Face Of Dam Research Articles

An investigation into the seismic behaviour of dams using dynamic centrifuge modelling

Dynamic response of dams is significantly influenced by foundation stiffness and dam-foundation interaction. This in turn, significantly effects the generation of hydrodynamic pressures on upstream face of a concrete dam due to inertia of reservoir water. This paper aims at investigating the dynamic response of dams on soil foundation using dynamic centrifuge modelling technique. From a series of centrifuge tests performed on model dams with varying stiffness and foundation conditions, significant co-relation was observed between the dynamic response of dams and the hydrodynamic pressures developed on their upstream faces. The vertical bearing pressures exerted by the concrete dam during shaking were measured using miniature earth pressure cells. These reveal the dynamic changes of earth pressures and changes in rocking behaviour of the concrete dam as the earthquake loading progresses. Pore water pressures were measured below the dam and in the free-field below the reservoir. Analysis of this data provides insights into the cyclic shear stresses and strains generated below concrete dams during earthquakes. In addition, the sliding and rocking movement of the dam and its settlement into the soil below are discussed.

The Formation and Persistence of the Matthieu Landslide-Dam Lake, Dominica, W.I

Research shows that the majority of natural dams formed by landslides exist for only a matter of days or weeks. Thus, the persistence of the 11-year-old Matthieu landslide dam and its resulting lake in Dominica, West Indies, is atypical. In addition, its association with the two earlier landslide dams, which formed and failed within weeks of emplacement of the persistent dam, adds to the unusual circumstances surrounding the Matthieu landslide dam. The persistence of the lake is attributed to the size and composition of the Matthieu landslide dam and the rate of inflow from the Matthieu River. Based on end-of-the-year measurements, the water impounded behind the Matthieu landslide dam rose rapidly by 64 m for the first 7 years before stabilizing at the current level. The stabilized lake level may be the result of seepage discharge from an area of springs on the dam face that equals inflow from the Matthieu drainage basin. Unquantified lake evaporation and seepage discharge to the regional groundwater system may also be factors that contribute to stabilized lake levels. The persistence of the lake behind the Matthieu landslide dam will depend on whether the decreased threat of dam overtopping is replaced by an increased threat of failure by piping.

Optimal design of stepped spillways using the HBMO algorithm

Studies on stepped spillways as flood energy dissipators have been conducted to understand the hydraulics on the stepped face of roller-compacted concrete dams as well as overlays of embankment dams. Significant energy losses occur along the stepped chute so that the energy dissipation structure becomes smaller and more economic. In addition, considering the design discharge, downstream face slope, height of spillway, different combinations of spillway width and number of spillway steps may lead to different head losses. In each feasible combination, the remaining head after the steps should be dissipated by downstream energy dissipators. Design and construction of spillways and energy disspators are very cost-consuming and build up a major part of the dam's construction expenses. Thus, the cost of a financially viable stepped spillway project that consists of the steps’ cost and downstream dissipator's cost should be minimised. In this paper, the honey-bee mating optimisation (HBMO) algorithm is used to determine the best combination of design variables so as to minimise the total cost of both spillway chute and stilling basin. Results are compared with those previously obtained by genetic algorithm (GA) and show the promising potential of the HBMO algorithm in this field of application.

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.

Evaluation of the streaming potential effect of piping phenomena using a finite cylinder model

Piping phenomena into the upstream face of an earth dam can be approximated by a finite cylinder model. A formula of the streaming potential (SP) effect of such a model was developed by integrating an equation of an infinite cylinder section. Numerical modelling allows the conclusion that the oblong SP field shape of a model is only for relatively long and shallow piping models. The SP field shape of a model can actually be circular below a certain ratio value between the depth and length of the model. The resulting SP field of a finite cylinder is symmetrical with respect to its middle point, which allows, in some cases, reaching conclusions about piping phenomena outside the measured area. This finite cylinder formula needs smaller values of moments of polarisation to generate SP data almost identical to the SP magnitudes obtained from the expression of an infinite cylinder section. A random component was added to the SP effect of several computed models. Relatively short and deep piping phenomena can pass unnoticed, especially for a low signal-to-noise ratio. However, detection of anomalous patterns can be improved if the measured data are pre-processed according to a “studentized” deviate concept, which is then subjected to a statistical test based on the Chebyshev inequality. A field example of an SP piping process was detected at the upstream face of an earth dam. Its existence was also confirmed by a geoelectrical survey.

A new technique for the calculation of aeration development zones and nonaerated zones in turbulent flows on the spillway faces of dams and in prismatic flumes and its field verification

A new technique for calculating turbulent aerated and nonaerated flows on spillway faces of dams and in prismatic flumes is developed and validated against field data. The technique is based on original relationships and hypotheses proposed by the author and allowing one to identify the position in a watercourse of the section where aeration appears and the section of its stabilization and to calculate, within these boundaries, the distribution of the mean velocity of liquid phase, averaged aeration factors, and the aeration depths corresponding to the conventional upper boundary of flow section with the local value of the aeration factor a loc = 0.99.

Liquefaction analysis and soil improvement in Beydag dam

Beydag dam is under construction on Kucukmenderes River for irrigation purposes. Due to the scarcity of core material and liquefaction of alluvium at the dam site, the original design was changed to Roller Compacted Concete (RCC) from rockfill dam with claycore. Although the new design was safer, it nearly doubled the cost of the dam, so the owner, State Hydraulic Works of Turkey, (DSI) set out to find more economical but equally safe alternative. Since jet-grouting is a cheap ground improvement tool in Turkey, such an alternative was developed for the ground improvement against liquefaction together with concrete face rockfill dam sitting on top of improved ground. This paper presents a detailed discussion of how the new alternative was developed and evaluated: it discusses the determination of jet grouting pattern, the placement of jet grouted blocks, and the assesment of liquefaction. On one hand the soil cement strength of jetgrout columns, internal friction angle of alluvium and rockfill were important in determining the dimensions of the blocks, on the other hand the location of the blocks were highly affected by the areas where liquefaction occurred. One of the most important parameter that has a considerable influence in delineating the boundary betweeen liquefaction and non-liquefaction was the value of stress reduction coefficient (r d), being primarily sensitive to the weight of overburden, which is calculated by the height from the face of dam to the depth where the calculation was made. This approach is justified by two-dimensional ground response analysis. Most importantly, this paper shows that there exists an alternative solution for building dams on the liquefaction prone sites without removing alluvium by using a well known jet grouting technique for improving ground at only selected places.

Earthquake Hydrodynamic Pressure on Dams

Hydrodynamic pressures on the vertical upstream face of straight dams during horizontal earthquakes were studied by Westergaad in 1933, and an analytical solution was obtained. Assuming that water is incompressible, an approximation can be made to reduce Westergaad’s mathematical formulation to the Laplace equation. The computer program SEEP2D, from the U.S. Army Corps of Engineers (COE), is available for the study of seepage flow in porous media; this flow can be expressed mathematically in a form of the Laplace equation. Therefore, we can use this computer program to study the hydrodynamic pressure on dams during a horizontal earthquake in the upstream/downstream direction. In practice, the proposed procedure is not limited to SEEP2D but can also be applied to any computer model capable of solving Laplace equations in bounded domains. Two examples are presented to show the application of the COE’s computer program, and the accuracy of the proposed method is discussed.

Earth Dam with Toe Drain on an Impervious Base

The required height of a toe drain for a homogeneous earth dam on an impervious base has been determined considering reservoir water level, capillary rise for the embankment soil, free board, top width of the earth dam, embankment slopes, and tail-water position, such that the surface of seepage does not develop on the downstream sloping face of the earth dam and capillary saturation above phreatic line is contained well within the downstream sloping face. Using Kozeny’s analytic function, exact solution to the unconfined flow through an earth dam having parabolic equipotential boundaries on either side has been obtained. For straight toe drain face, and for various positions of tailwater, approximate toe drain heights and heights of surface of seepage have been determined using the Kozeny’s function and the method of fragments. It has been found that for an earth dam with 1∕2 upstream slope, −1∕3 downstream slope, no tailwater, and 2 m capillary rise, capillary saturation is contained within the earth da...

Seismic stability of concrete gravity dams strengthened by rockfill buttressing

Rockfill buttressing resting on the downstream face of masonry or concrete gravity dam is often considered as a strengthening method to improve the stability of existing dam for hydrostatic and seismic loads. Simplified methods for seismic stability analysis of composite concrete-rockfill dams are discussed. Numerical analyses are performed using a nonlinear rockfill model and nonlinear dam-rockfill interface behavior to investigate the effects of backfill on dynamic response of composite dams. A typical 35 m concrete gravity dam, strengthened by rockfill buttressing is considered. The results of analyses confirm that backfill can improve the seismic stability of gravity dams by exerting pressure on the dam in opposition to hydrostatic loads. According to numerical analyses results, the backfill pressures vary during earthquake base excitations and the inertia forces of the backfill are the main source for those variations. It is also shown that significant passive (or active) pressure cannot develop in composite dams with a finite backfill width. A simplified model is also proposed for dynamic analysis of composite dam by replacing the backfill with by a series of vertical cantilever shear beams connected to each other and to the dam by flexible links.

Downstream passage of silver eels at a small hydroelectric facility

Abstract A 100‐mm diameter bypass was installed in the dam face at a small hydropower station on the Mokau River, New Zealand, and its use by downstream migrating silver eels, Anguilla spp., was monitored by trapping at the outlet in autumn 2002 and 2003. In addition, a passive integrated transponder system was used to monitor passage over the spillway. Migrant eels were able to find the bypass, with 544 and 744 eels recorded using it in 2002 and 2003 respectively. Although the bypass was the sole means of safe passage at low flow, migrant eels passed down the spillway in preference to the bypass when the dam was overtopped during floods. A combination of spilling and small diameter bypasses would provide safe downstream passage at hydroelectric facilities for silver eels, so long as entrainment and impingement at the intake screens can be prevented.

The specification of armourstone gradings and EN 13383 (2002)

The grading, whether in terms of mass or size distribution of rock, is critical in the design of hydraulic civil engineering works such as breakwaters, coastal protection revetments, river training works and dam face protection. In the quarry, more effort is needed to control these rock properties than all the others. However, in practice, a poor level of understanding of relatively simple statistical concepts and the recent introduction of an elaborate specification system have contributed to many pitfalls in quality control. The acceptable size and mass ranges for consignments of rock materials are set down in the European standard for armourstone, EN 13383:2002 ( BSI 2002 ). Armourstone pieces are substantially coarser than traditional aggregates and typically include large rock blocks sometimes weighing several tonnes. This standard, in force since 2004, introduced a system of standard gradings and requirements. Although similar to that promoted in CIRIA/CUR (1991) , a detailed explanation is long overdue. In this paper, the Rosin–Rammler equation for cumulative mass and size distributions is adopted. A purchaser or designer can then visualize from a single idealized curve, together with acceptance limits, the most reasonable expectation for a specified grading, rather than work with an envelope of acceptable grading limits. The research also draws upon actual mass distributions measured from projects dating from 1991. These are combined with theoretical data sets. The result is a new expression for what has become a contractually important ratio. The ratio is that between the mean mass as given by bulk weighing and counting, and the median mass used by designers. Non-standard grading specification is also treated, providing further background to recommended best practice as presented in the forthcoming update to the 1991 rock manual.

Local response of a glacier to annual filling and drainage of an ice-marginal lake

AbstractIce-marginal Hidden Creek Lake, Alaska, USA, outbursts annually over the course of 2–3 days. As the lake fills, survey targets on the surface of the ‘ice dam’ (the glacier adjacent to the lake) move obliquely to the ice margin and rise substantially. As the lake drains, ice motion speeds up, becomes nearly perpendicular to the face of the ice dam, and the ice surface drops. Vertical movement of the ice dam probably reflects growth and decay of a wedge of water beneath the ice dam, in line with established ideas about jökulhlaup mechanics. However, the distribution of vertical ice movement, with a narrow (50–100 m wide) zone where the uplift rate decreases by 90%, cannot be explained by invoking flexure of the ice dam in a fashion analogous to tidal flexure of a floating glacier tongue or ice shelf. Rather, the zone of large uplift-rate gradient is a fault zone: ice-dam deformation is dominated by movement along high-angle faults that cut the ice dam through its entire thickness, with the sense of fault slip reversing as the lake drains. Survey targets spanning the zone of steep uplift gradient move relative to one another in a nearly reversible fashion as the lake fills and drains. The horizontal strain rate also undergoes a reversal across this zone, being compressional as the lake fills, but extensional as the lake drains. Frictional resistance to fault-block motion probably accounts for the fact that lake level falls measurably before the onset of accelerated horizontal motion and vertical downdrop. As the overall fault pattern is the same from year to year, even though ice is lost by calving, the faults must be regularly regenerated, probably by linkage of surface and bottom crevasses as ice is advected toward the lake basin.

Treatment for a fully weathered rock dam foundation

The main dam at the upper reservoir of Tianhuanping pumped storage power station is a rockfill dam with an asphalt concrete impervious lining on the upstream face. It is constructed on a non-homogeneous fully weathered rock foundation. In this paper, we present the case study on the treatment for this non-homogeneous fully weathered rock dam foundation. The treatment includes the partial excavation of the fully weathered rock in different depths with respect to the dam deformation, and the enlargement of the transition curvature at the junctions of the inclined dam face and the reservoir floor, as well as the reinforcement for the asphalt concrete impervious lining with a layer of polyester mesh at the parts where tensile strains of the lining are large. A three-dimensional (3D) finite element analysis is carried out for the main dam to provide the basis for the proposed compound treatment method. To account for the effect of the intermediate principal stress σ 2 on the deformation and strength of soils, a simple constitutive soil model is proposed for the finite element (FE) analysis. So far, this project has operated well for more than 5 years without any maintenance for the main dam's asphalt concrete impervious lining, illustrating the success of the treatment for the fully weathered rock dam foundation.

Usoi Landslide Dam and Lake Sarez, Pamir Mountains, Tajikistan

In 1911, a 2-km 3 (0.5-mi 3 ) earthquake-triggered rock slide blocked the Murgab River, southeastern Tajikistan, forming a still-existing, 600-m-high (1,970-ft-high) natural dam—the highest dam, natural or man-made, in the world. Lake Sarez, impounded by this blockage, is 60 km (37 mi) long, with a maximum depth of 550 m (1,800 ft) and a volume of approximately 17 km 3 (∼4 mi 3 ). This lake, which has never overtopped the dam, exits the downstream face as a series of large springs that regroup as the Murgab River. Freeboard between lake surface and the lowest point on the dam crest currently is approximately 50 m (∼165 ft), and the lake is rising at an average rate of 18.5 cm/yr (7.3 in./yr). If the blockage were to fail, a worst-case scenario could endanger tens or possibly hundreds of thousands of people in the Murgab, Bartang, Panj, and Amu Darya valleys downstream. Dam failure potentially could result from: 1) seismic shaking, 2) catastrophic overtopping caused by a landslide entering the lake from the valley wall at high velocity, 3) surface erosion caused by natural overtopping by the rising lake, 4) internal erosion (piping), 5) instability caused by lake pressure against the dam, or 6) slope instability of the dam faces. Occurrence of an overtopping wave resulting from a potential landslide high on the right bank of Lake Sarez seems to be the most realistic of these slight possibilities for failure. Because of the high cost of installing physical remediation to the dam in this rugged mountain area (no roads lead to the site), the main protective measures now being undertaken are hydrological monitoring at the dam and installation of a flood early warning system downstream.

Toward policies and decision-making for dam removal.

Dam removal has emerged as a critical issue in environmental management. Agencies responsible for dams face a drastic increase in the number of potential dam removals in the near future. Given limited resources, these agencies need to develop ways to decide which dams should be removed and in what order. The underlying science of dam removal is relatively undeveloped and most agencies faced with dam removal lack a coherent purpose for removing dams. These shortcomings can be overcome by the implementation of two policies by agencies faced with dam removal: (1) the development and adoption of a prioritization scheme for what constitutes an important dam removal, and (2) the establishment of minimum levels of analysis prior to decision-making about a dam removal. Federal and state agencies and the scientific community must encourage an initial experimental phase of dam removal during which only a few dams are removed, and these are studied intensively. This will allow for the development of the fundamental scientific understanding needed to support effective decision-making in the future and minimize the risk of disasters arising from poorly thought out dam removal decisions.

Numerical Analysis of Multiple Discrete Cracks in Concrete Dams Using Extended Fictitious Crack Model

A rigorous analytical procedure for the crack analysis of concrete dams is established using a newly developed numerical technique for analyzing multiple discrete cracks in concrete. The theoretical aspect of the problem solution is addressed first, focusing on the cracking modes of multiple cracks, followed by a brief review on the numerical formulation of the Mode-I type crack propagation for multiple discrete cracks. Next, a simple technique for modeling curvilinear crack propagation is introduced, and the method is examined through numerical studies on the bending tests of simple plain concrete beams with multiple cracks. Then, a well-quoted scale model of a concrete gravity dam is used to study the cracking behaviors in concrete dams; the numerical modeling involves not only the original single-crack problems but also multiple-crack problems. Employing two different types of numerical models and assuming multiple initial notches of different sizes at different locations along the upstream face of the model dams, various kinds of cracking behaviors are obtained and discussed, focusing on the crack interactions.

Review of Dams in a European context edited by G. H. Midttømme, B. Honningsvåg, K. Repp, K. Vaskinn, and T. Westeren

802 / JOURNAL OF HYDRAULIC ENGINEERING / AUGUST 2002 this topic clearly explain the methods used in various European countries and in the United States. The papers show how the methodologies were developed and why they differ from country to country. Another subset of these papers deals with emergency procedures, warning systems, and training tools for managers of water systems. Mixed in between these sections are highly technical papers dealing with such detailed subjects as delayed response analysis of dam monitoring data, scouring of rock by highvelocity jets, irreversible deformations in arch dams, and nonlinear design of arch dams, to mention a few. Another subset of the papers deals with risk management. One paper addressed the risk being created due to the decrease in the number of highly skilled personnel who designed and built the dams roughly during the period 1950 to 1970. These engineers were completely familiar with weaknesses in the structures of which the modern engineer is completely unaware. Unfortunately, the papers in this section are jumbled together so that the reader has some difficulty in finding papers that deal with similar topics. As a result, if one finds an exceptional paper, trying to locate that same paper at a later time is difficult. The section on ‘‘New Trends in Rehabilitation of Dams’’ suffers from the same disorganization noted in the previous section. One subset of papers in this section presents case studies of dams that have been rehabilitated. These case studies are particularly instructive to engineers planning the rehabilitation of dams. Another subset of papers covers more general matters such as assessment criteria for rehabilitation, modern trends in rehabilitation, and methods to improve low and medium head dams. Finally, a couple of papers deal with sealing methods to be used on dam faces. The strength of this book lies in the outstanding quality of the papers. The papers were submitted on the basis of a general invitation, which in this case produced excellent papers from dam professionals who obviously have a great deal of experience and knowledge. The weakness of the book lies in the almost complete lack of organization and the omission of an index. Preparing an index is a difficult task, but with five editors the task could easily have been shared. I recommend the book for those that deal with the management, operation, and inspection of water storage, supply, and hydroelectric systems. Review of Dams in a European context edited by G. H. Midttomme, B. Honningsvag, K. Repp, K. Vaskinn, and T. Westeren

Hydrodynamic pressures acting on rigid gravity dams during earthquakes

A boundary integral equation model is developed based on the analytical integrals for three-dimensional potential problems. All necessary integrals are first converted into line integrals around a target element and then integrated analytically. The developed model is applied to a practical problem concerning computation of the hydrodynamic pressure acting on a dam face of a dam-reservoir system during earthquakes. The obtained numerical solutions are compared with available two-dimensional experimental data and analytical solutions. A very good agreement is observed. The model is then used to investigate three-dimensional effects of a complex dam-reservoir system.

Extensions to the theory of selective withdrawal

Most reservoirs contain stratified fluid and selective withdrawal is used to obtain water with the desired properties. We initially deal with a layered density distribution. The theory for the critical discharge for a single layer and a point sink is reviewed and extended to cover the case where there is gate discharge (a line sink). The theory for the case when the upper layer depth is large and the flow is coming from both layers is reviewed and it is shown that the valve controls the discharge and a virtual control determines the ratio of the discharge in each layer. This virtual control moves further from the valve as the total discharge increases. We determine the position of the virtual control and the criteria for the maximum for two layers when the upper layer is finite and below a stationary layer. Before this maximum, we show that when the discharge is increased above the critical discharge for the single layer, the finite upper layer does not affect the ratio of the flows from each layer until the virtual control reaches that for the maximum discharge. At this stage, the upper layer becomes tangential to the dam face and this condition and the smoothness of the lower interface determine both the total discharge and the ratio of the flow from each layer. Indeed, at this stage, virtual control and the control of the discharge are at the same section.In a similar way, with a stationary layer above and below two flowing layers, we derive the maximum discharge from the two flowing layers. For this case, the solution is self-similar. This is then extended to a stable stratified continuous density distribution. The experiments of Gariel (1949) and Lawrence & Imberger (1979) suggest that the predictions of the theory are within the experimental errors.