Embankment Dams Research Articles

Modeling the slope of embankment dam during static and dynamic stability analysis: a case study of Koga dam, Ethiopia

Quantitative assessment of the stability of slopes is very important for the evaluation of an earth fill dam in order to perform the intended function throughout the service life. This study presents the slope stability and analysis of the Koga earth fill dam. The analyses were carried out using finite element-based PLAXIS 2D software. The behavior of both the body and the foundation of the dam was described using the Mohr–Coulomb criterion. Based on the result of this study, the resulting factor of safety values during end of construction for both static and dynamic stability analysis was 1.6221 and 1.3592, respectively. For steady-state condition, the water level was fixed at normal pool level (2015.25 m). The factor of safety obtained for static stability analysis was 1.6136 and the dynamic analysis 1.3157. The rapid drawdown condition is analyzed with normal pool level of 2015.25 m lowered to 2008.5 m. The analysis results showed that the factor of safety for the static and dynamic analysis was 1.2199 and 1.0353, respectively. Using recommended design standards: United States Army Corps of Engineers, British Dam Society and the Canadian Dam Association the slope stability analysis of the Koga earth dam at all critical loading conditions are safe. The displacement result shows the maximum total displacements for static and dynamic analysis were 1.033% and 1.628% of the dam height, respectively. The displacement result coincides with Fell et al. (J Geotech Geoenviron Eng 129(4):307–314, 2003) standards.

Stability Analysis of Flood Spreading Systems in Arid Regions, Iran

Water spreading projects by controlling the floodwater, infiltrating to subsurface and recharging the groundwater, will result in a reliable source of water in dry seasons. In this study, an arid region in Ilam province of Iran was chosen and after careful evaluation, three water spreading projects, including mechanical and water structures, were selected to be executed in the area, and while estimating the discharge in each site using HEC-HMS model, the stability condition of the structures was studied using Geo-Slope software. Also, the stability and instability factors of the structures and dikes were analyzed in flood spreading systems using various methods at the end of construction, steady seepage, and rapid drawdown stages. Results showed that in both static and quasi-static stability analysis of downstream and upstream slopes of dikes based on the calculated safety factors compared to the allowed safety factor, the slopes of embankment dams in all three stages possess the required safety factor.

Dam Break Analysis of Temenggor Dam Using HEC-RAS

Embankment dam is commonly built in Malaysia as it provides benefits to the local population, mainly agricultural activity and flood control measures. However, its massive potential energy reservoir would impose risk of sudden containment breach leading to loss of life and property at inhabited downstream area. This paper deemed to provide a dam break analysis of Temenggor Dam to generate breach hydrograph and inundation map as a result of dam break event under piping and overtopping failure. The Hydrologic Engineering Center’s River Analysis System (HEC-RAS) is capable to model 1-dimensional (1-D) and 2-dimensional (2-D) dam failure event by utilizing hydrological and terrain information generating unsteady-state flow simulation of the dam breach. The process for gathering and preparing data, estimating breach parameters, creating one dimensional and two-dimensional unsteady-flow model in HEC-RAS, performing a dam failure analysis for two dam failure scenarios and mapping the flood propagation are outlined in this paper. From 1-D analysis, it is found that the breach flow of Temenggor Dam failure can achieve 281,588 m3/s for piping failure and 331,030 m3/s for overtopping failure. 2-D analysis’ breach flow attained 268,341 m3/s and 328,869 m3/s for piping and overtopping failure, respectively. Furthermore, the expected arrival time of flood wave at selected locations also presented in this paper. 1-D model produced comparable breach hydrograph result of Temenggor Dam against 2-D model with the advantage of significantly shorter simulation time requirement. However, 2-D model able to generate inundation map due to dam failure in wider area which can provide insight of flood hazard risk level and contribution for emergency action plan development.

Damflask reservoir: scour system reservoir safety improvements

Designed by Thomas Hawksley, and completed in 1896, Damflask reservoir was constructed to provide compensation flows to the growing industries downstream in Sheffield. The earth embankment dam incorporates two modified bottom outlets used to release water from the reservoir, each comprising sections of tunnel and pipework together with a series of guard and control valves, to form the reservoir scour system. In 2015, a statutory inspection recommended that improvements were made to comply with modern safety standards and enable the reservoir to be drawn down in a reasonable time, if required in an emergency. This paper provides a brief background to the works at Damflask reservoir and summarises the key technical challenges, which were overcome to improve the existing drawdown facilities; from design development through to construction, commissioning and ongoing operation of the final scheme. It provides an insight into the complex two-year project from the author's perspective as project leader and designer, within the design and build team, commissioned to investigate and undertake the upgrade works.

Change in mechanical behaviour of gap-graded soil subjected to internal erosion observed in triaxial compression and torsional shear

Internal erosion can be a cause of failure in hydraulic structures such as levees, dikes and embankment dams. Suffusion is a type of internal erosion in which the fine particles migrate through the voids between the coarse particles under seepage flow, leaving behind the coarse skeleton. In this study the impacts of suffusion on the mechanical properties of soil in triaxial compression and torsional shear were investigated using a gap-graded soil mix of Silica sand No.5 and non-plastic silt. It was found that the erosion process varied depending on the initial density of the soil and higher density specimens showed relatively lower rates of erosion, degree of erosion, and compressive straining during erosion as compared with loose specimens. Effects on the mechanical behaviour​ of the soil were also dependent on the initial density of the specimen, with changes in the small strain stiffness, secant stiffness degradation, yield loci, small strain peak strength and medium strain strength in both drained and undrained conditions. In triaxial loading, force chains of coarse particles’ skeleton reinforced by fines developed in the suffusion process in the direction of major principal stress, then the stiffness at small strain increased. On the other hand, in torsional shear testing, the reinforced soil skeleton established by the erosion did not resist against shear loading. Increase in stiffness at small strain range was not observed.

Cellular automata model-based numerical analysis for breaching process of embankment dam

It is of great significance to study the process and cause of embankment dam breach in order to ensure the dam safety. In this paper, the overtopping failure mode of embankment dam is selected as the research object, and the cellular automata (CA) method is introduced to explore the development law and influencing factors of the overtopping failure mode. Based on the physical and mechanical characteristics of embankment dam and the energy evolution law of the dam soil failure process, this paper discusses the realization method of CA for simulations of dam body heterogeneity, soil anisotropy, stress environment, etc., and proposes the determination method of cellular failure threshold, energy dissipation rate and energy transfer coefficient. Afterward, the loading mode of the CA model is determined based on the relationship between generalized energy and force deformation of the dam soil. Then, energy criterion for dam erosion failure and mechanical criterion of breach slope failure are put forward. Finally, the CA model is applied to a practical project so as to analyze the development and cause for scour depth and width of the overtopping failure breach, and the influence of overtopping water level and downstream slope ratio on the development of breach.

Breaches of the Baige Barrier Lake: Emergency response and dam breach flood

This paper documents the emergency response to the breaches of the Baige Barrier Lake. The lake was successively formed by landslides that occurred on October 10th and November 3rd, 2018 at the provincial border between Sichuan and Tibet in China. The barrier lake created by the “10.10” landslide breached on October 12th and triggered a flood with a peak discharge around 10000 m3/s. The residual landslide barrier was enhanced by a second landslide on November 3rd, resulting in a higher barrier with larger flood potential. An overflow channel was excavated in the crest of the barrier to prompt the breach to be triggered at a lower water level. The second breach happened on November 12th with a measured peak discharge of 31000 m3/s. Nearly 75000 people were evacuated before the two breaches. In order to prevent the downstream dams from possible over-topping, nearly 3.27 × 108 m3 of the stored volume was released from the Liyuan reservoir 688 km downstream of Baige Barrier Lake. This paper presents the measured hydrographs and the back-analysis results for the “11.03” barrier lake. It is shown that the modern models of dam breach hydraulics can reasonably reproduce the barrier breach hydrographs; however, further studies are needed to define the key parameters which highly influence the calculated results. Knowledge acquired during the emergency response to the case can be shared with experts working on breaches of embankment dams and can be referenced to promote both the theory study and the engineering practice to mitigate the potential risks caused by this type of catastrophic events.

Dam Breach Size Comparison for Flood Simulations. A HEC-RAS Based, GIS Approach for Drăcșani Lake, Sitna River, Romania

Floods are the most destructive natural phenomenon, by the total number of casualties, and value of property damage, compared to any other type of natural disaster. However, some of the most destructive flash floods are related to dam breaches or complete collapses, that release the large amounts of water, affecting inhabited areas. Worldwide, numerous dams have almost reached or surpassed the estimated construction life span, and pose an increasing risk to structure stability. Considering their continuous degrading state, increasing rainfall aggressiveness, due to climatic changes, technical error, or even human error, there are numerous, potential causes, for which dams could develop breaches and completely fail. This study aims to portray a comparative perspective of flood impact, with real-life consequences, measured by quantifiable parameters, generated from computer simulations of different breach sizes. These parameters include the total flooded surface, water velocity, maximum water depth, number of affected buildings, etc. The analysis was undergone by means of HEC-RAS based 2D hydraulic modeling and GIS, depending on high-accuracy Lidar terrain data and historical hydrological data. As a case study, Drăcșani Lake with the associated Sulița earthfill embankment dam was chosen, being one of the largest and oldest artificial lakes in Romania.

Numerical Analysis of Rapid Drawdown of an Embankment Dam

Numerical analysis for the safe rate determination of lowering of an embankment dam was performed in this study with the use of the finite element method. Coupled deformation and consolidation analysis were carried out for staged construction and drawdown of a 59m embankment dam for varying undrained shear strength of the clay core. The lowering of the reservoir was performed at different depths between two extreme scenarios, i.e. rapid lowering rate (1m/day) and slow lowering rate (0.1m/day). The reservoir of the dam was lowered to a depth from 10m to 55m in gradual increments. The results indicated that the safety of the dam was satisfactory when the reservoir was lowered at the quick rate for a depth of 10m, 20m, 30m respectively when the undrained shear strength of the clay core was taken as 20, 25 and 30kN/m2. Regarding the case of slow drawdown rate of the reservoir, it was found that the reservoir could be lowered up to a depth of 55m at a rate of 0.1m/day when the undrained strength of clay core was 25kN/m2. The stability of the dam was also found satisfactory even though the reservoir was lowered at a rate of 0.25m/day for a depth of 55m when the undrained shear strength of clay core was 30kN/m2.

Estimation of breach outflow hydrograph using selected regression breach equations

Embankment dam is commonly built in Malaysia as it provides essential benefits to the local population, such as agricultural activity and flood control measures. However, the release of high potential energy by the impoundment imposes risk of catastrophic event during the dam failure. Therefore, estimation of flood arrival time under dam break event can be beneficial as primary information using numerical model to simulate the breaching process of the embankment dam. The purpose of this study is to establish dam breach profile of Temenggor Dam in predicting breach outflow hydrograph. A few selected regression equations for breach parameters will be tested namely Froehlich, Macdonald and Langridge-Monopolis and Von Thun and Gillete. One-dimensional dam break modelling were performed based on the calculated breach parameters for overtopping and piping failure. Hydrologic Engineering Center’s River Analysis System (HEC-RAS) software is used for the dam break analysis. Results obtained from the study indicated that overtopping failure yields the highest peak breach flow of 202,099 m3/s, compared to piping failure’s highest peak discharge of 201,126 m3/s.

Assessing Land Use and Land Cover Change in River Beas Floodplain, Punjab

Floodplains are the most fragile ecosystems of the world which attracted the humans since the dawn of civilizations. Due to their resource enrichment, these remained center of attraction to fulfill the socio-economic needs of people. As a result, the natural land cover of these floodplains are under the influence of human induced activities. River Beas Floodplain of Punjab has also witnessed such changes. Human intervention in these landscapes has depleted natural wealth and has altered its land use. Construction of upstream dam and artificial embankments and diversion of water through canals further paved the ways for intensification of land use changes. The outcome of these human actions is that wetlands, barren land, and river channels has reduced. On the other hand, agriculture and settlements recorded a sharp increase in recent decades. The growth of agricultural area and human settlements are putting pressure on the natural resources and depleting the human environment relationship in the floodplain. This study utilized multi-temporal satellite data from Landsat for the classification of land use and land cover.

A numerical modeling study on the seepage under embankment dams

The present study focuses on the flow discharge under the embankment dams with clay core. Using numerical analysis, the effect of the cutoff wall and horizontal drain on the flow discharge, hydraulic gradient and uplift pressure beneath the dam was examined. The finite element program of SEEP/W was applied for modeling embankment dam. Comparing the results of numerical modeling of the embankment dam with the results of physical modeling demonstrated the acceptable accuracy of the numerical method in the flow evaluation. The effect of the position and depth of the cutoff wall on the seepage under embankment dam was also investigated. The seepage discharge was evaluated in terms of using horizontal drain and a combination of the cutoff wall and horizontal drain. The effect of dam’s layering foundation on the flow was investigated. The results indicated that the placement of the cutoff wall under the clay core would have the most reduction of seepage under the embankment dam. By increasing the cutoff wall depth, uplift pressure under the embankment dam was decreased and the hydraulic gradient was increased. The maximum hydraulic gradient occurred at the location of the cutoff wall. The effect of the cutoff wall on the seepage reduction under the embankment dam was decreased through decreasing permeability of the dam foundation. Increased horizontal drain length resulted in uplift pressure decrease. The results of modeling of embankment dam constructed on layering soil foundation suggested that the amount of hydraulic gradient, uplift pressure and seepage flow would change significantly when the cutoff wall depth ratio equals to the two-layer boundary depth.

Seepage Analysis in Short Embankments Using Developing a Metaheuristic Method Based on Governing Equations

Seepage is one of the most challenging issues in some procedures such as design, construction, and operation of embankment or earth fill dams. The purpose of this research is to develop a new solution based on governing equations to solve the seepage problem in an effective way. Therefore, by implementing the equations in the programming environment, more than 24,000 models were designed to be applicable to different conditions. Input data included different parameters such as slopes in upstream and downstream, embankment width, soil permeability coefficient, height, and freeboard. With the use of this big data, a new process was developed to provide simple mathematical models for the seepage rate analysis. The study first used intelligent models to simulate the seepage behavior. Finally, the accuracy of the models was optimized using a new metaheuristic algorithm. This led to the ultimate flexibility of the final model presented as a new solution capable of evaluating different conditions. Finally, using the best model, new mathematical relationships were developed based on this methodology. This new solution can be used as a proper alternative to the governing equations of seepage rate estimation. Another advantage of the proposed model is its high flexibility that can be well applied to engineering design in this field, which was not possible using the initial equations.

Tensile Testing of Soils: History, Equipment and Methodologies

Tensile strength of soil is indeed one of the important parameters to many civil engineering applications. It is related to wide range of cracks specially in places such as slops, embankment dams, retaining walls or landfills. Despite of the fact that tensile strength is usually presumed to be zero or negligible, its effect on the erosion and cracks development in soil is significant. Thus, to study the tensile strength and behavior of soil several techniques and devices were introduced. These testing methods are classified into direct and indirect ways depending on the loading conditions. The direct techniques including c-shaped mold and 8-shaped mold are in general complicated tests and require high accuracy as they are based on applying a uniaxial tension load directly to the specimen. On the other hand, the indirect tensile tests such as the Brazilian, flexure beam, double punch and hollow cylinder tests provide easy ways to assess the tensile strength of soil under controlled conditions. Although there are many studies in this topic the current state of the art lack of a detailed article that reviews these methodologies. Therefore, this paper is intended to summarize and compare available tests for investigating the tensile behavior of soils.

A parametric study on behavior of plastic concrete material in earth dams

In the current research, the mechanical behavior of plastic concrete in cut-off walls of embankment dams has been investigated. To do so, several triaxial compression tests have been carried out on the specimens with various mix designs under different confining pressures. It has been observed that the compressive strength of such a material increases dramatically with the confining pressures applied on the samples. Moreover, the material behavior is substantially dependent on the confining pressure values; so that, as the confining pressure increases, the material behavior intends to be more ductile. Furthermore, a parametric study has been done to investigate the influence of mix design on these materials. The results showed that the strength and elasticity modulus of plastic concrete increase with the increase of cement factor and decrease of bentonite content. However, the rate of increase is apparently dependent on the mix design changes.

Laboratory Study on the Cyclic and Postcyclic Behavior of Plastic Concrete Used in Cutoff Walls of Embankment Dams

AbstractIn this paper, the cyclic response of plastic concrete material used in cutoff walls of embankment dams has been studied. To investigate the dynamic behavior of such a material, an extensiv...

Total risk and seismic hazard analysis of large embankment dams: case study of Northwest Anatolia, Turkey

Resistance and resilience of dams should be controlled through a set of appropriate design metrics to prevent a catastrophic release of reservoir water, especially under seismic excitation. This is a crucial task in earthquake safety evaluation and risk management of existing dams. There are many large dams under the effect of near-source zones in Turkey. This paper provides the required guidelines to address the safety concerns of large dams subjected to earthquakes. It synthesizes the simulations performed for 15 large dams located in 2 separate basins in the Northwest Anatolia Region in Turkey. Most of these dams are impacted by nearby energy sources resulting from horst and graben fault systems. For dams with hydraulic heights ranging from 35 to 89 m, the seismic hazard ratings of the dam sites and the risk ratings of the complete structures were determined, and the potential failure modes were estimated. As a result of this study, 40% of dams have been classified as “extremely high” risk, while others fall into the “high” risk category.

Experimental Study of Cohesive Embankment Dam Breach Formation due to Overtopping

The recurrent floods in recent decades have imposed a challenge of embankment dam breaching, which needs great attention through improved design methods that are based on risk approach, the evacuation plans for people at risk, etc. In this study, based on the small-scale model tests a series of experiments were conducted to determine the breaching process of cohesive embankment dam using a simplified physical based breach model due to overtopping; the breach process observed during tests in the laboratory and the results from analyzed parameters are described. Five dam models, three of which were constructed with homogenous clay soil while two were sandy-clay mixture tested. The heights of the embankments dam were 0.45 m, and the widths at the crest were 0.20 m. The data from these examinations indicated that headcut erosion played an important role in the process of breach development. Initiation of erosion, flow shear erosion, sidewall bottom erosion, and distinct soil mechanical slope mass failure from the headcut vertically and laterally were all observed during these tests. In this physical based experimental model, the initial scouring position calculated by applying a hydraulic method, the broad crested weir formula used for breaching flow discharge and flow velocity computed based on breach flow discharge. The stability of the side slope failures was estimated by comparing the resisting and deriving force. Further, using data from laboratory experiments, the calculated peak breach discharge, breach characteristics times, breach widths, and breach flow velocity generally agreed well with the measured data and also the knowledge acquired from observed breach process at several stages. Finally, the accuracy of model was checked by root-mean-square-error.

Flow Resistance and Energy Dissipation in Supercritical Air‐Water Flows Down Vegetated Chutes

AbstractVegetation covers on dikes and embankment dams have proven as sustainable and cost‐effective surface protection against external erosion caused by hydraulic, mechanical, or climatic impacts. Determination of the hydraulic loads that act upon these covers requires the knowledge of the flow resistance. While the high‐velocity flows on vegetated slopes are often aerated, the flow aeration has rarely been considered, and no direct measurements of the air‐water flow properties have been conducted to date. The air‐water flow properties are needed for a direct estimation of important design parameters such as friction factors and residual head at the downstream end. Herein, unique air‐water flow measurements were conducted in high‐velocity air‐water flows down a vegetated chute with a 1:3 slope. Several vegetation covers were tested for a range of flow rates. The experiments revealed strong flow aeration within three‐dimensional, fragmented flows associated with complex interactions of vegetation and high‐velocity flows. The air‐water flow properties were measured with phase‐detection intrusive probes providing novel insights into aerated flows on vegetated chutes including distributions of void fraction, bubble count rate, and interfacial velocity as well as direct estimates of energy dissipation and flow resistance. The results highlighted strong flow aeration and energy dissipation for all vegetated configurations. The median equivalent Darcy‐Weisbach friction factors for all vegetations were within 0.19 to 0.45, comparable to aerated flows on stepped spillways. The present results highlighted the significant flow resistance of vegetated covers and the need to consider air‐water flow properties in the design of vegetated chutes.

Studies of the current state of anthropogenic transformation of the young river landscape of the Prut river (within Chernivtsi region)

Studies of the current state of anthropogenic transformation of the young river landscape of the Prut river (within Chernivtsi region)