Gravity Dam Research Articles

Blast-Resistance and Damage Evaluation of Concrete Gravity Dam Exposed to Underwater Explosion: Considering the Initial Stress Field

There is an increasing concern on the vulnerability of concrete gravity dams under blast loads. To a better evaluation of the blast-resistance, the effect of the initial stress field is taken into consideration herein. Firstly, a fluid-solid coupling numerical model is established to investigate the blast-resistance of concrete gravity dams. The numerical results indicate that the initial stress field has non-neglectable effect on the shock wave propagation, blast vibration, and failure mode of concrete gravity dams. The damage of dam base may be overestimated without the consideration of initial stress field. Moreover, a parametric study are carried out for further investigations of the dynamic responses and damage properties under various explosion scenarios (explosive charge, detonation depth, and standoff distance). With the consideration of the initial stress field, it can be concluded that the dam head nearest the explosive source is the weakest part, and the safety of the dam base is another important consideration, which may lead to severe dam-break floods. At last, a new method is proposed and recommended to evaluate the blast resistance of the whole concrete gravity dam, where the blast-induced vibration and penetration depth of cracks are suggested for the dam crest and dam base, respectively.

Three-dimensional linear seismic analysis of normal concrete gravity dam

The three-dimensional linear finite element model is established for the bottom outlet dam section of concrete gravity dam. Mode-superposition response spectrum method and the massless foundation time history method are adopted to analyze the static and dynamic comprehensive stress response and displacement response of the dam under the action of the standard response spectrum of the design earthquake or the corresponding artificial wave under the action of design earthquake and check earthquake. The results show that the dam works well in seismic condition. In addition, the influence of radiation damping of infinite foundation on the dynamic response of the dam section under different seismic waves is analysed. By comparing the dynamic and static comprehensive stress changes of the dam, it shows that after considering the radiation damping effect of the infinite foundation, the dynamic response of the dam body is significantly reduced.

Physical Modeling on Dynamic Responses of Gravity Dams by Underwater Explosion in a Centrifuge

AbstractGravity dams are important infrastructures, and their failure can affect public security. In this work, physical modeling was conducted to determine the dynamic responses and types of damag...

Water Forever: Warragamba and Wivenhoe Dams

Brisbane and Sydney's prewar dams and reservoirs were not sufficient to provide reticulated water to the hundreds of thousands of new households that settled in rapidly growing suburbs from the early 1950s. Following American precedent, large concrete gravity dams became easier to build. Hydrologists predicted the likely volume that catchments and valleys could both collect and hold if dammed. This article examines the decision-making trajectory of the two largest potable water urban dams in Australia, Warragamba and Wivenhoe, from conception and construction to operation. Per capita consumption of water rose sharply in the 1980s but subsequent droughts have forced both governments and the populace to change the way they use water and no longer imagine that supply is unlimited.

Lower Kaleköy Dam – A tailor made composite dam structure

AbstractWorldwide various type of dams are used to create reservoirs for multiple purposes. Particularly in usual cases, a single dam type is used to form a watertight barrier. Keeping safety and finance in mind, less challenging dam locations, that concerns with aspects like foundation conditions, seismicity at the dam sites, availability of construction materials, etc. are preferred. Ironically, where there is a demand for a reservoir, a suitable dam location is not always available. In those cases, these circumstances make advanced design of dam structures indispensable. An example of such a dam design is the Lower Kaleköy composite dam structure. The same consists of a roller compacted concrete gravity dam at the right bank, which is linked with one of the world's highest deformation joint to the very first asphalt core embankment dam in Turkey, situated on the left bank. The Lower Kaleköy Hydroelectric Power Plant (HEPP) constructed and operated by Kalehan Genç Enerji Üretim A.Ş. with an installed capacity of 500 MW, as part of the Beyhan Kaleköy HEPP cascade is located on the Murat River, a tributary to the Euphrat River in Eastern Turkey. This paper summarizes the design methodology developed by the design consortium (AFRY/Temelsu), headed by AFRY, for the tailored composite dam.

Effect of seismic wave propagation in massed medium on rate-dependent anisotropic damage growth in concrete gravity dams

Seismic modeling of massive structures requires special caution, as wave propagation effects significantly affect the responses. This becomes more crucial when the path-dependent behavior of the material is considered. The coexistence of these conditions renders numerical earthquake analysis of concrete dams challenging. Herein, a finite element model for a comprehensive nonlinear seismic simulation of concrete gravity dams, including realistic soil-structure interactions, is introduced. A semi-infinite medium is formulated based on the domain reduction method in conjunction with standard viscous boundaries. Accurate representation of radiation damping in a half-space medium and wave propagation effects in a massed foundation are verified using an analytical solution of vertically propagating shear waves in a viscoelastic half-space domain. A rigorous nonlinear finite element model requires a precise description of the material response. Hence, a microplane-based anisotropic damage-plastic model of concrete is formulated to reproduce irreversible deformations and tensorial degeneration of concrete in a coupled and rate-dependent manner. Finally, the Koyna concrete gravity dam is analyzed based on different assumptions of foundation, concrete response, and reservoir conditions. Comparison between responses obtained based on conventional assumptions with the results of the presented comprehensive model indicates the significance of considering radiation damping and employing a rigorous constitutive material model, which is pursued for the presented model.

Accounting for Uncertainties in the Safety Assessment of Concrete Gravity Dams: A Probabilistic Approach with Sample Optimization

Important advances have been made in the methodologies for assessing the safety of dams, resulting in the review and modification of design guidelines. Many existing dams fail to meet these revised criteria, and structural rehabilitation to achieve the updated standards may be costly and difficult. To this end, probabilistic methods have emerged as a promising alternative and constitute the basis of more adequate procedures of design and assessment. However, such methods, in addition to being computationally expensive, can produce very different solutions, depending on the input parameters, which can greatly influence the final results. Addressing the existing challenges of these procedures to analyze the stability of concrete dams, this study proposes a probabilistic-based methodology for assessing the safety of dams under usual, unusual, and extreme loading conditions. The proposed procedure allows the analysis to be updated while avoiding unnecessary simulation runs by classifying the load cases according to the annual probability of exceedance and by using an efficient progressive sampling strategy. In addition, a variance-based global sensitivity analysis is performed to identify the parameters most affecting the dam stability, and the parameter ranges that meet the safety guidelines are formulated. It is observed that the proposed methodology is more robust, more computationally efficient, and more easily interpretable than conventional methods.

Seismic fragility analysis of the Koyna gravity dam with layered rock foundation considering tensile crack failure

In the present investigation, the seismic fragility analysis of the Koyna dam-reservoir-layered rock foundation system is performed, considering foundation flexibility. For material non-linearity, the Concrete Damaged Plasticity (CDP) model and Mohr-Coulomb failure model are adopted for dam and foundation, respectively. The finite element modelling takes into account the material flexibility, inertial, and damping properties. For the seismic analysis, ground motions are picked according to the Conditional Mean Spectrum approach. An Incremental Dynamic Analysis (IDA) method is used in which each ground motion is scaled at different intensity levels and directly these ground motions are adopted for the time-history analysis. The ground motion Peak Ground Acceleration (PGA), Peak Ground Velocity (PGV), and Acceleration Spectrum Intensity (ASI) are preferred as an intensity measure (IM) parameter. For the seismic fragility analysis, the tensile crack failure in the dam is considered as a limit state. Analytical fragility curves are plotted for the various vulnerability states of the gravity dam based on the damage indices which are evaluated using crack length and dissipation energy in the dam. Numerical results indicate that the dam with more flexible rock layers is more sensitive against seismic forces; however, the dam with hard rock layers is on the safer side. The crest displacement and heel stress can be viewed as a damage measure (DM) parameter for the IDA method. It is observed that the ground motion PGV shows a distinct result in IDA curves as compared to PGA and ASI. However, in fragility analysis, the seismic risk of a gravity dam can be evaluated better against PGA and ASI as compared to PGV.

A Literature Review on Dynamic Analysis of Concrete Gravity and Arch Dams

This paper is devoted to a literature review for various treatments of dynamic analysis of concrete gravity and arch dams. The dynamic analysis of dams can be carried out by using analytical, semi-analytical, and numerical approaches, which may include nonlinear effects or ignore them. This kind of analysis can be conducted in the time or frequency domain. Different parameters significantly affect the dynamic behavior of dams, such as dam-water interaction, water compressibility, mass and damping of the foundation, sediments at the reservoir bottom, free surface waves, the infinite length of the foundation rock, reservoir and so on. As the analysis methods of dams developed, these parameters were gradually included in the process. Consequently, their capability enhanced in a more realistic investigation of the dams' behavior. This paper aims to illustrate these achievements by briefly reviewing the available published articles. Corresponding researches are categorizing based on the analysis techniques and considering or neglecting the dam-water interaction, sediments, and free surface motions. Assessing the current studies and suggesting future research are carried out. Expressing positive or negative aspects of the existing investigations are also offered.

Verification and application of 2-D DDA-SPH method in solving fluid–structure interaction problems

The study of fluid–structure interaction (FSI) is a challengeable topic, which concerns a coupled system with consideration of not only the behaviors of the fluid and the structure, but also the interaction process between both. In this paper a coupled method is introduced to simulate FSI problems in two-dimensional (2-D) case. In this coupled method (2-D DDA-SPH), the smoothed particle hydrodynamics (SPH) based on kernel approximation and particle approximation is employed to represent the fluid domain governed by Navier–Stokes equations and the discontinuous deformation analysis (DDA) based on the minimum total potential energy principle is used to model the real solid structure (with rigidity or elasticity) through virtual joints. A coupling scheme bridging both methods is used based on a penalty-force method, and an improved contact detection between particle and block is proposed. Several challenging examples, including breaking dam flow through an elastic plate, breaking dam flow on a rigid barrier or an elastic barrier are investigated to demonstrate the capability of the 2-D DDA-SPH method to capture the entire FSI process. Finally, two application examples, failure of gravity dam induced by water pressure, and dynamic response of armor blocks on breakwater under incident wave, are studied by using 2-D DDA-SPH. The simulation results show satisfactory agreements with available experimental, numerical, and analytical results, suggesting the applicability of the 2-D DDA-SPH method to solve FSI problems.

Deformation early-warning index for heightened gravity dam during impoundment period

The mechanical parameters of materials in a dam body and dam foundation tend to change when dams are reinforced in aging processes. It is important to use an early-warning index to reflect the safety status of dams, particularly of heightened projects in the impoundment period. Herein, a new method for monitoring the safety status of heightened dams is proposed based on the deformation monitoring data of a dam structure, a statistical model, and finite-element numerical simulation. First, a fast optimization inversion method for estimation of dam mechanical parameters was developed, which used the water pressure component extracted from a statistical model, an improved inversion objective function, and a genetic optimization iterative algorithm. Then, a finite element model of a heightened concrete gravity dam was established, and the deformation behavior of the dam with rising water levels in the impoundment period was simulated. Subsequently, mechanical parameters of aged dam parts were calculated using the fast optimization inversion method with simulated deformation and the water pressure deformation component obtained by the statistical model under the same conditions of water pressure change. Finally, a new early-warning index of dam deformation was constructed by means of the forward-simulated deformation and other components of the statistical model. The early-warning index is useful for forecasting dam deformation under different water levels, especially high water levels.

A System Identification-Based Damage-Detection Method for Gravity Dams

Dams are essential infrastructures as they provide a range of economic, environmental, and social benefits to the local populations. Damage in the body of these structures may lead to an irreparable disaster. This paper presents a cost-effective vibration-based framework to identify the dynamic properties and damage of the dams. To this end, four commonly occurred damage scenarios, including (1) damage in the neck of the dam, (2) damage in the toe of the structure, (3) simultaneous damage in the neck and the toe of the dam, and (4) damage in the lifting joints of the dam, are considered. The proposed method is based on processing the acceleration response of a gravity dam under ambient excitations. First, the random decrement technique (RDT) is applied to determine the free-vibration of the structure using the structural response. Then, a combined method based on Hilbert–Huang Transform (HHT) and Wavelet Transform (WT) is presented to obtain the dynamic properties of the structure. Next, the cubic-spline technique is used to make the mode shapes differentiable. Finally, Continuous Wavelet Transform (CWT) is applied to the residual values of mode shape curvatures between intact and damaged structures to estimate the damage location. In order to evaluate the efficiency of the proposed method in field condition, 10% noise is added to the structural response. Results show promising accuracy in estimating the location of damage even when the structure is subjected to simultaneous damage in different locations.

Effective Safety Assessment of Aged Concrete Gravity Dam based on the Reliability Index in a Seismically Induced Site

The seismic performance of the aged-concrete gravity dam (aged-CGD) by safety assessment based on the reliability-index is the main focal point of this study. Determination of reliability-index has been handled by the site seismic hazard analysis with the help of PSHRisk-tool (developed by the authors) and risk assessment. Incorporated with the uncertainties, the failure probability has been carried out by the IDA and fragility analysis. For the nonlinear finite element model of the CGD, the concrete damage plasticity (CDP) model is adopted. To investigate the aging effect, the hygro-chemo-mechanical model has been taken for different years consideration. Through the failure risk assessment of serviceability and safety level, the target reliability index has been determined here for an existing CGD in Korea. Despite several types of research on the CGD safety assessment, the main novelty of this proposed approach will help the dam operator to check the safety barrier for the aged-CGD. A safety index is investigated by comparing the target reliability-index of the age-CGD with the reliability-index for two potential earthquake levels. However, the proposed approach can implement to check the safety range of any seismic site for any set of earthquakes.

Hydration, Hardening Mechanism, and Performance of Tuff Normal Concrete

AbstractUsing admixtures to replace part of cement can effectively reduce environmental pollution. Many concrete gravity dams have been planned for Tibet, where the resource of fly ash (FA) is scar...

Modeling an environment-friendly and antiearthquake dam by probabilistic-FEM approach

A novel generation of gravity dams, known as cemented material dam (CMD), allows construction of dam body on almost every rock foundation even on very low modulus and weak rocks. Because of its rock weakness and antiearthquake features, more considerations are required for its design. Therefore, a probabilistic model code based on coupled Monte-Carlo and Fuzzy simulation is presented to put together regulations, rules and explanations necessary for serviceability assessment of CMD. The proposed code is contained of the sensitivities of tensile stress, compressive stress and sliding. Then, finite element method (FEM) is utilized to verify the overall strength security and stability for a case study. The results indicated that for the optimal cross-section, the upstream as same as downstream dam slopes are 1:0.45 to 1:0.80. In addition, the vertical and horizontal displacement contours increase from bottom to top of the dam. The maximum values of horizontal and vertical displacements are within the permissible limit of 1–2% dam height. The results also demonstrated that elastoplastic constitutive model is more suitable to safely predict the behavior of CMD than other models in statistical and dynamical conditions.

Multi-sensing investigation of crack problems for concrete dams based on detection and monitoring data: A case study

Cracks, a major issue in concrete structures, will reduce structural integrity, stability and impermeability. In this paper, a comprehensive site crack status monitoring system was constructed in a roller compacted concrete (RCC) gravity dam during the construction period, by combining acoustic emission (AE), micro-seismic (MS), cross-hole acoustic wave detection (CAWD), crack gauge and strain gauge techniques; this system was used to investigate crack development problems that may occur under varying construction conditions. Through knocking location tests, the acoustic wave transmission rate of RCC was determined by the AE and MS system, to monitor the real-time status of micro-cracks. Moreover, the crack tip displacement, adjacent concrete strain and concrete ultrasonic velocity were captured, to monitor the propagation of macroscopic cracks. By combining the information obtained at both the micro- and macro- levels, the development trend of a crack was analyzed. Results show that micro-crack signals were captured, but the sensitivity of the AE approach was relatively smaller than that of MS method, and the crack status was in the structural internal stress adjustment stage. On the macro-level, the macroscopic expansion phenomenon of the original crack was not captured by the crack gauge, strain gauge and acoustic penetration. Based on the size, the concentration of micro-cracks and the development trend of the macro-cracks monitored by the multi-sensing system, the crack behavior can be evaluated in huge concrete infrastructures.

Optimum design of concrete gravity dams using sequential quadratic programming algorithm

Large dams and their facilities are a part of the infrastructure of any society, and a huge amount of financial and human resources of the community are consumed to build them. Among the various types of dams, optimum design of concrete gravity dams requires special attention because these types of dams require a huge amount of concrete for their construction. In contrast, design optimisation of concrete gravity dams with regard to conditions and limitations, as well as geometric variables, can be complicated. With the appearance of various optimisation methods in recent decades, some researchers have worked on optimum design of dams. The objective of this study is to create an optimum design concrete gravity dam using a new method. For this purpose, a design methodology is proposed. According to the proposed method, a computer program is developed which carries out the optimisation process automatically. Also, numerical problems have been studied and the results obtained by the developed method have been compared to earlier studies in the literature. The results of this research study show that the novel developed method is very effective for the optimum design of gravity dams.

Role of negative pressure in structural responses of gravity dams to underwater explosion loadings: The need to consider local cavitation

Negative pressure tends to occur at a fluid–structure interface (FSI) in an underwater explosion (UNDEX) event. When the pressure drops to a value of vapor pressure, distributed cavities will form and maintain the pressure acting on the FSI during expansion, i.e. the local cavitation phenomenon. The local cavitation phenomenon is likely to occur at a dam-water interface when the dam is undergoing an UNDEX impact. It should significantly change the hydrodynamic-pressure distribution on the dam face and thus have an important influence on the response of the dam. Unfortunately, far too little attention has been paid to local cavitation in the current UNDEX resistant design and evaluation of dams. In this work, a dynamic analysis of a 72.12-m-high gravity dam (non-overflow monolith) undergoing an UNDEX impact is carried out with ABAQUS/Explicit. The ability of the employed software to capture the negative pressure at a FSI in an UNDEX event is validated by comparing the simulated pressure history at a water-plate interface with the analytical solution and experimental data reported in the literature. The simulation shows that significant negative pressure would arise at the dam-water interface without a zero-value cavitation limit considered. The negative pressure would produce overestimated tensile damage to the dam face but underestimated one to the dam base. A more reasonable prediction of the hydrodynamic-pressure distribution on the dam face should be obtained when the local cavitation effect is considered, which prevents the dam face from undergoing exaggerated negative pressure. It is therefore suggested that the local cavitation effect should be considered in future UNDEX resistant design and evaluation of dams, however, with cautious use of the cavitation threshold.

New explicit formulas for optimum design of concrete gravity dams

Large dams are a part of the infrastructure of any society, and a huge amount of resources are consumed to build them. Among the various types of dams, the optimum design of concrete gravity dams requires special attention because these types of dams require a huge amount of concrete for their construction. On the other hand, concrete gravity dams are among the structures whose design, regarding the acting forces, geometric parameters, and resistance and stability criteria, has some complexities. In the present study, an optimization methodology is proposed based on Sequential Quadratic Programming (SQP), and a computer program is developed to perform optimization of concrete gravity dams. The optimum results for 45 concrete gravity dams are studied and regression analyses are performed to obtain some explicit formulas for optimization of the gravity dams. The optimization of concrete gravity dams can be provided easily using the developed formulas, without the need to perform any more optimization process.

Effect of Drain Pipes on Uplift Force and Exit Hydraulic Gradient and the Design of Gravity Dams Using the Finite Element Method

The effects of diameter and location of drain pipes on the uplift force and exit hydraulic gradient for a gravity dam are investigated. A numerical model of a gravity dam is simulated using the finite element method. The results indicate that drain pipes under a gravity dam reduce the uplift force and exit hydraulic gradient. The optimal location of the drain pipe with respect to reducing uplift force is 0.25 L (where L is the dam width) from the dam heel, and is 0.75 L with respect to the exit hydraulic gradient. In addition, with increasing drain depth, the uplift force first decreases and then increases. The drain pipe diameter has little effect on uplift force and exit hydraulic gradient and thus its selection should depend on other considerations. When the drain pipe is located at its optimum location with respect to minimizing the uplift force, the volume of dam materials is reduced ~ 30–50%.