Analysis of the Impact of Uncertainties on the Estimation of Geotechnical Engineering Properties of Soil from SPT on the Design of Aerogenerators Foundation

In geotechnical engineering, it is common to use data from only one field test (SPT test) to predict input stiffness parameters in the study of stress vs. displacements behaviour of foundations. This is made from correlations available in the literature for different kinds of soils. As a result, the variation that occurs between different correlations may be significant and must be critically analysed with respect to the accuracy of the foundation design and, consequently, its safety. In this context, this paper aims to study the impact of the variations of friction angle (ϕ’) and Young’s modulus (E) predicted by several different correlations from field SPT measurements available in the literature. Based on the estimations, four groups of estimated results were defined with the corresponding values of ϕ’ and E within such groups (for high and low values of both ϕ’ and E). Such values were applied in a numerical Finite Elements Method (FEM) model of an aerogenerators foundation to calculate vertical displacements and stress fields. In the groups in which only one of the parameters was varied, it was observed that the Young’s modulus has a significant influence on the displacements, while that was not the case for the friction angle in the investigated foundation, due to predominant, linear-elastic condition in the investigated foundation. The paper demonstrated the significant variation in geotechnical analysis that can occur with the use of different input correlations in geotechnical studies. These uncertainties lead either to overestimate or to underestimate the foundation design, which may affect economy and safety, thus emphasizing the need for more accurate field tests and more laboratory investigation and control.