The paper presents results of tests conducted on a test site at Adam Mickiewicz University (AMU) in Poznań, Poland. The test site is located in the area of distribution of normally consolidated postglacial clayey silty sands and sandy clays. These soils are characterized by high porosity and are fully saturated, therefore, from a geotechnical point of view they can be defined as soft clays. There were 9 CPTU tests conducted along with research drillings and taking samples for laboratory analyses in the area of 8 ha. This paper focuses on the analysis of the uniformity of the soft clay layer found on the test site and on the analysis of variability of the CPTU tests conducted there. The results obtained enabled to separate a statistically homogeneous batch of soil in the subsoil and to form a reference set of CPTU results characteristic of the soft clay layer.