Upstream Face Of Dam Research Articles

Parametric study of the earth dam's behaviour subjected to earthquake

Abstract Static stability of an earth dam can be established by estimating the static safety factor equal to the ratio of the shear strength to the shear stress along a critical sliding area. In contrast, it is more complicated to evaluate the dynamic stability during an earthquake. The water filling the interstices of the earth dams cannot drain during the short duration of an earthquake. An excess pore water pressure ΔU develops, and its role is predominant in the destabilisation of the dam. The pore water increase causes a decrease in the soil shear strength. It is, therefore, crucial to evaluate and take into consideration ΔU in the dam dynamic stability analysis. This research is a contribution to reach this objective. A parametric study was conducted by varying the physical and mechanical soil characteristics constituting the dam, as well as its geometrical values, in order to evaluate their effects on the dynamic safety factor. The dynamic safety factor is calculated using the pseudo-static method, taking into account the excess pore water pressure that develops during cyclic loading into the granular soil of the earth dam upstream face. The results of the parametrical analytical study were also compared to the results of numerical simulations of the dam seismic stability trough pseudo-static method. The numerical simulations were done with three different software: PLAXIS and ABAQUS (based on the finite element method) and GEOSTAB (deals with the problem at the limit equilibrium using the simplified Bishop method). At the end, on one hand, we were able to describe how and at what level of the dam upstream face the sliding occurs, and on the other hand, we were able to underline the adequate combination between the dam geometric parameters and the mechanical soil characteristics which may ensure seismic stability.

A Novel Calculation Method of Hydrodynamic Pressure Based on Polyhedron SBFEM and Its Application in Nonlinear Cross-Scale CFRD-Reservoir Systems

Hydrodynamic pressure is an important factor that cannot be ignored in the seismic safety evaluation of dams. However, when the polyhedron-scaled boundary finite element method is used to simulate dams in a cross-scale dynamic analysis, polygonal surfaces often appear on the upstream face of dams, which is difficult to deal with for conventional methods of hydrodynamic pressure. In this paper, a three-dimensional calculation method of hydrodynamic pressure based on the polyhedron-scaled boundary finite element method is proposed, in which polygon (triangle, quadrilateral, pentagon, hexagon, heptagon, octagon, etc.) semi-infinite prismatic fluid elements are constructed using the mean-value shape function. The proposed method, with a high efficiency, overcomes the limitation of conventional methods in which only quadrangle or triangle boundary faces of elements are permitted. The accuracy of the proposed method is proved to be high when considering various factors. Furthermore, combined with the polyhedron-scaled boundary finite element method for a solid dam, the proposed method for reservoir water is used to develop a nonlinear dynamic coupling method for cross-scale concrete-faced rockfill dam-reservoir systems based on the polyhedron SBFEM. The results of the numerical analysis show that when the hydrodynamic pressure is not considered, the error of rockfill dynamic acceleration and displacement could reach 15.4% and 12.7%, respectively, and the error of dynamic face slabs’ stresses could be 24.9%, which is not conducive to a reasonable seismic safety evaluation of dams.

In Search of a Cost‐Effective Approach for Estimating Dam Passage Survival

AbstractPassage of downstream‐migrating fishes through hydropower dams poses a management issue in rivers throughout the world. As such, regulations have been enacted at many locales to understand and limit fish losses by requiring dam passage survival estimation. However, limiting estimates of survival to the dam and immediate tailrace presents a challenge to researchers. In this study, two alternative release–recapture methods were used to estimate dam passage survival of juvenile salmonids through Lower Granite Dam on the Snake River, Washington, in 2018. One approach, the virtual/paired‐release (ViPRe) model, was extensively used in the Columbia–Snake River basin at federally operated hydroelectric dams during 2010–2014. This existing approach uses three releases of tagged smolts to isolate dam passage survival, defined as survival from the upstream dam face to the tailrace mixing zone 1–2 km downstream of the dam. An alternative approach, the virtual release/dead‐fish correction (ViRDCt) model, uses one live‐release group paired with a release of dead tagged fish at the dam to estimate the same survival parameter. The alternative estimation approaches were tested on two spring out‐migrating stocks, yearling Chinook Salmon Oncorhynchus tshawytscha and steelhead Oncorhynchus mykiss, and on a summer out‐migrating stock of subyearling Chinook Salmon. The alternative estimates for these stocks were all within 1 SE. However, the ViRDCt model produced survival estimates with SEs that were 59% smaller than those of the existing ViPRe model and did so using 42% fewer tagged fish and one less downstream acoustic detection array. Because of the reduced sample size, nearly US$540,000 less in tag costs and 4,000 fewer labor‐hours were required to implement the ViRDCt model compared to the ViPRe model. As such, the ViRDCt model represents a cost‐effective and precise approach to characterizing dam passage survival.

Case Study of Dam Overtopping from Waves Generated by Landslides Impinging Perpendicular to a Reservoir’s Longitudinal Axis

Landslide-generated impulse waves in dammed reservoirs run up the reservoir banks as well as the upstream dam slope. If large enough, the waves may overtop and even breach the dam and cause flooding of the downstream area with hazardous consequences. Hence, for reservoirs in landslide-prone areas, it is important to provide a means to estimate the potential size of an event triggered by landslides along the reservoir banks. This research deals with landslide-generated waves and the overtopping process over the dam crest in a three-dimensional (3D) physical model test, presenting a case study. The model set-up describes the landslide impacting the reservoir in a perpendicular manner, which is often the case in natural settings. Based on the experimental results, dimensionless empirical relations are derived between the overtopping volume and the governing parameters, namely the slide volume, slide release height, slide impact velocity, still-water depth, and upstream dam face slope. Predictive relations for the overtopping volume are presented as applicable for cases relating to the specific model set-up. Measured overtopping volumes are further compared to a two-dimensional (2D) case reported in the literature. An important feature regarding the overtopping process for the 3D case is the variation in time and space, resulting in an uneven distribution of the volume of water overtopping the dam crest. This observation is made possible by the 3D model set-up, and is of value for dam safety considerations as well as for foundation-related issues, including erosion and scouring.

An Eulerian approach for dynamic analysis of reservoir adjacent to concrete gravity dam

The present paper deals with the finite element analysis of infinite reservoir adjacent to gravity dam. Two-dimensional eight-node isoparametric elements are used to discretize the domain. In order to reduce the degrees of freedom in the domain, the equation of motion for fluid motion is simulated by pressure-based Eulerian formulation. Different artificial boundary conditions are compared to obtain most suitable boundary condition. In this comparison of boundary conditions, it is noted that almost all the boundary conditions are frequency dependent. Some of the conditions are suitable for the exciting frequency less than the fundamental frequency of reservoir. However, the boundary condition proposed by Gogoi and Maity is suitable for all ranges of exciting frequencies. Further, the force vibration analysis is carried out with and without considering compressibility of water. The hydrodynamic pressure on dam is independent of exciting frequency when the compressibility of water in the reservoir is neglected. However, the effect of exciting frequency on the performances of reservoir is distinct for compressible fluid. Similarly, the magnitude and location of maximum hydrodynamic pressure change continuously, if the inclination of upstream face of dam is considered.

Research of concrete dam leakage detection based on anomaly current field of reservoir water

It's vital to determine the placement of the leakage inlets in the dam upstream face, because dam leakage usually results in engineering hazards such as increase in uplift pressure and aggravating frost-heaving and freeze-thaw damage. According to the numerical simulation of the constant electric field present around the concrete dam body, we analyzed the relationship between local potential difference (current density) and leakage areas, and the influence of low-resistance material on the detection of leakage areas. Numerical simulations show that under the on-site data of potential difference, we can detect inlets in the dam's upstream face successfully. This paper attempts to propose a field detection method to detect dam leakage inlets. This new technique and theoretical basis in operational testing and safety management can be applied to concrete dams. Practical application proves that leakage areas can be recognized accurately, and the results agree well with existing hydraulic observation data and geological information. We suggest that the electrical current field detection of reservoir water leakage areas can be used as a reasonable and effective method to detect concrete dam leakage.

Monitoring and characterizing the deformation of an earth dam in Guangxi Province, China

Failures and severe deformation of earth dams have been reported frequently in the past decades. Extensive studies have been performed to monitor dam displacements to develop dam remediation plans. However, the long-term monitoring of dam displacements and the effects of remediation on dam deformation are rarely studied. In this study, the vertical and lateral displacements of an earth dam in Guangxi Province, southwestern China, were monitored over an 18-year period. The piezometric pressure was measured for the analysis of triggered seepage. Furthermore, acoustic testing and borehole television tests were performed to examine the integrity of the cutoff wall that was built to prevent dam leakage and excessive deformation. The results show that the largest lateral displacement of 65.8 mm and the maximum settlement of 178 mm are both located at the center of the dam and that the lateral displacement and settlement decrease gradually from the center to both abutments. Moreover, greater settlements were observed on the side of the dam upstream of the cutoff wall. The lateral displacements are dominated by the hydraulic pressure of the impounded water. The dam settlements are generally determined by the thickness of the compacted soil along the longitudinal section. The analysis shows that the greater settlements on the upstream side of the dam are attributed to dynamic seepage induced by the water level changes in the reservoir, indicating that the cutoff wall effectively alleviated the seepage effects on the downstream side of the dam. Thus, the dam's upstream face should be remediated to minimize the dynamic water-level effects.

Impulsive forces distribution along the sediment storage dam upstream face for different mud–rock flow unit weight

Because of the huge damage caused by mud-rock flow for the downstream life and property, engineering prevention must be given. It is one of fast and effective measures to build sediment storage dams in the formation zone to the circulation area. Due to the undercutting, scour and impact effect of mud-rock flows to sediment storage dam foundation or the unreasonable reconnaissance design, sediment storage dams possibly cause damage in the design period. However, the impulsive forces of mud-rock flow are the main reason to lead the engineering control structures (sediment storage dams, drainage grooves and block structure of pipe group) to damage. It is very important to study the law of mud-rock flow impulsive forces, and it is of great significance to prevent the damage of sediment storage dam and provide data support and technical support for the construction of sediment storage dam. First, the distribution rules of the maximum and mean value of the impulsive forces of mud-rock flow for the sediment storage dam upstream surface were studied for four mud-rock flow slurry unit weight as the experiment variable. The mud-rock flow impulsive forces value was collected by a numerical collection device that connected eight pressure sensors positioned in various locations, which received the mud-rock flow impact signal. Then, the distribution roles of the maximum and mean impulsive forces value imparted by water or water-rock flows were compared. The results indicate that (1) due to the randomness of particle impacts, the distribution law of the maximum impulsive forces is not obvious, and the maximum mud-rock flow impulsive forces of 99.277 kPa occur in A(1)B(3)C(7) (for a range of particle sizes of 2-4.5 cm); (2) the mud-rock flow impulsive forces mean value first increases and then decreases as the unit weight of the mud-rock flow increases; and (3) the mud-rock flow impulsive forces mean value gradually decreases along the height direction of the sediment storage dams' upstream surface and gradually decreases as the direction changes to the overflow section toward the dam abutments.

Accuracy Analysis of a Dam Model from Drone Surveys.

This paper investigates the accuracy of models obtained by drone surveys. To this end, this work analyzes how the placement of ground control points (GCPs) used to georeference the dense point cloud of a dam affects the resulting three-dimensional (3D) model. Images of a double arch masonry dam upstream face are acquired from drone survey and used to build the 3D model of the dam for vulnerability analysis purposes. However, there still remained the issue of understanding the real impact of a correct GCPs location choice to properly georeference the images and thus, the model. To this end, a high number of GCPs configurations were investigated, building a series of dense point clouds. The accuracy of these resulting dense clouds was estimated comparing the coordinates of check points extracted from the model and their true coordinates measured via traditional topography. The paper aims at providing information about the optimal choice of GCPs placement not only for dams but also for all surveys of high-rise structures. The knowledge a priori of the effect of the GCPs number and location on the model accuracy can increase survey reliability and accuracy and speed up the survey set-up operations.

Technology Research of Underwater Repair on Dam Upstream Face

For any of a large reservoir, it will involve enormous consequences of economic, social and environmental protection to vent reservoir to leakage repair of upstream face of the dam. Thus, in the case of without venting reservoir, it is indeed a very challenging new topic how to repair the dam upstream face. The construction technology of the floating arch cofferdam is first surrounding part of the dam surface without venting the reservoir, which can create the "dry job" environments to repair cracks on concrete surface of dam. After completion of the construction, the water is discharged in the cavity of the arch cofferdam, and the arch cofferdam can automatically rise to float in the water. The floating arch cofferdam is towed to the next construction unit by tugboat, and is water-filled, sank, placed, water sealed, drained the stagnant water inside the cofferdam to create another "dry" environment for construction. Aiming to the most severely freezing-thaw damaged parts for Man tai city dam, a steel tube cofferdam of semi- round is constructed. We have no submariners’ assistance for this test, but arch cofferdam floating underwater install still be finished. When sealing is done, the water within the cofferdam is pulled out, and the "Dry work" environment is formed for construction.

Status after 5 Years of Survival Compliance Testing in the Federal Columbia River Power System (FCRPS)

AbstractSurvival studies of juvenile Pacific salmon Oncorhynchus spp. implanted with acoustic tags have been conducted at hydroelectric dams within the Federal Columbia River Power System in the Columbia and Snake rivers between 2010 and 2014 to assess compliance with the dam passage survival standards stipulated in the 2008 Biological Opinion. For juvenile yearling Chinook Salmon O. tshawytscha and steelhead O. mykiss that migrate downstream in the spring, dam passage survival (defined as survival from the upstream dam face to the tailrace mixing zone) must be ≥ 96%, and for subyearling Chinook Salmon that migrate downstream in summer, dam passage survival must be ≥ 93%. Precision requirement stipulates a standard error ≤ 1.5% (i.e., a 95% confidence interval of ± 3%). A total of 29 compliance tests have been conducted at six of eight main‐stem dams in the Federal Columbia River Power System, using over 109,000 acoustic‐tagged salmonid smolts. Of these 29 compliance studies, 23 met the survival standards and 26 met the precision requirements. Of the six dams evaluated to date, individual survival estimates range from 0.9597 to 0.9868 for yearling Chinook Salmon, from 0.9534 to 0.9952 for steelhead, and from 0.9076 to 0.9789 for subyearling Chinook Salmon. Averages across the six dams exceed the survival standards for all three migrant populations.Received November 9, 2015; accepted February 16, 2016 Published online June 27, 2016

Fluorescent tracer tests for detection of dam leakages: The case of the Bumbuna dam - Sierra Leone

The first impounding of the Bumbuna dam was subject to unexpected high seepages discharge (up to 550l/s) from the foundation drains. Fluorescent tracer tests, commonly used for hydrogeological study of porous and karst aquifer, were performed to locate the seepage zones. Solutions of 3 different fluorescent tracers (Uranine, Sulforhodamine-B and Tinopal CBS-X) were injected in the reservoir at regularly spaced points down to a depth of 80m. Tracer concentration in the seepage water from the foundation drains was continuously monitored by high resolution fluorometers with detection limit as low as 0.02ppb.A total of 107 tests were performed in two separate campaigns conducted in January–February and October–December 2009. Concentration curves recorded from each test were analyzed to determine the time of first response to the injection (detection time) and the quantity of tracer returned from each test (restitution). Maps of minimum detection time and maximum tracer restitution were generated to identify the position of leakages.Seepage mitigation works were planned on the base of test results and completed in the dry season after the drawdown of the reservoir. Works consisted in the additional grouting along the grout curtain, sealing of fissures on the bituminous layer and installation of a PVC membrane on the dam upstream face.Inspection of the upstream dam face confirmed the presence of damages in the areas identified by tracer tests. Since completion of seepage mitigation works the dam operated satisfactorily with maximum seepage from the foundation of 70l/s.

Effects of Increasing the Base on Concrete Dam Stability

The concrete dam is one of the most important hydraulic infrastructures which play a vital role in providing a wide range of water services and helps prevent many potential disasters such as floods. The concrete dam subjected to many kinds of static and hydrodynamic forces which almost needs taking into account of design under different circumstances to satisfy the safety requirements. The shape of dam is pertinent to the stability of dam regarding the major forces and stresses. One of the most common ways which is necessary to solve the problems in design due to the cases of unsafely for any mode of failures is to add mass to the dam upstream face. In this work, a parametric study is made to investigate the effects of the increase in the base of dam on the principal and shear stresses developed in the dam. In all cases, all the relevant factors of safety are satisfied. The stability analysis for all possible modes of failures is carried out to check the performance of the initial section of dam due several loading conditions. Parameters of importance are studied, discussed and conclusions are drawn.

Обеспечение надежности бетонной плотины Богучанской ГЭС на основе контроля состояния контактного шва со стороны верховой грани

Обеспечение надежности бетонной плотины Богучанской ГЭС на основе контроля состояния контактного шва со стороны верховой грани

The 3D finite element analysis of cold wave impact effect

In April, 1999, Guangdong Changsha arch dam application new technique of MgO-Admixed concrete arch dam without transverse joints, Changsha arch dam is only 90 d complete high 55.5 m, 31000 m3 concrete dam body, the reservoir filling and power generation, is initiative at home and abroad in the history of arch dam. In January 2000, downstream dam surface appear fine cracks, crack width only 0.2–0.3 mm, depth 1.3–4.2 m, all did not throughout the dam upstream face. With the hyperbolic model based on MgO-admixed concrete and APDL language, 3 d finite element in simulation analysis, cleared that design conditions of the stress of MgO-admixed concrete compensation accord with the stress state of conventional arch dam structure. Downstream dam surface crack and using the MgO-mixed concrete dams of new technology without necessarily linked. Before to the stationary temperature field in the dam, the role of heat preservation measures template made of polystyrene foamed plastic board for stress improvement is significant. Cold wave impact cracks appear to great effect, worsened the dam stress state greatly, and put the dam in a high stress state. The original design dam stress state is not ideal, crack resistance caused by concrete quality of dam project is reduced, especially heat preservation measures is invalid during the cold wave impact, caused cracks of ChangSha dam. 1–2 mm tiny cracks of Changsha arch dam used under no harmful effects. Concrete crack resistance of Changsha arch dam is improved greatly after dam grouting, the main performance indexes is also improved obviously, and dam is used has been more than 12 years under safety operation. The analysis of cold wave impact provides important basic material to promote the new technology application, and reference value to similar projects.

Factors Influencing Breach Risk of Quake Lake Group

Abstract Hundreds of Quake lakes were formed by the great Wenchuan Earthquake of May 12, 2008. Taking risk mitigation of Quake lakes on Mianyuan River for example, this paper qualitatively analyzes factors influencing breach risk of Quake lake group. These factors include river channel distance from landslide dam upstream to the upstream face of dam downstream, river channel characteristics, composition of landslide dam, breach water volume of upstream landslide dam, height and width of breach, and geometry of downstream landslide dams. Risk mitigation and retrofit measures are suggested for Quake lake group on Mianyuan River.

Pore Pressures in Concrete Dams

Assuming that concrete is a homogeneous porous material in gravity dams, pore pressure intensities at drain wells near the upstream face of dams were studied. In general, the piezometric head of the seepage flow through a gravity dam may be mathematically represented by the well-known Laplace equation. This equation can be solved numerically by the finite-difference equation developed from a block-centered formulation. By using the boundary conditions of the height of the seepage face in drain wells from the concept in hydraulics of wells and the seepage face along the downstream face of dams, piezometric heads, and in turn, pore pressures in the dam body were obtained. This approach of predicting pore pressures has been verified by 40 years of data from the Tennessee Valley Authority’s (TVA’s) Fontana Dam. The pore pressure intensities in dam bodies and at the drain wells are presented. They are expressed in dam heights, size of drains, and locations of drains from the face of the dams for inspection galleries located at the dam base. The results obtained show the location of the inspection galleries for the lowest pore pressures. The inspection galleries are usually used to intercept seeping water from the drain wells in the dam foundation and dam body. The seeping water intercepted by the dam body can be estimated when the values of hydraulic conductivity of concrete are known. The accumulation of calcium carbonate deposited in the drains can then be studied on the basis of the known values of the calcium carbonate concentration of the seeping water. The data presented may be useful for design engineers in the stability and stress analyses of concrete gravity dams. In addition, the effects of the location (i.e., elevation) of the inspection gallery and the tailwater pressures on pore pressures were studied by using the Fontana Dam as a case study.

A novel procedure for determination of hydrodynamic pressure along upstream face of dams due to earthquakes

The estimation of hydrodynamic pressures along the upstream face of the dam is a critical parameter for the accurate analysis and design of a dam. The accurate estimation of the hydrodynamic pressures necessitates the consideration of interaction between the dam, the reservoir and the foundation. The interaction effects of the unbounded domain of the reservoir and the absorptive materials deposited at the reservoir bottom are frequency dependent which can be incorporated in a frequency domain procedure easily. But in a time domain procedure the frequency dependent interaction effects are lost. In a frequency domain solution, the excitation frequencies are extracted from the earthquake signal using a Fourier transformation, but do not give any information about how it varies with time. To overcome this, a short-time Fourier transform based formulation is presented in this paper to evaluate the hydrodynamic pressures in time domain to account for the frequency dependent interaction effects of the dam–reservoir system. Thus, the adequate accuracy in the determination of hydrodynamic pressure under earthquake excitation is ensured with the proposed truncation boundary condition.

A new formulation and error analysis for vibrating dam–reservoir systems with upstream transmitting boundary conditions

This paper proposes and validates a new formulation to investigate the dynamic response of dam–reservoir systems with upstream transmitting boundary conditions (TBCs). The mathematical derivations are provided for the new formulation as well as for exact and various approximate TBCs. The developed analytical equations can be solved numerically to assess the accuracy of a given TBC and determine the associated error independently of FEM or BEM modeling of the reservoir. The method is first validated in the case of semi-infinite reservoirs and an excellent agreement is obtained against classical techniques. The paper presents a fundamental understanding of the behavior of various TBCs and a systematic identification of their influence on the system's dynamic response, considering: (i) dam flexibility, (ii) water compressibility, (iii) reservoir bottom wave absorption, (iv) reservoir truncation length, and (v) excitation frequency. The new method is used to obtain exact error estimators to evaluate the effects of various TBCs on the dam–reservoir first resonant frequency and hydrodynamic forces acting on the dam upstream face. The proposed formulation can be programmed easily and used efficiently for rigorous assessment of classical or newly developed TBCs for vibrating dam–reservoir systems or similar fluid–structure problems.

A new boundary condition for energy radiation in covered reservoirs using BEM

In this paper, a new boundary condition accounting for energy radiation at the far end of covered reservoirs is proposed. Using boundary element modelling (BEM), the boundary condition is investigated through analysis of the hydrodynamic pressure within a two-dimensional ice-covered reservoir impounded by a gravity dam. The proposed boundary condition accounts for reservoir bottom absorption effects and the presence of an ice cover at infinity. Seismic excitation is introduced by subjecting the dam and the reservoir to a horizontal harmonic ground motion. The effectiveness of the proposed method and the accuracy of the boundary condition are examined through a parametric study. The boundary condition is shown to be accurate even when placed near the dam upstream face, and the results obtained are in excellent agreement when compared to those from a mathematical model developed by the authors in a previous work. Some fundamental aspects of hydrodynamic pressure within ice-covered reservoirs are also discussed.