Huaizhi Su

Service Life Predicting of Dam Systems with Correlated Failure Modes

AbstractThe 50-year design reference period is coming to an end for many dam projects in China. In the last decade, it has become clear that remaining service life analysis of existing dams must be used to optimally manage the growing number of aging and deteriorating structures. The uncertainties associated with deteriorating dams require the use of probabilistic methods to properly assess their lifetime performance. A dam system involves multiple failure modes; however, conventional assessment and prediction models often neglect the correlations among failure modes. As a result, the remaining service life predicted by these methods is relatively rough. First, in this paper, conventional lifetime distribution functions are introduced. The influences of the correlations among failure modes on series, parallel, or series-parallel structure are discussed, respectively, and the approach for calculating correlation coefficients is proposed. Second, on the basis of the analysis of dam failure causes, failure m...

Rate effect on mechanical properties of hydraulic concrete flexural-tensile specimens under low loading rates using acoustic emission technique.

Acoustic emission (AE) waveform is generated by dislocation, microcracking and other irreversible changes in a concrete material. Based on the AE technique (AET), this paper focuses on strain rate effect on physical mechanisms of hydraulic concrete specimens during the entire fracture process of three point bending (TPB) flexural tests at quasi-static levels. More emphasis is placed on the influence of strain rate on AE hit rate and AE source location around peak stress. Under low strain rates, namely 0.77×10(-7)s(-1), 1×10(-7)s(-1) to 1×10(-6)s(-1) respectively, the results show that the tensile strength increases as the strain rate increases while the peak AE hit rate decreases. Meanwhile, the specimen under a relatively higher strain rate shows a relatively wider intrinsic process zone in a more diffuser manner, lots of distributed microcracks relatively decrease stress intensity, thus delay both microcracking localization and macrocrack propagation. These phenomena can be attributed to Stéfan effect. In addition, further tests, namely the combination of AE monitoring and strain measuring systems was designed to understand the correlation between AE event activity and microfracture (i.e., microcracking and microcracking localization). The relative variation trend of cumulative AE events accords well with that of the load-deformation curve.

Multifractal scaling behavior analysis for existing dams

The fractal theory was used to describe long term behavior of dam structures by means of determining (mono-) fractal exponents. Many records do not exhibit a simple monofractal scaling behavior, which can be accounted for by a single scaling exponent. In this paper the multifractal detrended fluctuation analysis (MF-DFA) is employed to analyze the time series of in situ observed data of existing dam which intrinsically reflects its long term behavior and structural evolution law. Deformation analysis of one gravity dam is taken as an example, the multifractal characteristic of the time series is obtained. The results show that this method can reliably determine the multifractal scaling behavior of time series of existing dams. The fractal theory can be applied to predict and diagnose dam behavior.

Deep Stability Evaluation of High-Gravity Dam under Combining Action of Powerhouse and Dam

AbstractThe rock foundation of a gravity dam is usually cut into slide blocks by the structural surfaces. Its stability is controlled by the characteristics and the combining action of these structural surfaces. The failure of a gravity dam can be caused by the destruction or large deformation of local rocks under the condition of certain loads. The coupling of continuous-discontinuous deformation is a typical characteristic of the process. As a new design idea, the powerhouse and dam are combined into an integer with one structural pattern to improve the antisliding stability of the gravity dam. The external loads are undertaken together by the powerhouse and dam. The loads acting on the dam can be transferred partly to the powerhouse, and the powerhouse weight and tail water pressure can increase the dam’s stability. The optimal design of a gravity dam section can be implemented, decreasing the project quantity, and reducing construction costs. This design idea has been adopted by the Yangtze Three Gorg...

Analysis and Back-Analysis for Temperature Field of Concrete Arch Dam During Construction Period Based on Temperature Data Measured by DTS

Based on the observed temperature information of arch dam, the mathematical and mechanical methods are combined usually with dam engineering theory to capture in real time and evaluate in time the developing status and space-time distribution of arch dam temperature, and implement the back analysis for temperature control measures. It is an important step for dam construction and safe operation. Some methods, namely transient temperature-field simulation, thermodynamic parameters back-calculation, and model correction, are used synthetically to solve the above problem. A method is proposed to back calculate the thermodynamic parameters of arch dam by use of the temperature data obtained by the distributed optical fiber temperature sensor (DTS). A problem is studied to couple the simulated temperature field by finite element method (FEM) and the observed temperature field by the DTS. A method is presented to update dynamically the FEM model on the basis of the observed temperature field. An actual engineering is analyzed by the proposed method. It is shown that the DTS system can implement the real-time observation of concrete arch dam temperature field. According to the observed temperature field by the DTS and the updated numerical simulation model of the temperature field, scientific guidance can be given during the pouring process of the arch dam, and reliable data can be provided to analyze and evaluated arch dam safety.

Dam safety prediction model considering chaotic characteristics in prototype monitoring data series

Support vector machine, chaos theory, and particle swarm optimization are combined to build the prediction model of dam safety. The approaches are proposed to optimize the input and parameter of prediction model. First, the phase space reconstruction of prototype monitoring data series on dam behavior is implemented. The method identifying chaotic characteristics in monitoring data series is presented. Second, support vector machine is adopted to build the prediction model of dam safety. The characteristic vector of historical monitoring data, which is taken as support vector machine input, is extracted by phase space reconstruction. The chaotic particle swarm optimization algorithm is introduced to determine support vector machine parameters. A chaotic support vector machine–based prediction model of dam safety is built. Finally, the displacement behavior of one actual dam is taken as an example. The prediction capability on the built prediction model of dam displacement is evaluated. It is indicated that the proposed chaotic support vector machine–based model can provide more accurate forecasted results and is more suitable to be used to identify efficiently the dam behavior.

Macro-comprehensive evaluation method of high rock slope stability in hydropower projects

Combining with the characteristics of the rock slope in hydropower engineering, the evaluation index system of rock slope stability in hydropower projects is determined based on multiple factors, and based on this, research, collect and establish the typical rock slope database of hydropower projects. Based on the fuzzy optimal recognition theory and Case-Based Reasoning, two different methods of slope stability evaluation are established respectively. Analyzing the rock slope stability of one hydropower project by the two methods, a comparison is made between the two methods and the effectiveness of the methods is verified.

A Method for Evaluating Sea Dike Safety

To implement the maintenance and management of the sea dike engineering, the qualitative factors and quantitative factors need to be combined to evaluate the sea dike safety. Firstly, the evaluation index system and evaluation grading criterions of sea dike safety are established. Secondly, a new weight structure of evaluation indexes is proposed to combine the subjective weight and objective weight. Fuzzy Analytic Hierarchy Process method is used to determine the subjective weight and implement the qualitative analysis for sea dike safety. Projection Pursuit algorithm is introduced to calculate the objective weight and implement the quantitative analysis for sea dike safety. Based on the minimum relative information entropy principle, above two weights are combined. Thirdly, an evaluation model of sea dike safety is built with the improved Set Pair Analysis method. Finally, the proposed analysis method is used to assess one sea dike safety in China. It is shown that the combined weight can describe both the subjective information of expert experience and objective variation information of samples values, the uncertainty of information can be handled by the improved Set Pair Analysis method. The evaluation model has the clear physical concepts and intuitive modeling process. The calculation result is reasonable. The proposed method can be applied to sea dike safety evaluation and other complex systems evaluation as well.

Dam Seepage Monitoring Based on Distributed Optical Fiber Temperature System

Dam seepage is monitored based on the character of the concealment, temporal-dimensional randomness. This paper gives the analysis on the relativity and coupling problem between fields of dam seepage and temperature. The principle, method, and implementation technology of dam seepage monitoring is elucidated based on distributed optical fiber temperature system. This technology is applied in actual project and the application effect is analyzed and evaluated.

Dam structural behavior identification and prediction by using variable dimension fractal model and iterated function system

Display OmittedThe better forecast effect can be obtained by the combination of IFS and variable dimension fractal model. The method has the certain adaptive ability with high forecasting speed and without convergence problem. Fractal characteristic of dam structural behavior is identified with MF-DFA method.IFS is introduced to build the model fitting the measured dam structural behavior.The variable dimension fractal model and IFS are combined to forecast the dam structural behavior. According to the observations of dam structural health monitoring, iterated function system is adopted to implement the analysis and forecast for dam structural behavior. Firstly, the multifractal detrended fluctuation analysis (MF-DFA) method is employed to identify the fractal characteristics in the measured data series of dam structural behavior. Secondly, the iterated function system algorithm is studied to build the fitting model. The ways to determine the interpolating points (position and number) and vertical scaling factors are given in detail. Thirdly, the variable dimension fractal model and iterated function system are combined to forecast the dam structural behavior. Lastly, the displacement behavior of one concrete gravity dam is analyzed and predicted by the proposed approach. It is shown that the whole trend and detail characteristics of dam structural behavior observed can be described well, and the prediction precision can be improved.