Reducing Uncertainty and Risk of a Dam by Site Investigation, Quantitative Analysis, Model Calibration, and Observational Method

Insufficient knowledge of the ground condition may lead to design failure or issues during/after construction, which is particularly critical for dam safety. Nevertheless, performing a comprehensive site investigation may not be practical due to limitations about time, budget, or accessibility. To better understand and further reduce the uncertainties and risks, the rational approach is combining multiple methods, such as site investigation, quantitative analysis, modeling, and instrumentation and monitoring, along with applying observational method throughout project. The paper introduces a project of constructing a new bridge adjacent to a more than 100-years reservoir dam, while keeping dam operational during construction. In the project, a combination of multiple means was applied to efficiently reduce the uncertainty and risk when very limited information was available. The paper presents the measures that have been taken to increase understanding about the site conditions. The uncertainty and probability of failure before and after acquiring more information were quantitively evaluated. The results show that the uncertainty in seepage and slope stability have been greatly reduced with the coefficient of variation values have been reduced from 0.62 to 0.41 and from 0.23 to 0.08, respectively, so as the probabilities of failure have also been reduced.