Wu ZhongRu

Review on hidden trouble detection and health diagnosis of hydraulic concrete structures

A large number of hydraulic concrete structures have hidden defects such as cracks, erosion, freeze and thaw, thermal fatigue, carbonization. These hidden defects seriously affect the strength, stability and durability of structures. These problems are studied mainly by single monitoring or diagnosis methods at present. The integration of multiple monitoring and diagnosis methods is not applied widely. Besides, the analysis theory on these problems is not developed very well. The systemic study on the aging mechanism of hydraulic concrete structures, time-variation model and health diagnosis is still not enough. The support for engineering practice is limited. Aimed at these major scientific and technological problems and combined with specific projects, study on detection of hidden defects and health diagnosis of hydraulic concrete structure has been carried out. This study includes the following content: field non-destructive examination of hidden defects of hydraulic concrete structures, seepage detection, the construction of in-situ sensing system, the combination of field detection and in-situ monitoring, the mechanism of crack, freeze and thaw, erosion and carbonization of hydraulic concrete structure, mechanism of combination aging; time-variation model of hydraulic concrete structure, theories and methods for health diagnosis of hydraulic concrete structures.

Assessment model of dam operation risk based on monitoring data

Although the dams produce remarkable social and economic benefits, the threat made by unsafe dams to the life and property of people who live in the lower river area is un-negligible. Based on the monitoring data which reflect the safety condition of dams, the risk degree concept is proposed and the analysis system and model for evaluating risk degree (rate) are established in this paper by combining the reliability theory and field monitoring data. The analysis method for risk degree is presented based on Bayesian approach. A five-grade risk degree system for dam operation risk and corresponding risk degree is put forward according to the safety condition of dams. The operation risks of four cascade dams on some river are analyzed by the model and approach presented here and the result is adopted by the owner.

Comprehensive evaluation methods for dam service status

More than 87000 dams have been built in China, and about one third of them are risky projects. A number of high and ultra-high dams are being constructed in China’s western region. The current dam construction practice tends to focus on socio-economic benefits and neglect the environment and ecology. Furthermore, periodic examinations are intended to ensure the structural safety of dams. This paper proposes a general evaluation principle for dam service. This principle stipulates that dam projects should have maximum socio-economic benefits and minimum negative effects on the environment and ecology. To satisfy the general principle of mutual harmony, socio-economic benefits, dam safety, environment, and ecology are analyzed, and the evaluation methods for dam service status are discussed. Then, a fusion algorithm of interlayer assessment is proposed on the basis of evidence theory and the fuzzy comprehensive analysis method. Finally, a comprehensive evaluation model is established. Example analysis shows that the proposed theories and methods can fulfill scientific assessment of the service status of dams.

Crack status analysis for concrete dams based on measured entropy

The integrity and safety of concrete dams are seriously affected by the existing cracks in dam bodies, and some serious cracks may cause dam failure or disaster. The propagation of cracks in concrete dams is accompanied by changes in energy distribution, which can be represented by changes in the structure’s system entropy. Therefore, the entropy theory can be used in analyzing the behavior of dam cracks. Due to the randomness and locality of crack propagation, it is difficult to predict the location of cracks by traditional monitoring methods. To solve this problem, the influence of spatial positions of monitoring points on inspection zones is represented by a weight index, and the weight index is determined by the distance measure method proposed in this paper. Through the weighted linear fusion method, the entropy of multiple monitoring points is obtained for analyzing the behavior of dam cracks in the selected zones. Meanwhile, the catastrophe theory is used as the variation criterion of an entropy sequence in order to predict the instability time of dam cracks. Case studies are put forward on a high arch dam, and the fusion entropy is calculated according to the monitoring data from strain gauges. Results show that the proposed method can effectively predict the occurrence time and location of dam cracks regardless of the layout of monitoring instruments, and it is a new way to analyze the occurrence and propagation of dam cracks.

Study on Coupling Influences of Concrete Dam Foundation Seepage, Stress, and Creep on Structure Behaviors of Dam Body

Abstract Accidents of some arch dams show that dam failures are mainly caused by crack or failure of their foundation rocks, which are directly related to water seepage in the rock. This kind of fluid-rock interaction has an important influence on deformation and stress characters of the dam-rock system. In this paper, the stress and flow fields of dams and their foundation rocks are studied as a coupled system, using visco-elastic constitutive models and finite element solution method. The developed models and FEM technique were applied for analysing the continuous displacement of the 13th dam section of the Longyangxia Dam, and the calculated results agree well with the measured ones.