Numerical Simulation of Water Impoundment at a High Arch Dam Site

Abstract

In a former study, water impoundment at a high arch dam (located in southwest China) was simulated using fluid-mechanical elasto-plastic analyses to predict deformation mechanisms taking place at the scale of the valley (Hou et al., IOP Conf Ser: Earth Environ Sci 570:022033, 2020). In this continuation work, we review the findings, clarify the mechanism of valley deformation caused by changes in impoundment level, and present the results of a sensibility study that accounts for the presence of drainage volumes at the site. With no account for drainage volumes, the model predicts valley expansion along measuring lines upstream from the dam, and valley contraction downstream. Also, valley contraction increases with measuring line elevation. Valley deformation occurs during changes of impoundment; this reflects the mechanical response to the change in dead weight of standing impoundment water. Deformation also takes place at constant impoundment level; this is caused by large-scale water seepage under and around the dam in the valley banks. A decrease in impoundment level generates a relative increase in valley contraction in the model, both upstream and downstream of the dam. This behavior is explained by the mechanical relaxation of lateral pressure that acts on the valley banks when the impoundment level is reduced. With drainage domains (associated with tunnels and powerhouse caverns) accounted for in the model, it was expected that the associated drop in fluid pressure would reduce the predicted valley contraction in the dam vicinity. Indeed, in this case, a mechanism of valley expansion is predicted to develop along all monitoring lines in the model.