The resistivity cone penetration test (RCPTU) and seismic cone penetration test (SCPTU) results may be used as well for quantitative and for qualitative analysis of the subsoil on tested sites. Electrical resistivity tomography (ERT) with RCPTU and SCPTU procedures are capable of detecting discrete horizons that would normally be missed using other tests at specific depth intervals. In the first tested site the RCPTU and SCPTU results have been used to define sub-surface stratigraphy and the soil porosity of the Pliocene clay deposits, while in the other site to identify the layers of organic subsoil and deformation parameters of subsoil. In the third tested site geotechnical in situ investigations were carried out using of 10 cm2 CPTU cone and 15 cm2 RCPTU cone. All these tests may be carried out in the preliminary investigation phase of ground conditions as well as supplementary studies and are most effective when are combined.