Several concrete dams all over the world exhibit severe cracks. It is very important to investigate the influence of cracks on the long-term behavior of dam structures to ensure safe operation. The interpretation of measured dam displacements is usually based on statistical hydrostatic-seasonal-time and hydrostatic-thermal-time models. The main purpose of this article is to present a statistical hydrostatic-thermal-crack-time model to interpret displacements of concrete arch dams with influential horizontal cracks. The hydrostatic-thermal-crack-time model is applied to analyze the Chencun dam, an arch–gravity dam with a large-scale horizontal crack on the downstream face. The crack stretches horizontally across most of the dam blocks. Its crack mouth opening displacement had been continually increasing even after reinforcement treatment, accompanied by abnormal deformation characteristics of the arch–cantilever system. A three-dimensional finite element model, containing the pre-existing crack using special gap elements, is built to reproduce the structural response, assess the contribution of the crack on the registered movements, and obtain the relationship between the crack mouth opening displacement and the dam crest displacement. Based on this, the hydrostatic-thermal-CMOD-time model considering crack mouth opening displacement is developed. Compared with the traditional models, the hydrostatic-thermal-crack-time model is expected to provide a better fit accuracy. The results also show that the crack and the corresponding reinforcement measure have a significant effect on the deformation behavior of the dam. This can provide some useful indications for concrete structures with similar problems.
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 timedependent 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 timedependent displacement. The proposed models yield to a better identification of the deformation mechanism for high arch dams during their initial impoundment periods. K E Y W O R D S clustering, dam, initial impoundment period, principal component analysis, structural health monitoring, time-dependent effect 1 | INTRODUCTION A number of super high arch dams of 200-300 m high have been built in China. Many of these dams have entered or will enter their initial impoundment periods. 1 Super high dams have strong interactions with air and water temperature, reservoir water level, uplift, rock deformability, and so on. During the initial impoundment period, a super high
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