Simulation of Complex Seepage Field of a Gravity Dam Foundation Using a CFD-Based Approach

Abstract

Dam foundation seepage is a major concern for the stability of a hydropower project in southwest China (referred to here as Project X). The complicated geological structure, multiple grouting curtains, and adjustable drainage system of Project X significantly increase the complexity of the dam foundation seepage field. In this work, a three-dimensional (3D) air-water two-phase seepage mathematical model, coupled with the volume of fluid (VOF) method, is developed based on the computational fluid dynamics (CFD) approach. The 3D unified model of Project X, including strata, unfavorable geological bodies, grouting curtains, adjustable drainage system, consolidation grouting, and gravity dam body, is later established in an integrated manner for the entire dam area. Furthermore, an extended “fissure to represent line of holes” method is proposed to model the drainage holes with adjustable opening degrees. Subsequently, the distributions of the water head, hydraulic gradient, and uplift pressure, both before and after adjusting the drainage system, are analyzed. The overall behavior of the seepage control system and the influence of the opening degrees of the drainage holes on the seepage field are comprehensively discussed, and an optimized operating state is recommended for the drainage system. The discussion reveals that the maximum hydraulic gradient at the grouting curtains decreases and the average uplift pressure on the dam foundation surface increases with decreasing water discharge of the drainage system. Comparisons with in situ monitoring data demonstrate the reliability of the proposed methodology.