This paper focuses on the use of field vane, a popular instrument for determining the undrained shear strength (s_u) of soft clays. In this regard, suitable corrections must be applied in order to adequately interpret the recorded measurements. Here the role played by some relevant factors (i.e., anisotropy and strain-rate effects) in influencing s_u values is investigated on the basis of FEM numerical analyses carried out via the adoption of PLAXIS-3D software. The results of the numerical analyses generally fit with information provided by the scientific literature using independent measurements. Moreover, they highlight a relevant effect of anisotropy for low values of the plasticity index of investigated clayey soils. On the contrary, for high values of the plasticity index, anisotropy plays a marginal role while strain rate effects prevail. All these considerations suggest the field vane tests most reliable for clayey soils with high plasticity index, although a correction is needed in order to limit strain rate effects.
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