Usefulness of the CPTU method in evaluating shear modulus G₀ changes in the subsoil

This article contains the analysis of the correlation between the cone resistance q_c from CPTU tests and shear modulus G₀ determined from seismic tests SDMT and SCPTU. The analysis was performed for sands located in Poland, characterised by differential grain size distribution and origin. The significant impact of the independent variables; grain size, preconsolidation stress σ’_p, geostatic vertical stress σ’_v0 and relative density index on the dependencies analysed, were examined in three stages. Firstly, a general relationship between the cone resistance and shear modulus G₀ was established; in the second stage, an analysis was carried out in selected groups of subsoil; and in the third stage, the influence of other independent variables was taken into account. In each stage, the functional form of the dependency was determined, and their statistical significance was assessed throughout coefficient of determination R². For more variables, multivariable regression analysis was applied for assessment. Conducted analysis showed that the overall view of the relation between the cone resistance q_c and shear modulus G₀ has low evaluation of the statistical significance. This fact is consistent with the theoretical assessment of this relationship. To obtain a satisfactory assessment of this dependency, it is necessary to construct empirical equations for individual groups of soil, taking into account other independent variables; preconsolidation stress σ’_p, vertical stress σ’_vo and relative density index. This approach allows to assess the local correlation relationship, which is very useful during the geological project.