Assessment and verification of correlations in CPTu testing on the example of soil from the Wroclaw surroundings (Poland)

The paper presents the results of a series of Cone Penetration Test CPTu performed near the city of Wroclaw (Poland). The tests were carried out in 13 testing points located in close distance to each other. To verify the results of the penetration tests, fine-grained soil samples from selected depths were taken for laboratory tests. The study focuses on the evaluation of soil type, unit weight, and undrained shear strength cu, and compression index Cc. The grain size distribution of the soil and its mechanical parameters on the basis of a uniaxial compression and an oedometer tests were estimated. A comparison of laboratory and CPTu for selected values is presented. Determination of soil type was carried out on the basis of ISBT and IC values and good agreement with the granulometric composition was found. For undrained shear strength, commonly used correlations based on Nk, Nkt and Nke were adopted. However, the values obtained from the CPT are significantly lower than the results from laboratory tests. Therefore, values of cone factors suitable for investigated soil type and reference test were proposed. In the case of the compression index, the coefficient values βc and αm obtained agreed with those available in the literature. The findings presented in the paper indicate that laboratory tests remain necessary to identify soil properties from CPTu. The presented results are also a contribution to the knowledge of local soil conditions in the Lower Silesia area (Poland).