Abstract:Building density and arrangement are important factors of the runoff process in urban resident area. Based on the two-dimensional shallow water equations and the building-hole method which was used to simulate the buildings, a rainfall run off model of urban community was established. Related artificial rainfall experimental results were used to validate the model parameters, and then the influences of building density and two arrangement types of inline layout and staggered layout in runoff process were studied. The results show that the time of concentration increases with the increasing building density, they satisfy the exporential function relation. For the same building density, the time of concentration in staggered layout is larger than that in inline layout. The difference between these two layouts is increasing as the building density increases. At the cross-sections where building exists, average water depth and average flow velocity are greater than non-building situation, and they increase with the building density. At the non-building cross-sections, the average depth is similar to the situation of non-building but the average velocity is lower and it decreases with the increasing building density. The resistance coefficient increases with the building density. When the building density is less than 16%, the resistance coefficient increases slowly, but it increases significantly when the building density surpasses 16%.

Abstract:To determine a reasonable bivariate design flood synthesis, three typical bivariate return period standards including C-measure return period, joint return period, and co-occurrence return period were selected for the frequency analysis of flood peak based on Copula function. The maximum likelihood method, conditional most likely combination, and bivariate equivalent frequency combination were chosen as the representative calculation methods. The optimum design flood synthesis was then obtained from the results calculated by the different methods. The calculation method was applied to the Xin’an River Basin. The result shows that C-measure return period can be a standard in bivariate frequency analysis as it defines rational dangerous regions. It can also avoid the potential safety hazard of co-occurrence return period and is more economic than joint return period.

Abstract:To intensively study and predict the lateral evolution of alluvial rivers, the theories of riverbank erosion and stability are used to discuss the patterns and the rates of riverbank collapse-retreat in this paper. Based on the mechanism of the riverbank collapse-retreat, three types of analysis models are proposed, which are the sinking-slipping failure, the sinking-toppling failure and the falling failure. Combined with the lateral erosion of river banks, the longitudinal scour of river bed and the critical condition of bank failure, the formula of bank erosion rates is derived. The hydrological data and soil properties of the Yellow River and the Yangtze River were used to validate the proposed formula. The results show that the estimated retreat distance and erosion rates are in consistent with the actual erosion rates of the Yellow River and the Yangtze River, indicating that the proposed collapse-retreat patterns and the formula of bank erosion rates are reasonable.

Abstract:The instability principles of density current are less studied at present, but they are significant to the life-span extension and the optimal operation of reservoirs. Mike3 was used to construct the three-dimensional numerical model for density current, which includes a hydrodynamic model, a turbulence model and the sediment transport diffusion equation. The model was validated by a flume experiment and the results show that the modeled sediment concentration agrees well with the measured value. Based on the model, the instability principles of turbidity current under the condition of rapidly varying topography is studied by using the Zipingpu Reservoir as an example. The influence of the bottom obstacle and the abrupt widening of the cross section on density current were analyzed and the discriminant conditions for the instability of density current are obtained for the two situations respectively. For the situation of bottom obstacle, the discriminant conditions are(1)the velocity of the density current decreases, (2)the sediment concentration decreases, and(3)the thickness of the front and the density current decreases. For the situation of abrupt widening at the cross section, they are(1)the velocity of the density current decreases, (2)the vertical profiles of sediment concentration change from parabolic distribution to logarithmic distribution, and(3)the thickness of the density current decreases.

Abstract:Self-made cement mortar was used as the rock-like materials to test the law of rock destruction under the coupling effect of water pressure and uniaxial axial compression. Under the premise of steady hydrostatic loading speed and axial pressure, cube specimens of different material strengths and sizes with prefabricated cracks in the center were made to perform hydraulic fracture tests by a self-developed hydraulic pressure and axial compression device. The results show that the axial compression loading direction has some influence on the crack initiation angles, and the rising of the internal water pressure is positively correlated with the strength of the specimen at a steady hydrostatic loading rate. The axial compression loading direction, whether parallel or vertical to the prefabricated cracks, can accelerate the rising of internal water pressure. The critical internal water pressure of hydraulic fracture is positively correlated with the strength of the specimen. The axial compression loading direction has a greater effect on the hydraulic fracture of a specimen with a single crack. When the axial compression direction is perpendicular to the direction of the prefabricated fracture, the crack initiation is inhibited. On the contrary, when the axial compression direction is parallel to the prefabricated fracture direction, the crack cracking is promoted.

Abstract:To ensure a stable standard of antimony concentration in the drinking water source in Yangcheng Lake area, the water environmental capacity of antimony was calculated on the basis of the monitoring data of water environment status and the survey of pollution sources. The total quantity control scheme of antimony is also proposed. The results show that the emission rate of antimony in the study area is 12.38kg/d, of which 9.38kg/d should be reduced with a reduction rate of 75.8% to achieve the standard limit of 0.005mg/L in the specific project standards for centralized drinking water sources. The limiting value of the emission concentration of antimony is 20μg/L in the waste water of textile, printing and dyeing enterprises and in the tail water of centralized sewage treatment plants.

Abstract:Based on the series-parallel spring stochastic damage model, the cohesive laws of concrete were obtained by the method of energy dissipation equivalence between the damage model and the fracture model. The failure strain of the micro-springs in the series-parallel spring model was assumed to be Weibull distribution and lognormal distribution, based on which the effect of different probability density functions on the cohesive laws was studied. The cohesive laws obtained by the present method were compared with those using the traditional displacement equivalence method. The obtained cohesive laws were also used to simulate the full crack propagation process of three-point notched concrete beams. The results show that the cohesive laws can be affected by the probability density functions and the cohesive laws based on the series-parallel spring stochastic damage model are not affected by the layer number of the model, avoiding the sensitivity problem of spring layers.

Abstract:To explore the hydrodynamic environment and sediment scouring and silting around the Yangtze estuary before and after the construction of the Qingcaosha Reservoir Project, a depth-averaged 2D tidal current and suspended sediment numerical model was established to simulate erosion and deposition. Combined with a modified empirical formula proposed by Wang Yigang, the numerical model can simulate the intensity of erosion and deposition simultaneously. The calculated results show that, after the construction of the reservoir, the diversion ratio and flow velocity in the north channel of the Changing Island decrease but increase in the south channel. The south channel of the reservoir shows a scouring state, while deposition dominates in the north channel. The variation in the south channel is less than that in the north channel, indicating that the construction of the reservoir project has a greater impact on the underwater topography in the north channel. The calculated results by the modified Wang Yigang’s formula are in good agreement with the measured topography and the numerical results after the project construction.

Abstract:Taken the Bahe river basin as the research object, the wavelet analysis method and the cumulative anomaly analysis were employed to analyze the variation trends of the sediment discharge and precipitation. It is revealed that the year 1988 and 2002 are two mutational points for the sediment discharge variation. The comparative method of the slope changing ratio of cumulative quantity was adopted to analyze the contributions of climate change and human activity to sediment discharge in different time periods. The results were obtained by taking 1960-1987 as the baseline period without considering the influence of evapotranspiration. It shows that the contribution rates of precipitation and human activities to the decreased sediment discharge were 12.22% and 87.78% from 1988 to 2001, and changed to be 6. 56% and 93. 44% from 2002 to 2012, respectively. The present study reveals the changing trend of sediment discharge of the Bahe river basin during 1960-2012 and the contribution rates of the main influencing factors, which is of great importance to the water loss and soil erosion control in the future.

Abstract:To discuss the real-time risk assessment methods for earth and rockfill dams, the point estimation method is adopted for the real-time dam-break probability analysis. The dam-break losses were analyzed based on BREACH and HEC-RAS. According to previous research, new risk evaluation criteria and corresponding risk early warning standards are proposed. A new synthetical early warning model is established combined with the current risk early warning standards for emergency events. The verification example shows that the real-time analysis method of earth and rockfill dam break probability based on point estimation method can meet the requirements of both computational accuracy and efficiency. The synthetical early warning model can effectively improve the early warning capability while reduce the loss caused by excessive early warning to a certain extent. It can provide theoretical basis and technical support for the risk management of earth and rockfill dams.

Abstract:To further understand the uplift deformation phenomenon that occurs at the left bank slope near the dam of Xiangjiaba Hydropower Station, hydro-mechanical coupling numerical tests were used to study the mechanism of rock mass expansion and deformation. Based on the hydro-mechanical coupling analysis, the uplift deformation process was simulated. The spatial distribution of the deformation was obtained and the control effect of the pressure relief holes on the uplift deformation was evaluated. The results indicate that the volume expansion strain of the rock mass increases with the permeability coefficient and decreases with the increase of deformation modulus. The initial stress has little effect on uplift deformation. Variation of the seepage field is the direct cause of uplift deformation and the uplift deformation is also the result of the interaction between seepage field and stress field. It is reasonable to use hydro-mechanical coupling theory to reveal the uplift deformation mechanism. Deep drainage holes for pressure relieving are effective for the controlling of the uplift deformation.

Abstract:To solve the problem of the ultimate bearing capacity in design and the difficulty in high strain test for nontraditional PHC-steel compound(PSC)piles, high strain test and vertical static load test were carried out. Three PSCs made of PHC and steel piles were designed with different length ratios. Pile-sinking was performed using the hammering method, and the vertical bearing capacity of the PSC was obtained by in situ high strain test and vertical static load test. Then, a modification for the high strain measured curve fitting method was proposed by theoretical analysis. The results show that the vertical bearing capacity of the PSCs measured by the high strain measured curve fitting method is higher than that from the static load tests while the results computed by the proposed modification method were in consistent with the static load tests. Therefore, the modification method can be applied to the measurement of the vertical bearing capacity of the PSCs.

Abstract:In order to reflect the variation characteristics of the vertical displacement of foundation under dynamic compaction load, the formula for the peak value of the equivalent contact quasi-static force is derived based on the principle of work and power. The numerical model of dynamic compaction is established by the finite element software ANSYS/LS-DYNA, and the dynamic compaction load is simplified to triangular impact load. The settlement calculation method is verified by an actual project of which the soft soil foundation was filled by dynamic compaction in Nantong. The calculation results show that the ratio of the vertical volume variation to the total volume change of the foundation calculated by the proposed method is close to the measured value, and the settlement calculated by the proportion of volume variation representing the energy distribution coefficient agrees well with the measured value. Therefore, the calculation method of settlement after tamping is applicable to dredger fill soft soil foundation.

Abstract:From the viewpoint of rock mass structure control, the research progress of dynamic stability and damage mechanisms for rock slopes of massive structures, layered structures, fragmented structures, and discrete structures in recent years is reviewed in terms of theoretical analysis, numerical simulation and experimental research. The failure modes of rock mass slopes with different structures under earthquake action are summarized systematically. Aiming at the shortcomings of the current research on the failure mechanism and stability of rock slopes under earthquake load, it is pointed out that the influence of spatial variation of earthquakes on the deformation and stability of rock slopes should be considered. The study on the internal structural characteristics of rock mass should be strengthened and the accuracy of physical model test should be improved. In addition, the failure mechanism of rock slopes under the joint action of groundwater and earthquakes should be further studied.

Abstract:The advances on the estimation of hydrological design values in changing environment in terms of univariate, multivariate design value estimation and uncertainty analysis of design values were systematically summarized. The series reconstruction method, weighted synthesis of distributed functions and varying-parameter probabilistic distribution model were reviewed with the emphasis for univariate hydrological design value estimation. In multivariate hydrological design value estimation, the varying-parameter joint distribution function model considering the inconsistency of marginal distribution and structural parameters of multivariate was analyzed and it is pointed out that the method for calculating the multivariate return period or design value cannot be applied to the multivariate cases under inconsistent conditions. This paper puts forward the problems to be further explored in the field of hydrological design value estimation under changing environments, including the design flood adjustment of the constructed projects, estimation of the combined design values in multivariate cases and the reliability evaluation of the calculation results.