Avaliação da influência da ruptura progressiva no cálculo do fator de segurança de aterros sobre solos compressíveis por métodos de equilíbrio limite

Abstract

In current geotechnical practice, it is common to use the Limit Equilibrium method to analyze the slope stability and define the factor of safety of the analyzed system. For cases involving soils with “strain-softening” behavior, characterized by a peak-residual strain-stress curve, these analyzes must contemplate the occurrence of the progressive failure mechanism, in order to correctly simulate the real behavior of the soil. However, conventional limit equilibrium methods ignore this behavior, treating the soil as an ideally plastic material, inducing the occurrence of a simultaneous failure and resulting in unreal factors of safety. The representative strength parameters must be intermediate to the peak and residual parameters, since these individually do not characterize the real strength of this kind of soil. Furthermore, it is necessary to emphasize the importance of the correct determination of the undrained strength parameters to be used in the analysis of soft soils, which requires a deeper knowledge about the influences that the sampling and testing processes generate on the results obtained in order to eliminate and/or reduce the interference caused by these processes. In this paper, a new retro-analysis of the failure of the Experimental Landfill I of Sarapuí-RJ was carried out, using methods based on the Limiting Equilibrium theory the Finite Elements method, using softwares (RS2 and Slide 2) and automated electronic spreadsheets. For the Limiting Equilibrium analyses, analytical proposals were incorporated into the conventional methods, in order to consider the progressive failure effect in their calculations. While in the classical analyses, using only the peak strength, the factor of safety is above unity (not characterizing the failure), the application of these proposals resulted in a FoS below unity, due to the consideration of the strength drop. When considering an abrupt strength drop, from peak to residual, the occurrence of failure is given in a loading stage prior to that seen in the field. With this, one can observe the need to incorporate the effects of progressive failure, considering a gradual strength drop.