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

Abstract

Abstract This article contains the analysis of the correlation between the cone resistance qc 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 qc 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.