Avaliação da influência da resistência ao cisalhamento das interfaces na estabilidade de barragens zonadas

Abstract

This study was carried out in order to verify the shear strength properties of the interface between a sandy and a clayey material in order to analyze its influence on stability of a slope of a zoned dam. For that, characterization tests were carried out on both materials in the laboratory; compaction tests to obtain the maximum apparent dry masses and optimum humidity; permeability tests at constant and variable load in sandy and clayey soils, respectively, to know the hydraulic behavior of the soils; and direct shear tests on the materials alone and at the interface between them to obtain the shear strength parameters. The results obtained in the direct shear tests showed that the sandy soil has a high friction angle and low cohesion, while the clay soil has a lower friction angle and greater cohesion; the interface showed a friction angle close to that obtained for the sandy soil and a lower cohesion value than the other materials. In a fictitious section of a zoned dam, flow and stability analyzes were performed. The flow analysis showed low values ​​of hydraulic gradients in the dam body. The slope stability analyzes, considering the method of Morgenstern and Price, were carried out adopting circular and non-circular potential rupture surfaces along the interface layer, taking into account in this layer the parameters of the sandy, clayey and interface materials. The results indicated that among the cases involving non-circular surfaces, the lowest safety factor was obtained considering the resistance parameters of the interface, however, the case with circular surface reached the lowest overall safety factor. All cases achieved safety factors in excess of the minimum required. Thus, it was possible to conclude that the shear resistance behavior of the interface was mainly driven by the characteristics of the sandy soil, losing its cohesion; in addition, the shear strength of the interface between sandy and clayey soil exerted a greater influence on the stability of the downstream slope of the zoned dam compared to the others materials isolated on non-circular surface; finally, the most favorable method for safety was the one that considered a circular potential rupture surface along the body of the dam and, therefore, the resistance of the interface did not influence the stability of the studied zoned dam.