Risk Analysis of Earth-Rock Dam Failures Based on Fuzzy Event Tree Method

Failure probability analysis of high fill levee considering multiple uncertainties and correlated failure modes

Such complex causative factors in current failure probability models are represented by simply random uncertainty and completely independent or correlation of failure modes, which can often limit the model utility. In this study, we developed a methodology to construct failure probability models for high fill levees, incorporating the identification of uncertainties and an analysis of failure modes. Based on quantification of stochastic-grey-fuzzy uncertainties, probability analysis involved with overtopping, instability and seepage failure modes was implemented combined with probability and non-probability methods. Given that the interaction among failure modes typically exhibits nonlinear behavior, rather than linear correlation or complete independence, a simple methodology for the binary Copula function was established and implemented in MATLAB. This methodology was applied to the high fill segments of a long-distance water transfer project characterized by high population density. It shows that the failure probability of a single failure mode is overestimated when uncertainties are not considered, because of the randomness and fuzziness of some parameters and the greyness of information. Meanwhile, it is found that the magnitude of failure probability related to levee breach is overestimated without respect to failure modes correlation, especially when the probabilities of seepage and instability are both significant and closely aligned.

Analysis of Social and Environmental Impact of Earth-Rock Dam Breaks Based on a Fuzzy Comprehensive Evaluation Method

A large proportion of the dams in China are earth-rock dams. Regarding the well-studied loss of life and economic consequences due to dam breaks, this paper introduces the causes and modes of earth-rock dam breaks and the corresponding dam-break losses in terms of the social and environmental aspects. This study formulates the evaluation index system and criteria of earth-rock dam breaks’ impact on society and the environment based on a fuzzy comprehensive evaluation method. The results show that the evaluation grade of the social and environmental impact of the dam break of the Liujiatai Reservoir was “serious”. Therefore, similar dams in China should take corresponding measures in advance to reduce the social and environmental impact of earth-rock dam breaks.

Risk Analysis of Earth-Rock Dam Breach Based on Dynamic Bayesian Network

Despite the fact that the Bayesian network has great advantages in logical reasoning and calculation compared with the other traditional risk analysis methods, there are still obvious shortcomings in the study of dynamic risk. The risk factors of the earth-rock dam breach are complex, which vary with time during the operation period. Static risk analysis, limited to a specific period of time, cannot meet the needs of comprehensive assessment and early warning. By introducing time factors, a dynamic Bayesian network model was established to study the dynamic characteristics of dam-breach probability. Combined with the calculation of the conditional probability of nodes based on the Leaky Noisy-Or gate extended model, the reasoning results of Bayesian networks were modified by updating the data of different time nodes. Taking an earth-rock dam as an example, the results show that it has less possibility to breach and keep stable along the time axis. Moreover, the factors with vulnerability and instability were found effective, which could provide guidance for dam risk management.

Human risk assessment of Panchet Dam in India using TOPSIS and WASPAS Multi-Criteria Decision-Making (MCDM) methods

Every river dam activity has definite beneficial effects but cannot circumvent its negative impact in the long run. The Panchet dam has been commissioned as a multipurpose river valley project under the authority of Damodar Valley Corporation (DVC) across the river Damodar at the border of West Bengal and Jharkhand states of India in 1959 to overcome some problems like flood control, supply of irrigation, domestic and industrial water, hydroelectric power generation etc. But it has now become a threat to the surrounding people, due to rapid sedimentation and reduction in its water holding capacity. Human risk assessment of the dam thus claims importance and such an effort is executed in this work using Delphi Questionnaire and two Multi-Criteria Decision-Making (MCDM) methods viz. Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) and Weighted Aggregated Sum Product Assessment (WASPAS). At first 9 human risk alternatives (A1-A9) of the dam are identified using Delphi Questionnaire and rated them in order to prioritize using TOPSIS and WASPAS methods. Risk prioritization results of TOPSIS and WASPAS show somewhat differences. The integrated ‘Mean-Rank’ method is applied to provide final priority ranking of the risk alternatives and the result is: A3 > A9 > A8 > A4, A6 > A1 > A7 > A5 > A2 (when WASPAS parameter λ = 0); A3 > A9 > A4, A8 > A2 > A6 > A1 > A5, A7 (when WASPAS parameter λ = 1); A3 > A9 > A8 > A4, A6 > A1 > A2 > A5 > A7 (when WASPAS parameter λ = 0.5). In all cases, A3 (Population Displacement) alternative ranks first and is identified as the top most risk prone alternative among all. The risk of displacement of people due to further inundation of land is rising gradually. This has motivated us for assessment of other human risks of the dam in the work.