Análise do comportamento da barragem engenheiro Armando Ribeiro Gonçalves - Açu/RN - durante sua construção, primeiro enchimento e operação do reservatório

Abstract

The Açu Dam is an important geotechnical built in Rio Grande do Norte and in Northeast Brazilian, especially because of its size and complexity. In addition to its size and importance, it has gained prominence in the national and international literature because of the collapse in upstream slope in the end of construction period. This paper aimed to analyze its behavior in stages of dam construction, first filling and operation of the reservoir. In each step, were analyzed: the stress-strain behavior, the flow and the pore-pressure variation, and the slope stability. These analyses were performed with the software Sigma/W, Seep/W and Slope/W, which are components in a suite of geotechnical products called GeoStudio, produced by Geo-Slope International Ltd. The results were compared with the instrumentation dates available in Rocha (2003). In the comparative analysis of vertical displacements, the largest difference between modeling results and instrumentation data was 8.9 cm, in the T7 extensometer, at the end of the first filling. In the stability analysis, the lowest safety factor was 1.3 for the upstream slope in the reservoir operation phase, but the media of the safety factors obtained by the methods based on limit equilibrium was 2.4. For a downstream slope, this factor was equal to 1.6 in all stages. These results confirm the dam stable condition. In pore-pressure analysis, the pneumatic piezometers presented greater divergences between modeling and instrumentation than those of the Casagrande type. The most significant difference was 46% (23 kPa), in the PZP1 piezometer, at the first filling of the reservoir. However, considering the differences obtained by other authors who also studied the water flow in this dam, we conclude that the results of the present analysis are satisfactory and that the adopted parameters are adequate to characterize the soils modeled.