Upstream Slope Research Articles

Influence of upstream wall slope on aerodynamic properties of a rectangular cavity in rarefied hypersonic flows

A comprehensive numerical study is performed to reveal influence of the upstream wall slope on aerodynamic properties as rarefied hypersonic flows pass through the two- and three-dimensional cavity configurations using the direct simulation Monte Carlo (DSMC) method. In this work, slope effect is obtained by the cavity upstream wall sloping upward and downward as well as bulging partially. Besides, cases of freestream with different velocities and altitudes are taken into account to examine the slope effect. It is found that cavity flow is transformed from the open type to the transitional and finally to the closed as the cavity upstream wall gradually slopes upward, promoting the heat energy exchange between gas molecules with the cavity floor, and meanwhile achieving a considerable rate of decrease of the peak heat flux on the reattachment corner. However, the upstream wall sloping downward or bulging partially seems to only have a slight effect on cavity flow and wall heat flux. It's worth noting that slope effect is closely related to velocity and altitude of the freestream, such as the greater the velocity and altitude, the stronger the slope effect. For the three-dimensional cavity configuration, influence of the upstream wall slope on cavity flow and wall heat flux is weaken considerably due to the three-dimensional effect. From the perspective of optimal design for the hypersonic thermal protection system, the cavity with an upward upstream wall is proposed because it not only reduces peak heat flux on the reattachment corner, but also decreases gas temperature inside the cavity.

Study on the Influence of Water Level on Earth Dam Reinforced by Cut-Off Wall: A Case Study in Wujing Reservoir

The construction of a cut-off wall is a common reinforcement method for earth rock dams. At present, compared with the in-depth study on homogeneous earth dams, more and more attention is being paid to the stability and deformation of earth dams strengthened by a concrete cut-off wall. In this study, aiming at the Wujing project of the earth dam strengthened by cut-off wall, the influence of the water level rise and fall on the stability of the dam slope, the deformation of the dam body, and the crack width on dam crest were analyzed by numerical calculation and in situ measurement. The analysis results show that when the reservoir encounters a sudden drawdown, the safety factor of the dam slope decreases sharply. The faster the sudden drawdown, the faster the safety factor decreases. When the reservoir water level rises, the dam’s horizontal displacement shifts to the upstream direction, and the change of horizontal displacement of the downstream slope is significantly larger than that at the measuring point of the upstream slope. The water level of the reservoir rises, and the surface of the dam body rises, and the fluctuation of settlement deformation shows that the upstream side is larger than the downstream side, especially during the period of abrupt change in the reservoir water level. The longitudinal cracks on the dam crest show a tendency of shrinkage when the reservoir water level rises, and opening decreases with the decrease of deformation gradient increment and increases with the increase of gradient increment.

Experimental investigation of sediment movement as a result of homogeneous earth-fill dam overtopping break over a simplified urban area

When an earth-fill dam breaks, dam body sediment and water flow simultaneously move to downstream area causing devastation. Dam break studies in the literature have concentrated mostly on the water flow part while ignoring the sediment movement by designing the dam body as a movable metal gate. This study, however, is the first one experimentally investigating flow and sediment transport due to an earth-fill dam break by constructing the dam body from sediment. Sediment propagation as a result of homogenous earth-fill dam overtopping break was experimentally studied in a laboratory flume of 18.4 m long and 2.0 m wide, and 0.88 m in height in the Hydraulics Laboratory of Izmir Katip Celebi University, Izmir, Turkey. Downstream section right after the dam body was designed as a smooth bed and rough bed. The rough bed, resembling a simplified urban area, was created by using thirteen 10 × 10 × 10 cm sized concrete blocks. The dam body was constructed as homogenous with uniform material having D50 = 0.441 mm. The earth-fill dam body was built using the standard compression methods; each layer of sediment with a thickness of 10 cm was laid in layers, and the body was prepared with a crest width of 10 cm, a transverse base width of 200 cm, a longitudinal base width of 202 cm and height of 60 cm with upstream and downstream slopes of 1:1.6. The water level behind the dam was gradually raised until it overtopped the crest level. A pre-breach was formed at the top of the dam to trigger the break. During each dam break event, water depths were measured by three ULS-40D level meter sensors at different locations, and the final sediment bathymetry map was generated using the ULS-40D Probes at 10 × 10 cm grids. The results showed that, in both smooth and rough downstream bed cases, the dam body eventually collapsed while a great portion of it was carried away by the flood flow. The sediment spreading occurred all over the downstream area, showing significant non-uniform variation in thickness both longitudinally and transversely, especially in the simulated urban area. All the residential areas, while breaking in motion, were submerged under the muddy flow. Some blocks were almost submerged while sediment heights reached half level of some blocks at the end of the experiment. Sediment heights were higher in the urban area.

Easy Equation for Estimating Seepage Discharge through Earth Dams Based on Impermeable Foundation

The goal of this work was to develop an easy and reliable equation for calculating seepage discharge through homogeneous earthen dams that operate with toe drains. For this purpose, many data were generated using (SEEP/W) program depending on the geometrical variables that affect this seepage, such as dam height (h), upstream water depth (H), dam top width (b), upstream and downstream slopes, and base length of toe drain. The seepage discharge quantity for 728 cases was determined using three different values for each of the aforementioned geometric variables. A straightforward and precise equation was created for computing the discharge via a homogeneous earth dam with chimney drain system using the dimensional analysis method and SPSS software, with an (R2) coefficient of 0.986. Then the dimensional analysis was applied to this information. A simple and accurate equation was obtained to calculate the discharge through a homogenous earth dam with a toe drain system with a coefficient (R2) of 0.986. The results indicated that the seepage discharge increases with an increase in the upstream water depth, the toe drain’s base length, and the angle of the upstream and downstream slopes, while it decreases with an increase in the dam top width.Additionally, utilizing the produced data, the artificial neural network model (ANN) was implemented. The results of this model revealed varying percentages of importance for the independent geometrical variables on the seepage quantity, where the upstream water depth (H) has the most important and amounted to 66.9%, while the upstream slope was the least important, where the importance percentage for this factor was 0.7%. The (ANN) model and predicted empirical equation results show excellent agreement when compared.

Theoretical Analysis and Development of an Artificial Neural Network Model to Evaluate Earthen Dam Slope Stability

In the design of earth dams, it must be considered that the water leakage through the earth dam generates upward and pore pressure, in addition to leakage forces that cause internal erosion, which has a direct influence on the structural stability of this system. Also, the rising and dropping in the water level has a direct effect on the stability of the dam's face slope. One way to solve these issues is the installation of a core or a horizontal water drainage system. The present study relied on the GEO-Studio computer tool to evaluate cross-sectional models of earthen dams by determining the safety factor under different situations represented by a change in filter type, and the flow state as a result of raising and lowering the water level at the dam reservoir and the full fill condition of the dam reservoir. The research found that the existence of a core substantially contributed to improving the safety coefficient for the case of rising the water level (2m) and rapidly rising by assigning it the greatest safety coefficient values. The absence of a filter had an opposite influence on the safety coefficient by decreasing it. Also, the factor of safety for the downstream slope was affected by less than 5% for different flow conditions, compared with the higher effect generated by the upstream slope. Furthermore, an artificial neural network model with an accuracy ratio of more than 97% was developed for the predicted safety factor.

Numerical modeling of debris flows using basic equations in generalized curvilinear coordinate system and its application to debris flows in Kinryu River Basin in Saga City, Japan

Each year, structures installed in rivers and valleys (e.g., bank protections, bridges, and sabo dams) are damaged by debris flows; therefore, it is necessary to predict the flow characteristics of debris flows accurately to design river and valley structures that are robust against such debris flows. In recent years, several two-dimensional models have been developed to simulate debris flow. However, the basic equations in the numerical simulation models are in the Cartesian coordinate system, and the shape of each numerical analysis grid is square or rectangular. It is impossible to use numerical grids that match the horizontal shape of the river or valley structures, such as bank protections and sabo dams, when employing square or rectangular grids. This makes it difficult to calculate the fluid forces acting on river or valley structures. In this study, the basic equations of debris flow are provided in the generalized curvilinear coordinate system and a numerical simulation model of debris flow designed using an orthogonal curved grid along the horizontal shape of rivers and valleys is developed. Numerical simulations of a periodical meandering valley are conducted using the basic equations in the generalized curvilinear and Cartesian coordinate systems; the difference between the two results is discussed. Further, numerical simulations of the debris flow that occurred in the Kinryu River Basin in Saga City, Japan, in 2019 are performed using the basic equations in the generalized curvilinear and Cartesian coordinate systems, and the difference between the two simulation results is discussed. The numerical simulation results of debris flow in a periodical meandering channel suggest a slow propagation of debris flow when equations in the Cartesian coordinate system are used; this is attributed to the rough boundaries of debris flow when a square grid is used, which causes numerical energy dissipation that does not exist physically. The inundation areas and land surface deformation of debris flow in Kinryu River Basin were reproduced well by the developed numerical analysis model; the basic equations were written in the generalized curvilinear coordinate system. The development and decrescence of debris flows were reproduced using the developed model; the first debris flow in Kinryu River Basin was stopped in the upstream mild slope area, while the second flowed into the residential area. Reproducing the flow depth, velocity, and discharge could be improved by the model using basic equations in the generalized curvilinear coordinate system, as compared with those reproduced using basic equations in the Cartesian coordinate system. When the Cartesian coordinate system was used, the volume of the debris flow was evaluated to be small and the travel distance of the debris flow was evaluated to be short; thus, the debris flow does not arrive at the residential area and the risk of debris flows is underestimated.

An update of the 3D analytical solution for the design of barricades made of waste rocks

Stope backfilling is increasingly used in underground mines. Barricades are necessary to retain slurried backfill poured in mine stopes . In Canada, waste rock barricades (WRB) have been becoming more and more popular to retain paste backfill in stopes. A few solutions have been developed to size the WRB. Among them, a solution developed by Yang and coworkers in 2017 is particularly relevant. However, this solution was calibrated and validated by 2D numerical modeling . Its validity in 3D conditions remains unknown. In addition, the local stability analysis was made by considering a horizontal sliding plane while their numerical modeling clearly showed an inclined plane. In this study, the validity of the Yang et al. solution is first evaluated against a few numerical results obtained with FLAC3D. The subjectivity in evaluating the instability onset of a structure in numerical modeling is further reduced by considering the first occurrence between displacement jump and coalescence of current yield zones passing through a WRB structure from the downstream to upstream slopes. The results show that both the global and local stability analysis equations of the Yang et al. solution need to be updated. For the global stability analysis, the value of the earth pressure coefficient needs to be modified while an inclined sliding plane needs to be considered for the local stability analysis. These considerations result in a considerable improvement because the updated solution does not contain any empirical calibration coefficient. Good agreements are obtained between the results obtained with numerical simulations and those predicted by the updated 3D analytical solution. The proposed solution is then further validated by an experimental result recently available in the literature. It can be used to design WRB to retain fluid-like paste backfill at the preliminary stage of a project.

Устойчивость откоса грунтовой плотины при сработке водохранилища

Introduction. One of the possible factors acting on the stability of the slopes of an earth dam is the change of water levels in the reservoir or the downstream reservoir. A hazardous event can be a rapid drawdown of the reservoir due to, for example, an emergency or a technological necessity. Examples of collapse of ground dam slopes caused by changes in water level in the reservoir are given, as well as the results of estimation of the effect of reservoir drawdown on the stability of the upstream slope. A homogeneous enclosing dam made of loam on a non-rock base with a height of 29 m and upper and lower slopes of 1:3.5 was considered. The research was conducted for two cases of drawdown: slow drawdown with the rate of vertical water level decrease v = 0.25 m/day and fast (emergency) drawdown with the rate of v = 4.4 m/day. Materials and methods. Calculations of filtration of soil dam for steady and unsteady modes and assessment of stability of the dam slope are carried out by numerical method of finite elements using PLAXIS software package. The research statement and theoretical foundations, laid in calculations of filtration and stability of slopes are given. Results. Researches have shown that at decrease in a water level of a reservoir with the big speed the danger of infringement of stability of a slope increases. Conclusions. According to the practice of designing, the evaluation of change in the upper slope stability coefficient of the uniform ground protecting dike taking into account decrease of the water level in the reservoir taking into account filtration forces of unsteady filtration has been carried out. Variants with different rates of drawdown are considered. It is established that at high rates of drawdown the coefficient of slope stability decreases. The obtained results testify to necessity of taking into account filtration forces of unsteady filtration in evaluation of slope stability when designing homogeneous dams made of low-permeable soils.

Response of the Headcut Erosion Process to Flow Energy Variation in the Loess Gully Region of China

In the headcut erosion process, flow energy is transformed and consumed when runoff is used to transport sediment. Therefore, flow energy variations are critical in the study of headcut erosion. The aim of this study was to illustrate the effects of the upslope inflow discharge and slope gradient on flow energy and the response of the sediment yield of headcut erosion to flow energy variations in China’s Loess Plateau. This study examined the headcut erosion using slope gradients ranging from 1° to 7° and designed and upslope inflow discharges of 3.6, 4.8, 6.0 and 7.2 m3·h−1. The rainfall intensity was set as invariable 0.8 mm·min−1. The results showed that the kinetic energy at the downstream gully bed was 0.03~0.16 J·s−1 lower than that in the upstream catchment area because of the concentrated flow drop at the gully head. The potential energy at the summit and bottom of the plot were both affected by upstream inflow discharge and slope gradient. The flow energy consumption values of the gully head increased by approximately 1.26 times as the inflow discharge increased by 1.2 m3·h−1. Greater energy consumption occurred at the gully head than in the upstream catchment area and downstream gully bed, and the gully head contribution to the flow energy consumption was 44.30~64.29%, which showed an increasing trend as the upslope inflow discharge increased and slope gradient decreased. The influence of the slope gradient on the sediment yield was stronger than that of the upslope inflow discharge, and a nonlinear regression equation was established to calculate the sediment yield. The flow energy consumption showed a significant correlation with the sediment yield (p < 0.01). Our results could enhance the understanding of the flow energy variations and headcut evolution process during headcut erosion and can also be helpful in the design of gully erosion prevention measures.

Effect of Orientation and Vegetation over the Embankment Crest for Energy Reduction at Downstream

Coastal embankments often collapse due to the tremendous destructive energy of an overtopping tsunami flow due to a deep scour by nappe flow. Hence, to clarify the nappe flow formation condition due to the overtopping, a series of tests were carried out within a laboratory flume with immobile settings by lowering the downstream surface angle of an embankment model while keeping the upstream surface slope constant (1:1) with five non-dimensional overtopping depths and six different crest conditions. The conditions imposed on the embankment crest in the flow direction were without vegetation; horizontal crest, (−)4% descending crest slope, (+)4% ascending crest slope, and adding vegetation model with three different densities across the horizontal crest to improve resistance to the flow. The increased resistance provided by the vegetation models were categorized based on the spacing ratio between cylinders to diameter: sparse, intermediate, and dense. Increased vegetation density above the crest results in a significant reduction of flow energy by approximately 30–50% at the downstream brink edge and 40–60% at the downstream plunge basin. In contrast, the maximum energy reduction was found to be by the dense vegetation model. Additionally, owing to the steep slope of the water surface profile and the increasing vegetation density, the impinging jet’s impact point moved closer to the toe of an embankment. This implies that vegetation covers a smaller area while increasing density to mitigate the destructive intensity of flood/tsunami movement. Meanwhile, the descending crest scenario results in a faster nappe flow formation. In contrast, the ascending crest scenario delays the nappe formation while reducing the downstream slope angle. It maintains the sub-critical flow at the crest, except near the downstream brink edge.

Numerical Simulation for Flow over A Broad-Crested Weir Using FLOW-3D Program

The free water flow over a broad-crested weir with different down- and upstream inclinations was studied numerically using computational fluid dynamics software (FLOW-3D v11.0.4). Weirs of four various upstream and downstream configurations were investigated to determine the effect of weir shape on the produced coefficient of discharge (C_d), upstream energy grade line (H₁), and depth-averaged flow velocity using five different flow discharges. The obtained numerical results revealed that FLOW-3D program can be depended to simulate the flow over broad-crested weir adequately, as the differences between the numerical and experimental upstream head (h₁) were in the range of 0.0 to 9.6%. Furthermore, reducing upstream slope played an essential role in increasing the discharge coefficient, and reducing the upstream energy grade line (i.e. static pressure above the crest), while downstream inclination showed a negligible influence. Generally, reducing the upstream slope by 50.0 and 70.5% increased discharge coefficient by 9.5 and 13.2%, while decreased the total energy grade line by 4.3 and 8.7%, respectively. According to flow velocity measurement, for the same upstream slope and discharge, the velocity resulted by the weir of inclined upstream and vertical downstream (BRV) was lower than that of the weir of vertical upstream and inclined downstream (VRB) by 28.0%.

Analysis of Slope Stability and Soil Liquefaction of Zoned Earth Dams Using Numerical Modeling

The design of dams requires comprehensive studies to ensure the safety and feasibility of these important engineering projects, as any possible failure case may lead to considerable losses in human life and properties. Specifically, analyses should be performed to evaluate seepage, slope stability, and soil liquefaction of large earth dams. In this study, numerical modeling, based on finite element methods, was used to analyze seepage, slope stability, and liquefaction of Makhoul Dam which is a large zoned dam, currently under construction on Tigris River in the north of Iraq. Earthquake shakings impose additional hysteric and short-term loads that may lead to dam failure due to high pore water pressure, piping, and soil liquefaction. Therefore, the dynamic stability of the dam and soil liquefaction were also evaluated, as a result of applying an earthquake shaking to the dam. For the static condition, the dam was safe against internal erosion and slope failure, as the calculated value of the safety factor was greater than the allowable value. However, the results obtained from the dynamic analysis indicated that a possible earthquake, with an acceleration of 0.38g and 10 seconds period, led to upstream slope failure, a relative displacement as high as 2 meters at the dam crest, and soil liquefaction at the upstream slope. As discussed herein, dam redesign or geotextile reinforcement may be considered to reduce the effects of earthquakes on the dam.

Flow over embankment gabion weirs in free flow conditions

In this study, a series of laboratory tests were performed to investigate the effects of side ramp slope, crest length, and porous media properties on the flow regimes, water-surface profiles, discharge coefficients, and energy dissipation in embankment gabion weirs with upstream and downstream slopes. 24 physical models of solid and gabion weirs with three different upstream/downstream slopes (90°, 45° and 26.5°) were created. To investigate the complexity of flow over the porous-fluid interface and through the porous material, three-dimensional (3D) numerical simulations were developed. In numerical simulation, the standard k-ε turbulence model was utilized. A structured mesh domain was used to simulate the physical model. Water surface profiles above the porous weirs were used for comparison between the numerical simulations and measured data. These comparisons helped determine variables in the numerical simulations. Numerical simulation enables visualization of streamlines around and through the gabion weirs. In addition, mean stream wise velocity profiles above and within the porous structures were obtained. Numerical simulations showed that a reduction in the slope of the upstream face leads to an increased curvature of streamlines and the velocity distribution exhibits a non-uniform wavy shape due to the geometrical properties of the weirs. As the velocity profiles move downstream, the velocity distribution within the porous structures were more affected by the presence of the pores. The experimental results show that decreasing upstream slopes, from 90° to 26.5°, leads to decreased discharge coefficients. However, in all cases, gabion weirs lead to greater discharge coefficients than those of similar solid weirs. For milder side slopes, discharge ratios (flow passing through all faces of the gabion weirs over the inlet discharge) decreased nonlinearly. Moreover, with increasing the inlet discharge, relative energy dissipation was reduced up to 45% in gabion weirs.

A cascading risk model for the failure of the concrete spillway of the Toddbrook dam, England during the August 2019 flooding

Dam break is considered as a major catastrophe with significant negative economic, social, and environmental consequences, and thus must be prevented at any cost. Here, we report and analyze a near-miss dam break incident in Toddbrook dam, England during the August 2019 flooding, where the spillway of the dam failed putting the entire dam at the risk of failure. A combination of field surveys, desk studies and numerical modelling is applied to analyze the incident and to develop a cascading risk model for the first time. Our hydraulic modelling showed that the spillway was under fast-flowing water having a speed of up to 15.0 m/s. Such a high-speed flow played a major role in the failure of the spillway through facilitating water injection beneath the spillway slabs. The spillway suffered from poor maintenance and was densely vegetated, which most likely undermined the foundation. The spillway was poorly designed as the concrete slabs were relatively thin and unreinforced, the profile of the spillway was not fit for purpose, and the spillway lacked a stilling basin. Due to rapid drawdown, a landslide was generated on the upstream slope of the dam, which was reconstructed through our geotechnical modelling, indicating that a slower pace must have been taken during the process of emptying the reservoir. We developed a cascading risk model which begins with three primary causes of insufficient maintenance, design shortcomings, and the torrential rainfall leading to flooding. Our risk model, which is among the first of its type, would help preventing future dam failures.

Performance Assessment of Shirin Earth Dam in Iraq Under Various Operational Conditions

Proper dam management should be ensured regularly to avoid breaches and failure. In this study, the finite element method was used to analyse the stability of the Shirin earthen dam under various conditions. The necessary laboratory tests for soils used in the construction of the dam were carried out in the laboratories of the College of the Engineering /University of Tikrit, and these data were employed in the GEO-STUDIO program to analyse the seepage and stability of the dam. The seepage was analysed at three levels of the water lake reservoir including the highest, middle and lowest water levels. In addition, factors such as the permeability of the shell layer, the presence and thickness of the dam’s core layer, the placement of filters at the back of the dam and the exit gradient have been considered. The results have shown that by increasing the permeability of the shell layer, the exit gradient is decreased while the seepage through the dam body is increased. The presence of the dam’s core layer has a significant effect on reducing the amount of seepage through the dam’s body as the amount of seepage is reduced by (99%). Moreover, it was found that the minimum safety factor is 1.95 and it occurs after (4 days) of the rapid emptying of the reservoir, and this indicates that the upstream slope of the dams is safe during water emptying.

Flow through a sluice gate over a broad crested weir under free- and submerged-flow conditions

ABSTRACT This paper describes the hydraulic characteristics of flow through a sluice gate over a broad-crested weir with a fixed upstream ramp slope of 1:2 and downstream ramp slopes of 1:2, 1:3, and 1:4. A relationship was proposed to determine the contraction coefficient of the flow passing through the gate, under free-flow conditions, in which the average value was 0.71 for all observed data. The developed relationship was used to calculate the head-loss coefficient from the studied structures under free-flow conditions, which averaged 0.31. The value of the mean absolute relative error for the proposed relationship to estimate the discharge coefficient under free-flow conditions was 1.7%. Examination of the different downstream slopes on the discharge coefficient under free-flow conditions showed that a downstream ramp slope of 1:3 is most appropriate when compared to the results for the other slopes. The value of the mean absolute relative error of the developed relationship to estimate the discharge coefficient under submerged flow conditions was 5.7%, while its corresponding value from the WinGate software was 13.1%. A survey of the effect of downstream ramp slope on the depth of submergence threshold showed that an increase in the downstream slope tends to increase the depth of the submergence threshold, whereby its value under low slopes was not significant.

Experimental study on pressure distribution of spur dike under the combined action of landslide surge and water flow

Combined with the physical model test of the force of landslide surge on the spur dike under the condition of water flow dynamics, this paper measures and analyzes the pressure distribution of the spur dike body, the wave pressure distribution along with the water depth, and the circumferential pressure distribution along with the near-surface layer, the middle layer, and a near-bottom layer of the upstream and downstream spur dikes of the river channel opposite the landslide entry point under the action of pure water flow and wave–current coupling, respectively. For the upstream spur dike, the maximum pressure is concentrated on the right side of the river slope of the spur dike body and the part of the backwater slope close to the spur dike head, that is, the position of the upstream slope; for the downstream spur dike, the pressure on the upstream slope and upstream slope of the spur dike head is the largest. Under the same test parameters, the pressure increase of the downstream spur dike is more significant than that of the upstream spur dike, and the downstream spur dike is easier to be damaged than the upstream spur dike.

Numerical Investigation on the Impact of Tailings Slurry on Catch Dams Built at the Downstream of a Breached Tailings Pond

Tailings storage facilities (TSFs) are known as a time-bomb. The numerous failures of TSFs and the heavy catastrophic consequences associated with each failure of TSFs indicate that preventing measures are necessary for existing TSFs. One of the preventing measures is to construct catch dams along the downstream near TSFs. The design of catch dams requires a good understanding of the dynamic interaction between the tailings slurry flow and the catch dams. There are, however, very few studies on this aspect. In this study, a numerical code, named LS-DYNA, that is based on a combination of smoothed particle hydrodynamics and a finite element method, was used. The numerical modeling shows that the tailings slurry flow can generally be divided into four stages. In terms of stability analysis, a catch dam should be built either very close to or very far from the TSF. When the catch dam with an upstream slope of a very small inclination angle is too close to the tailings pond, it can be necessary to build a very high catch dam or a secondary catch dam. As the impacting force can increase and decrease with the fluctuations back-and-forth of the tailings slurry flow, the ideal inclination angle of the upstream slope of the catch dam is between 30° and 37.5°, while the construction of a catch dam with a vertical upstream slope should be avoided. However, a catch dam with steeper upstream slopes seems to be more efficient in intercepting tailings flow and allowing the people downstream to have more time for evacuation. All these aspects need to be considered to optimize the design of catch dams.

Static Parametric Stress-Strain Analysis for Asphaltic Concrete Core of Rockfill Dams

Abstract This study was conducted to investigate the effect of variations in the asphaltic concrete core Rockfill dam geometric parameters on the core behavior at different upper, middle, and lower points under two-dimensional static stress-strain analysis. The mentioned analysis was performed using SIGMA/W software. In the modeling and analysis process, the geometry of a large number of dams constructed around the world was studied and many numerical models with variations in eight classes of height, three dams upstream/downstream slope modes, and three different asphaltic core positions and thicknesses on a rigid foundation were created and analyzed. In addition, for each of the above models, four dam operation stages including “End of Construction”, “Full Reservoir”, “Half-Full Reservoir”, and “Rapid Drawdown” were considered. The results show, in four different stages of construction and impounding and three different slope modes, the maximum stress as well as horizontal and vertical displacements at the upper, middle, and lower points of the core increase with increasing height. In all models, increasing upstream and downstream slopes results in an increase in the amount of vertical displacement for all construction and impounding stages at the upper, middle, and lower points of the core. In the middle and lower points of the core, with increasing height, the amount of deviatoric stress increases for all construction and impounding conditions. In addition, for all operation cases, the maximum strain increases in all points of the vertical and tilted cores as the core thickness increases. Additional results are presented in the next sections.

Seepage Characteristics of Agricultural Reservoir Embankment Based on Installation of Overtopping Prevention Structures

In this study, a structure that can effectively prevent overtopping caused by abnormal rainfall was installed in a deteriorative agricultural reservoir, and seepage characteristics were compared and analyzed through model experiments and numerical analysis. The experimental conditions were observed by installing a stepped gabion, vertical gabion, and parapet in combination with a gabion retaining wall, geomembrane, and core on the dam crest. Small horizontal and vertical displacements without defects were found, such as overturning and failure, to effectively prevent overtopping. A comparison of seepage line and pore water pressure results indicates that the seepage water drained smoothly to the toe drain through the filter from the upstream slope. It was perceived that the concentration of seepage water on the upper part of the dam crest might cause leakage to the upper part of the downstream slope and affect the stability of the overtopping prevention structures. The distribution of the hydraulic gradient was found to be stable in all cases on the downstream slope. The upper part of the downstream slope could be vulnerable to leakage, so careful management is required when constructing the geomembrane. Overall, among the three overtopping prevention structures applied, a stepped gabion retaining wall did not cause such problems as overturning and leakage. Therefore, it is considered better than the other types of overtopping prevention structure.