A influência da sensibilidade na estabilidade de solos moles brasileiros

Abstract

The Brazilian Code NBR 10905, which standardizes the Vane Test procedure, establishes that both undisturbed and remolded strengths should be measured. The remolded strength is defined as the soil strength after 10 revolutions of the vane apparatus in the soil. Even though the soil strength (undisturbed and remolded) is determined in the test, it is a common practice to consider only the peak strength in conventional analyses, in which the strength is assumed constant for post-peak deformations (elastic-perfectly plastic model). In fact, the Brazilian soft soils present much lower sensitivity when compared to Canadian or Scandinavian clays. However, the present Dissertation proposes the study of the influence of Brazilian soft soils sensitivity in the calculation of the safety factor in soil stability problems. The phenomenon of strain softening is related to the strength reduction after yielding experienced by clayey soils that present any sort of fabric/structuration. The higher the strain softening, the more relevant is its consideration when calculating the safety factor in stability problems. In traditional Limit Equilibrium Analysis, it is not possible to account for strain softening, thus becoming necessary the utilization of numerical methods (e.g. Finite Element Analysis). The numerical analyses of strain softening are generally very complex and therefore the mesh should be developed with special continua, known as generalized continua, which are not usually found in most commercial softwares, as in the case of the software used in the present Dissertation. As a consequence, it was necessary to adapt a constitutive model, which considers an abrupt post-peak strength reduction, in order to represent the gradual strength reduction observed in Vane Test results. The developed methodology was used to reproduce the failure of the trial embankment of Sarapuí I (Ortigão, 1980) and the failure of Porto de Santana. Satisfactory results for the safety factor and the location of the corresponding slip surfaces were obtained in both analysis. These two examples reinforce the importance of considering the effect of the post-peak strength reduction (strain softening) in soil stability problems.