Análise tridimensional de taludes em solos moles

Abstract

Even in soft soils of low to medium sensitivity, the softening effect, with a loss of post-peak strength ("strain softening"), is a phenomenon that should be considered in stability analyses when these soils are identified in the field. Analyses that do not contemplate these effects can be considered unrealistic and significantly contrary to safety, because they admit that the maximum strength of clay remains constant after the yielding beggins, thus, they provide safety factors always greater than in strain softening analyses, where in the elements already yielded the maximum shear strength is reduced to a residual value. In this Dissertation, are studied simultaneously the three-dimensional effect, sensitivity and failure of an alluvial deposit on the banks of the Amazon River, with low to medium sensitivity, measured from cone penetratrion tests and vane tests. It is shown that stability analyses by finite element method can incorporate the effect of strain-softening by the Mohr-Coulomb’s constitutive model extended to the concept of equivalent sensitivity, as introduced by Pereira Pinto (2017). The safety factors obtained in finite element analyses with application of the concept of equivalent sensitivity allow obtaining a correction factor equivalent to Bjerrum’s factor, represented in this dissertation by the ratio between the safety factor obtained with a strain softening and constant shear strength (classical analyses). The failure of the investigated deposit was verified by three-dimensional simulations using the limit equilibrium method (Slide3 software) and the finite element method (RS3 software). The classical analyses (without "strain softening") indicated safety factors always superior to the unit, without justifying, therefore, the failure occurred. On the other hand, by including the strain softening effect, safety factors decreased significantly, with values slightly higher than the unit without any external overload, and unit values by the action of an overload that inadvertently advanced through a soft sediment region.