Refined mathematical model for the breaching of concrete-face sand-gravel dams due to overtopping failure

Overtopping is one of the main reasons for the breaching of concrete-face sand-gravel dams(CFSGDs). In this study, a refined mathematical model was established based on the characteristics of the overtopping breaching of CFSGDs. The model characteristics were as follows:(1) Based on the Renormailzation Group(RNG) k-ε turbulence theory and volume of fluid(VOF) method, the turbulent characteristics of the dam-break flow were simulated,and the erosion surface of the water and soil was tracked;(2) I...     

Centrifugal model tests and numerical simulations for barrier dam break due to overtopping

The present study focuses on the breaching process and failure of barrier dams due to overtopping. In this work, a series of centrifugal model tests is presented to examine the failure mechanisms of landslide dams. Based on the experimental results, failure process and mechanism of barrier dam due to overtopping are analyzed and further verified by simulating the experimental overtopping failure process. The results indicate that the barrier dam will develop during the entire process of overtopping in the width direction, whereas the breach will cease to develop at an early stage in the depth direction because of the large particles that accumulate on the downstream slope. Moreover, headcut erosion can be clearly observed in the first two stages of overtopping, and coarsening on the downstream slope occurs in the last stage of overtopping. Thus, the bottom part of the barrier dam can survive after dam breaching and full dam failure becomes relatively rare for a barrier dam. Furthermore, the remaining breach would be smaller than that of a homogeneous cohesive dam under the same conditions.     

Physical modeling into outflow hydrographs and breach characteristics of homogeneous earthfill dams failure due to overtopping

The main objective of the present study is to introduce new empirical equations for the determination of breach geometrical dimensions and peak outflow discharge(Q_p).Therefore,a historic failure database of 109 embankments was collected and examined.The most important factors that affect the breach evolution,including grading size,hydraulic,and outflow characteristics are also studied.Some of the parameters used for the determination of Q_p and average breach width(Bave)have a significant effect on the erosion process,but they are less reflected in the technical literature.To study the behavior of noncohesive soils during overtopping,15 physical tests were performed at the laboratory,and the effects of interfering parameters were investigated.The experimental output hydrograph was used to simulate the hydrographs resulting from the failure of real dams,and recent artificial intelligence techniques along with linear and nonlinear regression models were employed.The area-time analysis of the laboratory hydrographs shows that the soil particle size and the characteristics of reservoir-basin significantly affect the rate of breach formation and outflow discharge.New relationships are introduced,based on the breach characteristics,by a combination of historical and experimental data,as well as case studies conducted on the hypothetical failure of 10 operational dams.The mathematical model is also used to simulate the process of breach evaluation.Based on statistical indices,comparison of the results,and sensitivity analysis,the developed equations can better express the susceptibility of materials to erosion and their application can minimize downstream vulnerabilities.     

A new approach to plane failure of rock slope stability based on water flow velocity in discontinuities for the Latian dam reservoir landslide

The stability of slopes is always of great concern in the field of rock engineering. The geometry and orientation of pre-existing discontinuities show a larger impact on the behavior of slopes that is often used to describe the measurement of the steepness, incline, gradient, or grade of a straight line. One of the structurally controlled modes of failure in jointed rock slopes is plane failure. There are numerous analytical methods for the rock slope stability including limit equilibrium, stress analysis and stereographic methods. The limiting equilibrium methods for slopes under various conditions against plane failure have been previously proposed by several investigators. However, these methods do not involve water pressure on sliding surfaces assessments due to water velocity and have not yet been validated by case study results. This paper has tried to explore the effects of forces due to water pressure on discontinuity surfaces in plane failure through applying the improved equations. It has studied the effect of water flow velocity on sliding surfaces in safety factor, as well. New equations for considering water velocity (fluid dynamics) are presented. To check the validity of the suggested equations, safety factor for a case study has been determined. Results show that velocity of water flow had significant effect on the amount of safety factor. Also, the suggested equations have higher validity rate compared to the current equations.     

Numerical modeling of hydrodynamic changes due to coastal reclamation projects in Xiamen Bay, China

Xiamen Bay in South China has experienced extensive coastal exploitation since the 1950s,resulting in some severe environmental problems.Local authorities now have completed or are implementing many environmental restoration projects.Evaluating the cumulative impact of exploitation and restoration activities on the environment is a complicated multi-disciplinary problem.However,hydrodynamic changes in the bay caused by such coastal projects can be characterized directly and definitively through numerical modeling.This paper assesses the cumulative effect of coastal projects on the hydrodynamic setting using a high-resolution numerical modeling method that makes use of tidal current speeds and the tidal prism as two hydrodynamic indices.Changes in tidal velocity and the characteristics of the tidal prism show that hydrodynamic conditions have declined from 1938 to 2007 in the full-tide area.The tidal current speed and tidal prism have decreased by 40% in the western part of the bay and 20% in the eastern part of the bay.Because of the linear relationship between tidal prism and area,the degraded hydrodynamic conditions are anticipated to be restored to 1972 levels following the completion of current and proposed restoration projects,i.e.33% and 15% decrease in the hydrodynamic conditions of 1938 for the western and eastern parts of the bay,respectively.The results indicate that hydrodynamic conditions can be restored to some extent with the implementation of a sustainable coastal development plan,although a full reversal of conditions is not possible.To fully assess the environmental changes in a region,more indices,e.g.,water quality and ecosystem parameters,should be considered in future evaluations.     

An estimation model for the fragmentation properties of brittle rock block due to the impacts against an obstruction

Mountain hazards with large masses of rock blocks in motion – such as rock falls, avalanches and landslides – threaten human lives and structures. Dynamic fragmentation is a common phenomenon during the movement process of rock blocks in rock avalanche, due to the high velocity and impacts against obstructions. In view of the energy consumption theory for brittle rock fragmentation proposed by Bond, which relates energy to size reduction, a theoretical model is proposed to estimate the average fragment size for a moving rock block when it impacts against an obstruction. Then, different forms of motion are studied, with various drop heights and slope angles for the moving rock block. The calculated results reveal that the average fragment size decreases as the drop height increases, whether for free-fall or for a sliding or rolling rock block, and the decline in size is rapid for low heights and slow for increasing heights in the corresponding curves. Moreover, the average fragment size also decreases as the slope angle increases for a slidingrock block. In addition, a rolling rock block has a higher degree of fragmentation than a sliding rock block, even for the same slope angle and block volume. Finally, to compare with others' results, the approximate number of fragments is estimated for each calculated example, and the results show that the proposed model is applicable to a relatively isotropic moving rock block.     

Hydro-mechanical response with respect to the air ventilation for water filtration in homogeneous soil

When water penetrates into soil,interstitial air can become trapped by the infiltrating water. Neglecting the effect of air ventilation could cause deviations in the predicted pore water pressure and the associated effective stress. This study aims at the effect of air ventilation on the coupled hydromechanical responses in homogeneous soil during infiltration. A schematic concept of infiltration conditions(open-and closed-valve) in homogeneous soil is proposed for investigating their impacts on the pore water pressure and effective stress. Experiments of vertical soil column filled with Ottawa sand(ASTM C778 20/30) were designed for two types of air ventilation(namely, open and closed infiltration). The evolution of pore water pressure at the cylinder bottom was recorded, and served as a benchmark problem for evaluating the coupled hydro-mechanical response. Coding with the commercial software,GeoStudio, was employed for the dynamic behaviors of pore-water and-air pressures as well as theevolving effective stress. It was found in both the experiments and numerical investigations that the infiltration condition plays a crucial role for the ascending rate of pore water pressure as well as the associated effective stress. These results illustrate the inevitable impacts of the air ventilation conditions on the mechanical properties of the soil during infiltration.     

A layered numerical model for simulating the generation and propagation of internal tides over continental slope III. Numerical experiments and simulation

The layered model in Part I was used to simulate the internal tide in a stratified, two layer, and rectangular sea area with step-like topography. The internal tide current velocities of the upper and lower layers and the interfacial elevations were computed and the effect of the upper layer water depth and density difference were studied. Numerical experiments verified that the model can correctly simulate internal tides. The model was also applied to the northwestern part of the South China Sea to simulate the internal tides there with real topography. The distributions of internal tide amplitude in interfaces were delineated. Contribution No. 3590 from the Institute of Oceanology, Chinese Academy of Sciences. Project 49676275 supported by NSFC and also supported by National Special Research Program 97-926-05-02.     

Development of a Cell-based model to derive direct runoff hydrographs for ungauged mountainous basins

A model to derive direct runoff hydrograph for an ungauged basin using the physical properties of the basin is presented. The basin is divided into grid cells and canal elements. Overland flow is generated from each grid cell of the basin by application of continuous effective rainfall of 1 mm/hr to the basin. The flow generated is routed through downstream grid cells and the canal elements using the kinematic wave approach. The travel time for direct runoff from each grid cell to the basin outlet is calculated and the S-curve is derived for the basin. The S-curve is used to derive the unit hydrograph of a given duration for the basin. The model, referred as Cell-basin model was applied to the Upper Kotmale Basin in Sri Lanka and the model predictions of direct runoff hydrographs for rainfall events agreed with the observations to a reasonable accuracy. Comparison of the unit hydrographs obtained from the model and from the conventional Snyder’s synthetic unit hydrograph using regionalized parameters assuming the basin as an ungauged basin, with the unit hydrograph derived from the observations showed that the model predicted unit hydrograph was more suitable than that obtained by Snyder’s method for Sri Lankan up country basins. Thus, the present model is a useful tool to obtain direct runoff hydrograph for ungauged basins.     

An uncertain programming model for land use structure optimization to promote effectiveness of land use planning

Land use structure optimization (LUSO) is an important issue for land use planning. In order for land use planning to have reasonable flexibility, uncertain optimization should be applied for LUSO. In this paper, the researcher first expounded the uncertainties of LUSO. Based on this, an interval programming model was developed, of which interval variables were to hold land use uncertainties. To solve the model, a heuristics based on Genetic Algorithm was designed according to Pareto Optimum principle with a confidence interval under given significance level to represent LUSO result. Proposed method was applied to a real case of Yangzhou, an eastern city in China. The following conclusions were reached. 1) Different forms of uncertainties ranged from certainty to indeterminacy lay in the five steps of LUSO, indicating necessary need of comprehensive approach to quantify them. 2) With regards to trade-offs of conflicted objectives and preferences to uncertainties, our proposed model displayed good ability of making planning decision process transparent, therefore providing an effective tool for flexible land use planning compiling. 3) Under uncertain conditions, land use planning effectiveness can be primarily enhanced by flexible management with reserved space to percept and hold uncertainties in advance.     

A system dynamics model for billion trees tsunami afforestation project of Khyber Pakhtunkhwa in Pakistan:Model application to afforestation activities

As part of the global effort to plant billion trees, an afforestation project is launched in Pakistan in Khyber Pakhtunkhwa(KP) province to conserve existing forests and to increase area under forest cover. The present study is designed to build a Systems' model by incorporating major activities of the Billion Tree Tsunami Afforestation Project(BTTAP) with special focus on afforestation activities to estimate the growth in forest area of KP.Availability of complete dataset was a challenge. To fix the model, the raw data taken from the project office has been utilized. Planning Commission Form 1-Phase I II helped us with additional information.We relied on the data available for one and half period of the project as rest of the data is subject to the completion of the project. Our results show that the project target to enhance area under forest differs from the target to afforest area under the project. The system dynamics' model projection shows that the forest area of KP would be 23.59 million hectares at the end of the BTTA project, thus having an increaseof 3.29% instead of 2% that has been initially proposed. However, the results show that the progress to meet the target in some afforestation classes is slow as compared to other categories. Farm forestry, plantation on communal lands and owners' plantation need special focus of the authority.Deforestation would affect 0.02 million hectares area of the project. The model under study may be used as a reference model that can be replicated to other areas where billion tree campaigns are going on.