High Arch Dam Research Articles

Overall Stability Analysis of Xiluodu High Arch Dam Based on Fine Three‐Dimension Numerical Modeling

The RFPA3D is used to establish a fine finite element model of 6.63 million elements, which realizes the fine simulation of the stability of the Xiluodu arch dam under layered, overall, multiworking conditions and multistress fields, and the cracking and failure process under overload. The structural design scheme of the arch dam and the corresponding foundation treatment design are evaluated. The model fully reflects the measures of dam shape structure design, angle fitting structure design, and foundation concrete replacement in the Xiluodu arch dam technical design stage. The RFPA3D adopts the mesoelement elastic damage model, which considers the Mohr–Coulomb criterion of shear fracture and the maximum tensile failure criterion, and assumes that the mechanical properties of the element satisfy Weibull distribution to consider its heterogeneity. The simulation results show that, under normal load conditions, the dam foundation surface after comprehensive reinforcement has better overall stability, the stress and deformation of the dam body have good symmetry, and the overload factor of crack initiation under overload calculation K1 = 2P0 (P0 is normal water load), the nonlinear deformation overload factor K2 = 3.5–4P0, and the limit load factor K3 = 7.5–8.0P0, dam safety can be satisfied. The RFPA3D is used to establish a superlarge fine model to study the overall stability of the high arch dam, which provides an effective method for analysis and research of other large hydraulic projects in the world.

Seismic response analysis of high arch dam considering the nonlinearity of the transverse joints

It is of great significance for dynamic response analysis of high arch dam considering the nonlinearity of transverse joints. Interaction between dam and reservoir water is taken into account, and static and dynamic combination algorithm is adopted. The result is that the opening of the transverse joint those are in the middle and close to the abutment is larger than others. Considering the deformation characteristics of transverse joints provides a basis for nonlinear dynamic study of arch dams in the future.

Variation in hydraulic conductivity of fractured rocks at a dam foundation during operation

Characterizing the permeability variation in fractured rocks is important in various subsurface applications, but how the permeability evolves in the foundation rocks of high dams during operation remains poorly understood. This permeability change is commonly evidenced by a continuous decrease in the amount of discharge (especially for dams on sediment-laden rivers), and can be attributed to fracture clogging and/or hydromechanical coupling. In this study, the permeability evolution of fractured rocks at a high arch dam foundation during operation was evaluated by inverse modeling based on the field time-series data of both pore pressure and discharge. A procedure combining orthogonal design, transient flow modeling, artificial neural network, and genetic algorithm was adopted to efficiently estimate the hydraulic conductivity values in each annual cycle after initial reservoir filling. The inverse results show that the permeability of the dam foundation rocks follows an exponential decay annually during operation (i.e. K / K 0 = 0.97e −0.59 t + 0.03), with good agreement between field observations and numerical simulations. The significance of the obtained permeability decay function was manifested by an assessment of the long-term seepage control performance and groundwater flow behaviors at the dam site. The proposed formula is also of merit for characterizing the permeability change in riverbed rocks induced by sediment transport and deposition.

Modification of direct-FE method for nonlinear seismic analysis of arch dam-reservoir-foundation system considering spatially varying ground motion

The present paper aims to modify an existing direct finite element method for nonlinear seismic analysis of high arch dam-reservoir-massed foundation systems to consider the effects of spatially varying ground motion at the bottom of the foundation rock with the non-stationary frequency characteristics. Viscous-damper boundaries are used to model the semi-unbounded foundation rock and the reservoir domains. In the existing direct finite element method, it is assumed that incident waves propagate vertically upwards from beneath the foundation rock towards the ground surface, and the effective seismic forces starting from the control motion on the foundation surface are applied to the bottom and the side vertical boundaries of the foundation rock. Three components of the motion recorded at Parkfield fault zone 16 during the 1983 Coalinga earthquake are selected as the free-field control motion at the surface of the foundation rock. On the other hand, in the modified direct FE method, fully non-stationary spectrum-compatible ground motion time histories, including both wave passage and incoherency effects, are simulated at a number of locations at the foundation bottom. Then the generated ground motions are used as multiple input incident motions to compute effective seismic forces applied to the bottom and the side boundaries of the foundation rock in the dam-reservoir-massed foundation system. Step-by-step procedures for computing the effective earthquake forces in the existing and the modified direct FE methods are presented. The nonlinearity originates from opening/sliding of the vertical contraction joints within the dam body. The reservoir–structure interaction is accounted for via the finite element method assuming compressible reservoir. The Karoun-I, a double curvature high arch dam, is selected as a case study. Several numerical validation models are conducted and compared with the benchmark solutions to indicate the accuracy of the existing direct FE method. It was seen that applying effective earthquake forces determined from the modified direct finite element method increases the nonlinear seismic response of the dam-reservoir-massed foundation system in terms of the crest displacements and stress levels.

A distance coefficient-multi objective information fusion algorithm for optimal sensor placement in structural health monitoring

Optimal sensor placement (OSP) plays a key role in the construction and implementation of an effective structural health monitoring system (SHM). In this study, a novel and effective method named the distance coefficient-multi objective information fusion algorithm (D-MOIF), which is different from the conventional method and easier to be implemented, is developed to select the best sensor location for large-scale structures. An integrated information matrix including mode independence, damage sensitivity and modal strain energy is deduced from the structural motion equation to meet multiple needs of SHM. A European distance derived from the analytic geometry is proposed to overcome the information redundancy between sensors. Based on the principle of information entropy, an optimized objective function is constructed, which could balance the sensitivity and robustness of the algorithm. A computational case of a high arch dam is implemented to demonstrate the effectiveness of the modified algorithm, and three classical evaluation criteria are used to estimate the comparison between the D-MOIF algorithm and four traditional OSP methods. Finally, the optimization of the number of sensors based on different algorithms is discussed in detail. Results indicate that the proposed D-MOIF algorithm could generate more applicable sensor configurations for large-scale structures.

Correlation Study between Seismic Intensity Measures and Nonlinear Response of Arch Dam via Endurance Time Analysis

Predicting the structural response efficiently and quickly is a major focus in civil engineering. For concrete dams, due to the structure’s complexity, it is difficult to obtain the structural performance timely through a large number of calculations. In this paper, the relationship between structural responses and seismic intensity mesures (IMs) is established under the framework of endurance time analysis method (ETAM) with its good accuracy and high efficiency. Baihetan arch dam is selected as a case study, and the dam-reservoir-foundation system is excited under fourteen sets of endurance time acceleration functions (ETAFs) which are generated through the response spectra of ground motion records. The results show that, compared with displacement-dependent damage indices (DIs), damage-dependent DIs can better reflect damage characteristics of the arch dam under different damage levels. Among the ETA-related IMs, the combined spectral acceleration is the most practical and proficient, followed by acceleration spectral intensity (ASI) and effective peak acceleration (EPA). For high arch dam, the influence of the higher order modes should be fully taken into account when establishing the correlation between the structural response and the IMs. The sufficiency of IMs based on structural response should also be fully demonstrated.

Detection of post-earthquake damage inside a concrete arch dam using the electromechanical impedance method

The detection of post-earthquake damage inside concrete dams has recently attracted great interest in academia and industry. A novel electromechanical impedance (EMI) method using embedded EMI sensors (EMISs) is proposed in this paper to detect earthquake-induced damage within concrete dams. The basic concept of the proposed EMI method is to use high-frequency excitations to monitor local changes in the monitored dams caused by damage. Based on the effective impedance, a three-dimensional (3D) EMI model for embedded EMISs is proposed. Then, a new damage-sensitive feature factor is derived based on the proposed 3D EMI model. A high arch dam model with embedded EMISs is studied experimentally. Moreover, shaking table tests are conducted on the dam model. The proposed 3D EMI method is used to monitor the evolution of earthquake-induced damage inside the dam model. The experimental results demonstrate the efficiency and feasibility of the proposed EMI method for detecting earthquake-induced damage in concrete dams.

An improved Hilbert–Huang transform method for modal parameter identification of a high arch dam

The vibration signal of a high arch dam flow discharge structure under the excitation of water flow is difficult to extract because the vibration signals are weak, low-frequency, and easily submerged by noise. To address the problem of modal confusion during the modal identification of dam structures, a combined decomposition method based on the combination of complete ensemble empirical mode decomposition with adaptive noise and a masking signal processing method is proposed based on the analysis of modal confusion mechanism. Based on the measured vibration response signals of the dam body's measuring points, the bandwidth signals that have modal confusion are mixed with the high-frequency part of the original signal by adding a masking signal. After decomposition distinguishes different frequency parts of the signal, better inhibition of modal confusion is obtained. The improved Hilbert–Huang transform and random decrement technique methods are used to identify the modal parameters of the high arch dam under the excitation of flow discharge. The analysis of engineering example shows that this method can effectively inhibit modal confusion, avoid loss of modal information, and accurately identify the modal parameters of the structure. It can be applied to the modal identification process of engineering structures in other related fields.

Study on the deformation mechanism of abutment slope and its influence on the dam during the impoundment of high arch dam

The deformation of abutment slope during impoundment poses great challenges to the working behavior and long-term safety of the arch dam. According to the monitoring data of impoundment and slope, slope deformation, valley width change, and arch dam chord length change are systematically analyzed and studied. It is pointed out that the deformation of the dam body and foundation is an irreversible plastic deformation and is evidently correlated with impoundment. Based on the unsaturated effective stress principle of fractured rock mass and the action mode of the reservoir basin pressure, the deformation mechanism of abutment slope has been discussed. The large-scale 3D nonlinear finite element model is established based on numerical analysis, and the deformation mechanism during impoundment and the effect of the effective stress change on the displacement and stress of the dam body are analyzed. The results indicate that effective stress can elucidate the valley contraction to some extent and that the contribution of the reservoir basin pressure is small. Slope deformation is beneficial to the dam displacement to some extent. Moreover, it has a negligible influence on the dam surface stress. However, the junction of the dam and foundation needs to be given special attention.

Automatic modal parameter identification of high arch dams: feasibility verification

Modal parameters, including fundamental frequencies, damping ratios, and mode shapes, could be used to evaluate the health condition of structures. Automatic modal parameter identification, which plays an essential role in realtime structural health monitoring, has become a popular topic in recent years. In this study, an automatic modal parameter identification procedure for high arch dams is proposed. The proposed procedure is implemented by combining the density-based spatial clustering of applications with noise (DBSCAN) algorithm and the stochastic subspace identification (SSI). The 210-m-high Dagangshan Dam is investigated as an example to verify the feasibility of the procedure. The results show that the DBSCAN algorithm is robust enough to interpret the stabilization diagram from SSI and may avoid outline modes. This leads to the proposed procedure obtaining a better performance than the partitioned clustering and hierarchical clustering algorithms. In addition, the errors of the identified frequencies of the arch dam are within 4%, and the identified mode shapes are in agreement with those obtained from the finite element model, which implies that the proposed procedure is accurate enough to use in modal parameter identification. The procedure is feasible for online modal parameter identification and modal tracking of arch dams.

Inverse Analysis of the Partitioning Deformation Modulusof High-Arch Dams Based on Quantum Genetic Algorithm

The physical and mechanical parameters of hydraulic structures in complicated operating conditions often change over time. Updating these parameters in a timely manner is important to comprehend the operating behaviors and monitor the safety of hydraulic structures. Conventional inverse analysis methods can only generate inversions on the comprehensive deformation modulus of concrete dam structures, which contradict practical conditions. Based on the researches on conventional reversion methods of the deformation modulus of the dam body, foundation, and reservoir basin, the objective fitness function is established in this paper according to engineering-measured data and finite element simulation results. The quantum genetic algorithm has high global search efficiency and population diversity. A mechanical parameter inversion of high-arch dams is built from the intelligent optimization of an established algorithm by applying the quantum genetic algorithm. The proposed algorithm is tested to be feasible and valid for practical engineering projects and therefore shows scientific and practical application values.

Statistical modelling for high arch dam deformation during the initial impoundment period

Although statistical models are efficient in most cases to analyze concrete dam displacements, these models are built on several hypotheses, leading to uncertainties especially for special periods. The special statistical models, improving estimations of the non-stationary thermal and the non-monotonic time-dependent effects, are proposed for the displacements of high arch dams during their initial impoundment periods in this paper. The hierarchical clustering on principal component analysis is developed to divide thermometers into groups and to choose representative thermometers or identify major principal components on measured temperature data to represent the non-stationary thermal effect on dam's displacements. The non-monotonic formula for the time-dependent deformation, emphasizing the creep and its restoration of dam concrete and its surrounding rock, is derived and further simplified when the reservoir water level exhibits an evident periodicity. Then, two improved statistical models accounting for these non-stationary thermal and non-monotonic time-dependent effects are proposed. The proposed statistical models with clear physical meanings are applied to investigate the measured displacements of the Xiluodu arch dam. Model performance comparisons indicate that the proposed models have significant improvement in fitting precision and prediction ability over the traditional and more recent models. Model results confirm the influence of reservoir thermal stratification and concrete temperature rise on the thermal displacement, and the non-monotonic effect on the time-dependent displacement. The proposed models yield to a better identification of the deformation mechanism for high arch dams during their initial impoundment periods.

Seismic and structural health monitoring of Cabril dam. Software development for informed management

Nowadays, the management and safety control of large dams is generally based on automatic monitoring, including the so-called seismic and structural health monitoring systems (SSHM), using the latest technology for automatic data measurement, acquisition and transmission. These systems should include software for automatic management and analysis of continuous monitoring data and software for numerical simulation of the dam dynamic behavior using 3D finite element models. This software should be designed to provide useful and reliable information to meet the needs and expectations of stakeholders, and to support the studies of researchers and engineers responsible for structural health monitoring. This paper is focused on the experience gathered from the SSHM system of Cabril dam, a 132 m high-arch dam, in Portugal, that has been under continuous dynamic monitoring since 2008. The importance of the software specifically developed for automatic modal identification, automatic detection of seismic vibrations (distinct from vibrations due to the operation of discharge gates and power groups), and automatic comparison between experimental data and computed results from a reference finite element model of the dam-reservoir-foundation system, is highlighted. This software includes: (1) the generation of graphics with the evolution of the identified natural frequencies over time and the comparison with calculated frequencies using different hypothesis for concrete damage evolution; and (2) a service to automatically send emails summarizing key dynamic monitoring results to stakeholders to provide the necessary support for informed management and engineering decision making. The main results from SSHM of Cabril dam are presented, namely regarding the evolution of modal parameter over time, considering the influence of water level variations, and the measured response during an earthquake event.

Mechanism for large-scale canyon deformations due to filling of large reservoir of hydropower project

Large storage dam projects may modify geo-environmental conditions in many ways. The reservoir impoundment of the 285.5 m high Xiluodu arch dam located on the Jinsha River (China) caused large-scale canyon deformations, including significant canyon contraction and uplift movements from reservoir to downstream valley. The dam experienced subsequent tilting towards upstream and raised a safety concern of the project. A Thermo-Hydro-Mechanical (THM) mechanism is proposed for this extraordinary behavior. Due to reservoir impounding and seepage, significant temperature drops and fluid pressure increase within the underlying geothermal limestone aquifer in a synclinal basin are primary root causes. Finite element THM simulations successfully reproduce these unique deformations. Recent observations of large quantities of thermalized discharge water downstream and high pore pressure in the limestone layer provide further support for the proposed mechanism. Furthermore, refined numerical modeling is adopted to evaluate the safety of Xiluodu dam subjected to potential larger canyon contractions. We conclude that these unprecedented phenomena are dominantly the consequence of THM response to regional hydrogeological evolution following the build-up of a large reservoir. The accumulated canyon contractions at the current stage would not pose a direct threat to the dam safety, but a tripled situation may cause severe safety issues.

The Hydrochemical and Isotopic Evolution of the Surface Water and Groundwater for Impoundment in the Xiluodu Reservoir, Jinsha River, China

The construction of a large reservoir with a high dam may cause irreversible changes in the water flow system and even affect the original environmental balance. Xiluodu reservoir, as a representative of the high arch dam reservoirs in China, clearly has this potential issue. Based on the monitoring data of the hydrochemistry and stable isotopes of the water (δD, δ18O) in the Xiluodu reservoir, this study presents the evolution of the hydrochemical and isotopic characteristics of the surface water and groundwater in the reservoir before and after impoundment using cluster analysis and saturation index analysis. The main cations in the reservoir water and groundwater change from Ca2+ and Mg2+ to Ca2+ and Na+, respectively, while the ratio of HCO 3 - to the total anions dropped from 0.86 to 0.7 as the main anion. The cluster analysis results show the high correlation between the groundwater and surface water before and after water impoundment. The calculation of saturation indices indicates that the hydrogeochemical process of the groundwater includes a different trend of the dissolution of minerals. The study of deuterium excess shows that the evaporation of the groundwater near the reservoir decreased after impoundment. Based on the above results and the recharge elevation, this research concludes that the interaction between the surface water and groundwater before and after impoundment is prominent and different. The groundwater replenished the river water before impoundment, while this relationship reversed after impoundment. This evolution process is caused by reservoir storage, and the drainage system and other conditions make this evolution possible. In addition, the influence of interaction evolution on the regional water decreases continuously along the dam site, and some areas even have irreversible changes.

Study on the failure process and nonlinear safety of high arch dam and foundation based on geomechanical model test

The nonlinear safety is very important for the system of arch dam and its foundation since it is statically indeterminate structure and the geomechanical model test is effective method to evaluate the stability of arch dam. The analysis of failure process for a double-curvature arch dam with 167.5-meter-high, located in the northwest of China, has been carried out based on overload method. A quantitative method for determining the safety factor of initial nonlinear deformation of model test is proposed based on the Pearson product-moment correlation coefficient. Through the defromation evolution of all monitoring points, the nolinear safety has been determined. Then it is verified by acoustic emission data. By comparing the model test results of arch dam with other arch dams, the overall stability and safety of narrow valley arch dam is higher, and its failure mode is more dominated by foundation, while that of wide valley arch dam is more dominated by dam. The safety factor of initial nonlinear deformation, which has the same meaning as the control index of compressive stress safety of arch dam in the design specification, correspond to the compressive stress failure of the downstream dam toe.

Seismic Damage Indexes of a High Arch Dam Based on the Monolith

To assess safety of a dam in an earthquake, establishing the performance evaluation index of the arch dam is significant. The finite-element model based on the 289 m-high Baihetan Dam in Southwest China is taken as a case for seismic response analysis, in which the radiation damping of infinite foundation and opening of contraction joints are taken into consideration. Using the incremental dynamic analysis (IDA) approach, a three-component earthquake scaled to 12 increasing intensity levels is applied to the model, and the seismic response of the model is analysed. In this paper, it is proposed to study the damage based on the monolith, so the monolith damage volume ratio and monolith damage area ratio are suggested to determine the most severe part of the dam. Meanwhile, to help identifying the damage of the dam, the response results of contraction joints are extracted to analyse the potential relationship between the proposed indexes, providing a reference for exploring new detection indexes and damage evaluation indexes. In order to explore the possibility of the simplified layout of dam damage monitoring, the dam body is partitioned according to the results of monolith damage development.

Correlation between valley deformation and water level fluctuations in high arch dam

The primary objective of this article is to present a case study of valley deformation in high arch dam and its relationship with water level fluctuations. Data of displacement versus reservoir level monitored over a five-year period are used to determine possible relationship between displacement and reservoir level. It is found that valley deformations are closely related to the filling-drawdown cycles of reservoir. Comparison of velocity of displacement of the valley with reservoir water level reveals that the reservoir water drawdown has a much stronger influence on the valley deformation. Based on these results, it is anticipated that the present research will provide additional insight into the mechanism of valley deformation and provide guidelines for preventive strategies and treatments.

Investigation of influencing factors for valley deformation of high arch dam using machine learning

During the operation period of the high arch dam in some canyon area, the valley deformation is obvious under complex geological environment. Several possible factors may influence this phenomenon. In this article, influencing factors are considered from the aspects of precipitation, temperature, reservoir water level elevation and the rate of reservoir water level variation. Two machine learning methods are employed to investigate these factors, namely, Lasso and Random forest, and serve as a basis for further studying the formation mechanism of valley deformation. Using the Lasso method, four variations are selected from 74 variations which are representative of precipitation and temperature, e.g. daily precipitation, 10-day antecedent precipitation, 10-day maximum rainfall difference, and 25-day maximum temperature difference. Combined with the reservoir water level elevation and the rate of reservoir water level variation, these six key factors are analyzed by the Random forest method so to carry out a quantitative analysis of their influence on valley deformation. Results show that the valley deformation is mainly affected by the rate of reservoir water level variation and the reservoir water level elevation among the selected factors, indicating valley deformation might be induced with hydrodynamic force.

Mechanism of valley narrowing deformation during reservoir filling of a high arch dam

During the reservoir filling of many high arch dams, it was observed that the valley slopes on both sides deformed towards the river. The measured value of valley narrowing lateral deformation (VNLD) reached 89.54 mm by October 2018. This rare phenomenon contradicts the traditional experience of dam engineering and lacks a convincing explanation. An arch dam project in China is selected as a case study to analyze the mechanism of the VNLD. Based on a comprehensive analysis of the geological background and the VNLD measurements, a numerical study is performed to identify the main factors that may contribute to the VNLD phenomenon. It is concluded that the time-dependent valley deformation is due to the rheological behaviour of rock mass with the change of hydrogeological conditions. The artesian water head in the deep-confined aquifer is increased and the mechanical parameters in fault and shear zones are weakened after reservoir filling, which is associated with the specific hydrogeological structures. The rise of artesian water head is the main induced factor that contributes to the uplift deformation, which is observed at the dam site, and can cause the VNLD in the horizontal direction. The simulated results considering these factors agreed well with the observed data.