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An adequate characterization of the soil stiffness is a fundamental aspect when modelling the behaviour of any geotechnical work. Studies show that the stiffness in this type of materials is highly nonlinear and that only for small strains, lower than about 0.001%, it is possible to assume an elastic behaviour. For such small strains it is assumed that the soil has a constant stiffness usually known as maximum shear modulus, Gmax. However, for higher strains, stiffness tends to decrease sharply, and a decrease of about 90% of its value can be reached for strains around 1%.
One of the major difficulties when characterizing the stiffness degradation curve is related with the determination of Gmax, as it can only be obtained by performing tests that induce very small strain levels in the sample. One of most frequently used possibilities in laboratory testing is using bender elements. This type of tests allows the determination of the propagation velocity of the shear waves VS, in the soil, which is directly related to Gmax, if it is assumed that the soil remains within the elastic threshold.
The work performed in this thesis primarily aims to evaluate the value of Gmax for two types of sandy soils of the Coimbra region, by performing bender elements tests at the Geotechnical Laboratory of the University of Coimbra.