Seismic safety assessment of arch dams using an ETA-based method with control of tensile and compressive damage

The seismic safety assessment of large concrete dams remains a significant challenge in dam engineering, as it requires appropriate analysis methods, modern performance criteria, and advanced numerical models to simulate the dam seismic behavior. This paper presents a method for seismic safety assessment of arch dams based on Endurance Time Analysis (ETA), using tensile and compressive damage results from a robust formulation for seismic analysis considering joint opening/sliding and concrete non-linear behavior (finite element program DamDySSA, under development in LNEC). The seismic performance is evaluated by controlling the evolution of the damage state of the dam, according to predefined performance criteria, to estimate acceleration endurance limits for tensile and compressive damage. These acceleration limits are compared, respectively, with the peak ground accelerations prescribed for the Operating Basis Earthquake (OBE) and Safety Evaluation Earthquake (SEE), aiming to evaluate the dam seismic performance relative to both earthquake levels efficiently, using a single intensifying acceleration time history. The ETA-based method is applied to the cases of Cabril Dam (132 m-high) and Cahora Bassa Dam (170 m-high), confirming its usefulness for future seismic safety studies, while the potential of DamDySSA for non-linear seismic analysis of arch dams is highlighted.info:eu-repo/semantics/publishedVersio

Stress-deformation analysis of a zoned earth dam with elasto-plastic hardening soil models

Zoned earth dams are challenging geotechnical structures for engineers due to the many uncertainties revolving around the behaviour of core and rockfill materials. This research focuses on validation of stress-deformation numerical analyses for better prediction of dam response during construction and first filling. The case study is Montedoglio dam, a 64 m high zoned earth-core dam located on the Tiber River at about 24 km from Arezzo (Central Italy). The construction of embankment dam started in 1977 and finished in 1986 and the reservoir was impounded in 1990. Numerical simulations are conducted using both the finite difference code FLAC2D and the finite element code ICFEP which implement elasto-plastic hardening models. Specifically, two constitutive models were employed for the simulation of the construction and reservoir impounding phases: the Cysoil model (Cap-Yield) implemented in FLAC2D and the Lade’s Double-hardening model implemented in ICFEP. Model parameters for the core and the shoulders were calibrated using laboratory data. The numerical analyses of the construction phase of the dam were carried out with both codes and well captured the monitoring data recorded. The simulation of the reservoir impounding was conducted only using ICFEP with the Double-hardening model and reproduced with reasonable accuracy piezometers measurements and, consequently, stresses and deformations within the dam. Some challenging issues around the model calibration with both codes are presented and discussed

Investigating the operational behaviour of a double curvature arch dam

The safety of dams is crucial in ensuring the continual availability of water, safety of the surrounding communities and infrastructure. Surveillance systems are implemented to monitor the structural integrity of certain dams which have a safety risk. The components and extent of the surveillance systems adopted depends on many factors, which include the type of dam wall structure used to impound the reservoir, geotechnical and environmental conditions. The case study used for this thesis is Kouga Dam located in the Eastern Cape Province of South Africa. It is a double curvature, concrete arch dam which supplies water for domestic, irrigation and industrial use to the Gamtoos River Valley and Nelson Mandela Metropolitan. During construction the stability of the right flank was questioned and subsequently, remedial measures were taken in order to increase the shear resistance of this flank. Previous dam safety evaluations also noted the possibility of Alkali Silica Reaction (ASR) occurring within the structure which resulted in concrete swelling and loss of strength. Due to these factors and the large hazard potential rating associated with this dam an intensive surveillance system has been used to monitor the dam's behaviour during operation. In this thesis the results of the surveillance system is analysed. A strong linear relationship exists between the temperature loading and displacement response of the dam wall. Changes in temperature initiate the response of the structure almost instantaneously. A more complex relationship exists between hydrostatic loading and the displacement response of the structure. A phase lag of approximately one to three months is evident between these two variables. Since construction the displacement and strain rates in the upstream (y) and upward (z) directions are 0.3mm/annum and 8.6με/annum respectively. However, since 1989 there has been a reduction in the average displacement and strain rates in all directions by approximately 70%. This may suggest that the ASR has stabilized. The vertical construction joints, especially the central and upper joints, are relatively open during low water levels. The structure is found to transfer the imposed loading mainly to the central foundation via dominant cantilever action. As a result the reaction forces on the upper foundation have been found to be relatively low, lowering the risk of potential shear failure of the right foundation. Small foundation movements of less than 0.3mm have been observed within the foundation downstream of the dam wall on the right flank. These movements are between 10 and 40m within the foundations

WATER MANAGEMENT IN BANGLADESH AGRICULTURE: OPTIMAL USE AND INVESTMENT POLICIES FOR ADAPTATION TO CLIMATE CHANGE

In Bangladesh, climatic change is likely to impact significantly upon surface and groundwater availability, as well as in other countries. The population of Bangladesh is projected to be double the current 2010 level by 2050. Demand for water will rise with the increasing demand for rice. This paper considers the optimal demand management of irrigation water with stochastic supply under climate change for a 3-year planning horizon. It also identifies the utilization of irrigation water from surface water sources to maximize the expected net social return from rice production. This is done by considering decision on dam release for rice production with reference to climate change. A stochastic dynamic programming model is developed for analyzing the levels and timing of the allocation of surface water for irrigation. The objective is to find the optimal dam release for irrigation which results in the maximum expected present value of the stream of annual net social return from rice production for the 3 years from 2012 to 2014. Net social return in a year consists of the value of rice consumed, measured by consumers’ willingness to pay for rice, less the total cost of rice production. The paper also identifies the need for irrigation infrastructure and determines the optimal investment policies for the adaptation to climate change in Bangladesh agriculture.climate change, dam release, dynamic programming, Environmental Economics and Policy,

Computer-aided design and analysis of arch dams

Double curvature arch dams feature geometrical complexity with a significant amount of parameters involved. Different criteria exist to assist in the design task, from simplified geometrical approaches to optimization procedures. However, most of them present a lack of flexibility and are not integrated in computer-aided design tools. In this contribution, an interactive and flexible software tool is presented to support the complete design process: geometrical definition, FEM model generation (including the mesh, the loads and the boundary conditions) and thermo-mechanical analysis. The design can be performed with different levels of detail to adapt to the information available in each stage of the project. The tool allows defining the shape of the reference cylinder, the excavation depth and slope along the foundation, the crown cantilever thickness and curvature, the shape and location of horizontal arcs; all these steps were described in former contributions. Here, special attention is paid to the introduction of additional features such as joints, spillways, abutments of varying shape and outlet works. All steps have been defined with a high degree of flexibility in the design process. The tool is integrated with the pre and post process software GiD, which allows taking advantage of its functionalities, such as mesh generation and results analysis. It is also coupled with a specific application for thermo-mechanical analysis of dams, developed in Kratos Multiphysics – a framework for building parallel multi-disciplinary simulation software. The whole design process can be followed in a unique environment, because the structural response of preliminary designs can be computed and the results considered to refine the dam geometry

Water Scarcity, Marketing, and Privatization

Most Americans take water for granted. Turn on the tap and a limitless quantity of high quality water flows for less money than it costs for cable television or a cell phone. The current drought has raised awareness of water scarcity, but most proposals for dealing with drought involve quick fixes-short-term palliatives, such as bans on washing cars or watering lawns except on alternate days. It is assumed that things will return to normal, and we will be able to wash our cars whenever we wish. But the nation's water supply is not inexhaustible. A just-released report of a White House subcommittee ominously begins: "Does the United States have enough water? We do not know." In a survey of states conducted by the U.S. General Accounting Office, only 14 states reported that they did not expect to suffer water shortages in the next 10 years. Is the sky falling? Not yet, but the United States is heading toward a water scarcity crisis: our current water use practices are unsustainable, and environmental factors threaten a water supply heavily burdened by increased demand. As the demand for water outstrips the supply, the stage is set for what Jared Diamond would call a collapse. How will we respond? When we needed more water in the past, we built a dam, dug a canal, or drilled a well. With some exceptions, these options are no longer viable due to a paucity of sites, dwindling supplies, escalating costs, and environmental objections. Instead, we are entering an era in which demand for new water will be satisfied by reallocating and conserving existing sources. The current water rights structure is the outcome of historical forces that conferred great wealth and power along with the water. The solution to tomorrow's water shortages will require creative answers to challenging issues of equity, community, and economics

Stability analysis of gravity dams for the maximum design earthquake

This thesis presents a two-dimensional hydrodynamic stability analysis of gravity dams for the maximum design earthquake. The coupled mechanical and hydraulic behavior of the dam’s rock mass foundation is taken into account. The main aspects concerning gravity dams are presented along with their main failure causes. The safety rules currently in use and approved by the International Commission on Large Dams (ICOLD) Seismic Committee are presented. The fundamental elements of seismic application relevant for the models used in this work are also presented, such as the dynamic interaction between the reservoir and the upstream face of the dam, adequate boundary conditions for an explicit method and different damping hypotheses. Two dams of different height are numerically analysed. Both dams have rock mass foundations with identical geometry, with horizontal and vertical discontinuities, and the grout and drainage curtains are simulated. Analysis is carried out with a discontinuum model, Parmac2D-FFlow. The displacements at the base of the dam, both on the dam’s heel and the dam’s toe, are compared for the Rayleigh damping hypothesis and the mass proportional term damping. In every case studied two different situations regarding the dam foundation behavior are considered: i) non-linear behavior of the dam/foundation interface and elastic behavior of the fractured rock mass area and ii) non-linear behavior of both the dam/foundation interface and the joints in the fractured rock mass area. The results presented allow the analysis of the effect of the peak ground acceleration to be carried out. Conclusions are drawn regarding the effect of joint normal stiffness on the behavior of gravity dams due to seismic loads

On the Dynamic Capacity of Concrete Dams

The purpose of this joint contribution is to study the maximum dynamic load concrete dams can withstand. The so-called "dynamic capacity functions" for these infrastructures seems now technically and commercially feasible thanks to the modern finite element techniques, hardware capabilities, and positive experiences collected so far. The key topics faced during the dynamic assessment of dams are also discussed using different point of view and examples, which include: the selection of dynamic parameters, the progressive level of detail for the numerical simulations, the implementation of nonlinear behaviors, and the concept of the service and collapse limit states. The approaches adopted by local institutions and engineers on the subject of dam capacity functions are discussed using the authors' experiences, and an overview of time and resources is outlined to help decision makers. Three different concrete dam types (i.e., gravity, buttress, and arch) are used as case studies with different complexities. Finally, the paper is wrapped up with a list of suggestions for analysts, the procedure limitations, and future research needs

Seismic Assessment of Arch Dams Using Fragility Curves

In the present paper, the IDA approach is applied to analyzing a thin high arch dam. The parameters of Sa, PGA and PGV are used as intensity measure (IM) and the overstressed area (OSA) is utilized as engineering demand parameter (EDP) and then, three limit states are assigned to the considered structure using the IDA curves. Subsequently, fragility curves are calculated and it is showed that the PGA is a better parameter to be taken as IM. In addition, it is found that the utilizing the proposed methodology, quantifying the qualitative limit states is probable. At last, having the fragility curves and considering their slope in addition to the other routine data which can be extracted from these curves, one may be able to conclude that in what performance level the considered dam body seems to be weak and needs retrofitting works