normal information diffusion. The effect quantity of dam safety monitoring was analyzed and predicted using the basic theory of fuzzy reasoning and information concentration, as well as the grey correlation degree method. The comprehensive effectiveness index was used to evaluate the effect of the information diffusion approach. The results show that the information diffusion approach avoids the difficulties in effect quantity prediction using small samples under the influence of some uncertain factors, and improves the fitting and forecast accuracies.

Abstract:In order to study the dynamic response of riverbed morphology of alluvial rivers to water and sediment conditions, the adjustment process of riverbed cross-sectional morphology at the Shashi segment of the upper Jingjiang Reach was investigated based on the delayed response principle of riverbed evolution. The multi-time scale rules of water and sediment series of the Shashi segment during the period from 1956 to 2011 were analyzed using the Morlet wavelet method, and a power-exponent relationship between the discharge, sediment load, and cross-sectional area was obtained with the moving average method. The results show that the adjustment of riverbed cross-sectional morphology of the Shashi segment is delayed with the change of water and sediment conditions and it is influenced by previous and present water and sediment conditions. The model for calculation of the cross-sectional area for water and sediment series in different time periods is established. The simulated results indicate that the simulated cross-sectional areas and actual values are in good agreement and their correlation coefficient R² is 0. 85, indicating that the established model can simulate the adjustment regularity of riverbed cross-sectional morphology of the Shashi segment of upper Jingjiang Reach.

Abstract:Using the latest ERA-Interim sea surface wind field and wave field data from every 6 h from 1979 to 2014 provided by the European Centre for Medium-Range Weather Forecasts(ECMWF), the wave characteristics in the North Pacific Ocean for the last 36 years were analyzed. The results show that the first mode decomposed from the empirical orthogonal function(EOF)of significant wave height(H_s)exhibits in-phase change rules and is teleconnected with the Pacific Decadal Oscillation(PDO)and El Niñ o-Southern Oscillation(ENSO); the second mode shows that H_s exhibits a significant increasing trend in the western region of the North Pacific Ocean, and a gradually decreasing trend in the eastern region of the North Pacific Ocean; and the third mode mainly exhibits inverse double-eddy-type distributions at high and low latitudes in the westerlies, with 45°N as a boundary. The maximum extremes of H_s and wind speed for different return periods appear in the westerlies; for a relatively long return period, wind speed shows a significant increase in the area to the south of Japanese islands. The area with increased extremes extends to the East China Sea or even the east coast of Philippine islands.

Abstract:Quantitative analysis of the error of the chart datum under the variations of mean sea level and harmonic constants can improve the accuracy of sea charts. Year-to-year harmonic analyses were carried out using multiyear monitoring data from the Zhapu, Dinghai, and Jiantiao stations in Zhejiang Province. The mean annual sea level of the three stations shows an increasing tendency with fluctuation, and the maximum interannual errors are 21 cm, 16 cm, and 16 cm. The interannual variations of the amplitudes of the main tidal constituents are not all the same: the relative change of annual constituents is larger than that of semidiurnal constituents, which in turn is larger than that of diurnal constituents. The maximum errors of the amplitudes of the Sa, M2, S2, K1, and O1 components are 13 cm, 20 cm, 10 cm, 3 cm, and 3 cm, respectively. As a result of the instability of the mean sea level and harmonic constants, the maximum errors of the chart datum of the Zhapu, Dinghai, and Jiantiao stations are 33 cm, 26 cm, and 31 cm, respectively, and even if Vladimir J Kis thirteen subtidal algorithm is used, the maximum errors can reach 28 cm, 22 cm, and 28 cm. In contrast, the cumulative frequency of shoals using the theoretical depth datum is below 1%, indicating wide applicability.