Determination of Soil Stiffness Parameters for Clays as a Construction Subsoil for Warsaw Underground

Abstract

Analysis of soil-structure interaction demands properly determined parameters for a particular calculation method. In the case of deformation modulus determination, it is essential to take actual construction activities into consideration. It means that these moduli should correspond to stress-strain range of a particular construction. The use of numerical methods, allowing for more realistic soil-structure interaction, compatibility of displacements, as well as to account for the stiffness of the structure and the soil, may provide more realistic prediction of displacements. The article presents the methods of stiffness parameters determination including all factors that should be taken into consideration in geotechnical design. The article characterizes clays of Poznań formation, a subsoil for many structures in almost 75% area of Poland. Investigations conducted for clays in Warsaw were used as a background with the focus on an underground Metro station. Direct measurements of the unloading of the bottom of the excavation in clays were used for validation. Finite Element Method (FEM) was used to verify stiffness parameters and their determination methods. The correctness of obtained results was verified by comparison with deformation measurements of station construction and displacement measurements in the adjacent area. As a conclusion, the article shows that the type of a construction and its character should be taken into consideration in geotechnical parameter determination. The analysis with stiffness parameters determined in the small-strain range of deformations allows to obtain displacement values approximate to real ones. In the case of an underground station, large area of soil interacts with a structure, and in this case, the deformations are small, which should be taken into account in a design analysis.