Avaliação de modelos numéricos para representar processos erosivos na formação de brechas em barragens de solo coesivo por galgamento

Abstract

Adverse weather conditions or inadequate sizing of erosive dams, there may be inefficiency in storing and absorbing an extreme flood event in the reservoir, culminating in the overtopping of the structure. With the overtopping flow over the dam, an erosion process begins on the downstream slope, which can result in a rupture. The erosive process of breach formation will have some peculiarities depending on the type of soil used in the dam, degree of compaction and drainage structures in dam, for example. Then, it is noted that the formation and evolution of the breach must be studied in accordance with the particularities of each structure, without there being a single methodology to cover the various scenarios observed in practice. Therefore, the objective of this work was to evaluate the geotechnical and hydraulic characteristics involved in this erosive process and adopted in numerical models. Initially, through the development and formation of gaps observed in the physical model built by Saliba (2009), the numerical parameters were determined using the physical characteristics of the soil and calculation of erosion coefficients during the model overtopping process. As a result, an oscillation of the erodibility coefficient (kd) between 0.42 and 31.6 cm³/N.s was obtained. It was observed that the variation of parameters could be justified by the influence or not of turbulent macrostructures when the coefficients were applied to one-dimensional deterministic models based on physical analysis proposed by Robinson and Hanson (1994) and Temple et al. (2005), through unidimentional models WINDAM C e DL BREACH. Aiming to qualitatively evaluate how turbulent flow behaves on the downstream slope during the surface erosion process and downstream of the headcut, different geometries were analyzed using Computational Fluid Dynamincs (CFD) in the FLOW-3D® software applying the SST κ - ⍵ and RNG turbulence models. Corroborating with laboratory observations and one-dimensional analyses, it was observed that the action of shear stress and flow velocity occur more significantly in the slope sections parallel to the flow, while downstream of the headcut occurs the scour hole with the formation of adverse pressure gradient, noting a lesser influence of shear stress on the face of the headcut.