To address the uncertainty problem in the assessment of the overall safety trend of dams and in the selection of safety trend warning indicators, an Extended Cloud Model (ECM) combined with the Extended Analytic Hierarchy Process (EAHP) method is proposed in this study. In this new approach, different factors re ecting dam safety monitoring have been considered as a fuzzy system. Considering the characteristics of the forward cloud model and the backward cloud model, the original data have been extended to classify the division interval and determine the respective indicators. The weight distribution for each indicator level has been determined using the EAHP method. The model developed was applied to evaluate the safety trend of the Jilintai concrete faced rock ll dam. Simulation resultsshowed that the proposed model can generate reliable results, in addition to being used to assess the uncertainty problem and the safety warning indicator. The proposed model is also more exible and easier to use than other methods.
Compared to the scour around a single pier, the local scour process around tandem double piers is much more complicated. Based on laboratory experiments in a flume, we conducted the scour process around tandem double piers under an ice-covered flow condition. The results showed that when the pier spacing ratio L/D = 2 (where L = the pier spacing distance, and D = the pier diameter), the rear pier (the downstream one) will intensify the horseshoe vortex process behind the front pier, and the scour depth around the front pier will increase by about 10%. As the pier spacing ratio L/D increases, the scour depth around the front pier will gradually decrease. When the pier spacing ratio L/D = 5, sediment scoured around the front pier begins to deposit between these two piers. To initiate a deposition dune between piers, the pier spacing distance under an ice-covered condition is about 20% more than that under an open flow condition. The results also showed that the existence of the rear pier will lead to an increase in the length of the scour hole but a decrease in the depth of the scour hole around the front pier. The local scour around the front pier interacts with the local scour of the rear pier. The maximum scour depth of the scour hole around the rear pier increases first, then decreases and increases again afterward. When the pier spacing ratio L/D = 9, the scour depth around the rear pier is the least. With an increase in the pier spacing ratio, the influence of the local scour around the front pier on the local scour around the rear pier gradually decreases. When the pier spacing ratio L/D is more than 17, the scour around the front pier has hardly any influence on that around the rear pier. The scour depth around the rear pier is about 90% of that around the front pier.
To address the uncertainty problem in the assessment of the overall safety trend of dams and in the selection of safety trend warning indicators, an Extended Cloud Model (ECM) combined with the Extended Analytic Hierarchy Process (EAHP) method is proposed in this study. In this new approach, different factors reflecting dam safety monitoring have been considered as a fuzzy system. Considering the characteristics of the forward cloud model and the backward cloud model, the original data have been extended to classify the division interval and determine the respective indicators. The weight distribution for each indicator level has been determined using the EAHP method. The model developed was applied to evaluate the safety trend of the Jilintai concrete faced rockfill dam. Simulation results showed that the proposed model can generate reliable results, in addition to being used to assess the uncertainty problem and the safety warning indicator. The proposed model is also more flexible and easier to use than other methods.
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